2001 TDI Golf ABS Bleeding

[iblackford]

Hi All, I am writing for a friend, we worked on his 2001 TDI Golf recently to fix a right rear brake caliper.
Background: Right Rear brake caliper had seized. E-brake would not work either as the piston would not self-return.
Actions taken:
1) Caliper was removed (banjo bolt removed) and removed from the car.
2) Caliper was torn down. Piston, bore, and all sealing surfaces polished with 1000grit wet sandpaper and rebuilt.
3) Caliper was put back onto the car and the banjo bolt reinstalled. It was then that we realized the bleeder screw was siezed solid, and cross threaded from a previous repair.
4) Attempts were made to bleed the system through the banjo bolt. We got partial hydraulic brakes, no leaks, but all air could not be removed from the system.
5) E-brake now worked.
6) Caliper was removed again. Bleeder screw was drilled out. Care was taken when drilling and no sealing surfaces were damaged from drilling. Small amounts of thread were damaged.
7) Since the bleeder screw was cross threaded, the thread was cleaned (M10 x 1.0) up with a tap. A new bleeder screw was installed, but we were not confident that the threads were strong enough to seal correctly.
8) Caliper was rebolted to the car. Attempts to bleed with the new bleeder screw resulted in stripping of the remaining weak threads.
9) Bleeder screw hole was tapped to 7/16" x 20 for using a larger bleeder screw. We used a marker on the bleed screw seat of the caliper and confirmed that the new bleeder screw was mating to this seat correctly.
10) Caliper was rebolted to the vehicle and another bleed attempt made. During this bleed procedure, the pedal suddenly got firm. No amount of pushing on the pedal resulted in fluid going to the rear caliper (even through the banjo bolt..). All other wheels work fine.
11) We then found through forum searches that the ABS system may have air in the system. We made an RS232-->OBD2 cable and installed VAG-COM.
12) By running the VAG-COM ABS tests we could hear the ABS pump engage and disengage.
13) During the bleed procedure, (NOT while it asks you to open the bleeders and pump 10x, but just before this) the pedal got soft for a few moments. During this few moments we were able to resume our bleeding. ABS output tests did not give us the same soft-pedal.
14) We cycled through the ABS bleed a few times and used the soft-pedal moments to bleed the rear brakes. We found that the bleeder screw leaked air in slightly even when in the closed position. The bleeder screw was further tightened until it better seated in the caliper and did not leak in the closed position. We now have partial hydraulic brakes on this caliper during this soft-pedal condition. No hydraulic brakes on this caliper in normal hard-pedal conditions.
15) Vehicle battery was removed. Hard pedal condition existed.
16) Battery attached and rear wheel was put back on. Vehicle was driven with no right rear brakes. He reported that the other 3 wheels were much more responsive than they had ever been (If the ABS system had some air in it previously, did we now purge some of it?). This is the current status of the car.
Questions:
1) What could be possibly causing this hard pedal condition? Why would the right rear wheel be locked out?
2) What is the ABS system doing during the bleed procedure that could cause our soft-pedal condition?
3) The ABS bleed procedure calls for loosening of the front right and front left bleeder screws. Is this necessary? Can any bleeder in the system be used? We were reluctant to touch the other bleeder screws as they may be stuck.
Thanks for any help that can be provided.

 

[tongsli]

Is his car a manual or automatic? Don't forget, if it's a 5 speed, the clutch slave cylinder is part of the brake system. You need to bleed it as well.

Your brake booster is also vacuum assisted. It will feel differently when the car is running vs when it's off. This may or may not be the "hard-pedal" condition you're describing. If you step on the brake(with the car off) it should stop, then go down slowly to the floor.

Do you have a Motive brake bleeder? It makes the job much easier.

 

[iblackford]

The car is a manual transmission. Although we did not bleed the clutch, it's function and feel is just as before. Would having air in that part of the system cause the symptoms we are seeing?

We're familiar with the difference in pedal feel with the engine vacuum present. This hard pedal situation is present even when the car is off.

I don't have a motive brake bleeder, but I don't see how it will help. Currently unless we're in the special part of the ABS test where the soft-pedal condition returns, NO brake fluid flows to the rear right caliper. Would a motive brake bleeder somehow force enough fluid pressure to overcome this situation?

 

[tongsli]

The car is a manual transmission. Although we did not bleed the clutch, it's function and feel is just as before. Would having air in that part of the system cause the symptoms we are seeing?
We're familiar with the difference in pedal feel with the engine vacuum present. This hard pedal situation is present even when the car is off.
I don't have a motive brake bleeder, but I don't see how it will help. Currently unless we're in the special part of the ABS test where the soft-pedal condition returns, NO brake fluid flows to the rear right caliper. Would a motive brake bleeder somehow force enough fluid pressure to overcome this situation?

Well, since the bleed screw(right rear) is giving you all the problems I presume you're sucking fluid from that caliper?

The motive bleeder pressurizes the system at the reservoir. So it's pushed through the system and not sucked from a specific caliper.

