"Stopped when parked" weird brake issue 2003 Golf

[macmatic]

1. The problem.
2. What I've tried
3. A little backstory

I have read... quite a few MK4 brake threads in the last couple of days.

With the engine OFF the brake pedal is good but not perfect. But also not anything I would question if that was the extent of the problem, I can't even rule out a little flex in worn slide pins causing what movement there is. I've felt similar play in motorcycle brakes with worn pins or bushings. It will move through the first 20-25% of the travel with fair resistance and then gets too hard to push further. I can keep pressing HARD for at least a minute and not feel any further movement.

As soon as the engine is running the pedal is totally different, very soft in the first 2/3 of travel and then feels about the way the first part of pedal travel feels when the engine is off but does not bottom out. Given that the pedal doesn't bleed down under very hard consistent pressure with the engine off I don't THINK the master cylinder a problem. There are no external fluid leaks. Front calipers are free, I have not retracted the rear pistons but the slides are free.

I have a parts car that also "stopped when parked" and the pedal is nice and firm on that from the start but I don't really want to start swapping parts in chasing what may be just a stubborn air bubble.

So far I have:
Gravity bled the brakes.
Pressure bled the brakes.
Flushed the ABS pump. Considering how much fluid that took I don't see how I could have any air in the ABS or front calipers.
Vacuum bled the rear calipers in place, with the bottom bolt out and tipped forward and finally removed from the axle and held so that there was no high spot in the flex line. I skipped the front because I'm assuming they must be fine after all the ABS flushing.
Bled the clutch.
Pressurized the master cylinder and cracked the two lines one at a time. I wouldn't know if air came out but plenty of fluid did.
Not run the master cylinder reservoir dry or low.


None of this has made any difference in the pedal with the engine on but it might have made it very slightly firmer with engine off. Too subjective to say for sure.

Backstory:

The car has been off the road and in the driveway for about two years. I worked a 3 minute walk from home and I have access to another car, but now I need to get this one back on the road. It was parked because I have to do a heater core and had enough else going on that I never got around to a PITA low priority job. I THINK that the last thing I did around the time the car was parked was replace arear caliper and the e-brake cables because one was seized up due to a break in the sheath.

 

[Seatman]

Sounds like what mine were doing, car had also been parked up for a while. After cleaning all the brakes and replacing what needed replacing I hooked up the pressure bleeder, bled them all thoroughly then went back to the rears. Bled again then diconnected the pressure bleeder then started the engine and pumped the brakes quite hard a few times. Then I'd reconnect the pressure bleeder and redo the rears. Did that a few times and kept getting some small bubbles out that eventually disappeared then my brakes were good.

Personally I've always found the rears to be the main issue with vag cars, getting the little bubbles out. Never managed to get it all out with just straight bleeding of any kind.

 

[macmatic]

Sounds like what mine were doing, car had also been parked up for a while. After cleaning all the brakes and replacing what needed replacing I hooked up the pressure bleeder, bled them all thoroughly then went back to the rears. Bled again then diconnected the pressure bleeder then started the engine and pumped the brakes quite hard a few times. Then I'd reconnect the pressure bleeder and redo the rears. Did that a few times and kept getting some small bubbles out that eventually disappeared then my brakes were good.

Personally I've always found the rears to be the main issue with vag cars, getting the little bubbles out. Never managed to get it all out with just straight bleeding of any kind.

Thank you, Seatman. I feel like I've been pretty aggressive but I'll go harder on the rears. I should have taken some notes on what I'd done last on the car but of course I wasn't planning to be away from it for such a long time.

P.s. I don't remember what info I was looking for at the time but I do remember your name from years ago when I was last here looking for help so thanks for chiming in again!

 

[snakeye]

Are the brakes rusted?

 

[macmatic]

Are the brakes rusted?

I know the front pistons are free and I know the rear brakes will lock up the wheels but tomorrow I guess I'll spin the rear pistons back in and make sure they move. The calipers are rusted externally but move freely on the sliders, front and rear. I had cleaned and greased them all around the time the car was parked.

No luck today and I'm about out of brake fluid so that's it for now. If the rear calipers check out I might throw a master cylinder at it, as much as I hate the thought of bleeding the whole system again.

Could I avoid that by bench bleeding the master then cracking the lines loose at the top of the ABS pump and pressure bleeding just those two lines? I also see a lot of references to bleeding an additional nipple or nipples on the master but I don't see or feel any on either of the ones here or see any in images of ESC or non ESC master cylinders. Are these posts just referencing the fittings for the pressure lines?

