Hey, guys... without boring everybody with the details of my woes, this afternoon I finally got the first caliper off and took it apart, cleaned up, and after installing the square piston seals (well lubed with brake fluid), the only way I was able to get the pistons in was to tap them carefully, keeping in mind to keep them straight in the bores, however, the last 3/8" or so, I was able to press them in with my hand. I suppose that is normal??? or is it??? .. just to get a feel about how tight the fit is it takes quite a bit of force with channel locks to rotate the pistons.

Back story is when I bought the rear end (used), and rebuilt it, I noticed that one of the pads was waaaay more worn than the other three. Present problem, after only 4,000 miles, is that one of the pads not sure it's the same one) has ground into the disc. the other pad on the same disc only has about 3/16" left on it. The other disc (the best I could see) looks about half worn (I could be wrong about that item).

I was careful during disassembly to see if there was any gunk or a chunk of something acting as a check valve or something holding that one caliper tight on the disc and not releasing pressure.

Any thoughts will be very much appreciated.

By the way here is one of the galleries on my website (among a lot of others) :
https://49fordcoupe.smugmug.com/Rebu...-Jag-Rear-End/

 

Sounds to me like the very top part of the cylinder (that part above the level of the piston seal) still had a layer of crud and rust, which is pretty normal. This area has to be cleaned and smooth like the rest of the cylinder lower down. As I remember, mine were fairly resistant and I think I used large channel-locks and piece of wood to squeeze them down flush with the housing. The uneven wear on the pads sounds like sticking pistons (usually from crud) not letting the square seal retract them slightly, as it should.

Dave

 

sorry I guess I should have been a little more clear after I cleaned everything up without the Square O-rings in the calipers the Pistons drop in very easily with no pressure whatsoever so it's not a mechanical interference. However once the O-ring is in the cylinder it just seems as if it's way too tight. And yes I used an angled pick and a tiny wire brush to clear out the O-ring Groove.

has anybody ever heard of a caliper having a machining error from the Factory? In view of the fact that it may have been stuck when I bought it. I'm nearly thinking that the O ring Groove isn't cut deep enough into the caliper housing.

 

The rubber brake hoses swell internally from age, often closing to the point that the fluid can be forced into the caliper with pressure, but not allowing it to flow back out. Even if the hoses look new, they may be beyond their usable life. If you haven't replaced them that could be your problem.

 

Well, the thing is, there are no rubber hoses in the system serving the rears.... however you just gave me an idea. I need to confirm that the STEEL tubes and Tee fitting mounted above the center section isn't blocked. Will check that later today and will report back. I had that exact issue you are speaking of on my Tahoe some years ago on the passenger side front caliper... burned the crap out of the brakes.. Thanks for reminding me... and another thing..... another thought... I have a disc/disc proportioning valve on the dual cylinder master cylinder that could be a problem... hmmm.. BUT, it seems the problem is only on the passenger side, so that's probably not the issue... hmmm..... The Driver's side looks ok... have not disassembled it yet...

 

Any reason for not posting in the XJS forum which is the next one down in the list ?

 

hmmmm, none other than ignorance or clicking on the wrong forum ....

 

hmmmm, none other than ignorance or clicking on the wrong forum ....
but as I understand the xj6 and xjs in 1985 are the same

 

LOL. Ah yes, the problem with jumping from one forum to another...I was just on the MG Experience forums and wasn't paying attention. Swollen hoses obviously not your problem but as you said, you need to check the hard lines.

 

FYI, just in case you need to know, or even better renew it if it is old, there is a flexible hose serving the rears, between the cage and the brakeline coming rearwards from the master cylinder, at the top, RHS of the cage going down to the chassis rail.

 

But, since I installed the rear end myself with a Snow White mounting system, and I piped the brake lines myself, there is no rubber anywhere in the system.

By the way, I just came in from the shop, and blew through all the tubes and fittings with my mouth, and all are clear.

However, after doing another thorough cleaning, scraping the o-ring seal groove with a small allen wrench, wiping out and spraying with brake cleaner, and sanding with 1000 grit any discoloration off of the pistons, lubed with fluid, I was able to push the pistons in with my hand, though fairly hard, but I would expect that... Still nervous that I won't have the same problem in the future. I can't tell you how hard it is to get the brakes off the car...Thinking about just buying a pair of Cardone rebuilt calipers... hate to spend the money.. but...

Here are some pics of what I'm dealing with.... just for grins...

Getting things arranged to drop the IRS

Passenger side caliper.. obliterated after 4,000 miles

This can cause one's ribs to really ache.. outside of disc is ruined..

 

I think if the piston moves in the cylinder a little easier with another cleaning/detailing, you at the right place. The piston will, by no means, slide up and down in the bore easily, the close tolerance metal-to-metal fit plus the beefy square seal have to manage hundreds (thousands?) of PSI when you stomp on the pedal, I know you know this. That square seal only needs to withdraw the piston a few thousands of an inch to be effective. I would say you are good to go with the piston/cylinder thing.

Dave

 

Thanks, Dave, but I just decided to get rebuilt calipers..the other caliper looks even worse than the one that was f'ed up...

 

I'll back you up on that decision, that caliper is not a pretty sight!

You have put together a VERY nice coupe, I can appreciate the fabrication and attention to detail. Congratulations!

Dave

 

Thanks again, Dave! It took 8 years to build it,..the only thing I didn't do myself was the interior..And what a pleasure to drive!!!!

