Serious brake bleed issues

[Tom W]

Have you tried pushing all the pistons back into the cylinders before bleeding?

[JerryL770]

I understand the reservations about pressurising the reservoirs.

One (I think) important thing is to start bleeding at the furthest caliper from the master cylinder, and then progress forwards - not the reverse.

[mark10337]

It is very important. Discussed recently viewtopic.php?f=4&t=12955&p=105103#p105103

You should bleed in the correct order
Nearside rear
Offside rear
Nearside front
Offside front

Ref. L10 Service Manual

[Gerry]

Hi Keith,feel bad for you,not much I can add given the thoughtful replies you have had already,in my Pm to you mentioned the inner tube method,which involves pressurizing the reservoir with an inner tube and bleeding the brakes in the conventional manner while maintaining pressure.A very tedious process that worked for me.

Regards Gerry,Ontario,Canada.

[MarkRado]

I had a similar problem, turned out to be an invisible leak at one of the reservoir hoses where the air entered the system on every pump stroke! On a friend's Ferrari 250 GTE the servo pulled air, again invisible. Remember that also new and restored components can fail. After bleeding several cans of brake fluid, I would start checking components where air can enter the system during pumping.

[phil.dobson@mac.com]

hmm. before you go any further you could try isolating the system at various points using blank brake fittings (or just use normal fitting with a crushed section of brake pipe) then bleed until it goes spongy. i.e. split the front circuit from the rear an see if you can get a hard pedal.

one other point I didn't notice if you responded to the suggestion to use the old fashioned bleeding procedure? system closed, press brake pedal, open bleed nipple, close bleed nipple, ONLY then release the pedal. repeat until no air. this is the ONLY way I have ever gotten all the air out for a new brake system.

after all that it would look like a new master (or strip it) is in order. there are recorded instances whee seals are reversed within.

[abowie]

I've been following this thread for a while.
Personally, I've never failed to successfully bleed a system with positive pressure/syringe.
I'd suspect that there is a mechanical problem within your system.
Common problems involve the shuttle valve in the booster getting stuck and the piston in the master getting stuck forwards.
I have seen a booster without a hole drilled in it
Irritating though it is, it's time to pull them out and inspect them.

[Series1 Stu]

I agree with Andrew, there is definitely a mechanical fault.

I had the same problem with my 420, which has essentially the same system. It turned out to be a defective 'brand new' master cylinder.

I must have pushed 3 litres of brake fluid through the system before I realised that just because everything is new doesn't necessarily mean that it all actually works.

Sent the master cylinder back, got a replacement and it bled through perfectly after I ensured that the shuttle in the slave cylinder was moving as it should.

Regards

[keithmac]

Have done the tradition pump ,close ,release,pump, twice now all round.

After reading the many great suggestions, I tried this today.

REmoved brake line from master to servo and plugged it with a bolt---pedal now hard ,good
This would seem to indicate there is no fault with the master and no air in it ?
( back bled the line so no air trapped on re assembly )

Next, bled the line from master to servo -no air, good

next ,remove front brake line from servo and plug it with bolt ( new style brakes so front brake line is in the middle of the servo ) So it would seem to me that the master , servo and rear brakes are now isolated from the fronts
Got a hard pedal !!!
This would seem to indicate me that I have no master , servo or rear brake issues and that the problem is somewhere in the fronts. ( does that sound right to all of you )
( re check and re tighten all connections in front and servo and master )
So, back off all front brake pistons and jam them in place ( as advised )
Syringe bleed right front ( left hand drive ) 100ml of Dot 5 , no bubbles.
Crack open the T junction for front brakes bleed it both ways , no bubbles. rebleed right front ( just to be thorough )
Syringe Bleed left front 50ml alternating hard and soft pulses.
Check all connections
SOFT PEDAL
aaaaarrrgghh
Having confirmed the function of master and servo with a hard pedal when front isolated , could it still be a faulty part????
What am I missing here?
The pedal stops an inch from the floor , first pump, and an inch higher up on second pump, very little difference if any on third pump.
Please keep the suggestions coming . I will try anything,I am in my fifth week of brake bleeding after a 15 month restoration and the car is ready to go
Fall is coming in Canada, soon the driving season will be over. It would be nice to brake the engine in this year or maybe even just drive the car.
It is encouraging to hear you all talk about what fun the car is to drive but this car has been so frustrating i look forward to the day when it is fun.
Keith

[288gto]

Hi Keith,

What do you mean by “front brake line is in the middle of the servo”?


http://s714.photobucket.com/user/vanqui ... 5.jpg.html


Edit, I think I know what you mean.