[Edit] Just a small update I'm editing in because it's not worth bumping the thread.

Time was short today so I verified that the pistons are moving in all four calipers and started prepping for the next step, swapping master cylinders and maybe boosters with the parts car. Parts car has a very low mile MS on it and I think I've got a plan to swap them pretty easily. Will update once that's done.

 

[macmatic]

Well I did a thing and now I know it isn't the master cylinder.

Today I swapped the MS from my parts car that has great brakes to the "runner" with a chronic spongy pedal and the suspect MS onto the parts car. Absolutely no difference, both cars are as they were before. Tomorrow I'm going to figure out a way to pressurize the MS and do a combination pressure/vacuum bleed at all four corners or until I see a slug of air come out.

Swapping the cylinders between cars went well and if I find myself having to replace a MS without the time or ability to do a full flush and ABS bleed I'll try this first

Here's how I swapped the cylinders between cars. The whole process of removing, swapping and reinstalling took about an hour and a quarter. I did already have the airboxes and hoses out of the way on both cars.

Removal
1. Cleaned the top of the ABS pump on both cars, put newsprint under the MS and ABS pump and on the ground under the car.
2. Made sure the input fittings at the tops of both ABS pumps could be loosened.
3. Removed the strainer from the MS, removed the threaded "band" from the cap/level sensor and capped the reservoir with plastic film and the threaded band.
4. Removed clutch hose and capped the output from the reservoir, tucked the hose out of the way.
5. Removed the MS retaining nuts to the booster.
6. Unthreaded first the rearmost ABS input line, capped the end and then the same with the front line and capped that.
(I would do this front first and then rear next time. I wanted to get the hard one first but very little fluid came out. Removing and capping the front input line gives better access to the rear line.)
7. Pulled MS off the studs on the booster and set aside on newsprint.

Installation
1. Pack in paper towel around the sides and front of the ABS pump now while there's great access. Be sure you've cleaned any debris that could get in the ports before removing the fittings previously.
2. Use a syringe and fill the ports in the top of the ABS pump with new fluid to minimize the chance put pushing air into the system.
3. Install the MS loosely on the booster studs with the nuts a few turns on to keep it captive.
4. Install the clutch hose on the reservoir. Don't forget the clamp!
5. Thread in first the rear and then the front ABS input lines, snugged.
6. Tighten the booster nuts. It was helpful to have a little wiggle room when getting the fittings started in the top of the ABS pump.
7. Remove the cap and plastic wrap from the reservoir.
8. Loosen first the rear ABS pump fitting until brake fluid starts to seep, tighten and repeat with the front fitting.
9. Pressurize the MS reservoir to about 12psi
10. Clean up the fluid that pushes out around the unclamped clutch hose.... clamp clutch hose, top up reservoir.
11. Re-pressurize reservoir to 12psi
12. Crack open one ABS fitting and bleed it. I got some fluid, then a bit of bubbles and then a stronger flow of fluid. Repeat with the other fitting. I went back and forth between them three times but only saw bubbles on the first pass.

Done. This seems to have worked perfectly from what I can tell right now. The car that had a good solid pedal still has a good solid pedal with the MS from the car that had and still has a soft pedal. The soft pedal car still feels the same. So I believe both MS are good and my problem lies elsewhere but this technique seemed to work well.

If I was installing a new MS I think it would work as well to install the ABS input hoses on the new MS, bench bleed them, cap them and then install as above. Especially if you don't have access to a VCDS to bleed the ABS pump on an otherwise functional system.

 

[macmatic]

Grasping at straws here but could the way I have the car jacked up be an issue? It's lifted and level on four jack stands now, the rear suspension is at normal travel as if it were on the ground but the front control arms are at full droop.

Today I ran another liter of fluid through the car gravity and pressure bleeding all four corners. No air seen, no difference in the pedal. I guess I'll try a few more rounds of ABS purging.

 

[Seatman]

Grasping at straws here but could the way I have the car jacked up be an issue? It's lifted and level on four jack stands now, the rear suspension is at normal travel as if it were on the ground but the front control arms are at full droop.

Today I ran another liter of fluid through the car gravity and pressure bleeding all four corners. No air seen, no difference in the pedal. I guess I'll try a few more rounds of ABS purging.

Did you try what I suggested regarding disconnecting the bleeder and pumping the pedal fairly hard a few times then bleeding again?

It was the only thing that seemed to work for me for whatever reason.

 

[macmatic]

Did you try what I suggested regarding disconnecting the bleeder and pumping the pedal fairly hard a few times then bleeding again?

