Bleedin' brakes!! Arrghhhh!!!

[junkuser]

Rear brakes could be using too much of the stroke volume if not adjusted correctly but the difference between blocking off L and R front brakes points to a problem with the caliper.
Is there something else that could be causing pistons to retract when the pressure is taken off?  
Piston seals the wrong way round more likely to allow leakage than pull the pistons back.

Is the replacement master cylinder the same bore size as the old one and is the brake pedal returning to the fully up position?  Only looking for any possible cause of reduced stroke volume asking this.

The caliper pistons are so large that even a small amount of retraction will account for a large volume fluid compared with the capacity of the master cylinder.

There is a simple cause somewhere.

" Clamp both pistons in the caliper and the pedal goes straight into the carpet"
Can't work that one out at all.  Seems to send the problem back from the caliper but clamping hose to that caliper, I think you said, gave a firm pedal.
Is there a red herring somewhere?
Would be odd if there was intermittent failure of the master cylinder valving to seal that has been coinciding with the tests you have been doing on the caliper.

All very interesting, but I understand your frustration.

[markcro]

Thanks guys.
Is there is an orientation to the caliper seals? I just randomly popped them in?
When I rebuild the calipers I didn't split them, I only cleaned them up, replaced the pistons, seals and dust seals.
But I just popped the seals in as they looked uniform to me and I didn't know there is a particular orientation?

[Spider]

Talking of orientation did you replace the pistons the way they came out? with the flat surface first. I know it is a long shot and you probably think "of course I did! What sort of an idiot would not?" I only say it as I have made some odd blunders in my time and your problem does not seem to follow usual fault characteristics and the problems do seem to have started after you rebuilt the calipers.

[markcro]

3762 wrote:

Talking of orientation did you replace the pistons the way they came out? with the flat surface first. I know it is a long shot and you probably think "of course I did! What sort of an idiot would not?" I only say it as I have made some odd blunders in my time and your problem does not seem to follow usual fault characteristics and the problems do seem to have started after you rebuilt the calipers.

No question or suggestion is too obvious or silly as we all make mistakes. However I did put the new pistons in the right way. The problem definitely started after I rebuilt the calipers. I went from sticky brakes with a seized piston to beautifully operating brakes that don't stop!  :B

[junkuser]

The experience I have with caliper piston seals is limited to one set fitted to the Spit4 so minimal.
These had a taper on the contact surface.  Can't even say they were of original design.
Doubt that it would be the cause of your problem Mark as the seals would be forced forward by the fluid when pressurised and if they are not leaking they are working.
Can't see that they could cause retraction.
Only mentioned to rule out or stimulate thoughts from others.

[junkuser]

"- no clamps- pedal digs into carpet."
             Consistent with air in system or master cylinder fault.
"- brake hose clamped - pedal goes firm"
             Consistent with air in that caliper and master working correctly.
"- Clamp one piston or the other in the caliper and the pedal goes firm."
             Suggests no air and master OK during that test.
"- Clamp both pistons in the caliper and the pedal goes straight into the carpet"
            Back to air or master cylinder problem.

Above, with no fluid leaks, could suggest intermittent failure of the non-return valve in the master cylinder to seal. Not high on the list of possibilities but possible.

How's about a photo of the caliper showing the positions of the hose and bleed nipple.

[markcro]

One step forward and two backwards, or two forward and one backwards....anyway some progress was made tonight but the mystery continues............... :-/
I forgot to take a photo of the caliper but the nipple is on top in the correct position. I bled the caliper fixed with the nipple in the highest point as normal, and I also bled the caliper in different angles while off the car no effect.

Anyway, since clamping the drivers side hose definitely firmed up the peddle (albeit 2 inches above the carpet) and I have gone over the caliper until the cows came home and can not see any issues. So I am sick to death of this problem so I decided to get rid of this caliper problem once and for all with one of these bad boys............





I fitted it tonight and bled the system again. And just like when the brake hose was clamped, this new caliper allowed the peddle to firm up at the same 2inches above the carpet.

So I took her out for a blast............big difference in brakes in the way that the car now actually has brakes!  :P
But it's still not right. Full application of the brakes causes the nose to dip and the car to slow quickly. But before even with 2 sticky pistons this would cause both front wheels to lock solid.
A jab of the peddle and then full application causes the wheels to lock as they should.

So the mystery continues........... I now have brakes, but they are crap. A pump brings them to what they should be. So the peddle should go firm way before 2 inches from the carpet. So back to the master cylinder even though it's brand new?

But then what was the issue with the driver's side corner that this new caliper fixed?!?!?

I was so looking forward to getting this issue finally put to bed... :B :-/

[thescrapman]

what do the brakes feel llike if you clamp off both rear hoses?

If still crap, clamp both front ones as well, then you should have no pedal movement at all.

Cheers

Colin

[Paudman]

markcro wrote:

So the mystery continues........... I now have brakes, but they are crap. A pump brings them to what they should be. So the peddle should go firm way before 2 inches from the carpet. So back to the master cylinder even though it's brand new?

