Bleedin' Brakes - help please
Discussion
I have standard servo, fluid reservoir & master cylinder, braided lines from connector block to front calipers, original copper line from connector block to rear & braided flexys to rear calipers, Hispec 2 pot rear calipers & WMS 4 pot front calipers. All upgraded components have been on the car for around 3 years with no problems.
I removed both front calipers over the winter during wishbone & wheel bearing replacement, rears were unbolted but not disconnected from brake lines.
Problem is after initially fully bleeding through to replace fluid, which resulted in decent but not perfect pedal feel I have re-bled the system 3 or 4 times, including the master cylinder on the last attempt but cannot get decent brake pedal pressure and on each bleed I'm getting air in both rear calipers but fronts are fine.
The pedal feels good & firm before and after starting engine but re-occurs after a couple of brake tests on the road. There are no fluid leaks anywhere and I cannot find any air/vacuum leaks.
Any thoughts very much appreciated.
I removed both front calipers over the winter during wishbone & wheel bearing replacement, rears were unbolted but not disconnected from brake lines.
Problem is after initially fully bleeding through to replace fluid, which resulted in decent but not perfect pedal feel I have re-bled the system 3 or 4 times, including the master cylinder on the last attempt but cannot get decent brake pedal pressure and on each bleed I'm getting air in both rear calipers but fronts are fine.
The pedal feels good & firm before and after starting engine but re-occurs after a couple of brake tests on the road. There are no fluid leaks anywhere and I cannot find any air/vacuum leaks.
Any thoughts very much appreciated.
And there's defo no light drips from the bleed nipples on the rears. I had to losen and tighten my bleed nipples a number of times which were new on my Brembos to get them to seat together. I'd bleed brakes then test car, come back and there'd be the smallest amount of fluid. Stopped after I did that and they bled better Richard.
When I rebuilt mine with all new components and pipes etc. we found that we had to crack off the pipe as it enters the T valve at the rear and run some fluid out of there first to clear the air and allow a good bleed at both rears afterwards. We pumped the fluid through very slowly to allow the master cylinder a chance to push as much volume with each depression which seemed to help.
Are you getting a solid pedal with little travel after pumping to dissipate any servo vacuum without the engine running? Is it the same post bleed after road test or does it have more travel? If it travels more and you suspect air then you should be able to see bubbles in the clear brake bleed pipe?
If you pump up the pedal to a solid feel, hold your foot on the brake and start the engine then you'll be able to feel how much travel is normal when the servo assistance comes in as the vacuum builds.
Are you getting a solid pedal with little travel after pumping to dissipate any servo vacuum without the engine running? Is it the same post bleed after road test or does it have more travel? If it travels more and you suspect air then you should be able to see bubbles in the clear brake bleed pipe?
If you pump up the pedal to a solid feel, hold your foot on the brake and start the engine then you'll be able to feel how much travel is normal when the servo assistance comes in as the vacuum builds.
Thanks for all the suggestions & tips chaps. I have bled this particular system a few times in the past without issue using both the traditional & easibleed methods, this time I'm using the traditional "mate pumping the foot pedal as required" method (as I've buggered my easibleed), although both the mates in question have gone through this process more than I have, Alun being one of them! The pedal is nice and firm after initial bleeding but air seems to be entering the rear calipers again only after driving the car, rather than just idling. This leads me to think it may be a servo issue, which I'll check over as best I can in the morning.
I can't get into much pulling apart tomorrow as I need to get them as good as I can for a Sprint on Sunday at Hethel (3 particularly hard braking points apparently!) which may mean a somewhat reduced performance as per last week at Rockingham for the same reason.
I'll check and crack the rear t-piece as suggested. It just seems odd that I only seem to get recurring air at both rear calipers and none seemingly at the front, I would assume if I had air being drawn in at the servo/master cylinder it would be distributed throughout the whole system?
Ho hum, I'll see what happens tomorrow and report back.
I can't get into much pulling apart tomorrow as I need to get them as good as I can for a Sprint on Sunday at Hethel (3 particularly hard braking points apparently!) which may mean a somewhat reduced performance as per last week at Rockingham for the same reason.
