Bleeding Brakes
Discussion
Thought I'd change the fluid today but having done so I have no brakes at all. Tried again without the non-return valve thing, just a pipe in some old fluid and found lots of air in the fluid. Seems to be no fluid in the front section of the master cylinder even when its full to the brim. Is that why? Any ideas?
Wierd! Presumably the reservoir ran out of fluid at some point during your original bleeding process? Otherwise I don't see how it could have got air in there. Anyway, on most systems, the pressure side is only connected to the reservoir during the very last bit of travel. If the pushrod has been adjusted to take out every little last bit of play, it may not be coming back far enough. You can get a similar problem if the seals are knackered or gunged up, preventing the piston from coming back far enough to open the port to the reservoir.
The brakes were fine before I started bleeding. I did have the mystery fluid loss over winter when most of the fluid disappeared (into the servo?)but after topping it up they worked OK without bleeding if a bit spongy but good and powerful. I did notice that when bv;leding the fomst I get the pedal down to the floor whereas the backs only seemed to give 3/4 travel on the pedal. Now its down to the floor all the time having bled 3 out of 4 wheels and still loads of bubbles.
I have bled each wheel at least twice more tonight and got lots of air out, especially the rears. Problem is after all this the pedal felt reasonable until I started the engine and then the pedal goes almost to the floor unless its pumped.Switch off and it goes hard. Is there a bleed valve on the servo that needs to be used or is it the dreaded servo that is going to have to be replaced? I have a horrible feeling I'm back to that afterall.
The servo is not supposed to be involved in the hydraulics, the only connection is mechanical. So starting the engine should have exactly the same effect as pushing down on the brake pedal a lot harder. Having said that, if the master cylinder seals have gone then it's conceivable you have a big fluid leak somewhere and the brake servo is a nice big place for it to be leaking into. I don't understand those symptoms yet but definitely something wrong there and my guess is one of the circuits has failed inside the master cylinder.
Appreciate you getting back. I would like to know form anyone if it is definitely the servo/master cylinder that has gone before embarking on getting it removed as I know it is a nasty/costly job to be entrusted to a specialist not a DIY task.
Strange thing is that before I bled the brakes they were fine apart from a bit more sponginess, but I put that down to the disappearance of fluid over winter.
During the bleeding yesterday it was worse. Every time we went round to a different wheel there was lots air in each line. But the real mystery was that when running the engine the pedal went to the floor first time and then after pumping got some brakes back. Could it be a seal has been reversed in the bleeding process? Even so I suppose it still means the servo has to come out.
Strange thing is that before I bled the brakes they were fine apart from a bit more sponginess, but I put that down to the disappearance of fluid over winter.
During the bleeding yesterday it was worse. Every time we went round to a different wheel there was lots air in each line. But the real mystery was that when running the engine the pedal went to the floor first time and then after pumping got some brakes back. Could it be a seal has been reversed in the bleeding process? Even so I suppose it still means the servo has to come out.
If the pedal is going down when the engine is running that means the servo is working. To test it otherwise you need pressure guages and so on. If it was leaking it would more than likly screw up the engine running as well. They don't fail usually because their location stops them rusting through which is the usual way that they die.
I think you have a duff/leaking master cylinder. Either way it is bite the bullet time.
I think you have a duff/leaking master cylinder. Either way it is bite the bullet time.
I've had a master cylinder go suddenly before and the symptoms were as you described. A gentle push would allow fluid to escape around the piston in the master cylinder, so the pedal just went to the floor. A sudden stab would disturb the piston seal enough for it to catch and work correctly. Over about 2 days this got worse and worse (why was I driving it???) to the point where it just didn't work.
There was no fluid leaking, it was just going past the piston and staying in the master cylinder.
The servo should be fine, and the M/C just bolts on the front of it. It was simple on my car, but then it wasn't tucked into the wing...
There was no fluid leaking, it was just going past the piston and staying in the master cylinder.
The servo should be fine, and the M/C just bolts on the front of it. It was simple on my car, but then it wasn't tucked into the wing...
Sounds like the master cylinder as I am not loosing fluid when in use (just over winter) and the enyine sounds fine and the vacuum pipe is dry.
Was this not on a Griff then? Is it possible that the master cylinder can be removed without taking the pedal box out. The acces through the clutch cylinder coveris awful but if it possible please let me know how. Does the clutch cylinder have to come out first as I would suspect to access the brakes cylinder. I cant even see the bolts.
Was this not on a Griff then? Is it possible that the master cylinder can be removed without taking the pedal box out. The acces through the clutch cylinder coveris awful but if it possible please let me know how. Does the clutch cylinder have to come out first as I would suspect to access the brakes cylinder. I cant even see the bolts.
shpub said: If the pedal is going down when the engine is running that means the servo is working. To test it otherwise you need pressure guages and so on. If it was leaking it would more than likly screw up the engine running as well. They don't fail usually because their location stops them rusting through which is the usual way that they die.
