Brakes messing about - any ideas?

Hi all,

I have a 300TDI Discovery, 1996. 154K

Recently, it has started to lock the rear wheels on whilst going along the road. You dont have to press the brake pedal or anything, and they still lock on.

The brake pedal starts off being about half way down when i set off to work, then about 10 min into the journey, the pedal goes extreemly stiff and bouncy.

I have had all new discs & pads all round, and a new rubber brake line on the rear, but still hasnt made any difference.

Any suggestions?

Cheers,

Josh

hi
many years ago i had this problem with my austin maxi , fine at the start of a run but after a couple of miles the brakes began to bind incrfeasingly untill the point that the car just wouldn't go anymore
turned out to be the servo and a replacment curerd the problem

Ok,

Just put fresh copper slip all over the brake pads & calipers, and went for a test drive - this time, both front and back wheels are binding - almost until it wont move.
At one point i had to put it in Low box!!!!

Cheers for now...


Josh

Joshd said:

Ok,

Just put fresh copper slip all over the brake pads & calipers, and went for a test drive - this time, both front and back wheels are binding - almost until it wont move.
At one point i had to put it in Low box!!!!

Cheers for now...


Josh

Click to expand...

Then the previous reply regarding the servo is correct..Almost certainly the servo is at fault..

Cheers,

I will now order a replacement!

Is it worth getting a new servo or getting a "Servo repair pack"?

Cheers,

Josh

Joshd said:

Cheers,

I will now order a replacement!

Is it worth getting a new servo or getting a "Servo repair pack"?

Cheers,

Josh

Click to expand...

Replace the whole thing, don't bother with repair kits for brakes, especially on a car with mileage like yours, they never work.

I agree..Where the servo is concerned i,d go for a new one..Try Craddocks or Paddocks..

Thanks for the advise!

Also - Do you recommend replacing the Master as well? or am wasting my money?

Thanks again,

Josh

clutchdust said:

Replace the whole thing, don't bother with repair kits for brakes, especially on a car with mileage like yours, they never work.

Click to expand...

Joshd said:

Thanks for the advise!

Also - Do you recommend replacing the Master as well? or am wasting my money?

Thanks again,

Josh

Click to expand...

Do the servo first and see what its like ...Process of ellimination and all that yeah? Unless of course you would prefer to change Master as well..One thing about brakes though...Never, NEVER cut corners....If it was mine i,d change Master as well but your the one paying out so its your choice,,, Least if you do both its done right?

Id take a bottle of water and drive about a couple of miles or so trying not to use the brakes. then stop and get out and squirt a little water onto the caliper and disk rotors... see if it sizzles! they shouldnt even be hot!

I had a problem almost identical to this but on a mountian bike with 4 pot hydraulic brakes, in a downhill racing scenario in the Alps.

adjusting the brakes for a 5km downhill biking is an art, as the brakes bind on the rotors, they get hotter. As the calipers get hotter so does the fluid, the fluid expands so the presure in the master system increases, the levers decrease in reach untill they hit their stops. At that point the process reverses itself, you cannot squeeze the levers, it is imposssible. the brakes are now binding and getting hotter and hotter, the more they bind the hotter they get, the pressure is building up in the system and the brake fluid is starting to boil, your bottom start twitching 'cos you're doing 30mph+ on a pushbike over rocks that would usually be covers by black ski run snow, and your brakes are now, almost completely uncontrollable.Then they just squeel like mad and lock. and you sit there waiting for them to cool down, contract, return to a normalized temperature, unlock themselves so you can carry on.

I would say that the new brake pads are too tight to start off with, they need backing off. you could just loose a little fluid out of each of the lines.
The water test will tell you how hot they get in just a few mins. (dont loose any fluid unless you have fresh un-opened fluid to top up with) In fact while your there why not just get a mate in and do a completete bleed, it wouldnt hurt as it sounds like you've been boiling your fluid anyway!

i think i need more medication if we keep getting posts like this...ffs just feel the wheel wiff yer hand to see of it hot.

Josh,
You could have seized calipers or partially seized calipers.
This would account for the brakes overheating and evetually bringing
the vehicle to a stop.

Just a thought!

RichardG

Just be careful about touching the brakes if they are hot... there is a difference between warm (normal driving!), hot (spirited driving!) and leaving your fingerprints behind on the rotors to the smell of pork crackling. Sizzling water is usually a good give away for the latter...!

Thanks for the feedback...

RichardJG - i dont think it is due to a seized/partially seized caliper - as i put all the new pads and disks in, and there were no problems with pushing the calipers back. Also - if it was a seized caliper, surely it would only act on 1 wheel (maybe 2), and not all 4????

battenberg - i know the brakes are getting red-hot, i can feel the heat coming off them, and can see steam in the morning within minutes of driving. You say 'loose some fluid from each line' - surely this would have happened when i first replaced the brakes, and the calipers were pushed back?

Not too sure really - i am struggling to find a solution!

If it is the servo, is there a temporary measure i can make to make the disco driveable temporally?> Or maybe a test i can perform to check it is the servo?

Ordered new Servo & Master Cylinder today from Haddocks - - god knows when they will arrive!

Cheers for now --

Josh

Josh,
If not the calipers, btw, you said it was the rear brakes that locked I think.
It is surely the servo/cylinder. Change the lot to be safe.

RichardG

yeah just trade the whole lot in fer a new one..just to be safe

Another thing it could be, and I would not have believed it until I saw it, the flexi brake pipe clips could have corroded around the pipe, thus restricting it, fluid can get out to the brakes under pressue but doesn't return easily, leading to brakes being on all the time.

Just thought I would throw that in, what else would one do at work!

most likely the servo, seems to me.
or possibly the master cyl.

and i agree with some others here, re the brakes. dont cut corners. this is one area where you must do it right.

Hi all,

Many thanks for all the feedback!

I had the new Servo and new Master Cylinder delivered today...so i have just finished putting them on.

I took it for a test drive, and so far so good - no problems at all, although the pedal was stiffening up by the end of it - though i believe that is probably the new parts settling in?

I 'accidently' ordered a new winch bumper from Haddocks at the same time - so will be fitting that soon!!!! Yay!
- Then find a winch...

I will take the disco to work tommorrow, and report back!

Thanks again,

Josh

Hope you get it sorted. Sounds like your replacements will do the job.

The servo is vacuum actuated with vacuum on both sides. If the valve on one side isnt working or leaks, the air gets in and its like you have put your foot on the btake. Most Master cylinders operate separately within themselves with the rear brakes actuating at a different time to the fronts. Had this problem on my SD1 Rover saloon and paid a couple of dollars for a valve that solved the problem without spending $3000 on a new servo.