My transmission has just started shifting with a bonk (an abrupt shift - that is cushioned, not slamming) between 1st and 2nd. It does not always do it and the rest of the shifts seem smooth. I first noticed it a couple of weeks ago and it seems to be happening more often. The original transmission was replaced with an eBay used unit at the end of 2014. I think the used trans mileage was in the 100-120K mi. range and I've done less than 10K since. The fluids and filter were replaced at the time.
The last time the transmission let go it went with a bang, the A drum, the trans was fine before hand.
Two questions:
How long do you think it will last like this?
Is it a fixable issue?

 

It seems well established that the cause of these broken drums is first a failure of the main hydraulic pressure regulating valve in the valve body. Shifting problems would certainly make one suspect hydraulic pressure too high or low. Sonnex produces an upgrade kit that hones out the worn bore of the main valve and replaces with a larger piston. Several sources on the internet offer a rebuilt valve body for between $500 and $800 with the Sonnex valve installed on an exchange basis. If the bore is not too badly worn, there is a replacement standard bore piston available. Probably a little over $1,000 if you have a shop remove and reinstall a repaired valve body, but that's far cheaper than replacing the whole transmission.

 

It seems like when the car is cold the shifting is better.

I've just read a bit about the Transgo pressure regulator repair kit which says it corrects/prevents/reduces harsh shifts, kickdown bang and drum breakage. The kit is only $71 on eBay, it definitely seems worth a try.
Link to Transgo thread:
https://www.jaguarforums.com/forum/x...ng-kit-146100/

I wonder what a transmission shop will charge to install it? ( I don't have access to a car lift)

 

You can remove the forward valve body with the car on jackstands. It took me about four hrs. to replace the main pressure valve without rushing. I used the ZF upgraded valve and I don't know if the Transgo part has any advantage.

It's not unusual to find a crack in the valve body, in which case the valve won't help. Also, the bore may be badly worn and require replacement or a sleeve kit.

 

I'm trying this Transgo repair tomorrow, we have a place locally where you can rent time on the car lift.
(I'm too chicken to try and put the car on four jack stands, plus don't have a good level area.)
I hope I have n't left it too long. The bonking has become worse and the transmission fault light came on today for the first time.
Fingers crossed that there are no cracks and the bore is not sloppy.

 

Good call.

 

What about just simple fluid flushrs/changes? Mine did bonk changing between gears sometimes. After seeing black ATF I changed the filter and filled new fluid and o bonk at all... 110k mies on it and it was def the first change... Going by service book and receipts...

 

Well working on the car on a lift was fun and far more civilized that crawling around on the ground. It took a few test drives to get the transmission filled. It would seem like the oil level was right- then I would drive it and the level had dropped to where I could put more in. 6 bottles of ATF1 in total. The previous oil was dark red, seemed okayish and no large amounts of crap in the pan. Unfortunately the car is no better than before. It now jumps to "transmission fault" about the second time you pull away from a stop. It then goes into some kind of mode where it is in one gear, so it is really slow to pull away but then will gradually accelerate without shifting.
The Transgo plunger seemed actually more sloppy in the bore than the existing plunger, which was fairly tight - needed pliers to pull it out (although the Transgo was ice cold at that point per their instructions.
I'm not sure where to go from here.

 

The fluid you removed being red indicates someone changed it from the OEM which is Gold, and costs like it. No telling what was used and if it is at least part of the problem.

You may have to replace the valve body, but the A drum may also be damaged.

I get the feeling a rebuild of the transmission may be in order, or a used one. But with used you don't know what condition it's in.

 

What color is the Esso stuff? That is what the installer of this tranny (which I bought off eBay in 2014 said he used).

 

I drove the car a few miles today, after doing a hard reset. The transmission fault light did not come on or go into the one gear mode, but it has some harsh shifts and some brief squealing sounds that I did not have before.
Is a valve body something that can be replaced as a unit? Or does it have to be taken apart to be removed (with lots of little pieces)?

 

The valve bodies are fairly easy to access, just remove pan and filter, then a lot of torx head screws.
It might be worthwhile to find a indy shop that can read your ECU for stored transmission codes.

 

find an honest transmission shop.... They do exist. Cap the worst case expense at say $2,600. If the repair is getting close to that, exchange it instead. Unless you do the work yourself, probably just as cheap to drive it until it blows up..... Good luck