I did, I think that was the first thing I tried the next day and thank you for the suggestion. I'm sure I'll be trying that again, too, because right now I'm at a loss. I was considering putting in the ABS pump from the parts car but the one in the car I'm shows no errors and has been bled several times now.

For the moment I'm going to take my foot off the brake pedal for a couple of days and do the heater core for what will probably be a genuinely relaxing change of pace. Hopefully I'll come back to the brakes refreshed and maybe with some new insights.

 

[oilhammer]

You may have done this, but have you run the ABS Output Test and Basic Settings bleed procedures?

 

[macmatic]

You may have done this, but have you run the ABS Output Test and Basic Settings bleed procedures?

Do you mean the basic settings ABS bleed procedure where you hold the brake while the pump runs, open the bleeders, press 10x, close bleeders and repeat? I've done that and the ABS Output test. I don't think have any options available on the dropdown menu but I'll check when I get the dash back together.

 

[KrashDH]

Have you checked the lines to ensure they haven't been compromised? Ie under pressure are any of them "bulging" indictive of failure?

Are you sure the pads move freely and aren't hung up at all? Not talking bout calipers sliding on pins, but actual pad moving in the knuckle...I've had them bind up. Usually need to hit the knuckle and pads with a file before installing new ones.

 

[macmatic]

Have you checked the lines to ensure they haven't been compromised? Ie under pressure are any of them "bulging" indictive of failure?

Are you sure the pads move freely and aren't hung up at all? Not talking bout calipers sliding on pins, but actual pad moving in the knuckle...I've had them bind up. Usually need to hit the knuckle and pads with a file before installing new ones.

Thanks for the ideas. I'll have to check the soft lines again with the car running since I think any problem would be most visible then, with the booster working. All the pads are free. I've pulled the calipers to check and replaced the stamped steel slider hardware on the RR because it was corroded in two on the bottom.

[edit] I'm kind of excited about that bad hose idea. This is far from my first go-around with bleeding brakes and I'm at a loss right now. I also remembered that I never checked the short hoses at the rear axle. So, fingers crossed? [edit]

 

[macmatic]

Have you checked the lines to ensure they haven't been compromised? Ie under pressure are any of them "bulging" indictive of failure?

This was a compelling enough idea that I closed off the heater hoses and got the car together enough to start for a couple of minutes while I checked and rechecked the hoses with the brake on. Unfortunately I couldn't feel any change in diameter in any of the hoses or see/feel any damage to the sheath.

I've changed hoses in the past preemptively but never actually had a bad one; I'm assuming there would be a pronounced swell somewhere and not a perfectly even swelling of the hose? I didn't get out the measuring calipers but I did run my fingers over the hose at each corner and the two short hoses at the rear axel. I didn't think to check the braided hoses at the MS but those were swapped between cars with the MS anyway.

Right now I have some speed bleeders on order that should be here after the weekend. My plan is to try Seatman's suggestion again a few times and then if that doesn't do it I'll pedal pump about a half liter of fluid through each corner until I hopefully get a hard pedal.

 

[KrashDH]

I'm assuming there would be a pronounced swell somewhere and not a perfectly even swelling of the hose?

Yeah usually it's a compromise in one area which causes a localized swelling, not an "entire" hose swelling up

 

[snakeye]

When I asked whether the brakes are rusted, I meant the actual rotors, since you say the car's been sitting for two years. If they are, they could create a soft pedal feel.

 

[macmatic]

When I asked whether the brakes are rusted, I meant the actual rotors, since you say the car's been sitting for two years. If they are, they could create a soft pedal feel.

I thought you meant the pistons or pins. I haven't moved the car, this is with the it sitting still.

The rotors did have some surface rust but I cleaned them up with one of those spongey looking paint stripper wheels. With luck the car will be driving before they need it again!

 

[Powder Hound]

I have a single comment. When you are working the ABS purge program and the computer says to hold the pedal down, stomp on it. Maintain high pressure on the pedal so that when the ABS kicks back at you when it is exercising, do not let the pedal come off the floor. Your leg will get tired. Push through that. I had crummy brakes in my Y2K Golf for a couple of years until I finally started doing this correctly.

Cheers,

PH

 

[macmatic]

I have a single comment. When you are working the ABS purge program and the computer says to hold the pedal down, stomp on it.

Thanks, I'll give that a shot! I was holding pretty good pressure on the pedal but I could have gone harder.

 

[macmatic]

I think I've got more time in this than in all other hydraulic bleeding jobs combined and I used to be a construction equipment mechanic.
It's ridiculous and just keeps getting worse.