The brake will always feel harder with the engine off. After the initial "hard-ness" does it release down to the floor?

check the vaccum connection/grommet at the brake booster (vacuum connection pipe) and make sure it's in good condition. You could even spray it with water to see if it's leaking. Test the grommet with the car running. The hard pedal could be a leaking brake booster vacuum seal and the soft pedal operation could be because you're not getting a good sucking from the right rear caliper.

As to the caliper, given all the work you've done to it I'm just wondering if you're getting a good suction/vacuum at that bleeder screw.

 

[iblackford]

Well, since the bleed screw(right rear) is giving you all the problems I presume you're sucking fluid from that caliper?

The motive bleeder pressurizes the system at the reservoir. So it's pushed through the system and not sucked from a specific caliper.

The brake will always feel harder with the engine off. After the initial "hard-ness" does it release down to the floor?

check the vaccum connection/grommet at the brake booster (vacuum connection pipe) and make sure it's in good condition. You could even spray it with water to see if it's leaking. Test the grommet with the car running. The hard pedal could be a leaking brake booster vacuum seal and the soft pedal operation could be because you're not getting a good sucking from the right rear caliper.

As to the caliper, given all the work you've done to it I'm just wondering if you're getting a good suction/vacuum at that bleeder screw.

The right rear bleeder doesn't appear to be leaking any longer, although it was. We confirmed this by cycling through the ABS test, which gave us a few seconds of a soft-pedal and we were able to get fluid flowing to the rear caliper. During this time we bled the rear caliper, but I still believe there is _some_ air in the right rear lines or caliper, as we don't have perfect brakes in this mode. Again, there is NO fluid flow to the right rear caliper during the hard pedal state.

The hard pedal/soft pedal condition comes only during the ABS cycle. There are no vacuum leaks. The hard pedal does not go down to the floor, from what I recall. The soft pedal state does for sure.

Essentially we want to get back to the soft pedal state, which is a normal brake feel for a system with some air in it still, but we can't seem to get there. Once back to the "normal" soft pedal I believe we can use either traditional bleeding methods or a motive brake bleeder to purge the remaining air out of the system.

Thanks, Ivan

 

[tongsli]

Well, good luck. Maybe someone else has some ideas for you. I've retrofitted ESP on my car, installed a new ABS pump, including a new brake booster and didn't have as much of a problem bleeding my brakes as you seem to be having.

I did use vag com to bleed my ABS pump but it was also pressurized by the Motive brake bleeder.

 

[PeterV]

Perhaps look closely at the booster. Perhaps it has failed. Mind did and it felt like I had manual brakes, much like our senior citizen 1965 Barracuda...

 

[davebugs]

Seriousely buy or borrow a Motive.

Much better the "push" than to "suck" when bleeding brakes.

You've paid for one likely several times already if you value your time at all.

One of the 3 essential tools for a VW IMO - although not VW specific. I add Vag-Com, Pella to the Motive pressure bleeder.

If you flush your brakes every 2 years it's priceless. And in my case I was lazy about bleeding and guess which caliper seems to fair first - yes the RR. Also on friends, family, and cars I part the RR seems to be the first to go, or has already been replaced. You can buy other adapters for other cars. It's very handy to have. And I NEVER put fluid in the actual Motive so no worries about cleaning between DOT4(for our MKIV's), DOT 3 for older stuff, and DOT5 for the antiques.

If you're cheap there are instructions on how to make one from a garden sprayer. But the original isn't that expensive and is a good piece of equipment with many uses.

I loan mine out locally for a deposit. Maybe someone local to you does the same.

 

[turbocharged798]

Sounds like something clogged in the system somewhere. The pedal should go right to the floor when a bleeder is opened. I would not drive the car until this is fixed.

 

[iblackford]

I think something is clogged as well, or at least a solenoid is closed when it should be opened, but given that:

1) a certain part of the ABS test returns the pedal to normal
2) The ABS output tests (where both input and output solenoids of the ABS system are actuated) doesn't return the pedal to normal

I'm stumped, the car isn't being driven at the moment from what I understand, his GF is driving him everywhere. But Winter tends to approach quickly, he'd like to have this fixed soon.

 

[turbocharged798]

I bet something is screwed in the ABS pump.

 

[iblackford]

I bet something is screwed in the ABS pump.

Perhaps, but I'm not one to throw parts at the problem until I have a firm diagnosis that it is that. My understanding is that the ABS pump is very expensive.

 

[turbocharged798]

They are almost free in junkyards and takes 20min to replace...

 

[iblackford]

They are almost free in junkyards and takes 20min to replace...

Maybe, junkyards around here are not that accomodating, going to wait until I have some more solid information that the ABS pump is at fault before I go replacing it.

I've been thinking of trying this: Since the ABS test gives a few moments of normal pedal, I could use that time to apply a power bleed with a motive pressure bleeder (or homemade equivalent). This could get me good brake response on that caliper, but I'm still not sure what would get me my normal pedal back outside of the ABS test...

Ivan