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Discussion Starter · #1 ·
All right heres whats going on. First I am getting new knee in 2 weeks have bad back and been out in garage for last two weeks doing everything I can think of? Am 66 been mechanic all my life and very seldom get defeated in a job but this has done it.
Started off just new front pads & turn rotors--Put on Bosh perfect-stop pads
OH brake pedal never was good but could slide tires on gravel road ok,
Now No brake pedal? Hard when engine off to floor when on?
New master cyl/ then that was bad [leaked at reservoir seal] took back then put up-graded New style MC on, No change?
Took to shop to power bleed they found combination valve leaking
Took back home I took off ABS and put on new combo valve Bleed and Bleed and Bleed the system there is no air in this.
OH put new rear cyl on last year checked and adj, there ok
Now took out on my gravel road with all this new and Dam pedal goes to floor and CANNOT slide tires on stone road???

Can the power booster do this? Theres nothing else to replace????

I QUIT!!!! I CANNOT DO THIS ANYMORE!!! I need the truck and with knee surgery around corner dont know what to do????

What can possibly be left to change???????????
Truck is like new NO rust very clean low miles?
 

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If you step on the brakes do you notice a changer in the idle? If so then it's the brake booster. Unless the master cylinder is defective. Just because it's new doesn't mean anything. I've gotten three bad fuel pumps, two from Advance one from Napa.
 

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‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
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Sorry about the brake woes, Charles.

Wolf’s right. Sometimes new doesn’t equal good.
Unfortunately, you‘re not the first to have MC issues.

I got sick of the soft pedal on my ‘95 short step and I put a MC from an’02 Tahoe on. Best braking ever.
You need an adapter for the front circuit since GM changed it in 1999.


This adapter will allow you to do a direct plug and play.
As you already know, bench bleeding is mandatory.
 
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Discussion Starter · #4 ·
Hi guys, well as far as engine changing I hear nothing? And you may be right, this second MC may be bad/?? Yesterday I thought I,d bench blead the MC again and see? Well got air out of it and when put back on truck I bleed two lines at MC then do all 4 wheels------I ran a quart of fluid threw this thing and still blowing air out bleeders???? I,m going nuts with this?? This MC is the New style type and I got the adapter for it also and I cant get a hard pedal at all? I am defeated---I ordered a booster for it and am taking to a local shop here in my little town I live in----- Let them see [again] what they think?? Where is this air coming from??? ------I checked all 3 hoses and all look good and done see any balloons when helper is pressing on pedal?
I been reading that a booster can cause soft pedal and put air into system but how?? This shop said years ago he ran into this--change everything and power bleed and ended up putting a booster on and it fixed it????????????????
 

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Hi guys, well as far as engine changing I hear nothing? And you may be right, this second MC may be bad/?? Yesterday I thought I,d bench blead the MC again and see? Well got air out of it and when put back on truck I bleed two lines at MC then do all 4 wheels------I ran a quart of fluid threw this thing and still blowing air out bleeders???? I,m going nuts with this?? This MC is the New style type and I got the adapter for it also and I cant get a hard pedal at all? I am defeated---I ordered a booster for it and am taking to a local shop here in my little town I live in----- Let them see [again] what they think?? Where is this air coming from??? ------I checked all 3 hoses and all look good and done see any balloons when helper is pressing on pedal?
I been reading that a booster can cause soft pedal and put air into system but how?? This shop said years ago he ran into this--change everything and power bleed and ended up putting a booster on and it fixed it????????????????
I've never heard of a brake booster putting air in the lines unless the master cylinder is leaking from the back. If you can find a helper, I would use a vacuum pump and go that route. But I'm still willing to bet it's the booster. Sounds like the mechanic is trying to get more money than what's required. If you were close by I would help.
 

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I'm late to the party, did you get it yet? The problem might be air in the ABS module. There is a rubber cap near the corner and if you take it off, there is a Schrader valve (a tire valve), You need a helper to push the pedal while you push it the pin to bleed the air out. I think the "factory method" of bleeding the ABS needs some sort of high-level code reader hook up that can activate the ABS. The shade tree mechanic way is to drive on a gravel road or across a grass field and stomp on the brakes to lock the wheels and make the ABS kick in, then go back and bleed at each wheel again. You might have to do it more than once.

