I am in the middle of replacing calipers, rotors, hoses and brake pads all around my car. After pulling off each rear caliper I observed no wear on the pads.
What can be going on?
I think that either both calipers seized up, the rotors are too worn down or no pressure is going to the rear(?)
What do you Jaguar folks think can be going on?
Thanks!

 

No wear both sides? Isn't there a pressure reduction valve in line to rear? My immediate thought it a failure in that junction.

How is the car at stopping? My car will SLAM your face into the steering wheel kind of stop if fully pressed to do so. It should be quite abrupt even for a 4000lb car.

 

Checking for seized calipers should be easy enough. You should be able to move the pistons with just a small amount of leverage from a screwdriver...or perhaps even with the pressure of both thumbs.

Perhaps also check the rear flex hose?

Cheers
DD

 

Rear flexible, agreed Doug.

 

Yes, both sides are not working. As far as the hoses go I already changed them. Unfortunately the rotors I received are the wrong ones so I can't put things back together yet to try the brakes while on the stands. I will say that on one side I had some brake fluid dripping out after I disconnected the hose but on the other side (passenger side) just a drop came out. I guess I will find out if there is fluid pressure when I bleed the rear brakes. I guess when I bought the car it came with an extra set of rear brake pads! The brakes have never been the best on this car and now I know why.

If I put air pressure to the caliper from a tire pump the pistons, if functioning, should close, correct? Since the pistons are open all the way I can't push the pistons in any more as suggested. Maybe with a screw driver I can pull the piston out.

Can I check the hoses? Just blow air through them?

 

I have a similar situation: rear brakes provide no stopping power -- certainly not the "slam your face into the steering wheel" dynamic that Vancouver describes -- but I was able to get a fair stream of fluid when I bled them. So I suspect the calipers are stuck. Will I will need to drop the rear cage to fix/replace them?

 

Just finished the whole “cage drop” a few weeks ago, and found that my ‘88 rear calipers had new pads recently installed by the previous owner, but that the piston seals were literally dust, and fell out onto the floor.
needless to say, they were not only leaking, but totally non-functional.
would highly recommend removing and either rebuilding or replacing.

 

If your brakes are inboard technically no, they can be done with the frame in the car but dropping it is an opportunity to poke around at all those things that it conceals, plus you can do the brakes relatively comfortably. I'm certain that the OP's brakes are outboard if he has a 95 XJS

A warning that I'd offer though - if you don't drop the subframe and the mounts are in any way failing the whole assembly can drop without warning - it is only held up by 4 rubber / metal bonded mounts and it is heavy - if it lands on you your chances aren't spectacular. You will be swinging and pulling on things to undo bolts etc - do yourself a favour and pull the subframe.

Removing IRS

 

Not long ago I had a small brake fluid leak at the front of the car, a line that heads to the back, with an inline brake pressure regulator. Funky little thing that ya may never even notice - til it leaks...

Anyways, during the process of figuring out what needed to be done I learned it is not uncommon for these reg valves to get gummed up and clogged, for debris to plug the small internals and to cause problems. I deleted mine thanks to confidence gained via voices here. It's a simple looking contraption. Don't even know if it's the same on your car, but the photo below shows mine. I believe they can be opened and cleaned out or gotten rid of all together.

 

YUP , mine is gone 26yrs ago!
ron

 

From looking at the parts manual, it looks like this valve was only used on the cars with ABS, not the early non-ABS cars. True?

 

My car doesn't have it for sure (1987 V12 HE)

 

Thanks. That's what I have also.

 

There's no easy way to avoid it you need to get under there and open up a bleed nipple - not as easy as it sounds I'm afraid.

One thing that I have seen (not on a Jaguar) is for a failing brake hose to collapse internally - sometimes as a result of inappropriate clamping - the collapse acts as a valve. If you open a bleed nipple on a caliper and you can shoot fluid out of it then your calipers aren't functional. If the pads haven't been making suitable contact for a while your discs may be in need of replacement also.

 

That^^^^^
There's no way around it. One would have to start opening brake lines and see what the hold up is... There is also a way to trigger all of the little valves/solenoids in the abs contraption up at the front near the reservoir under the hood. I don't have enough XJS experience to know what a stuck closed or open valve/solenoids will do as far as blocking brake fluid in the abs contraption,,, but I have bridged (finding the 12v lead on the loom going into the abs contraption and triggering all the valves/solenoids) leads as test. They can be heard opening and closing. Dig a little more deeply,,, I believe 12v will trigger them,,, 12v applied for milliseconds as to not burn'm up.

 

To test without the discs,,, take a piece of wood or some sort of object that will just fit in the calipers, zip tie the object in that space where the disc would ride. The object has to be the RIGHT size and not something that will collapse OR let the calipers piston shoot out... Press the brakes and test as you make adjustments and open lines, and such. You'll figure it out. Don't worry.

If you use air with ZERO discs or anything to stop the pistons movement, the pistons can and will be blown right out of the bore of the caliper - might be a good thing. If they are stuck/siezed this is a good a way of getting them out of the caliper.

Maybe the PO had the car and NEVER properly bled the rears and you got it that way and just figured this out?

 

Pictures speak 10000000000 words, btw

 

make sure you don't wedge the screwdriver on the pad surface, only the backing plate.
I know.
Not abnormal to not need rear brake parts for thousands of miles.
Will the rear wheels spin with the pedal depressed and the car jacked?

 

jomo,

You hadn't mentioned which of your cars has the problem. But I'm guessing (?) that because you have a "US 95" and a "US 96" car that they have differing brake systems. If it's on your earlier car and its VIN is prior to 198335 then you'll have the Teves ABS system which is quite complex. So, I'll assume that the problem is with your earlier Teves-equipped car?

The rear brakes always receive their fluid pressure via a pumped circuit, whereas the front brakes receive their initial fluid pressure without pump assistance. It's not unusual for the rear brakes not to have fluid run out when you crack the lines open.

If you have the rear calipers disconnected, I would first try and ensure that the pistons are working by connecting a footpump to the inlet port and then apply air pressure. As mentioned, make sure you have a piece of wood in place of the disc to stop the pistons flying out. The rear brakes don't do much on an XJS compared to the front so the pistons don't get exercised that much and can end up getting stuck.

If you do exercise the rear pistons forward and back and the calipers are in place with the lines connected, you MUST have the bleed nipples open. Whatever you do, do not push fluid back up the lines on a Teves system! There is a real chance that you can push tiny bits of sediment back to the ABS valve block and then you can have a real problem!

Good luck

Paul