Brakes help.....???

[entourageguy]

Just spent the weekend under my truck updating the brakes and I'm beat.I have dis/drums dual master with a power boster under the floor. I installed a combination valve with the residual valve built in for the rear and a residual (2lb) for the front discs. I have gone thru 3 bottles of brake fluid bleeding and brakes are still not any good. I know that there may be a problem bleeding because the master cylinder is almost as low as the wheel cylinders but come on!!! To top it off I leaned over this morning and put my back out. My kids legs (well right ones) are tired from all the pumping of the pedal. I was using a combination of the pedal pumping and a hand vacuum bleeding kit. I even tried raising the front to get the cylinder higher for doing the rears. any suggestions?

[dwcsr]

describe this statement - "brakes are still not any good"

whats not good about them. low pedal, spongy pedal, hard pedal?

[CAL 58 GMC]

I have the same master cylinder as you do. I had to use a Vacuum Pump Brakes Bleeding tool. Here's one on e-bay, but you can buy them at most parts stores. The bleeder suck the fulid through the lines getting all of the air out. http://cgi.ebay.com/MityVac-Vacuum-P...QQcmdZViewItem

[entourageguy]

Originally Posted by dwcsr

describe this statement - "brakes are still not any good"

whats not good about them. low pedal, spongy pedal, hard pedal?

Low pedal. After bleeding them for quite a while the pedal starts to firm up but will still go to the floor.
Cal I have been using one of those vacuum pumps as well.
Brian

[CAL 58 GMC]

You might want to go back and recheck all of your fittings. I found I had a residual valve fitting that was loose. Just a thought.

[dwcsr]

Is the rod to the booster adjusted properly and the rod to the master?
If the pedal is low but firm and the pedal does not feel spongy or firmer after pumping them up, it could be the rods are not adjusted to the proper length or the master has to small a bore.

I would first find the correct size plugs for the master to block off the out put flow. This will tell you if the rods are not set right or if the bore is too small or you have air in it.

All the steps below assume that the rubber lines are new, in good condition and are not budging under pressure.

You should get the following with the engine off:

You should have a seriously firm pedal at the correct height, rock hard on the first push with the plugs in.
If you don't and do after a second pump. You have air in the master, re bleed just the master.

If its rock hard and low then it’s the rods adjust the rods.

If its firm and the correct height then re connect the rear lines and adjust the rear brakes up tight so they can't turn by hand. See where the pedal is.

It should be firm and at the correct height, if not, is it after one pump? If firm after one pump then bleed the rear again.

Block off the rear brakes and connect the front disc line at the master and check to see if the front wheel bearings are tight, torque to 20 –ft/lbs, this will set the rotor straight and center the caliper . Push the pedal a few times and let it rest a few minutes.

Try it again. If it’s low but firm it’s the master (see Note*) if its firm after one pump bleed the front again.
Measure the bore. If it’s an inch go to 1.25” if 1.25” got to 1.5” be aware of the rear cup depth. Power brake systems have a shallow cup ½” or less and non power have a deep cup ¾” +- if you have a power system with a deep cup change it to a shallow cup master and try it again.

Readjust the front bearings.
While running it will be slightly lower pedal from the booster assist.

* There is one other possibility if you have GM calipers is that you have early 80’s calipers that are the low drag calipers. They retract further than the standard calipers and often give the feel of a low pedal when applied. The only way I know to test that is to remove the caliper, place a steel plate across the piston and put a clamp on it then tighten it to bottom it out. Then try the pedal again. If then its firm and correct height you have the low drag calipers change the calipers.

[entourageguy]

Thanks DW for all that info. When you say reconnect the rear brakes/front brakes do you mean thru the combination valve? Also before the combination valve was installed the brake pedal was firm but at the bottom of the stroke. Would this indicate that it might be the rod? Next which flight are you coming in on from Houston we can put you up for a day or two while you help me straighten out this problem!! I'm discovering one of the problems of having a lowered truck and loss of my youthful figure!
Brian

[dwcsr]

It would take a day to push my fat a$% under the truck and a day to get me back out.

If the pedal was firm but low I think you may need more volume coming out of the master.
It may be a really short rod and I would look at that first. Pull the master and see how deep the cup is and see if when you put the master back on does it set out a little and you need to use the nuts to draw it in or does it slide up tight to the booster without the nuts holding it. It should be approx. .050" -
.065" away from the booster and need the nuts to draw it up tight.

The real question is when it was low and firm did it stop good.

With a combo valve in there the shuttle valve may have shifted one way or the other so you don't get a good bleed or it has shut off front or back.

When I say connect or disconnect I mean at the master leaving the lines intact on the combo valve. But you can also try it at the combo valve pressure out side. it should be that same results

[entourageguy]

How would you reset the valve if the shuttle has moved?
Brian

[dwcsr]

if its new it should reset itself. They used to have a threaded pin that you would screw into the hole in the top where the switch connectort is. It would keep the valve from moving during bleeding. What does your look like. can you post a pic. some also has a pin on the end that you used a clip on to center it.

[entourageguy]

the combo valve looks like this

[entourageguy]

Crawled under my truck today and did some measuring. For my approx 6" of brake pedal travel the rod attached to the brake booster moves 1/2". Anybody with an aftermarket below the cab power set up that can give me a measurment on their brake pedal ratio would be greatly appreciated. I think I need to extend the arm on my pedal. Just trying to figure out how much. thanks
Brian

[entourageguy]

Well I crawled back under my truck today. Took the pedal and linkage out and made an extension for the booster side of the pedal linkage. That moved the clevis approx 3/4" to 1" farther away from the pedal pivot. Now the pedal moves about 2 inches and does it stop. When I picked up this truck you could not get into a panic stop situation as you could not stop quickly. Can't believe the p/o drove it this way. Although his mechanic told me he had alway had trouble with the brakes. Brakes are now fixed so now I can drive it to the place I will be storing it in for the winter.

now to find some of those white walls.......

Brian ..