I'll check and crack the rear t-piece as suggested. It just seems odd that I only seem to get recurring air at both rear calipers and none seemingly at the front, I would assume if I had air being drawn in at the servo/master cylinder it would be distributed throughout the whole system?
Ho hum, I'll see what happens tomorrow and report back.
Here's a very simple one that draws rather than shoves.
Mityvac 2 from the states I believe.
It's my mates and I've borrowed it before and found it excellent. One man operation.
I can try and get hold of it Richard. Let me know. Dunno if I should drivevover but I'm more than happy to mate
Mityvac 2 from the states I believe.
It's my mates and I've borrowed it before and found it excellent. One man operation.
I can try and get hold of it Richard. Let me know. Dunno if I should drivevover but I'm more than happy to mate
ClassicChimaera said:
Here's a very simple one that draws rather than shoves.
Mityvac 2 from the states I believe.
It's my mates and I've borrowed it before and found it excellent. One man operation.
I can try and get hold of it Richard. Let me know. Dunno if I should drivevover but I'm more than happy to mate
thanks for the offer, but i do need to buy myself oneMityvac 2 from the states I believe.
It's my mates and I've borrowed it before and found it excellent. One man operation.
I can try and get hold of it Richard. Let me know. Dunno if I should drivevover but I'm more than happy to mate
Thanks again chaps, and to Alun for the offer but I agree with you, you probably shouldn't put more miles on yours than you absolutely need to until you get it checked out. Unfortunately I won't have the time to get over to Mat's this morning but thanks for the suggestion Anthony. I'll post later with results, fingers crossed for a successful resolution!
id try lowering the rear of the car down as much as possible with the nose in the air.
I agree with the gravity thing. If the fronts are ok the servo and master must be ok Shirley
,,, and yes your right about mine too.
Your doing it correctly, there's something wrong with the rear set up if it doesn't work, ( states the obvious) but at times like this you question everything including what your doing
Goodluck.
I agree with the gravity thing. If the fronts are ok the servo and master must be ok Shirley
,,, and yes your right about mine too.
Your doing it correctly, there's something wrong with the rear set up if it doesn't work, ( states the obvious) but at times like this you question everything including what your doing
Goodluck.
Ok, I lowered the back end and adopted Gary's gravity method (but without the tea!) and got a really good firm pedal (thanks Gary). Kept foot pressed down on brake pedal on start up and pedal went down as it should so all ok at that stage. Drove steadily to filling station and all seemed pretty good although slightly variable pedal pressure to stop. Returned from filling station (approx 1.5 mile suburban journey) and soft pedal started to re-emerge but not to the same degree as before.
The problem only seems to arise when/after driving so I'm assuming it must be servo related? although, as I say the problem seems to be gradually diminishing?? I remain somewhat confused!
I'll be giving a good run over to \hethel in the morning so will monitor brake performance.
Missed a call earlier from Alex DD so may have more to go on later.
Thanks again for all the advice gents.
The problem only seems to arise when/after driving so I'm assuming it must be servo related? although, as I say the problem seems to be gradually diminishing?? I remain somewhat confused!
I'll be giving a good run over to \hethel in the morning so will monitor brake performance.
Missed a call earlier from Alex DD so may have more to go on later.
Thanks again for all the advice gents.
OK - another one worth a try is to wedge something in place holding the pedal pressed over night (or even between races)- an old bike racer's trick is to zip tie the brake lever on... normally results in a very firm feel and I think must by pressurising the circuits push the trapped air out.
Worth asking, and I'm sure I know the answer, it is newly opened fluid going in (ie not absorbed atmospheric moisture)?
Worth asking, and I'm sure I know the answer, it is newly opened fluid going in (ie not absorbed atmospheric moisture)?
Update - Sprinting at Hethel yesterday in the Speed Championship where good brakes are a must. Kept pressure on brake pedal before each race and it did improve things (thanks again Gary). Resulted in decent, but not brilliant performance. Now resolved to flushing out system with new fluid (again) as I have a niggle at the back of my mind about how well I carried out the initial fluid change.
Thanks for the suggestion Graeme but pads have only done a few miles and didn't have this issue on the last set (same type) that went in. It'll be Saturday before I can go through the system again but feel pretty confident that the problem is nearly solved. thanks again to all for suggestions and advice.
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