Maybe you'll have to pump the pedal a few times to get the wheels to lock if you have a lot of air in it. You need to be going over 25 mph too, I think it is, for the ABS to come on. You should hear the "brrrrr" and maybe feel the vibration in the pedal.

I would also advise that you bleed it enough that you bleed out all the old fluid and end up with a system full of new fluid. 20-something year old fluid might have been a lot of the reason for the soft pedal before.
 

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Discussion Starter · #7 ·
Hello All. Well one thing I,m sure of it has ALL new fluid, I ran 4qt threw it in all and just keep getting air & air out of all the bleeders?? As far as ABS it is gone anyways took it off -----and I could not drive it and stump on pedal and lock wheels?? ----- Thats what I,m saying I CAN.T even slide wheels on a gravel road?????? REALLY!!! I have no brakes even when I do get a little pedal??? The shop I take it to is small shop in little town and they do me right, They had it two days and three guys work on it on and off only charge me $100 bucks, and thats when they found combination vale leaking so I took home put new one on,,,
I have a new booster coming and new rubber lines and another new M.C [old type] that will be ALL new parts and No ABS so we will see I guess??

When I put new pads on front the cyls pushed back in real easy [I open bleeder when do this] and they seem to push back out first time I went to bleed,, I have bench bled this M/C 3 times on truck off truck and each time get bunch air out?? I be real carefull and quick when I put plugs in and hook up to lines on truck,--Has to be bad?----Heck I,ve done this 50 years and never had this trouble???????----------------------I will post when I get all new parts on ??
 

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Discussion Starter · #8 ·
Like I said before I,m getting a new knee in two weeks and with that and my back I just cant work on this thing anymore,,, Hate to admit defeat but I,m at lost, My drive is 170 feet long and steep so I need this truck.. Thanks will post few days when new parts get here.
 

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Like I said before I,m getting a new knee in two weeks and with that and my back I just cant work on this thing anymore,,, Hate to admit defeat but I,m at lost, My drive is 170 feet long and steep so I need this truck.. Thanks will post few days when new parts get here.
I don't know if this applies to Gm trucks but I bought a late 90's f-150 with no brakes,when we finally found the problem it was front calipers switched- solid fluid when bled but an air pocket above the fluid . Good luck
 

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Yep, same can happen to GM calipers, they put the bleed valve at the top for a reason.
Thanks for pointing that out Joe.
 

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Discussion Starter · #11 ·
Well, just picked up truck from shop and after NEW rubber lines--NEW Booster---NEW M/C-3rd one--and another set of NEW front pads and $420 later I still CANT--I mean CAN<T slide my tires on gravel road???????????????????????????--Pedal goes down to floor??????????????????????????????--I am so sick of this Dam truck if it wasn't in such good shape I,d BURN IT!!!!!!

What can possibly be wrong with this thing????????-----I am just plan at a F(*&^% lost with this???--OH new proportion valve too???--Whole dam system is new?? -- Back cyl new two years ago,,
 

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Yep, same can happen to GM calipers, they put the bleed valve at the top for a reason.
Thanks for pointing that out Joe.
Ray, I'm not commenting about the caliper issue that I quoted, but wanted to ask if you noticed up above where Charles said he removed the ABS? I can't find a brake system schematic right away and I'm wondering if there is some sort of check valve or other fluid control device that he inadvertently removed.
 

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Discussion Starter · #13 ·
Ray, I'm not commenting about the caliper issue that I quoted, but wanted to ask if you noticed up above where Charles said he removed the ABS? I can't find a brake system schematic right away and I'm wondering if there is some sort of check valve or other fluid control device that he inadvertently removed.
I,m thinking on clamping off the 3 rubber lines and see how pedal feels?? Then release rubber lines one at a time?? Maybe a M/C with larger bore will help?? Hyd system is sealed so should have hard pedal when I push down if no air in lines right?? Before I put new front pads on the pedal went down about two inch then STOPPED,, Did not go to floor and feel soft,----Now lines come out M/C go to proportion vale then straight to wheels, Heck what can be wrong????-----Sorry about other post I was kinda pissed then,,calm down some now,
 

