Problem with Wilwood Manual Brakes

[SouthernRodder]

Guys, I'm looking for some advice please. My application is 65 C10 with square body front stock disc setup, all new rear factory drum components, also every line on it is new. I had an older CPP style booster and MC. The MC started leaking and I wanted to neaten up my firewall so I decided to convert to a Wilwood manual MC and prop valve.

I have a 15/16" bore MC and Wilwood prop valve, a 10 psi residual pressure valve for the rear. I made sure the push rod was in the correct location for a manual brake setup.

Before i converted I had really good brakes. What I have now is not that.... My pedal pulsates when i press it. Pedal feels good and firm, but the brakes will not lock up, even on loose gravel. I feel they have been adequately bled but just can't comprehend what I'm feeling compared to what I had. I called Wilwood and they explained that those are super large factory piston calipers that require a lot of fluid and they questioned my choice of 15/16" bore, but I have several friends who have run the same setup with no issues. Then they questioned that my calipers may be bad, but again brakes worked just fine prior to converting.

Also I have adjusted the prop valve from top to bottom and no change at all.

Any ideas what may be going on here?

[Keith Seymore]

I'm going through the same thing with my Chevelle right now (converting from power to manual; I'm disc/disc, no prop valve). My pedal is "firm-ish" (not great; a little soft) and the brakes will stop the car but not skid the wheels.

Maybe we can work through this together.

Can you please report your actual pedal ratio (rather than "I made sure the push rod was in the correct location for a manual brake set up")?

K

[Keith Seymore]

Do you have a way to measure and report line pressures at the bleeder screws?

Summit Racing has an inexpensive brake pressure gage. I purchased this and measured at the front and rear and believe my line pressures are lower than they should be.

https://www.summitracing.com/parts/SUM-800114

One of the reasons I am taking an interest in this is that I was thinking my next move would be to a 15/16" bore m/c (the very one you have mentioned). You original post is making me rethink that, as I don't want to end up with a whole library of brake master cylinders before this is done. I started with a 1" bore (6.1:1 pedal ratio) and currently have a 1.125" bore (and 4.5:1 pedal ratio) on the car presently.

Next step for me is to re-install the 1" bore M/C with the 4.5:1 pedal ratio and get some line pressure data.

K

[Keith Seymore]

One other thing (just spitballing here) would be to make sure the front system of the master cylinder is hooked to the front brakes.

The front brake system could be the front port of the master, or the rear port of the master, depending on the type.


K

[theastronaut]

My '66 C10 has squarebody front discs, stock rear drums, stock 6.25:1 manual pedal ratio, and a 1" bore manual master cylinder. It stops very well, can lock up the brakes at speed on dry pavement and pedal feel/travel is great. I used a hold off valve in the front line, and a Wilwood adjustable proportioning valve and 10 psi residual valve in the rear line. It has semi-metalic pads that have been bedded in properly.

We have an Impala in the shop that I just converted to manual disc/drum and it has the same front calipers as my C10. I used a 7/8" on it (I originally thought the brake kit was coming with smaller Metric calipers) and the pedal is soft enough that I'm going to move up to a 15/16" bore. It has a 6:1 pedal ratio, so 1" might make the pedal too firm with not enough line pressure.


Have you bedded in the pads yet? If not they'll grab much harder once they're bedded in.

Are they ceramic pads? Pads are marked with a two letter coefficient of friction code, the first letter is cold stopping friction and the second is hot stopping friction. F/F is pretty good, you wouldn't want lower than E/E or lower with manual brakes.

A major issue I ran into on the Impala- the disc kit came with low-drag calipers that retract the pistons in the caliper farther than normal, so a small bore manual master cylinder couldn't move enough volume to get the piston back out to the pad and build pressure. Look up the difference in the way the piston seal groove is machined and check your calipers to see which version they are. Pre-77/78ish calipers are what you want but some kits are coming with the later 80s/90s low drag calipers that really need a step bore master cylinder to work correctly. The discs kits are coming with huge master cylinders and double chamber boosters to make up the volume and pressure instead of using the proper step bore master cylinder.

