[Flightsimmer2]

Okay the brakes did fine for one or two days, now it's back to the same old thing, right front brake and left rear brake are doing most of the breaking it pulls to the right just like it always has.
I'm not really convinced that the master cylinder is the problem but I'm beginning to think I need to change it just to eliminate that possibility. There's air in the system on the left front and right rear brake, it keeps coming back even though the brake cylinder and the caliper on that system has been replaced with new ones and I don't know how else air would get into the system.

 

[FabricGATOR]

Well, I sure am as curious as you as to what finally fixes this problem. I patiently await your report.

 

[Flightsimmer2]

Hey, something I noticed on the way home.
If I pump the pedal several times it comes all the way to the top and stays there and all the brakes work, is that a clue?

 

[LPete]

It’s unusual, but a bad wheel bearing (as in very loose) can push a caliper piston into the caliper, so you have to pump several times to push the piston out before the brake applies.

That doesn’t sound like air, but it could still be the master cylinder.

 

[Flightsimmer2]

Well I've got a bleeder kit coming from Amazon and I'll take the master cylinder off and take it apart and see what I can find.

 

[Flightsimmer2]

Hey, something I noticed on the way home.
If I pump the pedal several times it comes all the way to the top and stays there and all the brakes work, is that a clue?

Today when I backed out of the garage I pump the brakes several times as I was backing up and the pedal has been up all day? I'm beginning to think there's debris stuck in the valve someplace in the master cylinder.

 

[Flightsimmer2]

I'm going to remove the master cylinder sometime later today and take it apart to see if I can find anything wrong with it.

 

[LPete]

It’s hard to see down the bore, but that’s likely to be the problem — imperfections in the bore. There isn’t really a valve — they’re pretty simple.

 

[Flightsimmer2]

Well I got the master cylinder off and torn down and inspected and I find absolutely nothing wrong with it at all, matter of fact the whole unit looks new but I'm a little skeptical because when it took the nuts off at the brake booster it acted like they hadn't been taken off before. They don't sell rebuild kits anymore and I'm not going to pay for a new one when I can't find anything wrong with this one so.....

 

[atoman]

It wouldn't surprise me one bit if prior owner/shop tried fixing it by replacing the MC and when it didn't just gave up...

 

[Flightsimmer2]

I reassembled the master cylinder and bench bled it and put it back on and hooked everything up and then bled the entire system again.
Everything bled out just fine except the left front caliper, the new one, every time I bled it I got air out of it in big slugs and the more I bled it the more slugs of air got out of it, it seemed like I couldn't get a solid a steady stream like I did with the other three so after bleeding it multiple times I eventually just shut it off and tried the brakes they work so I may take it to a shop that can pressure bleed the entire system.

 

[hossross]

go to harbor freight or anyplace that sells infared thermometers. Measure brake temperature after different stops.
Left and right should be the same, Fronts will probably be hotter than rears, but depends on adj.

By coasting to a stop, and I mean don't touch the brake at all, use a slight hill for instance and when vehicle comes to a stop immediately put in park. Get out and measure brake temperature. if more than 10 degrees over ambient, then that brake is dragging. the hotest brake in any condition is doing the most work, so again looking for equal temps.

My 2 cents, if your pedal goes to floor, you have air in the system someplace, Do you have a shop manual to see how they recommend bleeding after replacement. I don't have any experience with ABS GM had a lot of ABS problems on their Suburbans and their was a rebuilder out west that was very reasonable. It is possible for the ABS to be bad, and the way the ABS pulses the brake is to dump pressure so could it be that a valve is faulty in the ABS

A junk yard should be cheap for an ABS they are too expensive from the dealer, especially when an accurate diagnoses is not available and you are just doing parts swapping.

