1965 C10 LWB Project Build Thread

[rbruno68]

I have a feeling I might go the same route as you. Start the lower control arm shafts in the A arm, but final torque on the truck.
Rob

[JohnIL]

Another productive weekend in the garage. I lost a couple of weeks to travel, but the brake conversion project is moving forward again.

When last we spoke, I was ready to dig into the manual to power master cylinder replacement. That led to new brake lines, new rear wheel cylinders, and new rear brake shoes. Brake work is always tedious. It's even more tedious when you don't have the right parts on hand. A few weeks ago, I starting accumulating components for this phase of the project. I ordered new wheel cylinders and brake shoes from my local parts store. I ordered copper-nickel brake lines and tube nuts from the Amazonians. While I was waiting for parts to arrive, I focused on mounting the new master cylinder.

The first (and biggest) challenge was the aluminum adapter plate that came with the kit. None of the holes lined up with the holes in the firewall. I chalk this up to minor stamping variations at the GM factory in 1965. The aluminum plate is very precisely machined. The tolerances are much too tight for an old pickup. I had to open all of the holes up about 1/8" to create enough adjustability to get all four of the mounting bolts to line up with the firewall. I wanted to sneak up on this modification, so I redrilled the holes in small increments. I feel like I redrilled those silly holes at least a hundred times. I had aluminum drill shavings everywhere. Once I finally got the adapter plate mounted, everything else fell into place. There is plenty of vertical adjustment in the spacer brackets to line up the brake rod with the factory pedal. So, I mounted the booster and master cylinder. I left everything just snug to allow for final adjustment later.

Meanwhile, the brake parts started arriving. My usually reliable parts store botched the order. I ordered three items: brake shoes, left wheel cylinder, and right wheel cylinder. Only one of those items was correct. They sent me two left wheel cylinders and brake shoes for a C20. Ugh. After two more trips to the store (40 minutes each way), I finally had the right parts in hand. The rear brake job itself only took about an hour (split over two days, of course). Between my son's G-body El Camino and his square body C10, I've gotten WAY too proficient with rear drum brakes.

Next it was time for new brake lines. I chose copper-nickel because it's easy to work with and it doesn't rust. I fell in love with this stuff while replacing the brake lines on the El Camino a few years ago. The challenge with the brake lines for this conversion is the wide variety of tube nut sizes needed for the various connections. Even though there are only two sizes of brake lines, I counted five different tube nut sizes. Unfortunately, I missed one. There is actually a sixth size. The connect where the front hard line connects to the soft line at each caliper uses a different size tube nut than anywhere else in the system. Curses, foiled again! So, I had to place another order for a handful of those tube nuts to finish up the front brake lines.

While I'm waiting for more brake parts to arrive, I fabbed up a vacuum line for the brake booster. I've always hated the looks of the black rubber hose snaking it's way from the back of the carburetor to the front of the brake booster. So, I bent up a hard line out of 3/8" aluminum. Even with a short rubber "coupler" hose at both ends, it looks much cleaner this way.

I'm particularly happy with the way the top end of the system (master cylinder, combination valve, and brake lines) turned out. This is the most visible part of the system. Unfortunately, it's also the most cluttered part. Most power brake conversion kits (this one included) come with a weird little bracket that mounts the combination valve to the side of the master cylinder. I've looked at that arrangement on lots of show vehicles and I've never seen one that I would call "clean". The little mounting bracket serves its purpose, but it places the combination valve front-and-center. With all the brake lines coming and going, the valve has a tendency to look like a baby squid. To minimize the squid look, I fabbed up a new bracket that mounts the combination valve on the inner fender, below the master cylinder and as far back toward the firewall as possible. It's only a few inches away from the intended mounting location on the side of the master cylinder, but it made a HUGE difference in the overall look. It also provided enough space for a pair of stress relief loops in the lines coming from the master cylinder. I think looks much more intentional this way. If you wanted to full "show car", you could hide the combination valve down on the frame, below the inner fender. I opted to keep it up in the engine bay to keep it accessible and protected. The combination valve (the same exact part#, by coincidence) on the El Camino is mounted on the frame, just below the driver's left foot. It's definitely hidden, but it's impossible to get to and it collects road debris like a magnet.

Before and after pictures of the master cylinder area included below.

