2nd Gen Non-Engine/Transmission "AIR" brakes . . .

[Joe Mc]

Taking on air somewhere but not loosing fluid so it's hard to find. Thought the pedal slowly creeping to floor was m-cyl old (154k) and so did a few folks here. So for $100 stuck new on on. Bled a ton of air out of the rears even though I bench bled the new cyl. Once all air out everything was fine, pedal high and hard . . . for almost a week. Now I have to pump to stop again - not fun. Feels like the back drums are not working at all till I give it a pump or two. When I bled the system after the new m-cly install I couldn't believe all the air that came out from the rear and very little, if any, from the front. So at least it seems like the air is getting in the back system. I know best is to hand over hand but haven't found any wet spots - like I said not leaking fluid - pulling air in from somewhere.



Any help/ideas how to find whgere air is getting in is appreciated.

 

[Hoefler]

Check the adjustment on your rear brakes. You could be over extending your wheel cylinders.

 

[Joe Mc]

Adjustment is dead on. Any other ideas anyone.

 

[jelag]

Joe... .

Tell us what dead on means... . have you mechanically adjusted the rear drums so that the shoes just start to drag..... Most rear drums don't adjust up like they should because we don't back up enough to make the self adjuster work...

 

[Joe Mc]

https://www.turbodieselregister.com/forums/showthread.php?t=175821



Maybe referring to the post I began about this earlier this year would have helped on my part. As far as what does "dead on" mean. I adjust the star wheel until the wheel will barely turn then back of 5 clicks - holding the locking tab just of the star wheel so I can count the clicks.

 

[MEby]

check the flexible rubber brake line sections... . they always seem to go first on my vehicles.

 

[DavidC]

Take a look here Joe. May not be your problem but it will at least it will put you on a hydro-boost brake site where maybe you will find the answer or post the question. I know you have had this issue for a while and I think the well here may have dried up (no offense to anyone intended).

http://www.hydratechbraking.com/forums/viewtopic.php?t=135



Dave

 

[Brand-X]

I just was talking to my son about a like problem, He did brake pads on his girlfriends mothers mustang and tightened the rear shoes. The repairs were done because the pedal was extremly soft he did get air out while bleading the system. The brakes were great for a couple of days then the same thing pedal was soft air in the system again. The fluid level did not go down so no leaks at all. After several atemps to find the problem He replaced the master and that was the final fix. Not saying this is your problem but it worked for him... George

 

[McCRam]

We went through two master cylinders on my uncles 98. 5 before we got a good one. It was quite frustrating. The symptoms were similiar to what you described, but the truck was not driveable, or should I say stoppable.

 

[surfbeetle]

Did the same on mine last week, new master cyl and new wheel cylinder on the rear. I had the same thing, I used a power flusher to bleed everything and completely changed the brake fluid to some Valvoline Synthetic DOT 4. I didn't bench bleed I probably should have. I ended up manually bleeding after the bench bleed and now everything is fine. My master cylinder came with a new reservoir on it, my old one had been leaking at the reservoir. Maybe you're getting air in there and losing prime at the master cylinder. Good luck.

 

[Joe Mc]

New (not reman) master cyl w/new reservoir was installed, bench bled and then after recognizing the pedal was still soft - I bled the system and go tons of air from the back system (drum) the front (disk) had no air. So the infiltration seems to be related to the rears not the front and there isn't any fluid leaking? I'm not sure how the hydo system would allow air into the brake hydrolics as they are two separate systems - correct?



I'm really looking for any hints on how to locate an air infiltration without having to go over all the fittings. I do have a new rear hose and plan to put on this weekend so maybe that's it. Will get back to you all thanks again.



Guys keep em coming.

 

[Joe Mc]

Latest:



New rotors & pads, new front bearing assemblies and new studs. Just because the rotors were thin and I've been trying to get rid of the front end wobble. New psi equlizer valve, new rear brake hose and line to rear load sensing valve. Took forever to get clear fluid in the rears and the front wasn't too bad. First press on the pedal after bleed - 3/4 to the floor#@$%! What in the world am I doing wrong here



Should I have the system power bled? I'm loosing my friggin mind here :{ :{ And the wife ain't too happy either :-{} :-laf



HELP!

