Braking Problem

[David Sleith]

Folks

Got crap brakes and not sure whats wrong.

The setup is a Mk2 master cylinder, ST205 fronts and Mk2 22V rears. The system has been bled a few times now and def no air in there now. Engine off and brake pedal pumped makes pedal go hard. Pedal depressed and engine started and the pedal depresses right to the bottom and continues to do so every time I depress the pedal with only a slight amount of pressure.

Traced the vacuum pipe all the way back to the engine and everything seems fine.

Not sure if I have a vacuum leak, faulty servo or a faulty master cylinder. There are no fluid leaks so I'm reckoning the brake system after the cylinder is ok.

Any help on testing the above would be most appreciated.

I have a spare servo and the original Mk1 master cylinder but thought I would ask first here before I start to rip it all to bits again.

The engine runs fine with a 800-900 rpm tickover when warm and revs freely so i'm thinking if i had a leak it would have a lumpy idle. Correct me if I'm wrong?

[David Sleith]

Just had a thought.

If the Mk2 master cylinder has a different plunger depth than the Mk1 then the operating rod from the Mk1 servo might need to be adjusted.

Not dug the haynes manual out but I think seen a bit about adjusting the rod length.

Anybody running a Mk2 master cylinder on a Mk1?

[msherry21]

Hi Mate, I think Paul is putting one on mine, can't remember if we had sorted that. So he's probably the man to see amongst others who know far more then me!

[adamh]

does sound like a cylinder problem dave, couldnt see the calipers bleeding bieng a problem.

[David Sleith]

If there were a problem with the master cylinder seal then would you not expect a run of fluid down the servo casing where it meets the master cylinder.

What about the small white valve about a foot away from the servo which I assume is a one way valve. Would this cause the above problem?

My brain is telling me it must be something that has been changed prior to the mods as the brakes worked fine beforehand. This would rule out the servo and that small white valve unless the fact its been standing has caused something to go.

[OlberJ]

Exact same thing happened when i fitted the ST165's at the weekend.

Was just air in the system though. Worked fine after a good bleed.

[David Sleith]

Thats what I'm thinking.

Think I'm gonna go buy a mityvac vacuum pump for brake bleeding

[GaryA]

I find using pressure to bleed is better than vacuum as you tend to pull air past the thread of the bleed nipple wich makes you think you still have air in it . If you have rubber flexi pipes you could clamp the hoses to see if it makes the brake pedal better , has it got new pads and discs ?

[OlberJ]

Aye, it'll stick halfway otherwise.

[Gary Symons]

Just had a thought.

Anybody running a Mk2 master cylinder on a Mk1?

Running the same setup on mine with no problems so far. Didnt modify anything to get it to fit.

Hope you get it sorted soon.

[jungle-jim]

just a quickie.

on my rover turbo i used a jar with pipes to bleed all 4 brakes after a track session.

i don't know if you guys can reach the DV hose pipe and take it off.

place one end of the hose on it and the end of the other pipe onto the bleed nipple.

this is negative vacuum ( sucking ) so don't rev it!!

turn the bleed nipple open and it sucks the life out of it!!

make sure you use a glass jar ( and keep the plastic seal thing in the lid )

http://www.twobrutal.co.uk/forum/images/recovered/2007/05/83.jpg

http://www.twobrutal.co.uk/forum/images/recovered/2007/05/84.jpg

http://www.twobrutal.co.uk/forum/images/recovered/2007/05/85.jpg

this works really well on slave cylinders too.

[adamh]

^ thats a keen trick :)

[David Sleith]

The vacuum pump I bought I found not to be very good as it draws in air through the threads of the bleed nipple as Wombat mentioned.

Have now bled using my old one way valve bleeder the brake system to death. If I'm doing something wrong I'm not sure, but I have bled systems before without any troubles. Never changed as many components right enough.

Tested the servo and vacuum system from the engine using the vacuum tester and also checked to make sure I was getting an adequate vacuum from the engine which seems to be ok. The one way white valve at the servo also seems to be ok. The servo test of pumping with engine off and goes hard and then turn engine on and brake pedal drops works ok also.

Finally took the plunge and changed over the master cylinder to the original Mk1 unit and bled the system all over again. Still no joy and no different. Brake pedal still goes to floor with a little resistance.

The calipers all have fresh pads and the rears were rebuilt with new seals.
Not sure where to go with this one. If I have a prob with a caliper how can I test each in turn to sectionalise the fault down a bit?

Either that or I'm an idiot and can't bleed my system

Calipers are also on the right way round with bleed nipples at the top

It must still be air. Prob need to get a second person to hold the brake pedal down next to try that

[lodgeman]

have you tried clamping off each flexi hose individually and testing or are you using braided?

[OlberJ]

I'll give you a hand if you need Davie, gonna be about tomorrow as need to go collect the bolts that the Toyota monkeys managed to get mixed up.

[David Sleith]

I'll give you a hand if you need Davie, gonna be about tomorrow as need to go collect the bolts that the Toyota monkeys managed to get mixed up.

Cheers mate. Got the wee guy this weekend so car on hold.

[David Sleith]

have you tried clamping off each flexi hose individually and testing or are you using braided?

Using braided. Got my neighbour to sit in the car and pump the pedal while I opened and locked of the nipples. Made a slight improvement so think its just air although never had as much trouble with this on any other car before.The vacuum pump method was telling me I was getting loads of air through the bleed nipple threads so maybe thats the problem.


Still got the MK1 master cylinder on so think I will prob swap them back over and start over a again using the two man approach.

I did have a thought that maybe with Mk2 rears and st205 fronts the master cylinder couln't cope with the amount of fluid needed.

[GaryA]

Are you sure it's not that with new pads and discs your getting a lot of movement in the caliper because they are not bedded in ? Or pressure bleed it or if you think it's in the calipers push the piston back as you open the nipple this should force the air out . Or try blocking the caliper with something that won't give that way you know if it is air or just spongy pads /discs that need driving .

[David Sleith]

Are you sure it's not that with new pads and discs your getting a lot of movement in the caliper because they are not bedded in ? Or pressure bleed it or if you think it's in the calipers push the piston back as you open the nipple this should force the air out . Or try blocking the caliper with something that won't give that way you know if it is air or just spongy pads /discs that need driving .

Good idea. Will give that a go