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[Graham]

Ok, possibly stoopid question but I'll ask anyway.

In the ZJ (4.0 auto) on the way home tonight. Traffic crawling for several miles and having to ride the brakes as the ZJ wants to drive faster than traffic just at idle. Traffic eventually clears and I get up to 60 and notice what feels like loss of power. Pull up at the exit and smoke pouring from front brakes.

Yes, cooked them, to the point where when jacked up, I can't turn a wheel by hand. Wheels were too hot to touch.

Thinking caliper rebuild, maybe replace pads/disks is they're shot.

Question is, how should I have driven it in such slow traffic, or did the heat build up just expand the already tired phenolic Pistons just that last bit too much.

[General Confusion]

Just stuck calipers. Nothing to do with your driving style. It's a common fault on XJ's ZJ's and TJ's. Strip them down and clean them up. Put some new pads in and just check the ridge they run along on the steering knuckle for crap.

[bigjeepzj]

 
but you will need this as the pistons will have warped

http://www.ebay.co.uk/itm/2-x-FRONT-CALIPER-REPAIR-KIT-JEEP-CHEROKEE-XJ-GRAND-CHEROKEE-ZJ-WRANGLER-YJ-TJ-/311529244016

as it will happen again. best change as you have the caliper bits anyway

[Graham]

Thanks. New Pistons, seals etc ordered. Rebuilt the ones on the TJ last year so familiar with what's involved. Sounds like I just brought on the inevitable.

[Dave69]

replace seals and piston, pads should be unaffected unless you have seriously cooked them

[LairdScooby]

Normally in heavy traffic i let a gap build up then let the brakes go until i need to stop again - this helps prevent build up of heat, not only on the brakes but the gearbox fluid too. Ideally when you're stationary, if you're going to be there longer than about 30s, snick it into "N" and stick the handbrake on. This helps circulate ATF without a load so cooling it down and prevents the brakes overheating too.
Just a slightly more "mechanically sympathetic" way of doing it and each to their own. 

[Brynjaminjones]

This has happened to me in both the XJ and the ZJ.


With the XJ I rebuilt the calipers and sanded down where they slide.
With the ZJ I replaced the calipers and that was all.


The XJ has been fine ever since (2 years now) but the ZJ didn't improve.
This has lead me to believe that the main cause of the problem is in fact the little wear groove on the knuckles where the calipers slide in and out. I believe that when everything gets warm and expands, the pads get physically stuck against this groove therefore preventing them from retracting.
I had the ZJ welded back to shape for no extra cost whilst having some bodywork done and the brakes have been perfect ever since. 

[Graham]

Thanks for the replies. I'll certainly try dropping into neutral rather than park in traffic. That's a good shout. Rebuild kits arrived and I'll give the calipers and knuckles a good clean up to make sure everything is moving smoothly. She's only done 30k miles so I'm not expecting much wear, more that things just need a bit of a re-life.

[paulbaron]

I had this happen on my zj several times, cured it with steel pistons and new seals all round from big red brakes.

cost about £150 but had no trouble since then and it stands for weeks at a time.

[isle of man]

Not forgetting to replace the brake fluid !!

[bigjeepzj]

WJ  knuckle upgrade 

[Uncas]

Did it have phonelic pistons fitted? I had a similar problem on A Dodge B250 a few years ago, fitted new steel pistons and seals and never had a repeat problem.

[Graham]

Yes it had phenolic pistons which have been renewed, new pads and brake fluid changed. Also welded up and ground flat a couple of small notches on the knuckle where the pads rest. All happy again now.

[Widjeeper62]

And the penny dropped !! 
That explains why I had twice seized front calipers with the JK !

It was on both occasions on the M25 during slow traffic.
Same as you Graham at idle with the torque of the V8 I was constantly on the brake so they never had any rest.