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Topic Review (Newest First)
05-18-2013 12:46 PM
T-bucket23 Are you sure you have the front calipers on the right way. The bleeder needs to be at the top. If it isnt you can bleed them forever and you will never get the air out. I have seen this several times and is an easy mistake to make.
05-17-2013 12:15 PM
bubbahotep If your brakes were locking up and then got better after you let the truck sit: you have the brake booster arm (where it goes into the master cylinder) out too far. You have the master cylinder partially compressed causing pressure to build every time you hit the pedal

Reduce the length at least 1 full turn in. They say 1/64" of play is ok but you can have more and still have a good pedal. Regardless, brakes rubbing and locking upward usually the booster arm is too long

Going farther back you said the pedal goes to the floor and you eventually found a leak. That should be the fix. If the pedal still drops then you're still losing fluid somewhere

Fluid squirting up from the master cylinder (with the cap off) is normal.

The combination valve you're picturing would have no effect on bleeding. If its not working properly you'd have hard brakes in the front or rear only. There's a way to test the valve position with a bulb but I don't think it's necessary

Hard pedal with engine off is normal and tells little.

Fix the brake booster rod length first.
05-13-2013 02:52 PM
RatPin This is the setup I am using:


When my pedal is at it's neutral position the booster linkage and pedal pivot are pretty much straight up and down from one another, but I don't think that should make a difference since I have the booster shaft fully extended out in the pedals neutral position.

I also noticed when I apply the brakes with the master cylinder lid off that fluid will jet up from the bottom of the resevior. I take it this is normal?

I noticed in the picture of the GM combo valve below that it says to hold the metering valve when bleeding the front brakes. I have just been bleeding the brakes the conventional way with pumping the pedal. Is this metering valve really necessary to properly bleed the front brakes?

05-13-2013 12:42 PM
RatPin Man I'm really having trouble getting these brakes dialed in! I drove it to work this week and after driving about 20 minutes pressure builds up and the brakes drag. Shut it off for a few minutes and it goes away for awhile only to come back. I have adjusted both rods all over the place and I either get pedal to the floor or full pedal stroke before solid pressure right at the end of the stroke, but that's when the pressure builds and causes dragging.

Am I supposed to have a firm brake pedal right at the top of the stroke? With mine I have about 80% pedal stroke with what feels like light vacuum assisted braking, but the pedal really does not get firm and stop until the very end of the stroke and thats when I get the pressure build up. If I adjust the rod ine turn off then the pedal gies to the floor without any stopping pressure.

My pedal ratio is 6:1 and have a vacuum line that is about 30" long from the floor mounted booster to the carb.

Any insight is help is very much appreciated guys. I dont want to buy a new master if it might be something else. I just want to drive my truck?
03-17-2013 05:58 PM
RatPin Got it figured out for the time being. Thanks for the help!

Here she is...
03-17-2013 01:11 PM
RatPin After closer investigation I found a banjo on a front caliper loose with a slow leak so that would explain the slow pressure loss. I'll re bleed the front reservoir and try again.
03-17-2013 12:40 PM
LATECH If the pedal was falling away from your foot towards the floor (pedal drop) , then you either have a leak, or the master is bad.
03-17-2013 12:29 PM
RatPin Ok, I extended the shaft between MS and boster about 2.5 turns out and it did give me a nice firm pedal and brakes grabbed well. I took the truck up and down the driveway and while turning around and holding pedal firm the pressure seemed to slowly fade and go away. Do you think I need to re bleed the system now since making that adjustment? Or should I extend that shaft out another half turn? The important part is we are making progress here!
03-17-2013 09:17 AM
RatPin I will follow the steps above today to see if I can solve the problem and report back. There is only one line going out to supply both front discs.
03-16-2013 10:50 PM
aosborn So the pushrod to the pedal sounds like it is adjusted properly. Next, you need to check the pushrod between the booster and the master cylinder.

Remove the master cylinder (you don't usually need to remove the brake lines) and check to see if the small pushrod coming out of the booster is threaded and adjustable. If it is, lengthen it 2 or 3 turns and then slip the master cylinder back into position and see if you can feel the pushrod touching the master cylinder. If you can, shorten the pushrod 1 turn and try again. Just when you get to the point where the master cylinder will mate back up with the booster without touching the pushrod, shorten it 1/2 turn more and you are done. If it is a little out of adjustment it makes a big difference in pedal travel.
03-16-2013 09:15 PM
RatPin I had to shorten the threaded shaft that comes out of the booster so it would extend out all the way when pedal is all the way out. It travels a long way so I would think it completes it's stroke. Pressure does not build when pleseing pedal.
03-16-2013 08:53 PM
aosborn That system utilizes a combination valve. No other additional valves need to be added. Just make sure you have the lines connected to the proper ports on the combi valve. Typically there are two ports at the front of the valve for the front brakes, and one out the rear for both rear brakes.

Make sure the pushrod between the booster and master cylinder is adjusted properly with minimal clearance, and that the pedal is installed with enough travel to bottom out the master cylinder.

Does the pedal pump up indicating that there is still air in the system?

Regards,

Andy
03-16-2013 08:39 PM
RatPin I'm using kit numer BR2918 from american classic.

Here it is:

American Classic Truck Parts Inc.

Does that tell you anything? I really appreciated.
03-16-2013 08:20 PM
enjenjo
Quote:
Originally Posted by LATECH View Post
Some GM masters did not have them. You need to find out if yours has them. Chances are it does...in the rear....but maybe not the front .
That needs some research...as you will want 10 PSI valves in the front an 2 PSI in the rear.
What bore size is the master and does it have a big and small reservoir?
That would be 10 PSI with drum, 2 PSI with disc. The Brake Man - ValveTechI
03-16-2013 07:45 PM
LATECH Some GM masters did not have them. You need to find out if yours has them. Chances are it does...in the rear....but maybe not the front .
That needs some research...as you will want 10 PSI valves in the front an 2 PSI in the rear.
What bore size is the master and does it have a big and small reservoir?
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