With a poly bushing, does it put more or less stress on the spring?
If more, than the extra $25 may be worth it.
With the mods you stated, only reason to remove mount again should be to change trans filter.
If the bushing absorbs more stress, than the aftermarket spring should be fine.
All this babble over $25. 
Wow. 30 years old and look that good? Was this car kept in a freezer somewhere?
I seem to recall some spring seats? It’s been a while, but I recall faking those with some rubber tubing split open and wrapped around the bottom coil of the spring.
The bushing should have no effect on the spring. The spring holds the tranny up, while the bushing limits side-to-side motion. When assembled properly, you should be able to move the tranny up and down easily with your hands, but it should not move side to side.
You might want to read up about the trans filter. There’s an issue with how it is held in place with either one or possibly two O-rings. If it falls down, you find you have to overfill the transmission to get it to work.
Oh, and if you wanna risk Shipwright’s Disease, there’s a plastic piston inside there that needs to get replaced with an aluminum piston. And of course you could consider a shift kit while you’re in the area.
Hmmm. Yeah that does ring a bell. Seems like my bushing came with a “seat” now that you say that…
Bob Brackney
Thanks, you guys are extremely helpful!
Here’s a photo, I assume a bushing is supposed to be in there somewhere? I pushed what was in there with a screwdriver, it looks like foam sponge material.
That plastic piston failing is why my trans. is sitting perched on a jack under my car- completely rebuilt and a Hughes converter- waiting for me to install it tomorrow! Second gear disappears, and so does kickdown!
Is the upgrade from plastic to aluminum a common t400 part? Is it something I can do, having zero transmission work ability?
Ok, looks like a common part. Although do I really need to remove valve body?! (Shudder)
And it looks like the changeover back to aluminum happened somewhere mid87 manufacture, so mine might not be plastic? Easy to tell with pan off?
Pulling the valve body is no big deal, but there are 5? 7? little check balls in there and you need to pay attention / keep track. If you’re doing a shift kit the instructions will cover all this, if not just lower the valve body straight down without tilting. I had never done it before and did the shift kit in my car no problem. Typical R&R car stuff. Apply a little common sense, patience and do a bit of research and things usually work out fine.
My 89 car has a “Pre 87” TH400 (based on which shift kid I needed) so the year of the car is not always a good indicator. I didn’t do anything with the piston, that’s new to me.
Bob
Jaguar always seemed to be a coupla steps behind with anything GM updated, like maybe they ordered their stuff a coupla years ahead. If I were you, I’d at least check it. Dropping the valve body is easy, although you do need to be careful not to lose any steel balls.
Shipwright’s disease…I look at it as save time for future me!
So I’ve ordered poly trans mount bushing, poly spring seat, and new spring from XK’s.
I got the fel pro gasket (I’ll throw away cork one I got with filter kit), and a drain plug.
I’ll order a b&m shift kit for pre88, I’ll use stage 1. (I couldn’t find identification tag on my TH400, but my XJS manufacture is 4/87.)
As for accumulator piston, I saw a mod (both here in forum and on many YouTube sites) that you simply grind off three tabs, remove spring, and install upside down. You can even reuse plastic if it’s not broken. This gives slightly firmer shifts between 2nd/3rd, which puts less wear on clutches. And no wear on plastic accumulator.
I will also sand/paint pan and trans mount plate to get rid of surface rust.
I had planned all this one day, but with bad mount, may as well do it now.
Keep your original spring; in fact, I’d kinda recommend you just reinstall it rather than installing the replacement. We’ve had a lot of trouble with replacement springs being too strong and cramming the tranny up against the upper limit of the travel of the mount rather than allowing it to float properly.
Really? Ok, thanks! My car only has 50K miles, so the spring prob isn’t too worn anyways.
Is it just an aftermarket manufacturing error?
(@Kirby ) I saw what you said in the book, you were talking about springs from John’s Cars. That was 10 years ago. I assume the spring I’m ordering from XK’s may be OK? I will make a judgement call when I get it.
I dunno what the hell it was. Perhaps vendors thinking a stronger spring would be better.
Gonna be fun attempting all this from garage floor on four jackstands. My joints are already aching thinking about all this labor.
Greg,
I removed and replaced the transmission mounts in my wife’s 1990 XJ-S convertible several years ago and it was a challenging job. I believe that I removed the hood (bonnet) and supported the engine from above with my large engine hoist while I supported the transmission from below with my transmission jack. I am a “belts and suspenders” kind of guy who likes redundancy in supporting very heavy parts while working beneath them.
You are correct to replace the transmission pan seal and filter while replacing the transmission mounts.
This was another one of those tasks that made me say something like “my, isn’t that an interesting design? I wonder why they did that?” but with more colorful language.
Paul
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Heh. Somebody, perhaps John’s Cars, once offered a replacement tranny mount that used a basic rubber mount from a Pontiac or some such. The Jaguar mount almost never works right after a trip to Quickie-Lube for a transmission fluid and filter change, as several of the important parts are still on the shop floor when you drive away.
The Book famously contains a cross-section diagram of that mount. Whether it helps or merely adds to the confusion, I dunno.
I’m not entirely sure poly is the way to go on the spool. Sponge is definitely not the way to go, but I’m still not convinced the original spool was really sponge. It just looks like sponge when it comes out in pieces. Whatever, this is an unusual application for rubber as the wide spot in the center post (a fat washer in the middle of the post assembly) is supposed to slide up and down within that rubber spool. Metal sliding within rubber is perhaps not wise engineering practice. It should definitely get lubed with rubber-compatible lube, but it seems the first drive through a deep puddle will flush that lube outta there.
I think the original trans mount bushing is the same yellow stuff they use for the upper shock mounts.
I will lube the poly bushing well when I put it in, which should also keep water out. I’ve put poly bushings on my Volvo’s trans mounts, and they lasted forever, and provided less slop during shifts, but they produced vibration at idle. Their design involved two bushings, I ended up putting the poly on the big one and a rubber bushing on the small one. No vibration but still good response, and the small one takes much less stress so lasts a decent amount of time.
IMO the Jaguar XJS spring design will let the transmission move a little, so it won’t all be on the poly bushing, so hopefully no vibration at idle. Worst thing, I’d guess I’d feel a bit more when the transmission shifts, especially with a shift kit. But hey, I’m de-clouding this car anyways. At least I’ll know this poly bushing will outlast the yellow one that turns to sponge.