 

[hossross]

I reassembled the master cylinder and bench bled it and put it back on and hooked everything up and then bled the entire system again.
Everything bled out just fine except the left front caliper, the new one, every time I bled it I got air out of it in big slugs and the more I bled it the more slugs of air got out of it, it seemed like I couldn't get a solid a steady stream like I did with the other three so after bleeding it multiple times I eventually just shut it off and tried the brakes they work so I may take it to a shop that can pressure bleed the entire system.

very strange, are you using a vacuum bleeder or depressing the pedal. are you closing the bleeder screw at the right time, and is the pedal staying down until you close the bleeder. and using a U tube on the bleeder to insure no air back flows? I like tygon tubing so I can see air bubbles and fluid motion when pedal is released. Is the caliper the proper piece, is the bleeder the highest point on the caliper. I can't think of any way the system is sucking in air once closed, that it wouldn't also leak under pressure as the pressure should be 100s of psi and vacuum is just atmospheric it 1 psi.

 

[LPete]

I can't think of any way the system is sucking in air once closed, that it wouldn't also leak under pressure as the pressure should be 100s of psi and vacuum is just atmospheric it 1 psi.

Master cylinders can suck air in the back when you let up on the pedal if the rear seal on the rear piston is leaking. That wouldn’t leak fluid out necessarily. Not common, but it can happen.

 

[atoman]

I couldn't get a solid a steady stream

did you apply thread sealing tape to the bleeder threads? it can leak quite a bit esp. on rebuilt calipers (if they re-traced damaged threads)...

 

[Flightsimmer2]

did you apply thread sealing tape to the bleeder threads? it can leak quite a bit esp. on rebuilt calipers (if they re-traced damaged threads)...

Yeah I thought about the bleed screw leaking air back into it but when she pressed the pedal down it should have leaked a little fluid out but it was dry I didn't get any leak out at all and I used clear tubing into a jar and held it up so that there wasn't any backflow on it so I don't know what else to do.
I'm looking for a brake shop that I can trust, ha, ha good luck on that. I've already had two that lied to me.
The brakes are working, there's just too long of a pedal travel it doesn't feel natural. I may try bleeding that right front caliper again to see if I can get a solid stream.
Something else, I pushed the emergency brake pedal down so that the rear the drum brakes were applied but it didn't change the pedal travel on the hydraulic brake one bit. So I believe the rear brakes are adjusted up where they should be.

 

[hossross]

Yeah I thought about the bleed screw leaking air back into it but when she pressed the pedal down it should have leaked a little fluid out but it was dry I didn't get any leak out at all and I used clear tubing into a jar and held it up so that there wasn't any backflow on it so I don't know what else to do.
I'm looking for a brake shop that I can trust, ha, ha good luck on that. I've already had two that lied to me.
The brakes are working, there's just too long of a pedal travel it doesn't feel natural. I may try bleeding that right front caliper again to see if I can get a solid stream.
Something else, I pushed the emergency brake pedal down so that the rear the drum brakes were applied but it didn't change the pedal travel on the hydraulic brake one bit. So I believe the rear brakes are adjusted up where they should be.

Don't know for sure, but if the parking brake is mechanically applied ie with separate cable and levers, it is totally independent of the hydraulic system. ie just because the parking brake moves the shoes out to contact the drum, the same amount of hydraulic fluid is needed to to move the piston ends out to recontact the shoes. Hence your test concludes nothing in this case.

You could clamp off the rear brakes at the hose, if the travel is still too long, then not the rear brakes

also could then clamp off the right hose and test, then go to left hose and test, just block off a section at a time.
just dont cut the hoses with the temporary clamp

 

[atoman]

but when she pressed the pedal down it should have leaked a little fluid out but it was dry I didn't get any leak out at all

that's not good, I assumed you vacuum bled them, if you also bled them with brake pedal and got no fluid out of the one caliper that points to that circuit being bad.

I'm not sure if your rear drums system is Teves or TRW, but here's a link to Teves Mk 20e Service Manual
also, additional info:

Teves Mark 20 Antilock Brakes

www.aa1car.com

 

[FabricGATOR]

You had that master cylinder removed and you didn't replace it?
You saved $50...

 

[Flightsimmer2]

I took the van to a repair shop that can test the ABS module, I'll find out what they have to say tomorrow.

Oh, and by the way I wasn't about to take a master cylinder off and replace it with a new $105 master cylinder if I couldn't find anything wrong with the one that's on it.

Also, I'm not an amateur, I've been an automotive technician for newly 60 years so I know how to get things done this just is something totally different.