New EVERYTHING. Brakes STILL soft!

[SPOT MY 6]

I have the vacuum brake conversion (master cylinder, brake booster, and brake pedal).

I just put on BRAND NEW:
-Calipers
-Master cylinder
-Front rotors cut with new pads
-Rear drums cut with new shoes

The rear brakes have 7/8" S-10 wheel cylinders about 2 years old. They were not wet or anything so I dont think they are leaking.

I took the car to Sears to have them bleed the brakes with the vacuum so I was 100% sure all the air was outta the system.

I took the rear drums off to verify that I put everything together correctly and that the adjusting stars were on the correct side of the car. All was well.

I put the drums and wheels back on, but left the rear end of the car jacked up off the ground. I slowly adjust the star and shook the wheel back and forth until I could hear the shoes drag a little bit.

I went for another ride and they were better, but not good enough. If I nail the brakes, the car will not lock up and wheels and just dont seem to be enough.

By the end of the night, I could push the pedal all the way to the floor (took just a little bit of effort).

What else can it be? Someone mentioned that it could be the factory porportioning valve. I dont see how that could be considering I know the fluid is getting to the brakes considering I bled them and saw for myself.

Im thinking about putting stock wheel cylinders back on to see if that does anything. Any thing else I should do? Thanks for the help.

 

[WSLN 6]

If you still have a cast iron proportioning valve, replace it with a new brass one. They were bad for sucking air in, and the pedal would get hard. (Ask my bodyshop, I found that out the hard way............)

 

[NJTurbo]

I do not agree

Are you sure you got all the air out of the system....
I would double, double check. Bleed in this order. First have someone in car pump up and hold and crack the master-cylinder lines one at a time, refill master make sure lines are tight and all air is out of master. Then bleed wheels in this order RR/LF/LR/RF. Car should still be jacked up in neutral adjust rear brakes until drag is on wheel spinning by hand. If pedal goes to floor after all this, i would say bad master cylinder.

 

[WSLN 6]

It was a safety recall back in 1990, so hopefully that's not what you disagree with......

 

[SPOT MY 6]

njturbo,

I did the brake bleeding myself EXACTLY as you just described and it was soft. I took it to Sears to have them use the vacuum and it got just a tad better, but still to the floor. I made sure the shoes were snug up against the drum. Got a tad better, but still to the floor. The master cylinder is BRAND NEW, and this problem was also happening with the last master cylinder, and the one before that.

So I have tried 3 different master cylinders with the one on the car now being brand new (rebuilt).

Im going to do the proportioning valve and see what happens. I need to fix this.

Unless my line-lock is leaking internally?

 

[NJTurbo]

If the pedal is going to the floor, you either have air somewhere or you are loosing pressure. Did you check for leaks.

 

[SPOT MY 6]

Originally posted by njturbo
Did you check for leaks.

Does Pinocchio have wooden balls?

 

[NJTurbo]

Originally posted by SPOT MY 6
Does Pinocchio have wooden balls?

I think he did
Just trying to help. Sorry i am not giving you a immediate diag to your problem, however i went down this road with my car. Did this start after the brake conversion

 

[SPOT MY 6]

Originally posted by njturbo
I think he did
Just trying to help. Sorry i am not giving you a immediate diag to your problem, however i went down this road with my car. Did this start after the brake conversion

Its cool.

Yes, this started after the conversion. Before with the powermaster I could lock up the front brakes but the PM motor was running pretty much constantly. I changed the rear brake cylinders at the same time as the vacuum conversion to the S-10 cylinders. I might try to put regular wheel cylinders on. Man I dont want to just buy parts and try them to see if that fixes it. I wish I could find the problem first.

 

[NJTurbo]

Originally posted by SPOT MY 6
Its cool.

Yes, this started after the conversion. Before with the powermaster I could lock up the front brakes but the PM motor was running pretty much constantly. I changed the rear brake cylinders at the same time as the vacuum conversion to the S-10 cylinders. I might try to put regular wheel cylinders on. Man I dont want to just buy parts and try them to see if that fixes it. I wish I could find the problem first.

Did you use manual S-10 wheel cylinders or Power? I would assume you have good vacuum coming of with the TA vac block, no leaks in vacuum hose, check ball ETC.

