Brakes again but this isnt simple...

just fitted the front discs and pads and cailpers off an st200, they work a treat, really really well. However after just a few high speed applications they lock on, hard, the only way to release them is to let out some of the fluid.

right the brakes were working perfectly two days before on the car I took them off.

when I release the pressure they open immediately..so no sticking piston etc...or bad discs.

I have changed a few of the hoses and the master cylinder, the brakes have always since I had it been a bit spongy, and ineffective hence the upgrade to the st 200, I intend to do this for the other std puma too even thought its brakes are not bad...

the back brakes are awful, the handbrake is bad...i have changed the wheel cylinders on the back...

any help or ideas as I am running out of things to change...and I dont have a puma I can use at the moment

I don't really know anything about brakes but is it possible you have air/water in the lines and when you brake it gets hot, expands and locks on the brakes until you release it?

could be if we had not bled them up so often and cleared all air and water...its very odd, apart from chagning the lines I cant see what else it could be...I assume there is a diverter valve under the car for the front and rear brakes, with the rear brakes being so bad i am wondering it this is stuck or something...

My thoughts are the same as yours, there must be some valve of some kind which isn't allowing the fluid to return thus reducing the pressure once you release the brake pedal.

If I'm not mistaken the brakes run on two circuits, a front and opposite rear for each circuit. There is also the fact that the fluid is used for the clutch slave cylinder so there has to be some valve/switch somewhere as I'm sure I read that if a brake line fails when braking the car SHOULD still be able to be brought to a stop in a somewhat straight line as you would still have a front and opposite side rear to slow you down.

On a different computer at the moment otherwise I'd have a look on my TIS disc for the exact details as no doubt that will probably detail this valve/switch your looking for - assuming it exists of course and all the above isn't some elaborate piece of BS in my head....lol.

Are you sure the master cylinder you fitted is working correctly?
Did you disconnect the battery before starting work, and not reconnect it until after you had finished bleeding the brakes?

sounds like master cylinder to me, out of interest try testing the brakes if possible with the cap off the brake fluid resevoir

I changed the master cylinder for a new one...no change...clearly the fluid is not going back to the reservoir but cant work out why...and it is both front brakes...its a 99 car...really foxing me this one is...is there a workshop manula for the pumas some where..and also for the FRP>..

did you try the cap off test?

if it was me id just strip the calipers down and rebuild them with new seals etc.

also make sure the cross shaft is well lubricated, does the pedal return ok?

And the answer to my earlier question "Did you disconnect the battery before starting work, and not reconnect it until after you had finished bleeding the brakes?" is?

no I am sure we would not have disconnected the battery, am i missing something here...

Caution: On models equipped with ABS, disconnect the battery before disconnecting any braking system hydraulic union and do not reconnect the battery until after the hydraulic system has been bled. Failure to do this could lead to air entering the ABS hydraulic unit, requiring the unit to be bled using special Ford test equipment (see Section 21).

21 Anti-lock braking system components - removal and refitting
Hydraulic unit
Removal and refitting of the hydraulic unit should be entrusted to a Ford dealer since special electronic test equipment will be required to bleed the hydraulic system on refitting. The electronic test equipment allows the hydraulic unit to be switched into a special mode which purges the unit of all trapped air - it is not possible to remove trapped air from the unit by bleeding the system conventionally.

ooh that sounds interesting.....will ask the boys about this

i wouoldnt worry too much i have had the brakes apart loads without disconnecting, its just a precaution measure really so the pump doesnt accidentally activate, but the chances of this happening are slim, even if air did get into the abs pump i doubt it would cause symptoms you are experiencing in fact, possibly the opposite.

It is a correct point by YOG and technically that is what you should do when taking brakes off, but id be surprised if it was the cause in this case

damn i was hoping you had chanced on something that was the cause...my feelings are that something is either restricting the flow, an old or damaged pipe or there is a stuck valve somewhere...what manuals are there for the FRP and the Puma...cant seem to find any on the net..

Had a look at my TIS disc and I can't see anything of use.

Is the vacuum pipe to the master cylinder connected properly, not kinked or blocked AND is there any leaks on the servo. This is just a stab in the dark as I'm thinking if it's blocked it may be stopping the release of pressure or allowing air in which may be stopping the system from returning to normal.

EDIT:- Had a google as I'm sure it's something to do with the vacuum/servo. Anyway, managed to find this page which may help. http://auto.howstuffworks.com/auto-parts/brakes/brake-types/power-brake2.htm" onclick="window.open(this.href);return false;

Had another look at my TIS disc and found something about the above:-

QUOTE

Brake Booster Functional Test
Inspect all hoses and connections. All unused vacuum connectors should be capped. Hoses and their connections should be correctly secured and in good condition with no holes and no collapsed areas. Inspect the check valve on the brake booster for damage.


Brake Booster Operation Check
1. Check the hydraulic brake system for leaks or low fluid.

2. With the transaxle in NEUTRAL, stop the engine and apply the parking brake. Apply the brake pedal several times to exhaust all vacuum in the system.

3. With the engine turned off and all vacuum in the system exhausted, apply the brake pedal and hold it down. Start the engine. If the vacuum system is operating, the brake pedal will tend to move downward under constant foot pressure. If no motion is felt, the vacuum booster system is not functioning.

4. Remove the vacuum hose from the brake booster. Manifold vacuum should be available at the brake booster end of the hose with the engine at idle speed and the transaxle in NEUTRAL. Make sure that all unused vacuum outlets are correctly capped, hose connectors are correctly secured and vacuum hoses are in good condition. When it is established that manifold vacuum is available to the brake booster, connector the vacuum hose to the brake booster and repeat Step 3. If no downward movement of the brake pedal is felt, install a new brake booster.

5. Operate the engine a minimum of 10 seconds at fast idle. Stop the engine and let the vehicle stand for 10 minutes. Then, apply the brake pedal with approximately 89 N (20 lb) force. The pedal feel (brake application) should be the same as that noted with the engine operating. If the brake pedal feels hard (no power assist), install a new vacuum check valve and then repeat the test. If the brake pedal still feels hard, install a new brake booster. If the brake pedal movement feels spongy, bleed the brake system.

UNQUOTE


Correct me if I'm wrong but I believe the brake booster is what we know as the Servo.

thanks will have a go...

okay this is getting even more silly. drive a few miles and the brakes just come on...it has to be air in the ABS...anyone know how to bleed this...I think the one time it happens has happened...scubasteve may have hit the nail on the head. any idea what to do...

abs will need to be bled using a specialist tool, might need to take it to ford for that.

however i still highly doubt its that, air wont make your brakes come on, it will make them bite less if anything

if it was me id have the calipers stripped, pistons out and cleaned etc

Dunno about the puma, but had to re-calibrate the rear axle/suspension brake equaliser on an AX GT many moons ago after fitting larger brakes and calipers.
They also locked up after a few minutes of driving and although two different systems, possible similarity?