Upgrade to power brakes didn't work

[LSUMurse]

I got a booster with everything from the rod to the pedal to the prop valve including all the brackets (it's off either a '67 or '71, I haven't gotten the info yet). I pulled my current master cylinder off the firewall (without disconnecting the lines) and installed the booster, bracket, and a vacuum line. I teed off the vacuum for the transmission (the one between the carb and distributor). Everything seems to be connected correctly.

The brakes barely work. The travel on the pedal is shorter, though it does not bottom out on the floorboard. I did the booster test (build up pressure and then turn the truck on and see if the pedal goes down further) and the pedal didn't move when I turned on the engine.

The booster came with a master cylinder of it's own (with equal sized reservoirs). Should I try using it in place of the stock one? Could it be an incorrect push rod between the booster and MC? I am using the one from the setup I bought. Should I just get a whole setup from Napa? The ones with the MC and booster connected.

Any help is appreciated.

[Stocker]

I'm confused -- you got a new prop. valve, and you re-used your old MC without disconnecting the lines? How is that possible? Can you post a pic or two to show your setup? Or did you just not use the prop valve? It's not needed with all drums.

Dunno what truck you have but I assume it's drum / drum. Your new MC has equal size reservoirs so it's from a '70 or older drum / drum. If it was from a '71 it would be for front discs.

[LockDoc]

Originally Posted by Stocker

I'm confused -- you got a new prop. valve, and you re-used your old MC without disconnecting the lines? How is that possible? Can you post a pic or two to show your setup? Or did you just not use the prop valve? It's not needed with all drums.

Dunno what truck you have but I assume it's drum / drum. Your new MC has equal size reservoirs so it's from a '70 or older drum / drum. If it was from a '71 it would be for front discs.

I upgraded my '67 drum/drum setup to power without unhooking the lines. There was enough slack in the lines to move it back and bolt it to the booster with no problem. He doesn't say he replaced the prop valve, the new setup just came with one.

LSUMurse: Your vacuum line needs to come from the intake manifold. There should be a fitting or plug in the intake manifold just behind the carb. You need to plumb it to that...

LockDoc

[PanelDeland]

Sounds like you have too little volume on the vacuum line.It shoud be a 3/8 IIRC.The rod is also slightly different.Longer I think for PB.Yours may be enough because it's a very minor difference.

[LSUMurse]

Originally Posted by LockDoc

I upgraded my '67 drum/drum setup to power without unhooking the lines. There was enough slack in the lines to move it back and bolt it to the booster with no problem. He doesn't say he replaced the prop valve, the new setup just came with one.

LSUMurse: Your vacuum line needs to come from the intake manifold. There should be a fitting or plug in the intake manifold just behind the carb. You need to plumb it to that...

LockDoc

I have a vacuum line. There was a fitting with a single line coming off the intake that I believe goes down to the transmission. I turned that into a tee and used it for the vacuum. When I pull the vacuum line out of the booster, it seems to have a pretty good amount of vacuum. Also, it runs rough now. I'm thinking the booster may be shot.
It won't let me upload a pic from my phone, but there is definitely a vacuum line.
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[LockDoc]

Originally Posted by LSUMurse

I have a vacuum line. There was a fitting with a single line coming off the intake that I believe goes down to the transmission. I turned that into a tee and used it for the vacuum. When I pull the vacuum line out of the booster, it seems to have a pretty good amount of vacuum. Also, it runs rough now. I'm thinking the booster may be shot.
It won't let me upload a pic from my phone, but there is definitely a vacuum line.
Posted via Mobile Device

Yes, if the booster diaphragm has a hole in it that could cause the symptoms you are experiencing.

LockDoc

[LSUMurse]

Do you think it's safer to buy the whole setup (master cylinder and booster together)? I've read on some threads that not all MC's and boosters use the same pushrods.
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[68gmsee]

Originally Posted by LSUMurse

Do you think it's safer to buy the whole setup (master cylinder and booster together)? I've read on some threads that not all MC's and boosters use the same pushrods.
Posted via Mobile Device

If the original m.c. was good, the way you have it set up should work. Like LockDoc I installed power brakes on my 68 and reused the original m.c. without disconnecting the brake lines.

Re. the pushrod: One thing you need to check is whether the m.c. piston is the shallow or the deep type. IIRC the shallow type is recessed about 1/4 to 1/2 inch and the deep is about 1-1/4 or so. If you have the correct pushrod for the application, it needs to be adjusted so it has just a slight amount of clearance between the end and the piston.

