XJS ( X27 ) 1975 - 1996 3.6 4.0 5.3 6.0

Need Rear Brake help 1988 xj-s

 
  #1  
Old 05-07-2014, 09:55 PM
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Default Need Rear Brake help 1988 xj-s

Since buying my xj-s I've been fixing up odds and ends and I've replaced the shocks and transmission mount. Today, on my way to buy new oil for the cat, I heard the dreaded metal on metal sound when braking and turned around and went straight home. (about a half mile)

Jacked car up in the air and the back passenger side (LHD) rotor showed what i feared to be true. Pictured below. I started pulling pads and discovered that all the pads are worn differently! the two pictured on the right are from the pass. side (you can see where it wore all the way through) and the two on the left are the driver's side.

The driver's side pads show significantly less wear and were very hard to get enough slack in the pistons to slide them out. One side felt seized but it's possible I just didn't put enough muscle into it. They also were covered in some sort of gunk.

SOOO...

1. The rotor barely has a lip on it. Can I just replace the pads and hope it wears back in with the rest of the rotor? I REALLY don't want to have to take that caliper off. Been there. done that.

2. What is going on with these wear patterns? I fear the driver's caliper is not working right. Perhaps a piston is leaking? I really don't know.

Any advise or insight is appreciated as always
 
Attached Thumbnails Need Rear Brake help 1988 xj-s-img_0343.jpg   Need Rear Brake help 1988 xj-s-img_0345.jpg  
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Old 05-07-2014, 10:12 PM
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Couple of things in my opinion.

1) Caliper piston/s are stuck/sticking. This can "sometimes" be sorted by a good fluid flush and bleed.

2) That rotor wear on the rear would be OK for me.

3) Put new pads in, or else the pistons will "pop", then get someone to assist, and bleed the rears SERIOUSLY. You will get messy, and the bleed nipples are a PAIN to get to (exhaust is in the way), and lots of "gunk" will come out.

This will either fix it, or it wont. I have had good success figures with that method, and I have dealt with some really sad rear brakes on Jags over the years.

I would also strongly look at replacing the single brake hose (RH side) that goes from the chassis to the cradle. It will possibly be degraded internally from this gooey fluid.

To strip and do teh calipers/rotors/park brake, really requires the cradle to be out of the car. OK, many have done it in situ, as I did ONCE, but with the cradle out (not so hard), it is waaaaay easier.
 
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Old 05-07-2014, 10:36 PM
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Someone did not center the calipers when installing new pads at an earlier time. There are shims that are put in the caliper brackets to center the caliper to rotor. Seen techs do this to meet flat rate times.
 
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Old 05-07-2014, 10:53 PM
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Default Grant has spoken!

Trust him, he knows his stuff. If it were me, time to drop the cradle and sort things out. Shes not my Dailey driver, so I can do this. Brakes are nothing to let slide! INMO.
 
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Old 05-08-2014, 01:09 AM
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Thanks all for your quick responses. Based on all your advise here's my plan:

I am going to try Grant's idea and bleed the HECK out of the rear brakes until the fluid coming out looks new and clean and replace that rubber hose. Hopefully this frees up the caliper that may or may not be sticking. Ordered new set of pads today so they should be here by this weekend.

The car only has 66k miles which means lots of sitting in the past 26 years and the pads are probably original to the car. The car will be gone the whole month of June getting a down to bare metal paint job so I don't really have the time or money at the moment to do a full refurb on the whole cradle/subframe. That took me about a month to complete on my last xjs. I need to get the car braking for now until she gets repainted and then after I get her back I can embark on a more extensive servicing in the back (brakes/shocks)

So that's where I'm at. Sound like a good plan?
 
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Old 05-08-2014, 04:00 AM
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Good or Bad, it is at least a plan.

Being down here, and water rotates Clockwise HAHA, and JD goes down no matter which way it rotates, I ALWAYS do the mechanical refurbish FIRST, then do the paint woark.

No matter how carefull you are, or how sober you are for that matter, you will ALWAYS damage that paint job.

Seen that way too many times. Last one was an '88 Convert, and had oil weeps from the engine for years, as some do, so he fixed the paint work???, then decided to do the engine out oil leak fix, then painted it again. Fair Dinkum, he that sucker wrapped up in all sorts of padding, and still marked it.
 
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Old 05-08-2014, 07:31 AM
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those rotors aren't too bad, but for future reference pads WILL NOT wear into a high section and level out the rotors. They HAVE to be machined to do that. The pads are softer than the rotors any anything that exaggerated will just be further exaggerated
 
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Old 05-08-2014, 07:57 AM
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Originally Posted by Jagfixer View Post
Someone did not center the calipers when installing new pads at an earlier time. There are shims that are put in the caliper brackets to center the caliper to rotor.


On the rear 'tis the other way around: the shims are used to center the rotor to the caliper. They fit between the rotor and the output shaft/stub axle flange.

I don't think caliper/rotor alignment is an issue here, though. If we look at the disparity of remaining pad thickness between left and right calipers, and between the two pads of one caliper, I think it's beyond what could be cause by incorrect shimming. The shims are only about .010" thick and I've never seen more than a couple used



Seen techs do this to meet flat rate times.


True enough....almost never done. Many people are not aware of it and even those who are seldom have a selection of shims to center the rotor even if they wanted to.

And it almost never *needs* to be done, IMHO.

If the rotor is obviously not centered....enough to see on casual observation....then there's likely a problem that goes beyond just shimming. But, more than that, the typical pad thickness is about .375" so the caliper pistons have about that much normal operating travel, at least. If the rotor was not centered by .010-.020" then you'd never know the difference until you got right down the the *very end* of the pad life.

Cheers
DD
 
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Old 05-08-2014, 04:32 PM
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I had a seized caliper piston and in my innocence, (yes, I was younger then !!), didn't realise it until I lost all brakes descending a steep hill with a sharp curve at the bottom. The caliper had heated up from the continuous braking and boiled the fluid so - no brakes !! Fortunately a quick pumping got a brake although the pedal then gradually sank to the floor. Anyway the upshot of all this was I had to fit exchange calipers and discs, and new diff oil seals as the heat destroyed them too. I managed to get away without replacing the output shaft bearings. Rear subframe had to come out.

So, always be cautious when you have a problem with those damn inboard brakes !
 
 
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