If you need to pump the pedal to get full braking then the master cylinder is getting insufficient fluid to the calipers and cylinders to fully activate the brakes. This could mean that there is air in the system, there is poor adjustment (possibly the rear cylinders) and so too much travel or too small a bore on the master cylinder.
I know you replaced the master cylinder.... but check it and confirm it's the right one, and I'd also get hold of a s/h one and try that. I suspect some of the brakes may need adjustment / bedding in, but my money is on the MC being faulty or incorrect and not supplying enough fluid. Did you use the original pushrod? A replacement one may be too short; try the old one again.

[markcro]

Thanks guys.

I will  clamp all four brake lines together as suggested as I only had tried one at a time and only the driver side front made a difference to the peddle. I fitted the new master cylinder as it came- cylinder and push rod. I never changed anything on it.
I have a rebuild kit lying in the garage for the old one. I’ll rebuild that and could fit it as a test.


So did I actually need the new caliper? How did the new caliper fix the no brakes? I’ll go mental if it was the new master cylinder all along.

If it is, I wonder do I have any come back with sending the new caliper back as well as they are from the same place? Although the new caliper did fix the no brakes issue which is strange....?!?!

[markcro]

Eur-fu<king-reeka!! This morning I rebuilt the old master cylinder, pulled off the brand new one and fitted the rebuilt original one. I did a quick bleed and found that the pedal was now even worse! Grr, I was about to jack it in but thought that at the very least it couldn't be worse, it should be at least be the same. So I bled all 4 corners properly, and bingo! I have brakes! I took her out for a quick blast and I can not easily lock up the front tyres!  8)

So the brand new brake master cylinder was the red herring....  What are the chances of the master cylinder failing and then the replacement brand new one being faulty??

But what I still don't understand is why the drivers side caliper made a difference? That was the real red herring, and the fact that clamping that hose/ replacing the caliper with a brand new one did improve braking???
Now do I leave the new caliper on or go back to the original rebuilt one? I wonder why it had any affect at all...does the new caliper have a smaller internal capacity?

Well for the moment I will drive her and enjoy her before winter comes.  8)

[Nick Moore]

Faulty, substandard master cylinders are a problem the TR boys have found over the past couple of years. One brand of remanufactured master cylinders aren't made to anything like the standard of the originals, despite appearing identical externally. The TR-ists have suffered from brake failure, inability to bleed out air and fluid leaks (with cases of stripped paint on the bulkhead). If you look on the TR Register website (http://www.tr-register.co.uk/forums/index.php?showtopic=35138) you can read all about it, including the response from the company selling the parts.

The TR master cylinders aren't the same as yours, I think, but it's another demonstration that repairing original parts is often a safer route than buying new parts. We assume new means better, but the quality control exercised by reproduction manufacturers sadly falls short of the OEM manufacturers.

[junkuser]

Great news.
Would still be nice to know the actual cause.
The calipers should use the same volume of fluid during operation as the pistons must be the same diameter and move a very similar amount. Would be a bit of a worry is the pistons were not the same size.

Was there any difference in the technique you used for bleeding this time?

The master cylinder should be checked out, especially the make up valve.  It must have unobstructed movement, undamaged rubber and seat.

Nick's input is rather worrying.  Whilst the problem with the TR masters sounds somewhat different it is very serious that the quality control is so poor and would be nice to know if your master was made by the same people.

We have all these safety requirements for motor vehicles yet somehow sub-standard, safety critical, components can find there way on to the market.
If the authorities tightened up on this area it would be more relevant than the EU ideas on non-standard cars.

Time to enjoy your car now Mark.

[nang]

I got an original off my 2500 resleeved in stainless and also rekitted at the same time years ago. No problems ever since. Was told if any problems just clean the bore with clean rag and rekit. Have never needed to.
Tony.

[markcro]

Thanks Guys, I am so p1ssed off with this whole affair as I have wasted the whole summer chasing my tail on this. Time and money wasted while the car sat unused.  :B I must gave put about 60 quids worth of brake fluid through the system at this point!  ??)
And I mad resprayed the bulkhead before fitting the brand new one, and all this messing about has chipped and removed bits of paint.

I actually used a more shoddy quick way of bleeding than before, as I was on my own and didn't have any faith in it working. But it did!  8)   (the other times I painstakingly did the two man bleed, with and without bleed kits, one man bleeds, etc. but to no avail.)

And yes this brand new master cylinder is a TRW one.  :-0  
Are there any brands of new ones that are recommended?

I would leave the old rebuilt one in except there is wear and a bit of corrosion on the metal piston thing in it. And when I was fitting the end dust seal over the fork thing it split. So I am worried about fluid seeping out and ruining my paintwork even worse.  (How are you meant to get that dust seal over the end of the rod fork?)

It was glorious driving her yesterday, made me even more fed up that this wasted my whole summer of driving!

[markcro]

Still I do not understand the red herring of the drivers side caliper?? So looks like I didn't need to buy a brand new one even though it did make a difference. The pistions look to be the same diammeter as the original, but maybe the caliper has less capacity? Strange...

[markcro]

My final update on this tedious story.....

The new master cylinder has been sent back to be exchanged, unfortunately they only stock TRW ones, so I'll see what the replacement is like. But in the meantime she is perfect on the rebuilt original one and I have driven over 100 miles in her since Friday!!  8) She has covered more distance in the last 48 hours than in the last 12 months!

Just got her undersealed and cavity wax injected too. :-)