On the brake pedal pushrod mine allows a couple of inches of travel before engaging the booster. It's normal for the pedal to go down a little farther than with manual brakes when stopping as long as it doesn't bottom out.

Re. the booster: I've heard of some of them coming in defective so be aware of that possibility. You can check the vacuum on the engine where it hooks up to the transmission with a vacuum guage. Every one should have one and they're not very expensive. I'm not sure about the operating vacuum number for it but my old 69 with 350/350 was hooked up like yours and read 15-16 inches. Power brakes worked fine.

[kevmac]

Make sure the pushrod is correct. I had a 70 years ago and it would go to the floor on panic stops and sometimes not at all. Ended badly, Anyway make sure its correct

[LSUMurse]

Ok, so I pulled the MC off of the booster and measured the push rod vs. the depth.

Push rod is 2 1/2"

Depth of the hole in the booster for the push rod is 2 1/8"

Depth of the hole for the push rod on the MC is 1 7/8" (stock MC) 1 3/4" (MC that came with the setup).

That means that the push rod has to travel (Booster hole + MC hole - Push rod length) 1 1/2" before it even makes contact with the business end of the MC.

Does that sound right? It doesn't seem like it should have to travel that far. Are these push rods made of hardened steel? Could I get a 3/8" steel dowel from a hardware store and make my own?

[LSUMurse]

Originally Posted by LSUMurse

Ok, so I pulled the MC off of the booster and measured the push rod vs. the depth.

Push rod is 2 1/2"

Depth of the hole in the booster for the push rod is 2 1/8"

Depth of the hole for the push rod on the MC is 1 7/8" (stock MC) 1 3/4" (MC that came with the setup).

That means that the push rod has to travel (Booster hole + MC hole - Push rod length) 1 1/2" before it even makes contact with the business end of the MC.

Does that sound right? It doesn't seem like it should have to travel that far. Are these push rods made of hardened steel? Could I get a 3/8" steel dowel from a hardware store and make my own?

Sorry, I meant to post these:

[68gmsee]

Originally Posted by LSUMurse

....... Could I get a 3/8" steel dowel from a hardware store and make my own?

There's lots of info on the net on the booster pushrod to master cylinder adjustments. Summit even sells the pushrods, however, I don't see why you couldn't make one. I don't believe it's hardened but not sure about that.

Look at the master cylinder that came with the booster. If it has the shorter recessed piston, you may want to just swap that one in. You just have to make sure you bench bleed per instructions and bleed the brake system to make sure no air got in while changing it.

Here's some info and the site where I got it from.

There are basically two different master cylinders that we use for our Chevy and Ford kits, the Deep Bore master cylinder and the Shallow Bore master cylinder. To determine which master cylinder your booster is setup to mate with, you can do the following simple check. For Shallow Bore master cylinders, the pushrod should be approximately flush with or below the booster face. Deep Bore master cylinders will protrude past the face of the booster body by about 1" to 1-1/2". Note that Deep Bore master cylinders are required for manual brakes and Shallow Bore master cylinders are generally used for power brake systems. We now supply a master cylinder piston adapter to accommodate both master cylinders. You will only use this adapter when you have a Deep Bore master cylinder with a short booster pushrod.
http://www.classicperform.com/TechBo...oubleshoot.htm

[jocko]

I believe your issue is a non-power master cylinder mated to a power booster, i.e. incorrect inter-booster/mc pushrod.

Generally, manual brake master cylinders have the deep bore pistons while power brake master cylinders have the shallow bore pistons. So, although you have power assist, the powered pushrod in the booster isn't engaging the bottom of the master cylinder bore.

You asked whether you should buy the master+booster together? Yes, that will elminate this problem because it will come as a matched set - power mc mated to booster with correct intermediate pushrod. Could you fiddle around all day and try to cobble together a homemade intermediate pushrod? Yes. But I wouldn't. I'd go buy the correct master that would have been mated to the booster that you bought if you had bought them as a set and install it. Sucks you will have to bleed some stuff, but, gotta be done.

I put a 67 dual res master on a 66 a while back - kept everything manual in the swap. Then, when I later opted to upgrade to power brakes, I learned the error of my ways... So, my lesson learned was to always buy a master cylinder WITH the booster when I am upgrading from manual to power brakes.

Hope that helps. Others have touched on the issue above and I believe that is the overall problem - your intermediate pushrod is not engaging the bottom of the master cylinder piston bore becuase you still have what was originally a manual brake master cylinder, and thus the "deep" bore piston. Easiest solution is to get the correct MC.