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Discussion Starter · #14 ·
I'm late to the party, did you get it yet? The problem might be air in the ABS module. There is a rubber cap near the corner and if you take it off, there is a Schrader valve (a tire valve), You need a helper to push the pedal while you push it the pin to bleed the air out. I think the "factory method" of bleeding the ABS needs some sort of high-level code reader hook up that can activate the ABS. The shade tree mechanic way is to drive on a gravel road or across a grass field and stomp on the brakes to lock the wheels and make the ABS kick in, then go back and bleed at each wheel again. You might have to do it more than once.

Maybe you'll have to pump the pedal a few times to get the wheels to lock if you have a lot of air in it. You need to be going over 25 mph too, I think it is, for the ABS to come on. You should hear the "brrrrr" and maybe feel the vibration in the pedal.

I would also advise that you bleed it enough that you bleed out all the old fluid and end up with a system full of new fluid. 20-something year old fluid might have been a lot of the reason for the soft pedal before.
Anybody have any more ideas???? I cant drive a truck that I cant even slide tires on a stone road???????????????????????????---HELP PLEASE
 

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Ok Charles, let's go back to the start.
You changed the front pads and then the pedal would go to the floor.
Is that correct?

What else did you do while you had the front wheels off?

How did you push the caliper piston in?
 

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Discussion Starter · #16 ·
Hello---I just did a test,, I clamped off all 3 rubber lines and with truck running pedal is rock Hard!! I take off rear and not much different still nice and hard,---BUT took one front off at a time and to the floor??--Squishy pedal for sure so has to be in front system???-----When I put new front pads on I used small C-clamp and piece of metal but they went back in real easy so thought all was ok???

And I open the bleeder when pushing them in.---SO--what the heck did I do?????
 

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Hyd system is sealed so should have hard pedal when I push down if no air in lines right??
Yes, if there is not a leak. You've done so much, I assume there is no way it has a leak. That's what made me wonder if there is some sort of fluid tie back from the proportioning valve to the ABS module. I have never messed with that part of the system, only calipers, hoses, and pads/shoes.
 

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Discussion Starter · #18 ·
I took ABS off so thats all gone--tried to make it simple,,, So I guess put new calipers on right??? What else could be in front systen to cause this??? I have that tool in the proportion valve to hold in center,,,,Something has to be going on in those calipers???? What I dont know??
 

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Hello---I just did a test,, I clamped off all 3 rubber lines and with truck running pedal is rock Hard!! I take off rear and not much different still nice and hard,---BUT took one front off at a time and to the floor??--Squishy pedal for sure so has to be in front system???-----When I put new front pads on I used small C-clamp and piece of metal but they went back in real easy so thought all was ok???

And I open the bleeder when pushing them in.---SO--what the heck did I do?????
It has to be either air in the lines, a piston leak, or the hoses. You said before that you watched them while a helper pushed the pedal. I've seen people say that the hoses can collapse internally when they get old, and this is what leads to sticking brakes. Maybe your hoses have collapsed inside and then they balloon but it's not enough to balloon the outer rubber to where you can see it, but it is enough to make the pedal soft.

That's my best guess. You said the shop power bled them, so I wouldn't think there is still air in the lines.

By the way, I never open the bleeder when pushing the piston back in. I've seen numerous instructions where they say to keep an eye on the MC so that the fluid coming back doesn't push the cap off, so that says to me that the "official" method is to leave the bleeder closed. I don't remember if I have ever seen it written, or been told, specifically not to open the bleeder though.
 

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Discussion Starter · #20 ·
Well just got done putting new front calipers on have to bleed them tomorrow,, Front rubber lines are new, -----If you have real nasty fluid in lines and push that piston back without open bleeder all that crap goes right up in the ABS system,,----I got that truck back from shop same way I took it to them [pedel goes to floor] and cant slide tires on stone road??? They still wanted to charge me to put these new calipers on so F(*&^ them!!!---between my knee & back & bone spur on my ankle I cant stand myself right now so bleeding tomorrow,,, -------This should work?????? That test I did diredtly pointed to the front system for sure????
 
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