[Keith Seymore]

Originally Posted by theastronaut

A major issue I ran into on the Impala- the disc kit came with low-drag calipers that retract the pistons in the caliper farther than normal, so a small bore manual master cylinder couldn't move enough volume to get the piston back out to the pad and build pressure. Look up the difference in the way the piston seal groove is machined and check your calipers to see which version they are. Pre-77/78ish calipers are what you want but some kits are coming with the later 80s/90s low drag calipers that really need a step bore master cylinder to work correctly. The discs kits are coming with huge master cylinders and double chamber boosters to make up the volume and pressure instead of using the proper step bore master cylinder.

"Quick take up" system is what that is called.

K

[Keith Seymore]

Originally Posted by theastronaut

My '66 C10 has squarebody front discs, stock rear drums, stock 6.25:1 manual pedal ratio, and a 1" bore manual master cylinder. It stops very well, can lock up the brakes at speed on dry pavement and pedal feel/travel is great. I used a hold off valve in the front line, and a Wilwood adjustable proportioning valve and 10 psi residual valve in the rear line. It has semi-metalic pads that have been bedded in properly.

Perfection. Sounds like a "no-brainer".

I don't know why my stuff always gotta be a "brainer".



I must be the worst former brake engineer in the history of brake engineers. Been fiddling with the brakes on this car for 30 years.

K

[VictoriaHardware]

You can't call yourself the worst unless you can claim to have Service Bulletin(s) or Warranty Recall(s) as a direct result of your work, and I don't think you can.

[Keith Seymore]

I appreciate the vote of confidence, JT.



I guess you can tell what I've been up to during my retirement.

K

[SouthernRodder]

keith, thanks for the info - i'm ordering a pressure gage kit and will do the calculation. i will return with some data.

[VictoriaHardware]

This is the best collection of information on brakes I have seen- http://www.billavista.com/tech/Artic...ble/index.html

Easy-to-understand explanations of everthing, the physics behind it, and equations to back it all up. It includes all aspects of the brake system- pedal, booster, lines, calipers, etc. for a light-duty drum or disc system. Heavy trucks follow many of the same principles but hydrovac or air brakes are not specifically covered.

Included is a downloadable spreadsheet (about 3/4 way down the page) with all the equations mentioned that you can input particular data for your vehicle. I used the spreadsheet ten years ago when I did a complete overhaul on my '66 Suburban. The completed brake system worked well, but I must admit I still have some bugs to work out.

[SouthernRodder]

Pedal Ratio is 6:1
Front Calipers pressure is 450-500 PSI

[HO455]

I believe those pressures are a bit low. I would expect to see 800 to 1000 psi. How hard are you pushing the pedal when checking the pressure?

You said you have stock calipers on the front but which stock ones exactly? There are several different caliper piston sizes that use the D52 style casting and will bolt to the spindles. I would confirm which diameter pistons are installed and calculate from there to see if the 15/16" master cylinder is appropriate.

Out of curiosity why the switch to manual brakes?

[SouthernRodder]

800-1000 is what I was looking for....

Stock square body single piston calipers, 1.25" rotors

My old MC was leaking, and I wanted to neaten up my firewall. I have some friends with this exact same setup (front to back) and have very good brakes. I realize "optimally" a power setup with a slightly larger bore would provide the optimal brakes, but i'd give up a little for a super neat firewall.

[HO455]

The stock squarebody calipers were available in multiple piston sizes depending on year and model options.

You need to measure what piston size your calipers use. If memory serves me correctly there are a 2.75" a 2.93" and a 3.23" sized pistons.

Here is an in depth calculator that may help you decide if a15/16" bore master cylinder is appropriate.

https://www.tceperformanceproducts.com/dual-bias-calc/

[Keith Seymore]

Sorry for the delay but I didn't want to report back until I had some success.

