So, I just today picked up a 1987 very stock xj-s, it is a project car - very projecty. The previous owner was pretty negligent about fluids and who knows what else at this point I have very little history on this vehicle. It runs, it drives, it doesnt stop very well lol but im working on it. What it absolutely wont do is go in reverse. Amongst the fluids that were very low - like barely on the stick low - was the transmission fluid. Now I've since topped that off and I was hoping that might solve it but no joy. Am I definitely looking at major transmission issues or could something else cause this problem ?

 

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I am assuming? since you are in the USA, a V12 beast??

TH400 trans if that is the case.

Since it goes forward, and not backwards, I suspect internal damage. There is a well known o/ring on the filter suction tube that splits, but usually stops both directions. I found that years ago, and topped up 1.5ltrs over the full mark, car moved, easy fix, I was lucky.

Good luck.

 

I'd start with changing the filter, which involves removing the sump and changing some of the fluid. The new fluid may help get things going. If worst comes to worst, its a common transmission so lots of shops can rebuild it easily.

 

I definitely plan a filter and fluid change just for maintenance sake. I have come upon some new information that may well explain my issue and potentially some other issues as well. There is a four prong vacuum port on the back of the right side intake manifold. Two of those ports were just empty. The little sticker tells me one should be capped so I capped one, and the other should go straight back to the transmission - that line is completely missing. The other two ports go to solenoids or to the inside, probably for the ac control. The vacuum system on this side is a mess, there are 3 solenoids over there that i will probably have to make a separate post about that either have all their lines missing or some of them missing. Anywho - would that transmission vacuum line being missing cause a loss of reverse?

 

Nope it wouldn't - reverse is done entirely using oil pressure via the third gear drum, it is either the reverse band itself or the servo that supplies it - do you have 3rd gear ?

 

I am very interested to hear what others have to say but I would think sadly not. Not for reverse... That missing vacuum line goes to a ----- oh shoot I am for getting the name (had to Google it) a vacuum modulator/actuator of sorts that controls shifting in forward gears... Going from 2 to third gear,,, holding second for longer or shorter duration depending on the amount of vac in the intake...and such.

Mine was shot. Worse, for the PO, the line flopping around down there caught fire and the fire climbed the hose and ended up doing damage in that entire corner of the engine bay.

Anyways... There are a LOT of great videos on YouTube of rebuilding these transmissions and it doesn't look hard. The removing and replacing is probably the hardest part - at least for me.

How did the fluid look when drained? You'll prolly find whole gears floating around in the pan when ya do take it down.

It's going to be alright. Is it a convertible? In my opinion the best O the XJS's... But I'm biased!

 

Wouldnt be the first transmission i've built, would be the first one of these though. I did a 4l60e for my firebird a few years back. lots of fiddly little bits. I don't know yet if I have third gear, I haven't had chance to really drive it yet save for going down my driveway with it when we took it off the trailer. The brakes are barely there, but I think they just need bled. the brake fluid res was almost empty so im sure the brake system will need a little work. For another day though lol I got all the vacuum leaks either routed properly or capped and it idles now, it likes to idle at about 1250ish. I haven't looked yet to see if thats normal. With the vacuum leaks taken care of its not running rich anymore either so yay for that.

 

As to your question about it being a convertible - no its not. I think the buttresses in the back or whatever they're called lol look super cool.

 

I suppose the only question i have left for this transmission issue is - will any turbo 400 rebuild kit work or is this one in some way special?


This is the kit I'm looking at - just want to make sure it'll do the job before I pull the trigger.
I am probably overthinking what parts will and wont work I just have this notion in my head - its a jag - its special - special sauce parts - lol

 

coupes are the best. Roadsters are second best but I like em too.

 

The bellhousing is special to fit the V12 but the internals are standard.

 

Excellent - so that kit should work then.

 

1250-ish isn't normal... When warm 650-to 700-800 is depending on where you've set it... And smooth... But you'll get it there. I started typing this before I went back and looked, but (depending on the year)- there is a idle adjust, a contraption stuck on the BACK of the water rail on the LH side near the fire wall. It's attached to the LH intake near the crossover pipe, a 90degree 1inch ID rubber elbow (that likes to crack)... When you remove the AAV and if the hose is old (unless you have a spare RIGHT there) it's best to just unbolt the AAV contraption first and carefully wiggle off the hose. It's a rubber air hose and brittle...

