Hey guys I have been lurking around here for a few days and just pick up an 85 XJS Saturday. The car is a one owner with 43k miles on it. It is in great condition and the engine is running well.

So I test drove the car for a good 30 minutes and all seemed well so the exchange was made. On my 40 mile trip home however the trans seem to get caught in 1st or 2nd gear and it still is. The car takes off fine but doesnt shift and if I let off the gas it goes into a neutral sort or thing until I bring the revs back up to 3 or 4k and then it grabs again.

So far I have pulled a vacuum on the modulator at the hose on the intake and it is holding vacuum.

Should I pull and replace this piece anyway???? Something else internally that could be wrong with it???

I also remove the access panel under the carpet and pulled out the trans governor to check the plastic gear, unfortunately this look fine also....

Another thing is that the shifter itself feels funny to me, I was putting the car through the gears on my test drive and it felt precise but now it seems different somehow. Could I possibly just be driving with 1 selected and not knowing it???

Lastly does this just sound like a failed trans? It wouldn't seem likely to me with the low mileage on the car, but who knows????

On top of this during my drive home which I continued at a slow pace because of the gear being stuck, I ended up blowing the upper radiator hose and ended up getting towed.

Help me out guys,

 

Welcome abaord.

I'd replace the vac modulator, yes.

Not sure about the feel of the gearshift. Sometimes the shift cables give trouble.

Looks like a nice XJS but it also sounds like it'll need the typcial "used XJS sorting out". The weak and troublesome spots are well known as many here will attest to and describe. You can tackle them en masse and be done with it.... or torture yourself by going alá carte :-)

Cheers
DD

 

Welcome to our side. Some say the dark side, who cares.

I agree 100% with Doug on this.

I would first and foremost, service the trans. It sounds horribly like the dacron filter is blocked, OR, the pick up plastic tube o/ring has gone AWOL. Fluid level may be low also, as 1ltr down on a TH400 will reek havoc.

NICE CAR.

 

Just replaced the modulator and the results are the same as before.
Checked the fluid and in was a little low Added and still the same.
Fluid looks clean and smells fine so I don't believe this is a wear issue.

When you guys say service the trans you mean a filter change and new fluid I assume?

Is this pick up tube oring replaceable with trans in the car?

A quick breakdown on other matters that should be taken care of????

 

Nope, the kick down switch on the throttle pedestal, or the wires to it are the issue. Should be a simple fix. I think when a modulator is bad, you get early up shifts even at wide throttle openings...

Dave
Atlanta

 

I haven't came across anyone having trouble with this dave, but I will have a look. I think there are two micro switches do you know which one it is. And have you had this issue before??

 

Sorry I don't have any mechanical advice, just wanted to say that the car looks mint!

 

Thanks, I will get some better pictures but the car is really nice that is why I had to crab it! The interior is almost perfect two dings in the whole car that can be removed by a PDR guy...

I should also mention that these cars are nothing like I expected. Very sporty feeling car, solid feeling and corners well.

 

Worth checking!





The typical symptom of a bum modulator is no upshift until the throttle is released


Cheers
DD

 

The kickdown switch is on the throttle cable near the throttle pedestal. If the switch.circuit is stuck "closed" it can cause odd shifting


Cheers
DD

 

sounds like a trans failure. i would check the kickdown switch anyways to make sure its releleasing.

the converter probably took a dump, but its hard to say from here.

p.s. i had a similar experience with an 85 XJS. started shifting funny, blew an upper rad hose on the way home, and now it wont run at all.

soon to be SBC for the lose.

 

The TH400 is a pretty rugged transmission, but as mentioned, they don't shift right if fluid is low.
Considering the low miles for the age, I think the filter/fluid change is an excellent idea and a flush is probably even better. Years of sitting could cause things to stick. As long as you have it open you might consider installing a shift-kit. It will help liven the shift points up a bit.

 

I don't get the SBC thing you can pick up the V12's cheap and its what makes the car what it is IMO... These motors can't be that bad can they???

 

I was thinking the same thing and ordered a shift kit and filter from summit today. I was also thing a flush may get it going again, just hard to believe that it gave up at 40k miles....

 

I don't believe these motors are bad at all. The wiring can be tricky but once it's sorted out the majority of the problems disappear.

 

Found this info. Sounds like things could just be blocked.

 

If I recall from a distant memory; the vac. modulator is a yellow plastic that breaks up with mileage and age. The replacement was made from aluminum and fairly inexpensive ($10.00 perhaps...) and easy to replace. I replaced the VM in the '83 I had... a long time ago and far, far away...

 

Well I finally got the trans pan dropped and it looks really clean, no Christmas tree just some minor filings.

I guess the next step is to drop the control valve and go ahead and install this shift kit I bought. Maybe I will find something in Tue process, but I'm a bit stumped at The moment.

 

Did you do a proper check of the kickdown switch and wires at the end of the throttle cable? The symptoms you describe are the kickdown circuit being made...

Dave

 

Not yet Dave, I had already started dropping the pan when you mentioned it I believe. Also it seemed unlikely to me that the switch was the problem because of the way the car feels like its in neutral when I let off the gas and it doesn't grab again until I reach the high revs I was at before I let off the accelerator.

Now that I think about it though it makes more sense especially since the pan is so clean. Hopefully this is the problem and I just end up with a serviced trans and a nice shift kit installed.