I'm getting close on the brake conversion project. Once the last of fiddly bits arrive, I need to finish the front brake hard lines, tighten everything up, fill the master cylinder, bleed the system, fix all the inevitable leaks, and get the C10 back on the road.

[SCOTI]

Clean install & agree 100% w/the 'squid' description on the typical aftermarket prop valve installation bracketry.

[JohnIL]

Thanks Scoti! The engine bay is kind of grungy, but I make an effort to declutter anytime I'm under the hood. The grunginess will be addressed someday when the engine comes out.

John

Originally Posted by SCOTI

Clean install & agree 100% w/the 'squid' description on the typical aftermarket prop valve installation bracketry.

[Braunschweiger]

Really, it looks great

[JohnIL]

Thanks Harald! I just hope that it works great too!

Originally Posted by Braunschweiger

Really, it looks great

[JohnIL]

I forgot to label my previous update as "Part 4". But, anyway, this is Part 5.

The bake system is all back together and the brakes are working. Sort of. At this point, I think I'm chasing air bubbles. The brakes stop the truck, but not well. The pedal is soft and it goes to the floor.

I started by gravity bleeding the whole system. Fluid started coming out the front bleeders in just a few minutes. But, I left the rears open for several hours and fluid never did come out. That led me to think there must be something going on with the combination valve. I thought maybe the internal shuttle was tripped and was cutting off fluid to the rears. I removed the combination valve and verified with air that it is flowing to both the front and rear.

Then I thought, OK, maybe there is just an air pocket somewhere in the line. After all, it runs downhill to the frame, back to the rear, then back up over the rear pumpkin. So, I connected a Bleed-O-Matic gizmo to one of the rear bleeders and gave the brake pedal 10 pumps. A hah! There was brake fluid at the bleeder. After 10 more pumps, I had a stream of fluid, but there were still bubbles.

At this point, I recruited my wife to help so I could keep an eye on what was happening at the bleeder. You know the routine. Pump the brakes, hold the pedal, crack the bleeder, repeat. After three repetitions at each corner, The brakes are actuating, but the pedal is WAY too soft.

I have a reverse bleeder kit on order. While I wait for it to arrive, we may try bleeding it a couple more times the "traditional" way. More to come...

[SCOTI]

Originally Posted by JohnIL

I forgot to label my previous update as "Part 4". But, anyway, this is Part 5.

The bake system is all back together and the brakes are working. Sort of. At this point, I think I'm chasing air bubbles. The brakes stop the truck, but not well. The pedal is soft and it goes to the floor.

I started by gravity bleeding the whole system. Fluid started coming out the front bleeders in just a few minutes. But, I left the rears open for several hours and fluid never did come out. That led me to think there must be something going on with the combination valve. I thought maybe the internal shuttle was tripped and was cutting off fluid to the rears. I removed the combination valve and verified with air that it is flowing to both the front and rear.

Then I thought, OK, maybe there is just an air pocket somewhere in the line. After all, it runs downhill to the frame, back to the rear, then back up over the rear pumpkin. So, I connected a Bleed-O-Matic gizmo to one of the rear bleeders and gave the brake pedal 10 pumps. A hah! There was brake fluid at the bleeder. After 10 more pumps, I had a stream of fluid, but there were still bubbles.

At this point, I recruited my wife to help so I could keep an eye on what was happening at the bleeder. You know the routine. Pump the brakes, hold the pedal, crack the bleeder, repeat. After three repetitions at each corner, The brakes are actuating, but the pedal is WAY too soft.

I have a reverse bleeder kit on order. While I wait for it to arrive, we may try bleeding it a couple more times the "traditional" way. More to come...

100% understand the bleeding frustrations.

[bigmoe]

Did you drill a new hole in the brake pedal arm 1" lower?

[JohnIL]

I discovered something strange tonight. I took the truck for a short drive to test the brakes. I still have some air in the lines. More on that in a later update. I while I was out driving around the block, the drive side front spring was making all kinds of racket. Once I got the truck back home and up on blocks, it was obvious that the driver side front spring is making contact with the edge of the upper spring pocket. The question is, why?

I posted a separate thread in the Suspension section:
https://67-72chevytrucks.com/vboard/...78#post9350178

Take a look at the pictures in that thread and let me know if you have any ideas.

[SCOTI]

Trim/open-up the opening on the side that is creeping in on things?

Re-clock & re-drill the shafts @ 1/2"?

