LT35/Sprinter brake issue.......

[RWP278]

Hi there,
Apologies for kinda hijacking this forum, but my LT35 is pretty much a Sprinter in disguise! Sort of brothers.
So, to my issue......about 6 months ago, keen on keeping the maintenance up on my van, whilst changing the rear pads, i decided to do a fluid change as well. It didn't start too well as 2 of the bleed screws snapped in the near side rear caliper and the off side front caliper. So, had to buy and fit 2 new calipers. At the same time i fitted all 4 new flexi pipes (also fitted new front pads).
Now i'm all ready to start bleeding. I use a pressure system where a spare wheel @ 20 psi is pressurising the master cylinder. Seemed to get adequate fluid out and at an adequate rate from all 4 calipers. Test the pedal with engine running and it goes straight to the floor and this is how it has stayed ever since.
At no point has the master cylinder been dry.
I have bled the system countless times. No air bubbles ever come out.
There are no leaks, no damaged pipes.
All calipers have been removed and double checked for correct installation etc.
Since then i have also replaced
the servo (for a second hand known working unit),
master cylinder (brand new) and
load proportioning valve (brand new).

I have driven it a couple of times just along the road and the pedal does just go to the floor. There is a small bit of actual braking action right at the bottom of the pedal.

I'm getting absolutely desperate now as this has been going on for months. I've had a mate who used to work for VW commercial have a look and he couldn't find anything wrong. I'm positive its something really stupid.
It used to be my pride and joy but now it sits on axle stands gradually going green. Its affected my business massively to the point where i'm having to close it down. I do what i can at home but its not easy and i've fallen out with the neighbours now as sometimes i have the van, 4 cars and a trailer on the drive and 2 cars on the road. I'm a mobile body repairer/self taught mechanic.
I'm suffering from from depression and anxiety, have massive debts and my marriage is close to breaking down.
A man needs his van.

My next thought was to try and get hold of a brake fluid pressure tester to see how much pressure is getting through to each caliper. My mate was going to borrow one from VW but simply can't get hold of it at the moment. I popped into the local garage i take all my customers cars to for mot's to see if they have one, but they use the mot rollers for such cases. I spotted one on Ebay but they're £130 and that's money i just haven't got. Plus its one of those tools i'll use once in a blue moon. I'm struggling to justify it.
There's no way i can take it to a dealer or indy because a) i can't drive it and b) i haven't got the money.

So guys, can anyone give me any advice/suggestions please.

Thank you so much

Roger
PS - If you reply or ask a question it might take a while for me to reply, but i will!!

 

[wu56Shoozz]

Well Roger, I'd try a VW Forum first, you may get a better response from them..

Secondly, how did you bleed the system, n/s rear, then o/side rear, n/side front, then o/side front ? that's the conventional method. are the calipers 4 pot and have two bleed nipples? Does the van have ABS fitted to it if so it may still have air in it..take your time on answering, we have all the time in the world..

 

[Railwayman]

Hi

This may not be the case, but I had a similar problem bleeding a MX 5, it turned out that the rear bleed nipples faced down at 45 degrees which trapped air in the top of the cylinders. Once I pivoted them up and bleed them all was well.

gary

 

[RWP278]

Well Roger, I'd try a VW Forum first, you may get a better response from them..

Secondly, how did you bleed the system, n/s rear, then o/side rear, n/side front, then o/side front ? that's the conventional method. are the calipers 4 pot and have two bleed nipples? Does the van have ABS fitted to it if so it may still have air in it..take your time on answering, we have all the time in the world..

Thanks for the reply.

I have tried VW Forums but unless you have a Transporter of some variant, its difficult to get relevent responses.

In reply to your questions.

How did you bleed the system, n/s rear, then o/side rear, n/side front, then o/side front - Yes.

Are the calipers 4 pot and have two bleed nipples - No, single nipple on each caliper.

Does the van have ABS fitted to it if so it may still have air in it - Yes it does have ABS. Fluid has never run out and ABS unit has not been removed. I was thinking that if it did have air in it, it would have been dispersed when i drove it those couple of times. Mind you, it has always been at the back of my mind that air remains.
I know BMW has a special 'cycle' process you have to go through with their software, that activates the ABS unit whilst bleeding. But this is only utilised when the whole system has been emptied or the ABS unit has been removed. Does VW/Mercedes have a similar process do you know?
Would i be able to back flow the brake fluid, so i force fluid from the caliper back up to the master cylinder?

Thanks

 

[RWP278]

Hi

This may not be the case, but I had a similar problem bleeding a MX 5, it turned out that the rear bleed nipples faced down at 45 degrees which trapped air in the top of the cylinders. Once I pivoted them up and bleed them all was well.

gary

Hi Railwayman,

I have heard of this issue before but the bleed nipple on the LT35 face upwards.

Thanks for the suggestion though.....