 

Thanks again, Dave! It took 8 years to build it,..the only thing I didn't do myself was the interior..And what a pleasure to drive!!!!

Do you know Ms. Palin???

 

Thanks again, Dave! It took 8 years to build it,..the only thing I didn't do myself was the interior..And what a pleasure to drive!!!!

Do you know Ms. Palin???

 

Sara? Yes I know her, she began working as a customer service person at the company I worked for when she was 18 years old. She lives about 3 miles from me, as the crow flies, but neither of us can see Russia from our houses.

My project is going into its third year and I hope to have it on the road this summer. Like you, I will have done everything except the engine machine work and the transmission rebuild myself. Sometimes maddening, but always rewarding when its been accomplished.

Dave

 

Hey, Dave !

Well, I just read through a lot of your posts, and I must say, I admire your stamina.... Down here in Texas, if the temperature is below 50, all work stops.. ahaha.. I just looked at my weather map and it looks like ya'll might be sittin' in about 15 degrees... holy COW ! !...and the SNOW ! ! ! ooooooohhhh..

As for the LT1, just curious why it seems it's popular with Jagsters... I know it has some advantages in performance, but in the "hot rod crowd" around here, they are not very popular. Is it due to clearance problems with the Gen 1 distributors??...

As for the grungy condition of my calipers, it's truly confusing to me how rusted everything is on the rear end-- Calipers, all the bolts, etc.... I have driven it in the rain ONCE, on New Years Day, this year. It has been garage kept it's entire life. When I rebuilt it the first time, 4,000 miles ago, I used new pistons, seals, etc., and Thought, of course, that all was done correctly. Guess I was wrong.

As an additional question to you guys, (as I have searched all over the place for the correct answer, but have found none), An old fella in California that's been building Jag rear suspensions for something like 40 years, told me that the calipers have to be placed (with spacers), within 0.005 centered on the disc... That seems so weird to me, as "hydraulics" pressing from opposite sides equally theoretically exert the exact same forces on the disc. I understand a "reasonable" centering, but 0.005? That just seems over the top .... Maybe somebody can chime in here...

And to take the question to another level, what would be wrong with removing the seals on the pistons and putting a layer of high temperature silicone grease on the *** end of the pistons and under the seals, then put the seals on just to help keep moisture out of the piston/caliper.. curious minds want to know..

 

Hi Coupe, I'll try to give you my opinions, some are WAG's and some are educated.

I'm pretty sure where you were brought up has a big influence on your tolerance for many things, including the weather. My shop is heated and so the weather is not a big problem, until I turn off the lights and walk the 100' back to the house. Funny story...I remember spending a week in northern Texas one day and after my guide cautioned me to tape up my pant cuffs and watch out for snakes, not to mention the 90-plus temperature, I was glad to get back home. It's all a matter of perspective, I guess.

This is my first LT1, it came with the car. All my previous engine work has been "old school" on small and big block Chevy's with carburetors. For over two years I have researched this engine and the S3 Jaguar on a daily basis and here's what I can say. The LT1 is the first SBC to have sequential port fuel injection and a reverse-flow cooling system. This allows for superior fuel management (more hp/torque/fuel economy) for the same amount of fuel used. Another big bonus is the reverse cooling where the coolant from the radiator enters the block normally, but is immediately routed up to the heads, through the heads, and entering the block at the rear and then forward in the block to exit normally into the radiator. This makes the combustion chambers run much cooler, allowing the static compression ratio to be increased quite a bit. (10.4 to 10.8 in the LT1/LT4 respectively). This allows more power again, mostly from improved timing.
There is a YouTube where the original LT1 of 1970 was run against a mid-90's LT1 (370hp vs 300-330hp) and the 90's version was equal or ahead in both hp and torque. And that while getting 20+ mpg easily and being able to balance a nickel on the air cleaner while the engine was running. Oh yah, having the distributor in the front makes life at the fire-wall much friendlier, but that advantage is over shadowed by the headache of R/R the LT1 unit. Instead of a 5-min, 1 bolt, mark your rotor, type project-----------it's not.

Caliper/Rotor alignment? That might very well be the chief cause for the uneven wear on your pads. The calipers (front/rear) are not floating or self adjusting like all modern cars today. You have a fixed, bolted caliper bridging a fixed, bolted rotor and need the pads to move the same distance and contact the rotor at exactly the same time. If the distance from the caliper to the rotor is different from side to side, the pad on the "close" side would wear more. I can see where you're saying that the common passage within the caliper that runs from one piston to the one on the other side should equalized their movement and therefore not cause a problem. I'm not an engineer and can't give you the correct reason, but I think the "close" side pad will always make contact first and create some pressure against the rotor before the off-side pad comes into play. Besides, if car makers today didn't think floating calipers are better, we would all be driving cars with old Jaguar brakes.

Silicone under the dust cover..... I don't know about that one. On one hand, it most probably would help keep more water out, but on the other hand, silicone does not absorb moisture and would leave any condensation under the boot to just sit there and create havoc. Standard brake fluid will absorb moisture, which is why replacing it every XXX years is a good idea. Aside from that, I will fall back on my comment on brakes. If car makers had thought a glob of silicone under the dust boots was a good thing, they would have put it there themselves.

By the way, you didn't say anything more about Ms. Palin?!.

I appreciate your comment on my apparent stamina, but if you have followed my original thread you will see that I have managed to accomplish about 6 months work in a little over 2 years. I can only claim perseverance.

Dave