Brakes on my 87 XJ 12 cyl Vanden Plas have started a curious pulsing through the brake pedal. Still have 40% left on pads, brake fluid changed last year, and the odometer reading is 91,000 km. Brakes stop fine but pulse. Anyone experience this?

 

Warped rotors is one possibility, use a dial gauge or suitable pointer positioned to just touch the disk, then spin the wheel to see if contact is made/broken

 

In Alberta in January/February, maybe you got your brakes Really hot in a sort of panic stop, and then they immediately got wet from icy water. That would certainly warp a rotor. That would give you a pulsating pedal.

If it's bad enough it can't be machined out you need a new rotor.
(';')

 

In the Rangey it was sticking caliper pins...is the jag the same setup?
Just some high temp grease?

 

Hi ChuckR,

Pulsing brake pedal has always proved to be warped rotors in my experience.

After a heavy application of brakes you really need to get the brake pads off the rotor surface (ie. take your foot off the brake pedal) as the two hot surfaces can create a hot spot and subsequent warping.

It's not intuitive and it is difficult to do in traffic.

Dabbing the brakes and releasing them as long as there is no one or anything in front of you works.

If you have to remain stationary, pulling the handbrake on and releasing the foot brake also works, assuming you are on level ground. This transfers the braking from front to rear. Just don't drive off with the handbrake still on. That creates other problems.

Just my two bobs worth.

Good luck,

Nigel

 

Most cases of warpage as referenced above is not actual distortion of the rotor itself, but spots of brake pad material (binding agents) that have transferred from the pad to the friction surface of the rotor. This creates a high spot that feels like a pulsing through the pedal or causes the steering wheel to shake during braking.

Although the rotor can be machined to remove the material, this heavy handed action results in a thinner rotor with a reduced service life.

Any decent mechanic will simply remove the spots of pad material with an abrasive wheel made for the purpose.

 

Thanks all for the comments, yes warped front Rotors was the problem which was only noticeable once Rotors warmed up. The brakes were all original from 1987 so Had the front rotors replaced, new pads all round, repack bearings, new fluid, etc. just before drive home to Comox BC. Paid dividends during panic stop North of Kansas City. Need service when in central Florida? go to All Jaguar in Longwood North of Orlando.