 

[wu56Shoozz]

You're not going to like this but if you've done the above then you may still have a faulty Master Cylinder. Its easy to "Turn the seal" on itself whilst aggressively pumping the pedal..

Speaking of pumping "Mr Bond" doe the pedal pump up hard then go soft to the floor?

Take the reservoir cap off and look into it whilst someone pumps the pedal, you're looking for air bubbles in the B/fluid reservoir - if it has then it new MC Time..

 

[toolman1954]

So, some things I would suggest. You have a new MC , did you get all the air out if it?
I would pressurise the system and slacken off the brake pipe union that is connected to the MC hopefully you might get some air out of that.
Then I would clamp off all 4 flexible pipes. I have 4 old Girling flexible clamps in my tool cabinet just for this purpose, but you can make up some clamps using tube spanners if you are stuck.
With all 4 flexible pipes clamped up and the system pressurised, you should have a hard pedal. The fluid can go nowhere else.
If it is going down then investigate the ABS ( do you have ABS on it ) As I recall there is some special proceedure for dealing with the ABS unit to purge the valves of air. Although last time I put brake pipes on my Sprinter I just bled it as normal.
With it all clamped up and pressurised leave it overnight, try to wedge the pedal down hard as well, a bit of 2 x2 for this helps.
In the morning, check for leaks, use a paper towel on all the unions. Check you have plenty of pressure in the pot. Then bleed a rear caliper, clamp it up. Bleed the other caliper, clamp it up. Crack off the unions on the loading valve just a smidgen so they weep. Bleed the fronts in a similar fashion and then release the clamps one by one.
It is very easy to cross thread a brake union, check them all. Oh... and inside the van stick your finger up to the master cylinder piston rod and make sure it is dry. Use some paper towel.
Hope this helps ....Best of luck

Steve

 

[RWP278]

So, some things I would suggest. You have a new MC , did you get all the air out if it?
I would pressurise the system and slacken off the brake pipe union that is connected to the MC hopefully you might get some air out of that.
Then I would clamp off all 4 flexible pipes. I have 4 old Girling flexible clamps in my tool cabinet just for this purpose, but you can make up some clamps using tube spanners if you are stuck.
With all 4 flexible pipes clamped up and the system pressurised, you should have a hard pedal. The fluid can go nowhere else.
If it is going down then investigate the ABS ( do you have ABS on it ) As I recall there is some special proceedure for dealing with the ABS unit to purge the valves of air. Although last time I put brake pipes on my Sprinter I just bled it as normal.
With it all clamped up and pressurised leave it overnight, try to wedge the pedal down hard as well, a bit of 2 x2 for this helps.
In the morning, check for leaks, use a paper towel on all the unions. Check you have plenty of pressure in the pot. Then bleed a rear caliper, clamp it up. Bleed the other caliper, clamp it up. Crack off the unions on the loading valve just a smidgen so they weep. Bleed the fronts in a similar fashion and then release the clamps one by one.
It is very easy to cross thread a brake union, check them all. Oh... and inside the van stick your finger up to the master cylinder piston rod and make sure it is dry. Use some paper towel.
Hope this helps ....Best of luck

Steve

Thanks very much for your input Steve. I'll be taking your advice above once I've eliminated the possible ABS issue below....

I managed to get hold of a proper set of fluid pressure gauges, which i spent a few hours testing pressures. Maybe you or anyone else could comment on the results.
So, the backs were fine holding 150 bar pressure firm with no drop.
Fronts were a different story.
Braking hard, the pedal would get to about half way down and firm up, but then it slowly dips to the floor. The gauges show something strange. The initial 'jump' on the pedal hits a pressure (on both sides) of about 100 bar, but then the pressure starts to creep up with the left side eventually reaching around 180 bar (new caliper), the other reaches around 150 bar or so.
I'm kinda thinking I could have a problem with the ABS unit (although I'm not sure how). Its like some of the valves are half closed, therefore restricting the flow of fluid to the front calipers (I've checked for squashed brake pipes).

Can anyone suggest a method of of confirming the issue is with the ABS unit, or do i have to remove it and send it away for testing?

Any input would be much appreciated........

 

[wu56Shoozz]

I don't think its your ABS.. I still think you have a faulty MC. Its easy enough to turn the seals against themselves whilst bleeding the system the slow pedal would suggest this..did you check for air bubbles in the reservoir whilst pumping?? (Oooeerr)

 

[wu56Shoozz]

Photos of the Master Cylinder please, on the van preferably..

 

[RWP278]

I don't think its your ABS.. I still think you have a faulty MC. Its easy enough to turn the seals against themselves whilst bleeding the system the slow pedal would suggest this..did you check for air bubbles in the reservoir whilst pumping?? (Oooeerr)

Interesting....

Must admit that I forgot to look for bubble in the mc whilst pumping. Will wait until one of the kids gets home from school and get them involved (no doubt to groans and a five pound note!).

Will get a couple of pictures a bit later on......

Thanks for staying with me!!

