The Stovebolt Site Forums The Shop Area General Truck Talk Power brake conversion troubles

I have a 1957 Chevrolet 1/2 ton truck that I have restored nearly single-handedly, as close to original as possible. My only variances are a 1960's V8 and a 1980's 5 speed manual transmission.
I initially converted my master cylinder to a manual dual cylinder, but I wasn't pleased with my stopping ability. I then purchased a power brake conversion that stayed in the original location but have had loads of trouble with it as well. I've adjusted the rod between the booster and master cylinder, going from too much brake to not enough and never finding the happy medium (even purchased a tool to adjust it). I currently have brakes at times, and none at others (quite a thrill ride and too dangerous for me to risk wrecking my labor of love).
I've read a dozen articles on brakes, and still can't get them correct--bled system many times, new brake line are not above the master, residual check valves in place, etc. CPP tells me that due to the manual transmission, my only other option is a unit that mounts to my firewall and replaces the brake pedal--that is more hacking than I want to do on my truck (want to keep it as original looking as possible).
Any ideas?

I don't have the answer to your question, but just wanted to welcome you to the Bolt!

Questions.
Did your brakes always work with your old duel mc. even though you didn't like there performance?
When no brakes happens Is the pedal rock hard or does it go to the floor?
Do you lose brakes after hardly driven or only after a longer drive?

I have a CPP system on a 55 2nd that I'm very happy with.
Could it be something simple like bench bleeding the master cylinder. I don't see the problem having manual transmission.

The brakes did work with the manual dual cylinder, but I had trouble stopping going down some of the steep hills here in West Virginia. If I adjusted the brake shoes out to help, then they would drag and smoke.
Currently, when I start the truck up, I find the pedal is soft at first, but firms up with a few pumps. Then I'll drive and find the brakes work good for a while. Driving about 30 minutes or so, I will hit the brakes to find the pedal goes to the floor and I have no stopping ability.
I feel like giving up and starting with a new MC, but as I said, CPP tells me my only option (due to the manual trans) is for the firewall based unit.
Any help is appreciated.

Is your CPP unit under the floor, like original?
Bench bleeding could be the issue--my MC came from a fellow who sells online (Old Irish Dave), and was supposed to have been bench bled already. I didn't attempt any further bleeding, but wonder if there could have been air in the system. When I first put the unit on last year, I had a devil of a time bleeding the brakes, as it seemed there was so much air in the lines. I have considered taking truck to a
"real garage" and asking them to bleed the system with a vacuum pump.
I don't see the issue with the manual trans either, but CPP says that all under floor power brake systems should not be used with a manual trans--the worker that I spoke with there couldn't explain why, but said that I shouldn't buy one.
I've heard nothing but good about CPP, so I'm sure they have some reason.
Thanks for the help!

You may still have a tiny bit of air in the MC and depending on the angle that it is mounted, you may not be able to purge it completely. This is why bench bleeding is so important. Raising the front or back of the rig to level the MC will help with bleeding this air. You could also have a MC issue, fluid bypassing the seals inside.
Now for another question.
How close is your exhaust pipe to the MC or brake lines? I have seen several times where the exhaust has been to close causing brake fluid to boil causing brake issues. Rerouting the lines, shielding lines or moving exhaust cured many problems.

As far as manual versus auto trans, I just don't see the correlation.

Do you have drum brakes? Are they getting hot and fading or could a drum be cracked? What shape are the wheel cylinders in? First though, I'd bleed the master like others have suggested. Probably easier to remove it and bench bleed. If you have a proportioning valve, I'm not sure if it needs bleed too

Hy WVPharmer, welcome, so just to clarify, at the moment your truck is equipped with an underfloor boosted dual master cylinder, is that correct? When you say too much brake, do you mean the brakes would lock up on every application, or was it just the rear brakes that locked up? In order to bleed the brakes properly first the brake shoes should be adjusted as per the procedure in the manual, brake shoe adjustment can also cause problems with braking performance. You said you have the residual pressure valves in place, was the master cylinder you installed designed for a drum/drum, disc/drum, or disc/disc system?

My MC is level, but I think taking it off and bench bleeding is a great idea--going to work on that today.
One article suggested testing the seals by plugging the outlets and seeing if the brake pedal is stiff. I'll do that as well before I remove it to bench bleed.
I haven't heard about the exhaust issue, but my MC is pretty close, and may explain why the brakes get worse once I drive about 30 minutes. I'll look into either rerouting the lines or shielding.
Thanks!

Yes, I do have drums on front and back. My drums aren't brand new, but do not have many miles on them, so I think they are OK. The wheel cylinders were replaced a few years back, and also only have a few thousand miles on them. I replaced the brake lines with new stainless steel ones (since I had to reroute due to change from single to dual reservoir MC)--they were made by Inline Tube.
No prop valve, since all drums.
Thanks!