[JohnIL]

Scoti,
Thanks for the suggestions. Responses below.

Originally Posted by SCOTI

Trim/open-up the opening on the side that is creeping in on things?

That would probably work, but it's odd that only one side is interfering. Could it be because both springs are wound the same direction? If you look at the top of the springs, the tail of one is at the rear. The tail of the other is toward the front. Maybe the tail of the driver side spring isn't concentric with the spring?

Originally Posted by SCOTI

Re-clock & re-drill the shafts @ 1/2"?

I'm not ready to give up ground on the caster mod yet. Considering I had occasional interference with the control arms in the orginal position, I'm afraid that 1/2" won't be enough to solve the problem. I think I would end up back in the original position. Not the end of the world, but I'd rather figure out what's different about the springs. It might be worth dropping the the lower control arms and switching the springs from one side to the other.
It might even be worth the cost of a new set of springs.

[rbruno68]

Following your brake thread closely as well as others. This is one of the upgrades to my 63 that makes me nervous. All of the aftermarket parts needed to work and all the confusion around which MC and proportioning valve to use and the quality of each. Much less the size of the MC push rod, shot depth vs deep, larger front reservoir vs the same size. I will be doing disk/drum NON power which seems to be difficult to set up. Or, at least I am finding it to be a challenge. Good luck on sorting it out and keeping up to date with what you are trying. I am sure I will be doing the same process at some point in my build.
Rob

[88Stanger]

Damn sir, I hate to hear the frustrating issues. I HATE brake issues with such a passion!! I have spent hours and hours chasing "bubbles" and so on. So please excuse any ideas that I post below that you may have already done.
1.) Bench bleed the Master Cylinder? Fully... This can be a pain, but very very important.
2.) Check that you have correct Proportioning valve (Combo Valve) Disc / Drum , Disc / Disc and so on, this caused me nothing but headaches for days...
3.) I got so mad, I just converted over to HydroBoost, but really had to. I had maybe 7lbs of vacuum.. .so it was needed. But I will say this, it is really nice system, but not cheap
4.) I bought one of those brake machines. I got the one that puts pressure to the master Cylinder with Air and then I start the process. It works really good, but it takes time to set up. I have tried a reverse system where you vacuum at the bleeder... it was not a good kit that I got, cheap one and it did not work good, but I would not be apposed to trying one the nicer kits for this.

I just hope you have success. I feel for you on this!

[JohnIL]

Bruno,
I cheated a little bit. I bought all the brake components (booster, master, spindles, rotors, and calipers) as a kit from Speedway Motors. That takes out a lot of the guessing. The parts aren't all made by the same manufacturer, but Speedway puts them says they put the kits together using known compatible parts. Most of the components are CCP brand. It's nothing exotic, but it should all work together. I'm doing vacuum boosted power with front discs and rear drums. Your mileage may vary with a manual setup. If I find any caveats or wisdom along the way, I will definitely post it here in the build thread.

John

Originally Posted by rbruno68

Following your brake thread closely as well as others. This is one of the upgrades to my 63 that makes me nervous. All of the aftermarket parts needed to work and all the confusion around which MC and proportioning valve to use and the quality of each. Much less the size of the MC push rod, shot depth vs deep, larger front reservoir vs the same size. I will be doing disk/drum NON power which seems to be difficult to set up. Or, at least I am finding it to be a challenge. Good luck on sorting it out and keeping up to date with what you are trying. I am sure I will be doing the same process at some point in my build.
Rob

[JohnIL]

Stranger,
Thanks for the reply and the suggestions.

1. I bench bled the master. I worked at it until the bubbles stopped, then two more pumps. I'm reasonably confident I got all the air out. Of course, there's always a chance three are bubbles hiding somewhere.

2. The proportioning valve came with the Speedway Motors kit. It's actually a combination valve. It's a PV2 valve, for front disc/rear drum. It happens to be the same valve as my son's square body with the same disc/drum arrangement.

3. My engine is stock. 14+ vacuum. I should be fine with vacuum assist. But, you're absolutely right about hydroboost. If/when I LS swap the truck, I will keep this in mind. Hydroboost would take the braking system to the next level.