When cold, on start up, in the AAV, there is a piston in a hollow cylindrical chamber that is driven up as the coolant warms to seal off the extra air. If you Google AAV and XJS or alternate air valve XJS, you will find lots of information. Lots of times if a car sits this piston will get a bit stuck down in the bottom of the cylinder. It needs to be freed up. It operates like a thermostat in a way, a wax filled capsule drives up the piston 3/4 of an inch more or less to block of the extra air as the coolant/engine warms.

Speaking of coolant and such,,, WATCH the temp on these first rounds of long idling for tests and repair. Don't let it overheat!!!!

The brakes, you might get off as lucky as bleeding, but I doubt it. Have you seen the rear brakes yit? They might be siezed up (inboard brakes???). Not such an easy thing. Many will say drop the cage to address the rear brake stuff - and ya should...

It's all solveable. I wish I was familiar with the transmission stuff... Someday, I know...

You'll get it there no doubt!

Also, often an unfound air leak is UNDER the RH intake... There is another extra air valve that connects with a hose that opens when the AC is on... The hose lives in a HOT environment and will crack off. If you reach you hand under the RH intake,,, directly in line with the RH throttle body,,, you'll feel a 3/4inch spout that accepts this hose. Make sure the hose is good or it's covered. It's larger than most of the vac hoses and will allow a lot of extra air.

The rest of the vac hoses are visible up top but EASY to miss. Just keep poking around. And, check the front and back plates of the intakes where the little spouts are. Leaks there too...

There is also a lil secret for the TPS,,,, the rotor with the throttle arms in the center. It often needs to be reset. .32 to .36v (Grant is the Man!)... Resetting this helps a lot too and there are great write ups for this!

(Saying this quietly and humbly)
Convertibles is where it's at!
Jus say'n!

 

Until today I had never heard of inboard brakes lol. I had just assumed after a quick look through the wheel that the back brakes were missing. Learning new stuff all over the place with this lol. It does kinda act like there is a brake dragging somewhere - as it is almost impossible to push in neutral. I tend to replace all the brake components in project vehicles anyway but I am glad that they aren't just missing lol. One less mystery.

 

So now I'm thinking since I need to pull the transmission soon anyway that I might just take that opportunity to pull the whole back end out of it to give everything a good cleaning and maybe some paint. Maybe find some other issues while im in there that can be more easily addressed with everything apart already.

 

Hahaha. You will certainly find a thing or two... Honestly, "dropping the rear cage", as it is said, is not such a bad job at all... The dropping part that is... I'm excited to be following your progress... These are GREAT cars...

Always ask here... This place is an amazing source of information! Can't overstate that...

 

I am pretty excited to have it - I knew it would be a project when I bought it. Wasnt really expecting a transmission rebuild right out of the gate, but since thats something I can easily do myself its not that big a deal. Im sure tracking down all the vacuum leaks will be fun lol - its only like my least favorite kind of problem to deal with. I figure by the end I will probably just replace all the vacuum lines. Makes troubleshooting easier that way rather than trying to figure out which ones are still good and which aren't.

 

At long last victory is within sight. Got the transmission out today. Didn't have much trouble with that spring loaded rear mount. I am most definitely not the first person to be under here as some of the bolts for that mount were wrong and missing those oblong washers jag seems to like putting everywhere. the torque converter bolts were actually my biggest headache. I am thinking the previous owner may have started taking things apart to attempt to rectify this problem, got their *** kicked by the torque converter bolts and gave up, but not before doing some very annoying damage to the bolt heads. They will need replacing for sure. In a last act of defiance it slipped off the jack while I was pulling it out and nose dived onto the floor puking what fluid it had left all over the floor like a gut shot caribou. On the bright side though the floor will be an interesting red color for awhile. Really hoping not to find any surprises inside once I crack it open but this car is just full of surprises so probably not getting that lucky lol

 

With a story like that we would like to see pictures!
Some of us can't read that well!
And picture tell a thousand tails!

 

lol I will see what I can do.