Hello,

I had some wonky old calipers on, and it was evident they had seen better days, so I bought some reconditioned M16 calipers from rally design.

Sadly i had a bit of a problem on route to SVA. I was driving along minding my own business as you do, and then it started getting slower, and slower, down to the point where i was in first gear and the front brakes where smoking as I tried to find somewhere off the main road to stop.

Upon stopping the brakes where locked on. At first I thought the pedal had stuck, so i checked that, plenty of wiggle, car still not moving freely.

Prior to this, the brakes where working perfectly, both wheels had equal effort, and releasing the pedal released the wheels.

After about ten minutes i started wiggling the car back and forward, and then as if by magic, the brakes are no longer locked on. The front left appears to be more locked thean the front right, as it was hotter, and it was pulling slightly to the left.

Before and after the problem, the brakes function normally.

When i noticed the problem, it appeared as if the brakes where getting more stuck, wheras i had expected them to fade out eventually and become easier to drive. I don't recall pressing the brake pedal at all, let alone hard enough to cause that much braking force.

Any ideas? I'm at my tethers end

Cheers


David

What type of braking m/cyl' do you use?

Two cylinders and a balance-bar or one tandem cyl'?

With or without a servo/booster?

Two cylinders .75 and .6something, Luego bias bar without servo.

I should add, the previous SVA run used the old calipers, and did not give me this problem. (The effort was out by about 20% though.)

[Edited on 13/7/06 by irvined]

If both calipers were afffected it is unlikely to be a caliper problem. Could it be that the master cylinder piston is not returning fully every time and the hydraulic pressure not releasing. Perhaps it is a question of adjusting the pushrod in the balance bar.

John

Does the caliper line centrally with the disc ?

Check by removing the pads, bolt up the caliper and bolt up the disc.

If they are not central and the one pad is clamped then the expanded disc will cause binding.

I had a the same problem with mine. Check the bias bar is letting the m/c fully return as mine was not and every time you used the brakes the pressure built up until the brkes were on.

To rectify the problem I increased the gap between the pedal and the bias bar fitting.

Keith

Or - take the MasterCylinder apart and make the hole in the washer bigger - it's this the bar 'fouls' on apparently.

Gent from yukspeed pointed this out to me - so I've ordered a new MasterCylinder and going to give it a go

If you look in the Rally Design catalogue, they show the pushrods should be parallel with each other. The bias being obtained by screwing each pushrod in more or less into the balance bar. If you use a dashboard adjuster, then the balance bar moves the pushrods at an angle to each other by screwing or unscrewing and I can see that if this happens at some point there will be an issue with the washer inside the master cylinder. If both pushrods are parallel then I think it points to the pressure not being relased becuause the front pushrod cannot retract sufficiently.

John

I agree with John, but just check that the front cylinder is not seized as one did it to me whilst driving in anger ! got better in the pits then !!!

Andrew

Yes the lads have spotted it defo a master cylinder pushrod problem -- as already stated usually the mushroom end of one or both of the mastercylinder pushrods is fowling on the washer in the end of the cylinder -- really critical even loss 0.5 mm of movement can cause the hydraulic lock you describe.

Are the new calipers opposed-piston type, or "sliders" (where the caliper centres itself about the rotor by sliding back & forth on pins)? If they're sliders, you're likely to find that the slider pins are corroded/dry/over-greased, any of which will cause the slider to push over to one side. Thus, one of the brake puck pushes constantly on one side of the rotor, the rotor gets hot & expands, causing even more pressure, causing more heat, etc. This happened to me on a motorcycle at speedfinally it seized (front wheel, of course), instant lockup/crash. In my case, it was over-vigilance - I put too much brake grease on the end of the pin (which went in a closed hole), caused an airlock, etc....

if you have a pin or slider problem it will be identified imediately in the travel and exerted pressure needed to apply a brakign force ..

definatley sounds like a master cylinder problem

The new calipers should be the M16 cortina ones - twin cylinder not the slider ones.

Well, it definitely looks like a master cyl problem, it worked before i changed the calipers though, but as its been sitting for two months pretty exposed to the elements, i wouldnt be surprised if something in the master cyl got a bit sticky.

I'll whip it out and have a look next time i'm over. Contemplating hiring an other luton van and taking itin the back of that for the SVA, I know it will pass SVA, or at least i'm 99.99% confident this time around, at least after i can drive it, i'll be able to give it a proper drive to find out whats wrong. Talk about chicken and egg.

Cheers guys.

you could always drop it off at mine

i'd fix it and get it through SVA then "look after" it for a while

aka the rest of the summer.

Ahah,

Sounds like a plan, tell you what, you go up north, fix the brakes for me, and i'll drive it down to yours via Carlisle SVA, then you can look after it for the afternoon whilst I register it

hmmm, i'm spotting a flaw in the plan here......

involves me doing all the work and getting none of the benefits.

oh, just realised, i'm busy :p