4. I've never used a reverse bleeder. I've always bled brakes manually. I'm interested to try a reverse bleeder because I'm having so much trouble pushing the air out the manual way. The one I ordered is the Phoenix v-5 kit. It's been on the market for a few years. I hope the quality level matches the reputation. I like the idea of the kit you use. I'm just not confident in the expense. Which one do you have?

Thanks!
John

Originally Posted by 88Stanger

Damn sir, I hate to hear the frustrating issues. I HATE brake issues with such a passion!! I have spent hours and hours chasing "bubbles" and so on. So please excuse any ideas that I post below that you may have already done.
1.) Bench bleed the Master Cylinder? Fully... This can be a pain, but very very important.
2.) Check that you have correct Proportioning valve (Combo Valve) Disc / Drum , Disc / Disc and so on, this caused me nothing but headaches for days...
3.) I got so mad, I just converted over to HydroBoost, but really had to. I had maybe 7lbs of vacuum.. .so it was needed. But I will say this, it is really nice system, but not cheap
4.) I bought one of those brake machines. I got the one that puts pressure to the master Cylinder with Air and then I start the process. It works really good, but it takes time to set up. I have tried a reverse system where you vacuum at the bleeder... it was not a good kit that I got, cheap one and it did not work good, but I would not be apposed to trying one the nicer kits for this.

I just hope you have success. I feel for you on this!

[Braunschweiger]

When I have problems, I briefly loosen the brake line screw connections under pressure on the master brake cylinder
and then tighten them again straight away;
bubbles often still appear there.

[SCOTI]

John.... What is your manual bleeding strategy (step-by-step)?

I know, I know...... But humor me & walk us through it.

[JohnIL]

Scoti,
I'll be happy to walk you through it. Hopefully you guys will tell me what I'm doing wrong!

I actually used three different strategies on this truck.

1. Gravity.
I filled the reservoir, opened the bleeders and waited. The front calipers started dripping fluid in just a few minutes. Of course there was still air bubbles, but that got the lines filled with fluid. I closed off the front bleeders and left the rear bleeders open for about three hours. I never got fluid out of the rears using this strategy.

2. Manual bleeding using a Performance Tools Bleed-O-Matic.
If you're not familiar, it's a little bottle with a check valve built into the top. You connect a tube from the bleeder to the check valve and crack the bleeder. As you pump the brakes, fluid and air flow into the bottle. The check valve is supposed to keep air from getting sucked back into the brake line. After about 10 pumps, this strategy got fluid back to the rear wheel cylinders. The brake lines were all new, so there was LOTS of air. So, 10 more pumps, check for air bubbles, repeat. After I thought I got all the air out, the pedal was still soft. That led me to strategy 3.

3. Manual bleeding with a helper.
I think this is the process you're asking about. My wife and I have developed a routine for bleeding brakes. Luckily, she's a good sport. We've used this routine on LOTS of other vehicles and it's never failed us before. Here's how it goes:

-I start at the brake furthest from the master cylinder. In this case, that's the driver side rear wheel cylinder.
-She pumps the brake pedal four times and holds it to the floor.
-I crack open the bleeder for a split second to let it spit out any air.
-I close the bleeder and we repeat the process until I get only fluid out of the bleeder.
-Then I move to the next closest brake and we repeat the process. Etc.

After going through all four brakes, I took the truck for a drive. The brakes would stop the truck, but the pedal was still soft and I could easily push it all the way to the floor.

So, we went through another round of bleeding. This time, I only got air at the 1st brake (driver side rear). The other three were fluid only. Afterward, the pedal feel was better, but still way too soft.

At this point, I think I'm chasing air bubbles in the hard line that goes up over the top of the rear pumpkin. Before I try the reverse bleeder, I plan to go through another round of manual bleeding. Hopefully the pedal firmness comes around and I can forgo the reverse bleeder entirely.

I'll take any suggestions I can get!

Thanks.
John

Originally Posted by SCOTI

John.... What is your manual bleeding strategy (step-by-step)?

I know, I know...... But humor me & walk us through it.

[SCOTI]

Originally Posted by JohnIL

Scoti,
I'll be happy to walk you through it. Hopefully you guys will tell me what I'm doing wrong!

I actually used three different strategies on this truck.

1. Gravity.
I filled the reservoir, opened the bleeders and waited. The front calipers started dripping fluid in just a few minutes. Of course there was still air bubbles, but that got the lines filled with fluid. I closed off the front bleeders and left the rear bleeders open for about three hours. I never got fluid out of the rears using this strategy.

