Hi. It seems that this subject may have been covered but nothing found so will ask again. The car shifts normally under no stress driving. It kicks down when I need it to and feels normal there. But, if I want to run the car up to the limit occasionally, 6k at least, it won’t come close before shifting. If I do it manually then I can get it up there but not when stomping on the accelerator.
Is that normal? I wouldn’t think so but since it is a GM product and maybe never correctly set up for a V12’s higher rev capabilities, is this normal? Is there something I should look to replace or modify to keep the revs going higher without manually operating the shifter?
I know that unfortunately it isn’t computer programmed so all mechanical controlled. Anyone out there have a solution, a fix, an opinion (lots of those!) .
Russ, the shift points when you are pushing the car are controlled by the mechanical governor. A spinning contraption with flyweights and springs, located under a round cover on the RHS of the transmission.The weights can be lightened,and the springs changed. Removing the governor can be awkward, depending on whether your car has an access plate on the RHS of the transmission tunnel, or not. You may be able to buy a kit from one of the normal transmission specialists,too.
At what RPM does it shift under wide open throttle?
I’ve never driven a V12 that’ll go all the way up 6000-6500 before shifting itself. Typically, about 5000 RPM is the norm in my experience. With both my V12s I used a mild shift kit and that increased the WOT shift point to about 5500. If I want more I have to hold the lower gears manually
Circa 1989 Jaguar re-calibrated things a bit for higher RPM shifts but I can’t remember the specifics.
ATF oil change, hmmmm. I have owned it for 3 years and I got no records of maintenance when I bought it. The original ownner spent money on it though and owned it for 32 years. I would bet at least once but its worth changing for sure.
It shifts around 4500 floored! Just when it is starting to sound and pull really good too. Such a smooth engine up to 6K. It has 125k miles on it so I don’t push the high revs much but still 5500 would feel good. I always wondered how a car with a manual transmission would be used as far as higher revving. If I wasn’t trying to sell it, I would put in a 5 speed tranny. Oh well.
I remember seeing the round cover mentioned while working under the car. I will go to a transmission specialist tomorrow and see what they say. I have talked to them before about replacing the splined driveshaft with a solid one after modifying the tranny yoke to a sliding yoke. So they are familiar with the Jaguar.
Thanks again guys for your knowledge and advice.
Russ
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
6
You may be using the term “kicks down” incorrectly. If you apply a bit more throttle, the reduced manifold vacuum is sent to the vacuum modulator and encourages the transmission to downshift. This is NOT kickdown. Kickdown is when you cram the pedal to the floor and then push it a bit farther yet, causing the microswitch on the throttle cable to actuate and send an electrical signal to the transmission. When that happens, and pretty much ONLY when that happens, the engine will stay in low gears to near redline.
On most XJ-S’s, that kickdown switch doesn’t work. It’s not because the switch itself is faulty; it typically works fine. But pushing the pedal to the floor doesn’t actuate it. This is because the pedal itself consists of an L-shaped lever that pulls the throttle cable, and the L flexes too much, absorbing your stomp rather than transmitting it on to the switch.
Take the pedal assembly out (easy), bend the two ends of the L just a tad toward each other to correct the amount they’ve been spread over the years, and then weld in a brace between the legs of the L. Make sure your brace isn’t too close to the pedal itself or your toe might hit it. Reinstall and readjust the throttle linkage so that the bellcrank runs against its full throttle stop while the pedal is still a 1/4" or so off the button on the floor. Make sure that when you push it fully to the floor, that microswitch at the end of the cable housing actually clicks. Then take it out for a test drive.
Thanks Kirbert. I thought I tested that one time with a friend “stomping” the gas pedal and seeing it pull the cable to activate the switch. I will check again though. And if that is the way it is supposed to kick down into a passing gear and hold the car in that gear until I let off, well that is what I haven’t felt yet.
What does it activate in the transmission to keep it in that lower gear to near redline if I so wanted it too? If mine has no other problems to cause it not to downshift with that switch then I can’t wait to fix that problem. These engines love revving, especially with the torque kit AJ6engineering that had been installed by the original owner.
Thanks again guys!
Russ
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
9
Note that some owners have decided that the cable-operated kickdown isn’t worth the trouble and simply relocate the microswitch to somewhere where it is readily actuated when you floor it. Like, they’ll mount it somewhere where one of the throttle pullrods hits it. The guys who have done this are generally really happy with it, because they get kickdown at the drop of a hat.
I disconnected my kick down switch, and went with a B&M adjustable vacuum switch, set it almost all the way aggressive. I can downshift with only half throttle, car will delay upshift a lot longer. When I’m light on the throttle, it shifts as you’d expect. It really transformed the car. I posted about it a month or two ago. Only about $40 if I remember, and half an hour of work, alas under the middle of car, which is claustrophobic if you’re on jack stands.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
11
You should reconnect it. It gets you into low gear faster.
Or, you could just reach out your hand, and move the lever that is attached to the gearbox. I find this preferable as I can better judge the torque on hand ahead of time, rather than maybe have a gearbox switch ratios in the middle of a corner. Once I have the front suspension fixed, next job on my car is a manual gear box. Futzing around with an autobox, even with a shift kit, is just annoying.
If you’re aggressive mechanically, and handy, you can drop the pan, pull the valve body, and put a B&M shift kit in it that will let you more easily manually shift as well as adjust the way the trans shifts. This is also when you can get to the governor and make changes there. There are several very good TH400 books should you choose to go the get-your-hands-dirty route.
I removed valve body on my 88 TH400 did a write-up about it. Quite intimidating, but doable. I did a simple B&M shift kit, left the valves alone. The vacuum shift switch helped when it shifted, and the B&M shift kit made the shifting quicker/smoother. New ATF and filter probably helped too.
I did check out my gas pedal but mine was more solid than what you described on posting. A pivot point then a strong bar that was bent at 90 degrees that the end of the cable slotted into. My problem was that the new floor carpet I installed, covered the pedal stop on the floor/transmission housing. Once I cut that part out the pedal could then pull the cable to allow it to engage the micro switch. I also had the micro switch plugged in wrong too. I looked at my manual and after switching the wires correctly, it worked great. Now kicks down and stays revved up to 5500 rpm every time. I love the sound. I really pulls great along with AJ6engineerings working of the manifold, butterfly and ECU reprogramming. And like Roger Bywater mentioned in the brochure, it feels like a shift kit was installed in the tranny, even though one never has been.
Thanks again for the help. Wish I had the mid muffler deletes now!