I think you have a duff/leaking master cylinder. Either way it is bite the bullet time.
Steve
Cant even see the brake cylinder bolts in the access cover!
Would you by good enough to let me have the dismantle instructions for the brake master cylinder as I only bought the Bible (1st edition )at Duxford and there is nothing in it about this subject. For example I know you said s/column out, does this mean remove s/wheel and all stalk and horn wiring or unbolt at joint in footwell, also which bolts actually hold the pedal box in place?
Thanks
Chris
The descrption is not much more than I have already described as I found no one that wanted to DIY it because it is such a difficult job. So it explains in general what the main techniques are, the problems and why the best thing to do is to pay someone else to do it. I still think that is the case as I suspect that the pros have special spanners that they have made to help solve access problems. ANyway... here are my latest thoughts...
The steering column really only gets in the way so its removal is optional. You could remove just the steering wheel but taking the seat out fress up a lot more room. I would definitely remove the seat so you have room to work. That may be all you need to do. Both the clutch and master cylinders are bolted through the pedal box so they will have to be undone and that means disconnecting them from the hydraulic system. They are usually connected into a distribution block. Unless the cylinders are seperated from the pedal box/servo, they won't move. If you can't get access past the clutch master, I would suggest that you need to take that out first which will allow you to get to the master cylinder and allow that to be unbolted.
Normally the master cylinder is unbolted from the servo first but because the reservoir is located in the wing... that is going to be difficult so the cylinder needs to be unbolted, the servo and pedal box removed and seperated and then the master cylinder is ready to be extracted. I would then disconnect the hydraulic lines from the master cylinder, grovelling in the footwell and remove the master cylinder. Worth draining the hydraulic system first in both cases to minimise the amount of fluid that there could be.
It is a probably one of the worst jobs there is on the car.
>> Edited by shpub on Wednesday 9th April 11:30
The steering column really only gets in the way so its removal is optional. You could remove just the steering wheel but taking the seat out fress up a lot more room. I would definitely remove the seat so you have room to work. That may be all you need to do. Both the clutch and master cylinders are bolted through the pedal box so they will have to be undone and that means disconnecting them from the hydraulic system. They are usually connected into a distribution block. Unless the cylinders are seperated from the pedal box/servo, they won't move. If you can't get access past the clutch master, I would suggest that you need to take that out first which will allow you to get to the master cylinder and allow that to be unbolted.
Normally the master cylinder is unbolted from the servo first but because the reservoir is located in the wing... that is going to be difficult so the cylinder needs to be unbolted, the servo and pedal box removed and seperated and then the master cylinder is ready to be extracted. I would then disconnect the hydraulic lines from the master cylinder, grovelling in the footwell and remove the master cylinder. Worth draining the hydraulic system first in both cases to minimise the amount of fluid that there could be.
It is a probably one of the worst jobs there is on the car.
>> Edited by shpub on Wednesday 9th April 11:30
Steve,
Thanks for the details. I'm not sure who will do the job yet as the local guy isn't too keen and Fernhurst are too far away when you have almost no brakes to risk. They quoted 5 hrs so that gives me a pretty good idea. One point is how to drain the clutch system? Through the slave bleed valve no doubt; if so is it accessable by crawling underneath (without need for a 4 poster)?
I think most jobs on TVR are much worse than on other cars!
Chris
Thanks for the details. I'm not sure who will do the job yet as the local guy isn't too keen and Fernhurst are too far away when you have almost no brakes to risk. They quoted 5 hrs so that gives me a pretty good idea. One point is how to drain the clutch system? Through the slave bleed valve no doubt; if so is it accessable by crawling underneath (without need for a 4 poster)?
I think most jobs on TVR are much worse than on other cars!
Chris
chrish said: .. I'm not sure who will do the job yet as the local guy isn't too keen and Fernhurst are too far away when you have almost no brakes to risk. They quoted 5 hrs so that gives me a pretty good idea. .......Chris
I see you're in W sussex have you tried Andy at APM near Liphook, I suppose it depends where exactly in W Sussex you are though as he's at the eastern end of Hants, if thats local to you give him a try, highly recommended.
Harry
I heard a new twist to this mystery yesterday. Apparently a similar problem on a 2.8 Capri revealed porous rubber brake hoses between the calipers and the pipework that would let air in but not fluid out. He actually changed the master cylinder and servo only to find the problem was still there. He then fitted stainless flexi hoses and the problem was solved. I was thinking of fitting flexis anyway as the car is 5 years old - maybe I should that next? Anyone like to comment on this one?
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