I'll give the detail first and then provide a summary at the end.

I ended up testing four different master cylinder diameters, with two different pedal ratios, verifying the pressure at the master cylinder port and brake bleeders. Including a bad master cylinder from Wilwood, plus my final setup, that ended up being about 10 or 11 iterations. That's a lot of brake bleeding.

In short, I don't believe the 7/8 or 15/16 bore Wilwoods could move enough fluid to provide pressure with my calipers. The pressure from the m/c to the bleeders was too far off, for no other reason (ie, good bleed, no proportioning, no leaks).

The 1.032" Strange Engineering/MOPAR and 1.125 Strange/MOPAR gave me in the order of 800-950 psi at the wheels. This slowed the car nicely but didn't really feel like there was enough for an emergency situation.

I figured that was all the line pressure I was going to get and I needed to do more with that pressure at the wheel. I ended up replacing the stock GM front calipers with some bolt on Wilwood dual piston calipers. That put me over the top. I'm now satisfied enough to drive it some and try it at the track. If I need more yet I can probably go to a more aggressive pad.

I still never got a firm pedal with 6:1 pedal ratio, which I can't really explain. I had the ability to drop to 4.5:1, which I preferred for the slightly less pedal travel and a little firmer feel (I don't mind pushing hard).

I also blew the pistons out of the original GM calipers and I'm thinking somewhere along the last 30 years I got some "quick take up" calipers on there accidentally. I believe the additional fluid requirements for those was not favorable. Probably time for some new front calipers anyway (they were the only remaining parts not new).

Final set up for those keeping score: Strange/MOPAR 1.032" bore M/C, with 4.5:1 pedal ratio, feeding Wilwood dual piston fronts and GM E car rear calipers (2.4" diameter); no proportioning.

K

[HO455]

Great work and thanks for sharing. I seem to remember the early 2nd gen Firebirds had a 1.125 master cylinder on the manual disc brake optioned cars.

[Keith Seymore]

Originally Posted by SouthernRodder

800-1000 is what I was looking for....

Stock square body single piston calipers, 1.25" rotors

My old MC was leaking, and I wanted to neaten up my firewall. I have some friends with this exact same setup (front to back) and have very good brakes. I realize "optimally" a power setup with a slightly larger bore would provide the optimal brakes, but i'd give up a little for a super neat firewall.

So - I think you need to bump up to a 1" diameter bore to move enough fluid.

If you do a Wilwood then you can leave the lines as they are (front m/c port => front brakes). If you do the Strange Engineering m/c you'll need to swap the lines (rear port => front system).

One other nuance is the pushrod travel for the Wilwood is 1"; for the Strange it is 1.5".

I liked them both.

K

[theastronaut]

Originally Posted by Keith Seymore

I ended up replacing the stock GM front calipers with some bolt on Wilwood dual piston calipers. That put me over the top. I'm now satisfied enough to drive it some and try it at the track. If I need more yet I can probably go to a more aggressive pad.

I still never got a firm pedal with 6:1 pedal ratio, which I can't really explain. I had the ability to drop to 4.5:1, which I preferred for the slightly less pedal travel and a little firmer feel (I don't mind pushing hard).

I also blew the pistons out of the original GM calipers and I'm thinking somewhere along the last 30 years I got some "quick take up" calipers on there accidentally. I believe the additional fluid requirements for those was not favorable. Probably time for some new front calipers anyway (they were the only remaining parts not new).

Sounds like quick take up calipers were the issue, they have to travel farther before the pads contact the rotor to actually start building pressure, by then you're out of pedal travel to build enough pressure. The Wilwood dual piston calipers that go in place of a D52 actually have less piston area than a D52 so they're making less clamping force than D52s, but since they're acting sooner (less piston retraction) you're starting to build pressure sooner in the pedal travel. If you swap back to regular early/non-QTU D52s you'd have even more clamping force.