Personally, I don't like to cobble things together when it comes to my brakes - and when you consider the master cylinder is probably $20 at Oreily or something like that, why monkey with a homemade intermediate pushrod? Boosters weren't designed to work with deep bore mc pistons, but of course it could be done. Best $20 you'll ever spend though - my 2 cents only.

[LSUMurse]

Thank you both for your replies. I will go from here. I am inclined to attempt to make my own push rod. It's not that I mind bleeding the brakes, it's more a money issue. I hate fiddling with safety equipment, though.

I have decided that this truck is VERY resistant to change. I was calling her Rosie (after the AC/DC song "Whole Lotta Rosie"), but I may switch to Christine. She's certainly going to kill me!!

[jocko]

the whole enchilada: http://www.oreillyauto.com/site/c/de...1305&ppt=C0066

just the mc:
Oreilly lists three, only one specifies "manual or power" which means they don't know what they are talking about (pic of the middle one with this wording looks like deep bore - and wouldn't work) - really have to follow "buyer beware" (i.e. know what you need and ignore the parts counter gal).
http://www.oreillyauto.com/site/c/se...make=Chevrolet



Easiest route: return your Booster - and buy the combo (1st link), that way you know you're good to go. I understand $ are an issue, but doing this would only be sinking about $20 more into the project.

[SS Tim]

Really think the travel is a matter of incorrect pushrod length. Since the factory sold booster kits for dealer installation (C10 P/N 987446) it would seem that this is a simple swap given the right parts. Unfortunately I don't have a kit breakdown, but given the dealer price of $28.60 plus a 1.0 flat rate for installation vs $45 for the factory J70 option I'd say it was a dry swap kit (booster&pushrod only).

But even with the correct installation if the booster is used and unknown ("it's off either a '67 or '71, I haven't gotten the info yet")that may very well be the root problem. Have you tried pulling a vacuum on the booster with a vacuum pump or even another engine to verify it does not leak.

Last thing is the vacuum source, a transmission modulator line is generally a lot smaller than a brake booster vacuum port. Have you reviewed the factory service manual on the brake and vacuum systems?

[hyatt]

Your vacumn line needs to be at least 5/16 to provide enough vacume to power the boosted I always use 3/8 line

[chipflyer]

LSUMurse, take a look at this old link http://67-72chevytrucks.com/vboard/s...d.php?t=214559
If you start at post # 6, look at the pictures, AND read the descriptions I think you will find the info you are after.
Hope it helps

Jeff

[kevmic28]

I had the same problem when I did mine. I think I may see your problem. There should be a rubber gasket that fits on the end of the master cylinder between the master and the booster. With the engine running can you hear a vacuum leak from the booster?

[First c10]

I installed the mc from a 72. Even though my truck is still a drum/drum truck. But soon I will be upgrading to front discs. I picked up the the complete setup from oriellys. 103$. All I had to do was drill a hole 1" lower then the stock Manual mc. The hardest part was lowering the column to install the bolt that attaches the rod to the peddle.
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[LSUMurse]

Chipflyer: I read that, thanks though. The setup I bought was complete from the pedal rod to the prop valve. I assumed it was a matching set, but it's looking like it wasn't. I do appreciate the heads up though. I have a lot to learn about these trucks.
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[68gmsee]

The manual master cylinder will work with the power booster. I used my original one with the booster for about 15 years on my 68 with manual drum/drum. But, the push rod has to be the correct length. Pull the one you have off the booster to look at how it's made. If it's like mine you'll need access to a machine shop to do it. Just depends on which booster you have.

[Steve Hafner]

I'm having the same type of problem . . .

[68gmsee]

fyi: Another thread on the subject of pushrods...
http://67-72chevytrucks.com/vboard/s....php?p=5066561

[LSUMurse]

So, here's the latest:

I went to Home Depot and bought a 3/8 x 6" grade 8 bolt. I cut the head and threads off. This left me with a rod that was 3 7/8" long. By my measurement, the depth of the booster and master cylinder is 4". Seems like it should be a perfect fit.


Unfortunately, it did nothing to fix my problem. I called Carquest and they're supposed to have a new booster to me this afternoon. The engine still runs rough with the vac line connected to the booster. So, I am hoping I actually have a blown diaphragm in the booster and this new one will solve my problems. I was going to buy the MC and booster together but nobody in my area stocks them. The counter guy said the picture showed a plunger in the booster that stuck out almost as long as the bolts.

I guess we'll see. Everybody say a little prayer.