KZN185 brake help please!!

[_cj_]

hi - this is for a friend so details are a bit sketchy but any help would be really gratefully received

Symptoms

Both front calipers locked on - it was driven with siezed front brakes so discs are shagged - it looks like they got so hot they melted

Mechanic has taken the pads out of the calipers which will clamp on but will not withdraw when you take the foot off the brake with engine on or off - they will retract if the pressure is released through the bleed valve

rear brakes seem unafected

swapping over the master cylinder connections the rear brakes still function ok which would suggest not a master cylinder problem.

any suggestions guys ???

Kindest Regards,

alex

[_cj_]

p.s it seems to indicate a problem with both n/s and o/s front brakes

[TonyN]

I'm sure theres a relief valve in the master cylinder that gets jammed on 3rd Gens, might just be for the back brakes though. Do a liitle searching on Google, for US 4Runners of the same year, you might find it.

[_cj_]

i thought there were only two pipes out of the master cylinder and both went the abs - is the relief somewhere else??

Thanks for the prompt reply btw

regards,

alex

[_cj_]

a bump please for all you mechanical guru's out there

thanks

alex

[Spart]

Sounds like corrosion around the pistons. The part of the barrels in the caliper that are outside of the piston seals can corrode. This can lead to the pistons getting sticking & not retracting properly as there is no force to retract them.

You can check this by removing the brake hose to the caliper & seeing how easy it is to push the piston back in.

It may be possible to remove the pistons & clean the barrels etc. But you have to be very careful not to damage the seals or scratch the barrel. I don't know if seal sets are available. If not you may have to replace the calipers.

[ukwineman]

Thanks Spart

Its actually my surf that has the problem, the pistons are fine and move freely when the bleed nipple is open. When you depress the brake the pistons move and then stick, open the bleed again and they ok. The master cylinder has been checked by swapping over front to back and works ok, we had thought about sending off the calipers to be looked at but they seem to be fine.

It was a sudden failure which has caused the front breaks to lock on, there was nothing gradual in it and it affects both sides. No one has ever heard of an abs failure and at the moment everyone is stumped.

[Vagrant No2]

Sticking ABS unit . The feed from the master cylider will be fine but the valve inside the ABS unit is faulty.Will cause the sudden fault you have .
You need to get the ABS unit checked by a specialist place .

[ukwineman]

Sticking ABS unit . The feed from the master cylider will be fine but the valve inside the ABS unit is faulty.Will cause the sudden fault you have .
You need to get the ABS unit checked by a specialist place .

thanks Vagrant well so far noone has ever heard of a faulty abs unit before, but everything does seem to point to it

Any ideas on who repairs these things ??

[Streetsurfer]

It could be a failure of the ABS ECU rather than the ABS unit itself. I would expect the best bet for either would probably be to get a replacement from a breakers rather than repair.

Try..
http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=006

or

http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=006


Does the ABS warning light indicate any error?
Is the bulb working?