Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
22
Around the time these cars were in production, there was some noise about designing motor mounts to allow the engine to fall underneath the car in a front-end collision. I think Volvo may have pioneered the idea. It’s about making pieces fail in a deliberate manner so the engine drops downward rather than being pushed rearward into the passenger compartment. And the key component is the transmission mount.
Did Jaguar have this objective in mind when they designed this mount? I have no idea, and have heard or read nothing making such a claim. But that mount is stupid complicated for a simple task. I’m just sayin’, if that’s what the design intent was, it might be wise to put it back together exactly as it was intended.
I kinda like it! It’s cool having a mount that bounces up and down like that. I wonder if they had made it more normal and rigid, would our cars feel more vibration and jerking when shifting?
First time I removed/installed it, I was a bit shocked/confused.
But second time, it wasn’t really that bad.
That diagram is a must have, printed out and in the garage!
Well the concept of having a metal washer rubbing along the inside of a rubber damper, weakening and eventually destroying it is a questionable design, in my opinion. I recently replaced the mount on a 95 Mercedes. Much better designed and they managed to eliminate all vibrations as well.
Well, there’s that odd bracket thingy (#9 in the illustrations) which I thought had some “in event of a collision” significance and is even called a “collision plate” in one of pics above. I’ve never bothered trying to figure out exactly what it’s supposed to do. I removed it and use it as a paperweight.
Not that I’ve checked but I’ll bet Jaguar’s love affair with complex mounts pre-dates the era when manufacturers thought about that sort of thing. I think it was all about eliminating NVH…but it’s certainly a complex way to go about it. Heck, the USA luxo-barges basically used a single chunk of rubber bonded to a metal plate…and they were as smooth as a baby’s bottom.
You know the Jaguar motto: “Never use six parts when twelve will do the job perfectly well”
Hi Tex, All you need is a welder. Easy fabrication. As the underside of my car was oily, I used a Poly mount meant for a full-size GM car. That was a mistake because I could feel some vibration around 45MPH. Put a rubber mount below the trans, and fixed all the leaks, and all is well. Probably more info. in the archives.
DAVE - Will try to search archives for your posts referencing your transmission rear mount change - not quite understanding the two photos above, as to placement for transmission tail shaft support and routing for drives haft- looks like you installed heat shielding metal and mat within tunnel, something I have considered doing also.
As far as the driveshaft goes, nothing is changed. It hides above the shield that prevents you from tightening the bolts on the front “U” joint. The best way I can describe the mod is that first you completely remove the trans. mount. Everything. Supporting the trans, of course. Then, with a disc cut-off wheel, modify the strange looking support with the four ears. Then weld a plate onto it, boxing it .Attach your new GM mount to the tailshaft housing. Place the "four-eared " metal plate below the GM mount and mark where two holes will have to be drilled into it. The height of the rear of the trans. can be changed with shims/spacers made from strip steel plate.
Hi
My mount is also off (currently fixing transmission noise when cold, resulting from suction pipe o-ring NOK and my incorect filter fixing that removed the floppyness…)
→ #15 washer thicknes : 1/4 inch
The #21 washer on my car ('86 V12) is a slighty thinner: 6.1mm.
It 's also asymmetrically shaped. Here’s a picture with the #15 washers also visible in the bottom part.
The bigger hole has a slight offset w.r.t. the smaller hole.
I wouldn’t be supprised if this is original and there is some Rube-Goldberg related reasoning for the asymmetry. Any votes on this, should the offset be to the front or the back of the car?
Ptipon
(Ptipon, Sonora, CA, USA, 1990 XJS, Conv.)
34
Hi Evert, Thanks for the #15 washer/spacer measurement, very much appreciated.
There was also a thread about a moaning noise when the engine was cold several months ago and everyone made a best guess but the answer was never settled. Could you go into that fix you are doing a little more, the sound, it only occurs at start up, what’s causing it, does it change with gear selection, etcetera?
Hi
I read the posts about the moaning noise from the engine as indeed it sounded farmiliar. The noise in my case, however, clearly comes from the transmission. It changes when shifting / selecting gears. After some googling it turns out to be a well known thing with the TH400 transmission.
“My” noise originates (according to what i found) from the transmission oil pump sucking in air which in turn results in bubbles & cavitation throughout the tranny (and torque convertor). As the oil gets warm and it gets easier to suck it in and less chance of air being succked in.
Reasons for this failure mode can be that the o ring on case side of suction tube is leaking. (in my case suctiontube was very loose) Other reason that I found on inter-web is that someone (in this case mysefl) fixed the floppy attachment of the trasnsmission oil filter. It is supposed to just hang there. No one really knows why and how it is realted to faliure mode.
My geuss it that the floppy fit makes the filter push upwards on the connection to the suction tube side and as it makes the filter lay non-horizontal it promotes air from moving out of the filter easier…
1 Like
Ptipon
(Ptipon, Sonora, CA, USA, 1990 XJS, Conv.)
36
Got my tranny mount mounted correctly and all is fine now. Thanks for the help everyone.
Update: I finally received the special (thick) washer and put everything back together. The clearance between the tie plate and the carrier is now in line with what I’ve seen on Greg’s photo. A particular challenge was to deal with several stripped bolts and threads - somebody was here before! Thanks again to all for the support!
Yeah, funny how you can easily tell that a PO did something wrong on an XJ-S. Obviously, in your case they didn’t know what they were doing, and actually threw away some of the parts! Luckily, my trans mount was original, so everything was there. Except for the bushing that had disintegrated.
My PO findings were luckily just the distributor. Someone thought the magnetic pickup gap should be 0.00, and it actually ground down the 12 point star wheel! Wow.
