'Bleeding' Brakes!!!!
Discussion
Hi guys. Just fitted a HiSpec brake conversion (295mm discs) to my 450, including new braided hoses. All good with getting them on but still not happy with the brake pedal pressure. When I'm braking I get initial good pressure but whilst the car is slowing the pedal will then move again further to the floor. I have spent hours/days with my mechanic bleeding the system. We've bled starting from the outside bleed nipple furthest away from MC. We've bled the rear brakes also. There are no leaks from the hoses. We've clamped the rear hose to check it wasn't the rear causing the problems. Does this sound like there's still air in the system or maybe some issue with the MC? The MC resevoir seals look a little worn! Cheers Clive
Info in case it helps....
I did have a similar problem with my Vixen (a TR6 master cyl) where it did work, but pedal would slowly sink to the floor over about 3-4 secs. Discovered that it also would not quite lock the front wheels in a panic stop. It WAS the master cyl and a new one was the solution.
Can't verify same for yours, but may be.
If you have a Cortina IV Mcyl, they tend to leak fluid at the join to servo when they are worn out.
I did have a similar problem with my Vixen (a TR6 master cyl) where it did work, but pedal would slowly sink to the floor over about 3-4 secs. Discovered that it also would not quite lock the front wheels in a panic stop. It WAS the master cyl and a new one was the solution.
Can't verify same for yours, but may be.
If you have a Cortina IV Mcyl, they tend to leak fluid at the join to servo when they are worn out.
If you aren't losing any fluid then it could be the seal in the master cylinder is allowing fluid back into the reservoir.
Does it work fine in a panic stop but slowly sink to the floor with gentle pressure - then this is probably the cause.
You should be able to cure it with a M/C seal kit.
Does it work fine in a panic stop but slowly sink to the floor with gentle pressure - then this is probably the cause.
You should be able to cure it with a M/C seal kit.
If you are happy that all the air has been removed from the system, I would test the function of the servo. To do this, start the engine with your foot on the brake pedal. The pedal should travel down a short distance once the engine starts. This is normal function. If all is well there, I would suspect the master cylinder seals. I would change the master cylinder rather than the seals in order to eliminate problems within the master cylinder bore.
Tony. TCB.
Tony. TCB.
Check the pedal feel with the engine off, does the pedal go solid if you push really hard, if so it isn't the MC. By fitting Hi Spec you've probably changed the piston sizes in the callipers which could also mean a change in MC size, have you gone from 2 pot callipers to 4? There is also a problem called over servoing which happens more with higher compression cars and diesels which this sounds like whcih probably relates to superwedge's post.
Edited by jagracer on Monday 10th December 12:26
superwedge said:
hi. my brakes are spot on, my one was doing the same, there is a nut inside the servo unit, you have undo that 8mm nut out more ,till the pedel don;t move down to much. my one is great now,
I did that on my leaky Master cylinder in the wedge - it helps, along with new seals, but I still get a slight weep out the back (servo join). I think that adjustmant moves the rear piston out of its 'worst wear' point. When I looked at cyl bore, there is a big shiny area around rear piston, which will be the wear, and it's obviously marginal even for a new seal. Brakes work fine, but I'm looking for a new master cyl right now... I had a lot of trouble getting the air out of the rear end, those up and over pipes don't help at all, I reckon air gets stuck in those 'humps'.
Bigger calipers will cause more pedal movement, 'cause there's more fluid required to operate 4 pistons, but pedal should still go solid, but it will be nearer the floor.
Edited by RCK974X on Monday 10th December 20:18
Edited by RCK974X on Monday 10th December 20:20
Latest news...new brake MC seal kit ordered/received....took 3 weeks to get here in Oz. Brake MC dismantled & about to replace the 2 seals + washers around the piston. But unlike the clutch MC seals which were a doddle to replace, how on earth does one dismantle this piston to replace the seals? Your assistance much needed...
Cannot see the end of the piston but this looks like one I did on a XRi many moons ago! I used a g clamp to compress the spring and it was like head valve springs and had a collet holding it on. once the spring is off then you can get to the rear piston seal. As they say re assembly was the reverse!
Chris
Chris
If it's the Cortina one, remove the plastic reservior (carefully !!) by levering it off gently with a WIDE bar between the feeds (so plastic doesn't break).
On mine, there was a plastic circlip at the end which you can see, but the secret is that
on the forward feed, hidden by the seal, is a pin which holds the front piston in. It's almost impossible to spot this without being told.... Push the pistons in slightly to release pressure on the pin, and it should come out easily (slim nose pliers are good). After that it's straightforward.
I was told that some aftermarket ones have a classic circlip at the end of the bore as well, and no pin....but not seen one like this.
NB. My master cyl still weeps very slightly after new seals, but at least now develops a solid pedal so it's safe. I will need a new one soon....
On mine, there was a plastic circlip at the end which you can see, but the secret is that
on the forward feed, hidden by the seal, is a pin which holds the front piston in. It's almost impossible to spot this without being told.... Push the pistons in slightly to release pressure on the pin, and it should come out easily (slim nose pliers are good). After that it's straightforward.
I was told that some aftermarket ones have a classic circlip at the end of the bore as well, and no pin....but not seen one like this.
NB. My master cyl still weeps very slightly after new seals, but at least now develops a solid pedal so it's safe. I will need a new one soon....
Edited by RCK974X on Thursday 27th December 19:50
Latest....re-checked the Brake Master Cylinder chamber & there is some scoring inside so it has to be a new MC. My Girling unit (3 pipes, stamped 7466-0294, bore 13/16" I believe) I think is from a Mk3/4 Cortina. I'll try flea bay but anyone else recently bought one & from where? My car is the 450 (1988) by the way. Cheers
Here in New Zealand, the local place reckons they can resleeve them if desperate, but I've heard that the Girling originals are relatively thin castings and can crack...
I have found a replacement but it's not a Girling one - it is an offical aftermarket replacement though, and got it a few days ago - not fitted it yet.
Not sure what else will fit, perhaps a Sierra one (22 mm) - pics look similar.
I have found a replacement but it's not a Girling one - it is an offical aftermarket replacement though, and got it a few days ago - not fitted it yet.
Not sure what else will fit, perhaps a Sierra one (22 mm) - pics look similar.
Hello Clive
This is the one:
http://www.ebay.co.uk/itm/TVR-TASMIN-BRAKE-MASTER-...
Contact details are on this listing - very helpful chap - I used him when I replaced the master cylinder on my seac.
Chris
This is the one:
http://www.ebay.co.uk/itm/TVR-TASMIN-BRAKE-MASTER-...
Contact details are on this listing - very helpful chap - I used him when I replaced the master cylinder on my seac.
Chris
hueb said:
Thanks Chris. Item ordered from ebay. Thanks also Andy....I was going to look into re-boring but too expensive, especially here in Oz...my bore is 20.4mm. Cheers Clive
Yeah, I did know, but with bigger calipers, you could get away with next size up, pedal won't move as far, but will be slightly firmer - I don't know if Oz got Sierras or not, NZ did get a few.There doesn't seem to be any definite alternative MC for the Cortina one, unless anyone has suggestions ?
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