Possible failing modulator?
Possible stripped governor gear?

Both common problems with the TH400, both easy to fix. Worth investigating.

I fear worse in this case but let's hope I'm wrong.

Cheers
DD

 

I am with Doug here.

Also, check the hose TO that Modulator, it lasts about 5 years, exhaust pipe is TOO close. I wrap a small bit of header wrap around the exhaust at that point, worked so far.

Remember, when replacing that hose, it MUST travel BEHIND that heat shield, or you will do it again in a few days. Use the old hose to drag the new hose through the gap, simple.

 

Got a chance to get under it today.

The hose to the modulator is intact, no signs of heat (or other) damage.

I take it that if I replace the modulator that I'll need to drain the fluid again?

I replaced the governor (due to stripping) earlier this year. I'll pull it out and examine it since I'm nearing the end-of-the-line on what to do.

Thanks,

John
1987 XJ-S V12
about 75,000 miles

 

No need to drain the fluid to change the modulator.

 

If it helps, I recently refreshed my transmission fluid with multiple suction/refill sessions.

I used this 12v pump:
https:/www.ebay.co.uk/itm/353531098461

Very easy operation, warm fluid was all sucked out & within about 5 minutes max.

The amount of fluid I removed each time was completely consistent - between 3.4 & 3.6L each time - I think this is close to the amount you'd get out when dropping the pan so I would recommend the suction method for ease/quickness.
I jus replaced exactly what I removed each time, & now have nice red fluid instead of reddy-brown.

 

End of the line maybe...

Finally found someone who will work on the transmission. They said it either needs to be rebuilt or replaced, at an estimated cost of $7,000!

I don't have the capability, knowledge or equipment to even take the thing out, let alone rebuild it.

I see rebuilt TH400's available for around $2,000. But if I understand correctly, the case for a typical TH400 won't fit in a Jag? Is that correct?

Thanks,

John
1987 XJ-S V12
75,000 or so miles

 

It doesn't cost $7K to rebuild a TH400.

The TH400 for GM cars won't fit the jag engine block.

I believe all the internal parts are the same, though.

I remember back about 1988, I needed some work done on my '76 XJS, it was simple work, like replacing the brake pads.

I took it to a shop across the street from where i worked at the time, to get a quote.

The owner came out and looked at the car and said $5000.

I said a brake job doesn't cost $5K, even on this car, and he said "Jag owners and Porsche owners are all ********, they complain about everything, so it costs more to work on their cars".

Essentially telling me to get lost.

Doug

 

I think, unfortunately, you may have to call around and see if there's anyone more interested in doing this work. This clearly isn't a job for anyone.

You'll want to do some research on Yelp and such and hopefully you'll be able to find someone that wants to do this for you.

 

I finally found a place that will remove, rebuild and reinstall the transmission for around $3,000. I have to wait until January 16th to take (tow) it in, so there is hope for it.

Thanks for all the comments and suggestions,

John
1987 XJ-S V12
75,000 or so miles

 

Thats a much more realistic price.

Couple hours to get the trans out, 2-3 hours to clean and rebuild it, couple hours to reinstall, plus some parts like clutches and bearings and bands. Maybe new valve body

You probably have something in your valve body, or some other issue with it.

Doug

 

Yep, I don't know how places stay in business charging twice what a job should cost.

What's also annoying about the first place I tried is that they didn't trouble themselves to reattach the shifter, so I can't even back it up a foot (it's sitting on a slight downhill slope). Jerks :-)

Thanks,

John
1987 XJ-S V12
75,000 or so miles

 

See my post #27.

Go back to the original shop later and say you have a 1987 Chevy Silverado 2 WD truck with TH400 and ask how much to R&R and rebuild the auto trans.

I bet its a lot less than $7K.

Doug

 

They give such inflated "estimates" because they really don't want to mess with anything from the previous century, no matter how current or common the specific component is.
I had a counter staff tell me just about exactly that once. I've never darkened their door again.
(';')