 

[Brand-X]

Before you pay some one to power blead check these out http://motiveproducts.com/frame-bleeders.htm

 

[jelag]

I would suggest the following... . and thanks for your answer on dead on... . we do adjust ours... . but we run them up until they lightly touch and do not back them off the 5 clicks you do... . I suggest you try this... .

Remember that the self adjuster will bring the brakes closer than your process...

The other item we've found in some vehicles is a relationship problem between when the pedal goes down and when the brake rod connects to the piston in the master cylinder... . We've seen some vehicles with the correct diameter piston in the master cylinder but the wrong depth of hole in the piston... the hole is too deep and or the rod is too short... so part of the pedal stroke is lost taking up the distance... ... . the piston goes down but not past the port in the top of the master cylinder connecting the reservoir to the piston chamber...

You build up pressure..... only to find part of it bleeding back and the pedal drifting to the floor... the test for this is to pull the master and put it on a bench plugging both ports to the front and rear brakes with a plug..... if the piston in the master cylinder moves and stops half stroke because its come up to pressure than your master is good..... on the bench... . look for either the rod issue I've talked about above... . or something in the abs system..... those are the only things that can allow the pedal to drift to the floor...

BTW we had one of these today... . it had, had 3 masters on it... . and each drifted to the floor..... we bench tested it and found it to be good... . we found that the pedal would mover almost 2 inches before the rod would connect to the piston in the master, we corrected this by installing a rod long enough to take up the stroke... I think it was close to 3/4" longer.....

We find that someone has either overhauled the master with the wrong parts, installed the wrong parts..... or in one case the rod was the wrong rod... .

Hope this helps.....

 

[Joe Mc]

Pedal is High and Hard again ...

Just a ton of air in the back system - again. Never had this problem before and I've done a good deal of brake (hyd syst) work over the years on this truck.



Jim thanks for the reply. I've had what you are referring to happen (short rod - "story of my life" LOL) on autos when using remaned m-cyl, which is why I bought "new" for a few dollars more. What you are saying makes perfectly good sense. Now my pedal is high and hard again - for how long will be the test . . . I know even "new" can be bad so if it happens again I'm going after what you've suggested.



BrandX thanks for the site.

 

[surfbeetle]

I know it seems a little obvious, but I have to say it. When installing the Master Cylinder, did you use teflon paste on the threads of the brake lines where they seal into the Master Cylinder? The teflon tape doesn't work as good as the paste. It seems to me that it may be gradually sucking air into the system. Just a thought.

 

[Joe Mc]

Surfbeetle - I have "never" in my experiences used teflon paste on a brakes system connection as the lines and ports are set-up with double flares. This doesn't mean I won't try a logical suggestion. The thing that troubles me about what I'm experiencing is the air is "only" getting into the rear drum system. So I'll probably look at the rear wheel cylinders and replace this weekend. That's what I get for installing GM parts on my Dodge - did the 3500 rear cylinder upgrade about a year + ago . . . . .

 

[Joe Mc]

Haven't R & R the rear cyls yet, talking with friend who think maybe the rear load sensor (thingy on frame w/rod going to rear housing) is taking in air??? Anyone ever by-pass this unit? Sucker costs out at almost $300 !!!!

I'm bald enough and am starting to pull hair from areas other than my head now "OUCH" that smarts!!! HELP.

 

[Brand-X]

We did not take it out of the syster but my buddy lifted his truck so we wire tied it in one position for a year or so he moves campers for a local rv dealer and never noticed the diffrence... George



Also I have seen them on ebay...

 

[Joe Mc]

Here's the end result - Those "supposed up-grade" 3500 GMC Dually wheel cylinders that I put on last summer . . . both of them were bad - they were "new".



I changed the rear shoes a week or so back and while doing so I noticed a little bit of dust on the front stems (both L & R, that come out of the cyl) and decided to pull out and clean "dribble" out came brake fluid. So the leak was in the cyl, but didn't reveal fluid - sucked air in but didn't reveal fluid #@%#^@ at least I found out what it was - need I say I replaced them with stockers. %#$&&*#^



Thanks