So... update and new problem, which may point to the actual problem?

I didn't have a lot of time today but I got my speed bleeders and went to do a circuit of the car. FL and FR were fine, moved about 300 to 400ml of fluid through both manually pumping. (No change in pedal) I moved on to the LR caliper and it started out the same but after I closed the bleeder to check the pedal (no change) and top off the master cylinder and then went back to pumping I was getting nothing out of the bleeder and the pedal felt like the bleeder was closed.

I opened the bleeder a little more, no change. I thought maybe the valve in the speed bleeder was stuck so I swapped the normal bleeder back in, no change, pedal felt like the bleeder was closed. Uh oh... I cracked the line loose at the caliper and tried both pressure and pump bleeding. Nothing. Feels like a closed system. So, there's something up there. I've got penetrant on the fittings for the short hose at the axle right now so I can break them loose tomorrow.

I went on and bled the RR caliper with the speed bleeder and that was normal although I'm going to bleed it some more. I only did 200ml and it looked like there might have been a little old fluid mixed in with the new. I had recently retracted the rear pistons so maybe I moved a pocket of old fluid.

The plan for tomorrow is to try pressure bleeding the fittings at the master cylinder. I believe the rear line on the MS feeds the LR and RF calipers via the ABS pump but I'm not sure and I'll check both. If I get fluid there I'll try the RF caliper which I think but am not positive is part of the same circuit with the LR. If I get fluid there, I'll try bleeding from the ports on the ABS pump for the LR and maybe all of them. Assuming I get fluid out of the ABS pump I'll try to crack a line loose at the rear axle.

I tried not to go full-stroke with the MS while bleeding, and it isn't very old, but one theory is that I moved some crud and blocked one of the circuits in the MS. I guess I'll know that when I test for fluid at the front again tomorrow. This MS from the parts car is a VW part and had one been in use for about a year.

Looking in the Bentley today I see that it's recommended to do a reverse pressure bleed of the caliper from the nipple to the banjo and then a normal bleed once you get any air out that way so, once I figure out what's going on with the LR I'll give that a try. Maybe that's been the problem all along?

Right now I'm applying 750ml of Cabernet to the affected area.

 

[macmatic]

Well there's a problem in the ABS unit but I don't know if it's the reason I had trapped air or a new issue.

Question: Could pedal bleeding somehow "vacuum lock" a valve body in the ABS module? I don't think so but if cycling the pump would resolve this issue it would be easier than what I have planned... I just don't want to cycle the pump right now out of concern for worsening the issue below. i.e. pushing possible contamination further into the system.

I'm definitely open to other ideas!

Short version: Fluid is still moving normally to all but the Left Rear caliper, fluid is flowing under pressure from all output fittings on the ABS module except for that wheel's line when I crack open the fittings with pressure in the MS. So there's a new internal blockage of the ABS unit that appeared in the midst of pump bleeding the calipers with speed bleeders.
I suspect the newish master cylinder I put on from the parts car must have had some crud get dislodged and pushed to the ABS unit OR something in the ABS unit got dislodged in all the ABS purge cycles I did and chose that time to make itself known.

Here's the plan of attack for tomorrow/this weekend.

I'm going to remove the input lines from the master into the ABS and pump bleed them into two plastic bottles. I want to capture the fluid and see if there's anything suspicious in it. Then I'm going to remove and disassemble the MS. There's no kit for it but it looks like it should disassemble like any other. If I don't see any faults I'll make sure it's clean and reassemble. I still have the one that came off this car last week which I have no reason to suspect has any issues since it gives a good hard pedal on the parts car and worst case I'll buy a new one.

Next I'll remove the ABS pump. I plan to see if I can clear the blockage, if not I've got a spare on the parts car. Chances are fair I can fix a mechanical blockage. This ABS unit is a lot less complicated than an excavator swing motor.

I want to blow out the lines for the rear calipers and probably all four wheels to make sure there's no crud in those lines. I'm going to be bleeding from dry basically anyway so why not?

Basically take things apart and clear the blockage if possible then reassemble and start be checking fluid output from the ABS unit. If that looks good I'll start bleeding again, and reverse pressure bleed the rear calipers as per Bentley.

Hopefully I don't have to swap in the other ABS unit because I THINK I'd have to code it to the car, which I've never done before, and the one key I have has gone missing. It's probably in plain sight somewhere and it'll turn up but it's AWOL as of now. I guess I could swap the mechanical portion only.

Thanks for coming to my TedTalk