 

[toolman1954]

Hi,
I thought you would have had this sorted by now !
O.K. As you still want to concentrate on the ABS unit, and air inside it, which I have my doubts, although to an extent it would depend on how you replaced the Master Cylinder and other components to let air into the system.
You really do not want to get air into the ABS unit as it has to be bled through on STAR to purge the valves, although I dare say VW have thier own system. There is no difference in the braking components Sprinter/ VW, all the rear end brakes on my Sprinter are VW ( cheap off of Ebay ! ) Now with the mantra of NOT getting air into the ABS unit I would have filled the MC reservoir and pressure bled the MC through the unions, just crack them off a tiny bit and let the pressure purge out the air. Then I would head down to the ABS unit and gently open up a union there, just enough so the pressure pushed out any trapped air that may be left in the pipe. At that time the chances of any air getting into the ABS unit are very remote. (although not impossible) Also I would have used a bit more than 20 psi to keep the pressure high.
So did you do anything similar or did you let air get into the ABS unit by just trying to bleed it from the wheels. This is a bit of a no no in my opinion, you need to take care with ABS units. In other words know what you are doing.!
I am not convinced as yet, that you have all the air out of the MC, but then I am not standing there with the bleeder in hand !
Do check what wu56Shoozz has to say, it is possible. Somewhere in my toolbox, I have a brake union with a short piece of pipe with end soldered up for testing master cylinders for leaks. Very cheap to make.
Have you clamped off all the flexi pipes yet? There is air in their somewhere, you just need to find it and purge it out.
Many setting suns ago I had a similar problem with a Land Cruiser, that turned out to be some locked air in the rear balance valve. Was a right pig to find and only solved by clamping off the flexibles.
One thing I forgot, are you getting the brake servo working.? There is a pressure tank tucked away in the engine bay that holds air for the servo. The pipe can become detached or the tank can leak. You need the tank because of the lack of manifold pressure that petrol vans have.
Onwards and upwards ... good luck.

Steve

 

[RWP278]

Hi,
I thought you would have had this sorted by now ! - I wish, but i have a business and a family with too many children!
O.K. As you still want to concentrate on the ABS unit, and air inside it, which I have my doubts, although to an extent it would depend on how you replaced the Master Cylinder and other components to let air into the system.
You really do not want to get air into the ABS unit as it has to be bled through on STAR to purge the valves, although I dare say VW have thier own system. There is no difference in the braking components Sprinter/ VW, all the rear end brakes on my Sprinter are VW ( cheap off of Ebay ! ) Now with the mantra of NOT getting air into the ABS unit I would have filled the MC reservoir and pressure bled the MC through the unions, just crack them off a tiny bit and let the pressure purge out the air. Then I would head down to the ABS unit and gently open up a union there, just enough so the pressure pushed out any trapped air that may be left in the pipe.- I pretty much did this apart from a) bleeding each wheel in the correct order (after doing the mc) because calipers had been changed and b) cracking off any union on the ABS unit. At that time the chances of any air getting into the ABS unit are very remote. (although not impossible) Also I would have used a bit more than 20 psi to keep the pressure high.- I only used 20 psi as that was the maximum stated on the device. I must admit that it doesn't really seem that much.
So did you do anything similar or did you let air get into the ABS unit by just trying to bleed it from the wheels. This is a bit of a no no in my opinion, you need to take care with ABS units. In other words know what you are doing.!- Bugger, so has me bleeding the calipers possibly introduced air into the ABS unit?
I am not convinced as yet, that you have all the air out of the MC, but then I am not standing there with the bleeder in hand !
Do check what wu56Shoozz has to say, it is possible.- This is next on my list of things to do when i get a bit of free time. Somewhere in my toolbox, I have a brake union with a short piece of pipe with end soldered up for testing master cylinders for leaks. Very cheap to make.
Have you clamped off all the flexi pipes yet?- I did clamp each flexi pipe off in turn but I couldn't sense any difference. There is air in their somewhere, you just need to find it and purge it out.
Many setting suns ago I had a similar problem with a Land Cruiser, that turned out to be some locked air in the rear balance valve. Was a right pig to find and only solved by clamping off the flexibles.
One thing I forgot, are you getting the brake servo working.? There is a pressure tank tucked away in the engine bay that holds air for the servo. The pipe can become detached or the tank can leak. You need the tank because of the lack of manifold pressure that petrol vans have.- Servo was replaced with a known working second hand item which does work. Will check out the pressure tank you mention.
Onwards and upwards ... good luck.

Steve

Evening Steve,

Thanks for such an in depth response. I've entered my answers in red next to your question/comment.

 

[RWP278]

Photos of the Master Cylinder please, on the van preferably..

Hi wu56Shoozz

Not sure what kind of angle you were after but I've taken 2 or 3 for you......

Oh god, trying to download them but it even says that one file is too large (at 1.48 mb).

Maybe i could draw them!!

 

[toolman1954]

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