 

[SPOT MY 6]

I used the manual (7/8") S10 cylinders. The billet vacuum block and hose is free of leaks. I dont know about the check valve in the line though. I did check it before I put it on last year and it was working properly. Is it possible that its the brake booster? I would think that if the pedal is going the floor, then the booster is working more than enough.

 

[NJTurbo]

Originally posted by SPOT MY 6
I used the manual (7/8") S10 cylinders. The billet vacuum block and hose is free of leaks. I dont know about the check valve in the line though. I did check it before I put it on last year and it was working properly. Is it possible that its the brake booster? I would think that if the pedal is going the floor, then the booster is working more than enough.

Normally when the booster goes bad, brakes are rock hard. Brake pedal to the floor, i still say you have a leak and or air in the system. Have you contacted RED REGAL T as he has sold hundreds of these and maybe he ran into this problem before.

 

[Red Regal T]

I've been reading this and although you replaced the master cylinder, that's what it sounds like to me. Do the brakes pump up when the pedal goes low? Anyway, I'd think about trying another mastercylinder. You may have got a defective one.

 

[SPOT MY 6]

Well it did the same thing with the other 2 master cylinders. I just cant see how 3 in a row would all be bad. When the car is off and the pedal is pushed to the floor, the next push is just about impossible as the pedal is so hard you cant move it. When I pump the brakes with the car on, it seems to get a little harder but will still go to the floor when held down. Im not saying that it cant be bad, I just think the chances are awfully slim.

Im wondering if my line lock is leaking internally? The only other thing I havent replaced is the proportioning valve. I hope I bought the right wheel cylinders 2 years ago. Im pretty sure I asked for 85 S-10 with manual 7/8" brakes.

 

[Nick Micale]

Originally posted by SPOT MY 6
Well it did the same thing with the other 2 master cylinders. I just cant see how 3 in a row would all be bad. When the car is off and the pedal is pushed to the floor, the next push is just about impossible as the pedal is so hard you cant move it. When I pump the brakes with the car on, it seems to get a little harder but will still go to the floor when held down. Im not saying that it cant be bad, I just think the chances are awfully slim.

Im wondering if my line lock is leaking internally? The only other thing I havent replaced is the proportioning valve. ....

Everything pointed to an bad, or improperly bled, master cylinder in your original post. You neglected to mention a line lock initially?

My guess would be, depending on how the LL is plumbed, there is air in one or more of those lines, or as you say, leaking internally?

Having worked on many hundred G-body brake systems and never seen a bad prop valve, doubt you have a problem there.

 

[Nick Micale]

Originally posted by WSLN 6
It was a safety recall back in 1990, so hopefully that's not what you disagree with......

Apparently Buick USA disagreed, as the prop valve was never recalled in the states, only Canada.

 

[Red Regal T]

Re-plumb the linelock out of the system to see if that's your problem. Should be easy to do........easier than replacing the proportioning valve. I agree with Nick on that not being the problem.

 

[Brian Mc]

Originally posted by Red Regal T
Re-plumb the linelock out of the system to see if that's your problem. Should be easy to do........easier than replacing the proportioning valve. I agree with Nick on that not being the problem.

Ditto on the LL. that was my problem

 

[zam70]

ABSOLUTELY
What you describe can ONLY be caused by a few things:
fluid leak (verified none)
air
or leak around/inside pressurized items (line lock or master cylinder)

I'd get the line lock out of the fluid circuit, rebleed from GO (start with internally bleeding the MC then go to all the lines, staring with the furthest and work your way to the MC)

Your problem should be solved...if not, swap the MC again. I have gotten up to 5 bad rebuilt MCs before finding a good one (unusual, but it happens)

I'd say, with all else you've done...LINE LOCK is the culprit.

 

[Matt Weiser]

With the problem as you describe it, and no leaks detected, sounds to me like you have brake fluid leaking past an internal seal, either in the MC or in your line lock. I've seen this problem before and it is bedeviling, but I can't think of anything else that could be causing this. I agree, start by taking the LL out of the system, rebleed, and see where you're at. Still a problem, try a new MC.