Yes, I do have an under floor dual MC with booster.
By too much brake, I'd find that the brakes would drag, and brakes would get hot and smoke (also impossible to go backwards). The issue there was the adjuster screw between the MD and the booster.
The MC was designed for drum/drum (like I have), and was supposed to be appropriate for a manual transmission.
Thanks!

Hy WVPharmer, "(also impossible to go backwards)", could you have your brake shoes on backwards, should be the shoe with the shorter lining on the forward side of the backing plate on all brakes, please check that that is the way they are. Now adjust the booster to pedal rod to have a little clearance to make sure that the master cylinder can return to its correct at rest position and uncover the compensating port, adjust the brakes and try them again. As others have suggested you may want to remove your master cylinder and bench bleed it just to be sure there is no air trapped in it, if you do do that then you'll have to bleed your brakes one more time. Once you get your brakes working correctly you may find you are getting more rear wheel lockup than you like, you can install a proportioning valve in the line to the rear brakes to stop the lockup. Most manufacturers have installed an adjustable proportioning valve in their pickups rear brake line to give the vehicle less rear brake when unloaded, hope that helps.

No, the shoes are on correctly. When the system is working, things go fine and I can back up. That occurred when the adjusting rod between the booster and MC was too far out, and the fluid was not able to go back in the MC, causing brakes to be "on" all of the time.
I did bench bleed the MC today. I also capped both ports and put MC back on truck, to find the pedal solid (indicating no leak in the MC seals). I also found that, per an article that I read, it does not appear that the MC has residual pressure valves in it ( I couldn't see them with flashlight, and a paper clip pushed into the outlet port went in over an inch). I'm thinking that also could be the issue.
Next steps are adding residual valves, bleeding system again (running this time, as has been suggested) and seeing how that helps. If still a problem, will add heat shield, as MC and lines are only about 3-1/2 inches from the exhaust pipe on that side. If all that doesn't work, then I guess I'll have to put a unit on the firewall, as much as I don't want to do that.
Thanks for all of the help!

Im not sure about bench bleeding, it's so hard to keep air out while you get it back in the truck. Any master cylinder will expell residual air out the fluid inlet hole on the first small part of the stroke. As above, set the truck so the master cyl is level or so the fluid inlet hole from the reservoir is slightly high.
I cannot think of any reason why a manual trans makes any difference.
Try bleeding with vacuum. With out vacuum, make sure you have a solid pedal and working unboosted brakes. Check that remote valves, proportioning valves, etc, are mounted the rightway up so as not to trap air.
it takes some heat to boil fluid but its possible. Any brake line should be at least a foot away from an exhaust. You could rig a temporary shield from tin cans and duct tape on the lines, not the exhaust, to test that one.
good luck.

The person at CPP is full of it regarding having a standard transmission. There is no logical reason that it would make any difference. I have installed many conversions on TF trucks and others, both disc and drum and not had a problem. I have not used CPP however. You have a defective booster/master combination, or they gave you the incorrect components for the system. Kits sold today are almost bullet proof, install, bleed, adjust and go on down the road. You are having way too many problems for this to be anything but defective components that they provided.
Fred

Hey guys,
Sorry I didn't get back with you for a month or so--life gets in the way sometimes. Update: I tested the MC by placing plugs in both outlets--very firm pedal tells me the seals are OK. While lines were off, I looked for signs of residual check valves and found none. I purchased and added 10 lb check valves for front and back, then bled the system again (first with engine off, then with engine on). What I found is that now the brakes on the first push of the pedal have almost no resistance (just before going to the floor a little, just enough to slow truck down but not stop it). The second push, though, has perfect resistance and great stopping power--so I can stop but only with the second pump of the brake pedal (not great reaction time, that's for sure).
Any ideas?
The only thing that I can think of at this point (from all that I have read) is that the new brake lines may have a point where the arch up and may have some air caught in them that is not coming out with bleeding. I'm just about to give up and convert to a system on the firewall, but hate to not be original (with MC under the cab).

Hy WVPharmer, I was beginning to think you fell off the earth. Are your brake shoes adjusted as per the manual, what you are describing is the wheel cylinders pushing their pistons out to the drums on the initial application and after that the braking action is correct. This is also an indicator of possibly trapped air, hope that helps.

If the booster is like others I have driven with, removing the vacuum feed should give you a normal manual unassisted system. This would be a good test to see if it is the booster or or the rest of the system.

They may claim will not work with standard trans due to the way the stock clutch linkage works- shares the
shaft with the brake petal and their bracket would be
in the way for the stock clutch linkage. As stated if your setup is ok then it should not effect the brake.
If you have as much clearance to the exhaust as stated
I find it hard to believe it is causing your problem but be sure to check it with the weight of the driver
in place

There is nothing in the way of the stock linkage vs the aftermarket under the floor booster/master. My truck is living proof, I did the conversion 15 years ago. 350 V-8, 3 speed OD trans, daily driver. I just did another one about 6 months ago on a 55. No problem what so ever with bleeding or any performance.
They more than likely provided mis-matched or defective parts!
Fred