55.2-59 59 3100 rear brakes

[2001convertable]

Hi everyone, I did the power brake conversion over the summer. My rear brake have been locking up on a full traffic light or quick stop. I took the truck into a friends shop to have the brakes adjusted which are four wheel drum. After leaving the trouble was still there and the rear brakes are getting hot. The fronts are not getting hot. I was told to install a manual valve on the rear brake line. I bought a wildwood 260-8419 which would cut down to 57% of pressure. Well after the install and a good day I started adjusting. With the valve turned in all the way its still the same. The rear wheels are also still getting hot after a short drive. I checked my e brake cable and they are loose even with no drag. I even shorten the linkage to my new master. I took off my rear drums and used a caliber to get the shoes close.Maybe I need a valve which will give me more than 57%? Im at my Witts end with this. Please if anyone can help.

[mr48chev]

It sounds like the rears are doing most of the braking when the fronts should be doing most of the braking.

If you have a dual master cylinder you do have the correct ports on the cylinder hooked to the correct end of the truck?

Inside the brakes, all springs correctly installed and in good condition? I've seen a couple of "we did my brakes on Saturday and now they don't work right" rigs on Mondays that had the springs installed wrong.

I've also seen some older rigs that had springs that had been stretched out so much over the years that they didn't have enough tension.

The brakes should get hot to some level as friction creates heat and if you have no heat after driving you didn't have any friction inside that drum.

[2001convertable]

Hi, the master is facing backwards under the cab. The port toward the booster is going to the rear brakes. I put all new springs in as well recently.

[bobinbc]

It sounds like you may have disc/drum master instead of a drum/drum one.
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[2001convertable]

I was told it didn't matter when I ordered it. I didn't mind putting it in as if I decided to go with front disc it would be ok. When I ordered it from brothers I selected the drum/ drum.Do you think that is the problem?

[bobinbc]

Easy way to tell - if both chambers are the same size then it is drum/drum. Did you put a residual pressure valve in the system?
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Also it most definitely matters what master you put in there. Your tech advisor should be pushing a broom!

[2001convertable]

Thanks. I called Brothers today and spoke to Mark. He checked with the techs there and got back to me asap. He said the master is ok no problem but he said I had to install a residual pressure valve in the system like Bobinbc just mentioned. I ordered it and I will mount it in front of the wilwood valve I already installed. After the install I will back out the wilwood valve all the way and adjust as needed. I hope this works or Im just going to do a disc brake install and call it a day.I will keep posting after this. If anyone has any more input Im listening. Thanks to all

[2001convertable]

Ok, Im back. Mark from Brothers called me to tell me the residual pressure valve wouldn't work as he spoke to the guys in the shop. He asked me to lift the front of the truck to see if the front brakes are applying and call him back. Well I did and the front brakes work fine. I called him back four times only NOT TO GET A REPLY. So I was thinking perhaps they sold me the wrong master with the set up. I think I will call inline tube or Cpp. If anyone else can help that would be great.

[bobinbc]

Sorry when I was asking about a residual pressure valve I should have been more clear. Drum brakes require a 10 lb. residual pressure to counteract the spring tension in the drum system which tends to pull the shoes away from the drums. With out it you will have a longer pedal travel and "spongy" brakes. The residual valve holds a pressure keeping the shoes near the drums giving a higher firmer pedal. On a drum/drum system you'll need RPV's on the front and rear brakes. Also required is a metering valve to the front (the metering valve prevents nose dive). You can run without the metering valve to keep the plumbing simpler, and then would only need one RPV on the front line and one on the rear. Some master cylinders already contain RPV's like in this diagram. A lot of parts places sell a "Corvette style' master which has no valves, equal size chambers and exit ports. When used with disc/disc and mounted on the firewall no RPV's are needed. If used underfloor and with disc/drum or drum/drum RPV's will be needed. You should NOT need an adjustable prop valve if all of your wheels have the stock brakes on them.

Brothers should be able to tell you if your master has valves in it or not. This may not be the only cause of your trouble but if all you changed was the master and booster and the brakes were working fine before then I would start there. BTW my 56 GMC with rebuilt stock brakes is capable of locking all four wheels if needed at 50 mph, no power assist. Hope this helps...

[1project2many]

Is RPV the best solution for rear brakes applied when pedal is not engaged or for rear brakes engaging to quickly or too hard?

2001convertable, some questions:

1) Were the rear brakes locking before the power brake conversion?
2) Were the rear brakes getting hot before your friend's shop adjusted them?
3) What size tires are you running in front and rear?
4) Do you have any information about the manufacturer of the m/cyl? Original part no?

Thanks

[qbeanie]

You may need to rebleed the master cylinder

[2001convertable]

I will look over the weekend. thanks to all

[2001convertable]

I called Brothers back and could never get the same person who started to help me so I just called CPP and ordered everything thing needed for a disc brake conversion. The only concern is the front rims fitting. Is there a way in which to get them to fit via spacers and are they safe? I don't think I have an original set on there to begin with.