Just musing on a rainy day about the Torque Convertor lockup on my 98 D1 being at 53 mph and wondering if anyone has figured out a way to change it to a lower speed. Searching the archives I find:

"The D1 does not have an electronic transmission, the shift points are rpm/pressure based. There is no electronic sensor that can send a signal to a D1 transmission, no tranny ECU, no CAN buss, etc"

I went through the official kick down cable adjustment procedure a long time ago but had to set it back to where it had been to let the butterfly close to idle position; the TC lock up speed has always remained at 53 MPH which is a pita when driving in a 55 mph speed limit zone because any slight road variation has it going in and out of lockup, so I have to drive around 60 to maintain overdrive engagement. I wish it kicked in sooner like around 45 to 50 MPH so I didn't have to push the speed limit.

Anything new on this front?

 

Hmmm, are you sure, that seems strange. I agree though, that would be a PITA.

Have you changed the fluid before? If so, did it have any effect? Might consider putting a can of transmission medic (TransX/Gunk/Lucus) into it, run it for a while, see if anything happens. Like this:
https://www.ruralking.com/transmedic...ype%20Shopping

I've seen with my own eyes, transmission 'repair' solutions in a can make a car that wouldn't move ...start working again (and lasted quite a long time). I'm generally not in favor of additives, I haven't used any in years, but my brother and I used to turn a lot of cars when we were young and we tried anything and everything as a last ditch effort if needed. I've seen that tranny stuff make 'dead' tranny's come alive again almost like a miracle from above (long enough for us to sell anyway). Worth a shot, especially if you're thinking about changing the fluid again anyway. Put some in, run it for a couple hundred miles.

Also, I had a situation with my Chevy truck years ago where after replacing the ATF it developed some whacky shift characteristics, the vehicle would shudder all over the place. It was alarming and uncomfortable. I was sure I was in for a rebuild. It had high mileage anyway. Well, as a last ditch effort I replaced the ATF with another brand (read some posts where some people with similar problem went away by going with Penzoil ATF). Thinking it was a crock and a waste of money, I tried it anyway figuring if it didn't help I'd get it rebuilt. Well guess what, the problems went away in about 50 miles and that was literally 8-9 years ago... maybe 10!

If you do change the fluid again, try to get it 'all' out. Generally after you've filled it with new fluid (but before starting the vehicle), overfill by 1-2 quarts, remove one of the cooling lines that go to the radiator attach a hose to it and run the hose into a bucket. I like to use clear hose. Then have a helper start the vehicle while you closely watch the fluid as it's flowing into the bucket. It comes out fast. When the ATF turns from dull brown to nice, bright red (new fluid), shut the vehicle off and top off. Sometimes you might have to shut the vehicle off and add more fluid midway and continue because it can take a couple 3-4 or 5 quarts to pump out what's in the torque converter.

Other than that, have you performed any general Google searches on the issue? Search for ZF TCC (Torque Converter Clutch) problems/delay. There might be someone from another board, or Range Rover forum who's experienced the same issue. I believe this tranny was used in other non-land rover products too, so be worth checking what else might be similar. Could check with a tranny shop that is familiar with Land Rovers, like an import shop, or if you could find a local Land Rover guru machanic. Pick their brain.

I don't know the Land Rover (RAVE) manual very well for the transmission problems diagnosis section because I haven't experienced any tranny related problems, but see if there are diagnostic trees. If there isn't much in the Rave manual in terms of transmission diagnosis, I bet there's a comprehensive ZF manual for this transmission out there somewhere with a comprehensive diagnostic tree on how to debug TCC lock-up issues that would include how and where to check pressures and what they should be. I know in my Chevy truck factory manual, they have a very LONG chapter on transmission problems diagnosis and pages of diagnostic trees and processes.

Sorry I don't know the answer specifically, but just trying to throw ideas out there..

 

Like Mark said, try changing the fluid first and go from there. These transmissions are surprisingly tough. When I had my D2 (same transmission), the ATF had been flushed every 30k miles. Filter was never changed and it shifted very well. Admittedly, it's not the smoothest transmission but it doesn't shift roughly at all.

I just purchased a D1 a little over a week ago with 119k (not bad for a 20 year old truck). The previous owner had no records of the transmission fluid being changed. I doubt that it was never changed, but it was certainly changed well over 30k miles ago. Fluid looked bad. Almost like engine oil. It shifted roughly but I wasn't too concerned because the TC still locked up and it never slipped. Fast forward a few days, I drained the transmission and refilled it with about 5 quarts of Castrol Transmax fluid. I drove it for about 200 miles then repeated the same procedure. The fluid is now a reddish pink and the transmission responded very well to the fluid change. Shifts smoothly and TC locks up well. No slipping or any of that nonsense that most people describe happens to an old and neglected transmission. So far I have driven about 500 miles after the second drain and refill without an issues (took it on a road trip).

So try a fluid change. I have had my fair share of failed automatics but the one in the Discovery is surprisingly good and quite durable. Castrol Transmax is only $15 a gallon. All you need to do it is 5-6quarts of fluid and a 5mm allen key for the drain plug.

 

Per you reported speeds just a bit out of spec. Have you checked the accuracy of your speedometer?
......

 

TORQUE CONVERTER
Lock up (IN) D 51 - 54 81 - 86 1875 - 2000
Unlock (OUT) D 49 - 52 78 - 83 1825 - 1930

I didn't understand the 81 - 86 and 78 - 83; is that kilometers per hour?

My TC consistently locks up at 53 MPH and unlocks not much below that; I watch the digital read out for speed on my UltraGauge which matches the speedometer pretty well. I haven't specifically watched the RPM at lockup.

Apparently it is doing what the spec says, although the drop out point seems to be at the top of the unlock range, like 53 in and 52.5 out. I was hoping there might be some adjustment to lower that range since most of the rural roads around here have a 55 limit and are twisty and hilly so your speed often varies a few MPH from that. My other vehicles lock up at a lower speed with moderate throttle use and drop out at a much lower speed too.

The one good thing about it is that the fellow who sold it to my brother-in-law for scrap did so because he thought the transmission was going out and I assume he thought so because of the TC doing its little in and out dance at 53. Other than that the tranny seems to be fine so I guess I'll just have to continue to live with it if there is no simple adjustment.

 

What's your engine temp (per the Ultragauge)?

 

I think it runs 190 to 195 F with a 192 degree thermostat. It might get up to 200 F sometimes, but I may be thinking of our Jag SV8 which also has a semi-permanent Ultra Gauge. I'll pay more attention the next time I take it out.

 

There is a mod you can do to the valve body to make it lockup in 3rd.

 

My 99 same thing. 53mph on the head. If I recall that's like dead center of specs, 51-55 I think....??? I know 53 is good as I had to adjust my tv cable and it was in spec per Rave. And YES, it is a freaking miserable point to occur at. "Hypothetically" I could prefer to drive 5 to 10 over the 45mph speed common in my area and that puts me right at that annoying point where it wants to break, but muuuuuusssstttt hit that 53 then if you let off a little....repeat.
ive often played out the scenario in my head where I'm like well officer, you see, I have to do 55 minimum because anything from 45 to 54 puts my truck at higher RPMs and it wants to kick but I need these extra mph to drive her smoother.....