2. Manual bleeding using a Performance Tools Bleed-O-Matic.
If you're not familiar, it's a little bottle with a check valve built into the top. You connect a tube from the bleeder to the check valve and crack the bleeder. As you pump the brakes, fluid and air flow into the bottle. The check valve is supposed to keep air from getting sucked back into the brake line. After about 10 pumps, this strategy got fluid back to the rear wheel cylinders. The brake lines were all new, so there was LOTS of air. So, 10 more pumps, check for air bubbles, repeat. After I thought I got all the air out, the pedal was still soft. That led me to strategy 3.

3. Manual bleeding with a helper.
I think this is the process you're asking about. My wife and I have developed a routine for bleeding brakes. Luckily, she's a good sport. We've used this routine on LOTS of other vehicles and it's never failed us before. Here's how it goes:

-I start at the brake furthest from the master cylinder. In this case, that's the driver side rear wheel cylinder.
-She pumps the brake pedal four times and holds it to the floor.
-I crack open the bleeder for a split second to let it spit out any air.
-I close the bleeder and we repeat the process until I get only fluid out of the bleeder.
-Then I move to the next closest brake and we repeat the process. Etc.

After going through all four brakes, I took the truck for a drive. The brakes would stop the truck, but the pedal was still soft and I could easily push it all the way to the floor.

So, we went through another round of bleeding. This time, I only got air at the 1st brake (driver side rear). The other three were fluid only. Afterward, the pedal feel was better, but still way too soft.

At this point, I think I'm chasing air bubbles in the hard line that goes up over the top of the rear pumpkin. Before I try the reverse bleeder, I plan to go through another round of manual bleeding. Hopefully the pedal firmness comes around and I can forgo the reverse bleeder entirely.

I'll take any suggestions I can get!

Thanks.
John

Two things....

Order.
Which frame rail are your lines routed down?
Where (which side) is the rear inline splitter/'T'?

The process.
The multiple pump thing? Try this instead:

One single pump (SLOWLY) & hold it. *Think slow, consistent stop vs panic or quick stop.*

Hold/keep the pedal down/under pressure. Once the pedal is pressurized, crack the bleeder to purge air/fluid & then close the bleeder. Once the bleeder is closed, have your helper SLOWLY release the pedal back to its normal state.

Repeat this multiple times @ each bleeder. I do this 3x @ each corner (on problematic vehicles) checking reservoir fluid level after each corner. Then follow the traditional order farthest to closest doing each corner 3x the same way.

I've found this to work better on problematic vehicles & actually do it all the time now when there is a helper involved.
Maybe it will help?

[JohnIL]

Scoti,
Thanks for the suggestions. We'll try bleeding again tonight, using your method.

To answer your questions, the rear brake line runs down the passenger side frame rail. This appears to be the factory arrangement, but I don't know that for sure. At the rear axle, just forward of the shock mount, there is a mounting tab that holds the end of the rubber flex line. The rubber flex line screws into a T fitting mounted to the top of the axle housing just to the right of the pumpkin. From there, there is a short hard line to the passenger side wheel cylinder and a longer hard line up over the pumpkin to the driver side wheel cylinder. That makes the passenger side rear the longest run to/from the master cylinder.

The multiple pump bleeding method comes from an uncle who was a pro mechanic most of his career. That's the way he was taught in tech school back in the late '60's. He taught me, so I just assumed that was the "right" way. Like anything else, there's more than one way. I hope your way gives us better results.

Thanks.
John

Originally Posted by SCOTI

Two things....

Order.
Which frame rail are your lines routed down?
Where (which side) is the rear inline splitter/'T'?

The process.
The multiple pump thing? Try this instead:

One single pump (SLOWLY) & hold it. *Think slow, consistent stop vs panic or quick stop.*

Hold/keep the pedal down/under pressure. Once the pedal is pressurized, crack the bleeder to purge air/fluid & then close the bleeder. Once the bleeder is closed, have your helper SLOWLY release the pedal back to its normal state.

Repeat this multiple times @ each bleeder. I do this 3x @ each corner (on problematic vehicles) checking reservoir fluid level after each corner. Then follow the traditional order farthest to closest doing each corner 3x the same way.

I've found this to work better on problematic vehicles & actually do it all the time now when there is a helper involved.
Maybe it will help?