It would seem the problem lies in the front brakes. Perhaps there is too much travel for some reason on the front pistons? Are the pistons retracting for some reason?
Do you notice a lot of movement in the pads on the first stroke?
I’m baffled to be honest and feel your frustration.




Simon

[mgcjag]

This may help..early car on left...later car on right

[288gto]

If blanking the front brake line port gives a solid pedal the problem has to be the front brakes.

Air in system
Too much travel in Caliper pistons on first stroke
One pad/piston sticking and other one distorting disc then pushing back?
Anything else???

Simon

[ALAN COCHRANE]

Hi Keith

I’ve been reading this thread with great interest and admire your perseverance. I’ve always found the braking system awkward to bleed if that’s ant comfort.
Two things I would suggest:-
You’ve isolated the problem to the front brakes, but don’t say if you’ve bled the system with only one calliper connected then tried again with the other only connected. This would narrow it down to one front brake or the other. At least this would be a small step forward.
Secondly no one has mentioned the notorious otter switch which operates the brake lights. From memory this is fitted to the front brake line although I can’t remember where exactly in the circuit. It might be worth having a friend check the brake lights come on with the first push of the brake pedal. If not this may indicate a problem with the switch. Although I’m not sure this would cause a soft pedal.
Sorry I’m a bit vague about the switch as I’m away from the car and in Vancouver at the moment. Thoroughly enjoying a fabulous holiday in your great country!

Cheers

Alan

[keithmac]

H Alan,
further isolation of the problem is a great idea. It will help me find which caliper/piston is the culprit.I will report.
As regards the brake light otter switch , it is located on the rear brake circuit near the servo on the 4.2 S1 and it was full of air . I caught it last week, but very good advise by the way .
Glad you are enjoying Canada as much as we enjoy visiting the UK !
Cheers,
Keith

[ALAN COCHRANE]

Hi Keith

Sorry the otter switch suggestion was based on my car, a 1962 SI where it’s located on the right hand side near the radiator header tank.
A further test if it turns out that one of the callipers is faulty would be to disconnect it, then remove the pads and replace them with pieces of wood. These would be shaped the same as the pads but thinner. The calliper pistons can then be operated by compressed air and their relative movement clearly observed without fear of them being fired out of the calliper.
I’ve found this useful when the pads are new and restrict the piston movement.
This would confirm one way or another if there are any internal blockages within the calliper or a sticky piston. This may not be the cause of your soft pedal but who knows, you seem to have tried everything else.

Cheers

Alan

[Tom W]

Do you get a decent pedal after bleeding, then get a soft pedal when the car is driven? If so, this may not even be a brake bleeding problem.

Now you’ve isolated the problem to the front circuit, I would look at the front wheel bearings and stub axles. Any excessive play or flex here can cause the disc to knock the pads back into the calipers, giving an excessively long first pedal stroke. Once the pistons have moved towards , the second press feels like norma, until they’re knocked back againl. This is a known problem in racing. Rob Beere even makes a spacer to fit between the bearings to stiffen the stub axle up, but this shouldn’t be necessary on a road car. Look for excessive wheel bearing play and look at the condition of the stub axle. Also check the calipers are bolted to the uprights tightly and that the lockwire is in place.

[keithmac]

Thanks Tom
I will check that next !
Todays results. So ,
It is the right front brakes. Plugged the right front lines at the T junction,.... hard pedal. Took the pistons off a few odd things but nothing that really looks like the cause. Pins appear straight, seals appear good ( in wrong way round though chamfer facing away from pad they are new ) Piston bores are all the same size ( not warped )
So I checked the bolts , three out of four on the inboard piston bolts vary in thickness from 5 to 10 thou from thread end to thread start ,the others do not. not sure if this is it , but it aint good. I may go for new pistons and bolts anyway but I will continue to report back until this issue is fully resolved
Take a look.

[keithmac]

New info
Three other of the caliper bolts have threads that do not extend up the bolt far enough ( after market offshore parts ? ) . So with the wrong combination of stretched and or short threaded bolts , one or both of the calipers would be loose no matter how tight the bolts felt and would move back under pressure while looking like they are flush to the caliper bracket when the pedal was released , likely resulting in a "soft pedal feel" and mimicking air trapped in the system
WHO WOULD HAVE THOUGHT THIS WAS THE CAUSE OF A SOFT PEDAL !!!!

I will report back when I have new bolts etc. and have confirmed the cure
Keith

[Series1 Stu]

I'm not fully familiar with the set up but, as is good practice, shouldn't there be plain washers under the bolt heads?

Regards

[Tom W]

Very good, looks like it could be the cause. Make sure you buy the correct strength of bolt when you source your replacements, as well as size.