[SCOTI]

Originally Posted by JohnIL

Scoti,
Thanks for the suggestions. We'll try bleeding again tonight, using your method.

To answer your questions, the rear brake line runs down the passenger side frame rail. This appears to be the factory arrangement, but I don't know that for sure. At the rear axle, just forward of the shock mount, there is a mounting tab that holds the end of the rubber flex line. The rubber flex line screws into a T fitting mounted to the top of the axle housing just to the right of the pumpkin. From there, there is a short hard line to the passenger side wheel cylinder and a longer hard line up over the pumpkin to the driver side wheel cylinder. That makes the passenger side rear the longest run to/from the master cylinder.

The multiple pump bleeding method comes from an uncle who was a pro mechanic most of his career. That's the way he was taught in tech school back in the late '60's. He taught me, so I just assumed that was the "right" way. Like anything else, there's more than one way. I hope your way gives us better results.

Thanks.
John

Exactly how I was taught as well. But I've ran across more than one problematic set-up & it would be frustrating. Plus, it seemed every 'helper' would pump the pedal @ different speeds.

I started wondering if there is air trapped in the system what actually happens when the pedal is compressed/released multiple times? Pumping multiple times doesn't increase the line pressure on a sealed system; volume, ratio, & line size dictate the pressure. A single pump applies the needed force w/o possibly agitating/aerating the fluid in the line.

Whether it's that logic or just slowing things down..... It has helped more than once.

[88Stanger]

Originally Posted by JohnIL

Stranger,
Thanks for the reply and the suggestions.

1. I bench bled the master. I worked at it until the bubbles stopped, then two more pumps. I'm reasonably confident I got all the air out. Of course, there's always a chance three are bubbles hiding somewhere.

2. The proportioning valve came with the Speedway Motors kit. It's actually a combination valve. It's a PV2 valve, for front disc/rear drum. It happens to be the same valve as my son's square body with the same disc/drum arrangement.

3. My engine is stock. 14+ vacuum. I should be fine with vacuum assist. But, you're absolutely right about hydroboost. If/when I LS swap the truck, I will keep this in mind. Hydroboost would take the braking system to the next level.

4. I've never used a reverse bleeder. I've always bled brakes manually. I'm interested to try a reverse bleeder because I'm having so much trouble pushing the air out the manual way. The one I ordered is the Phoenix v-5 kit. It's been on the market for a few years. I hope the quality level matches the reputation. I like the idea of the kit you use. I'm just not confident in the expense. Which one do you have?

Thanks!
John

Please update us on the Phoenix V-5 Kit. I have seen it and very tempted to get one.... very interested in how it works.

[JohnIL]

Stranger,
I didn't end up using the V-5 kit, at least not yet. I'll add a more thorough update in a few minutes to explain where I'm at with the brakes.

John

Originally Posted by 88Stanger

Please update us on the Phoenix V-5 Kit. I have seen it and very tempted to get one.... very interested in how it works.

[JohnIL]

I want to start this installment by thanking Scoti for his advice on an alternate procedure for manually bleeding brakes. His process is much more controlled and methodical than the way I've always done it. After three rounds of bleeding Scoti's way, I don't think I'm chasing air bubbles anymore. In fact, I didn't see any air bubbles at all. Now, I'm pretty sure I have a different challenge.

After bleeding again, the pedal was still soft. The brakes stop the truck, but the pedal feel was awful. I've felt air in the lines before (on other vehicles) and this felt different. It felt like maybe I wasn't getting enough brake pedal travel, like the pedal was hitting the floor before the master cylinder was maxed out. After thinking about the geometry of the booster and master cylinder, I lengthened the brake rod by adjusting it out one full turn. This improved the pedal feel. It's still softer than I would expect, but I finally got resistance at the end of the pedal stroke. So, I adjusted the rod out two more full turns and the pedal is starting to feel normal-ish.

All of this begs the question, how do you properly adjust the brake rod length?

With the old manual drum setup, I just took all the slack out of the pedal and adjusted the rod so there was 1/8" of free play before the brakes started to engage. I tried to do the same thing with the new power setup, but that appears to be way to loose. With the cushioned resistance of the brake booster, it's very difficult to tell when the brakes begin to engage. Is there a magic formula or should I just keep lengthening the rod until the brakes drag?

As always, I appreciate any wisdom you guys can share.