Torque Convertor Lock-Up query

[Aidan]

I finally managed to take the new wagon for a good long run today and I've noticed a "fault" with the convertor lock-up. According to the owners manual, it should lock between 45 and 65 mph, depending on throttle position. Mine will only lock at 55 mph, regardless of throttle position, and when slowing down it unlocks at 54 mph (the 740 stayed locked down to 45 mph). Also, it will not lock at all in 3rd gear (the 740 did). How does the convertor lock work, and is there anything I can check/adjust to correct this or am I looking at a new convertor? The box itself behaves fine, very responsive with excellent kick down etc, its a touch "thumpy" on upshifts, but most of them seem to be like that anyway, my 740 was excactly the same. The fluid is very clean, looks like new, no unusual smells from it etc, and I cant see any pipes or wires adrift. The car itself has 109k miles genuine, full main dealer service history and the guy I bought it from (he bought it new) really looked after the car so its unlikely to be an "abuse" or "worn out" problem (I hope). Its a '95 940 LT6 with the ZF autobox. Any idea's or suggesions would be greatly appreciated, thanks,
Aidan..

[bigbillyboy11]

mine locks up at 48, regardless of throttle position

[Aidan]

mine locks up at 48, regardless of throttle position

I wish my one did, due to the nature of the roads (and hopeless drivers) over here, it is very rare that you can get above 50mph, even on roads with a 60 mph limit so on the rare occasion I can get above 55, it is usually only for a few seconds or so, plus with their habit of "speed up slow down speed up slow down" driving, I'm constantly on and off the throttle and no doubt loosing fuel economy due to convertor slippage, if I could get the convertor to lock at what the factory specs say it should (46mph) it would make a noticable difference for me.

[v8volvo]

Both of my ZF 'boxes also lock up at around 45-50 mph regardless of throttle.

If you want yours to lock up sooner, just about the only option is to swap in a shorter rear end, which would have to be a 4.10 (hard to find) since the automatic diesels already came with Volvo's second-shortest available R&P, a 3.93. I suppose the only other possible way, if you wanted to get radical, would be a valve body modification of some kind to alter the output shaft speed at which lockup occurred.. You might be able to use a different spring on whatever circuit controls the converter lockup to play with lockup speed... but unless you know your way around the inside of an automatic trans and have a pretty exact idea of what you are doing, I don't think you would be well advised to go playing around in there too much.

[Aidan]

Both of my ZF 'boxes also lock up at around 45-50 mph regardless of throttle.

If you want yours to lock up sooner, just about the only option is to swap in a shorter rear end, which would have to be a 4.10 (hard to find) since the automatic diesels already came with Volvo's second-shortest available R&P, a 3.93. I suppose the only other possible way, if you wanted to get radical, would be a valve body modification of some kind to alter the output shaft speed at which lockup occurred.. You might be able to use a different spring on whatever circuit controls the converter lockup to play with lockup speed... but unless you know your way around the inside of an automatic trans and have a pretty exact idea of what you are doing, I don't think you would be well advised to go playing around in there too much.

I was thinking that it is a valve/spring problem. Although I have been out of the motor trade for about 15 years I am a Ford trained mechanic and used to specialise in auto boxes, albiet older 3 speed units such as the C3, C4 and C6, TH350, TH400, Torqueflight, Cruise-o-matic etc so I wouldn't have any problem pulling the valve body providing I can get a good manual showing what valve does what. I was searching thru the web and found some article's re ZF's in BMW's (vomits all over the place, I hate blingmobile's) that mention a number of check balls in the valve body that wear out after time, effectively their diameter reduces and results in late and/or slushy changes. From what I could make out the same type of check ball in conjuntion with a pre tensioned spring controls the convertor lock up point. So I'm reasonably certain that either the ball or spring, or both, are causing the late lock up. I intend to change the auto box fluid, drop the sump and change the filter so while I'm doing that I'll strip the valve body and change all the check balls and springs at the same time, hopefully that should sort things out.

[Jason]

It locks depending on gov pressure, which is directly related to transmission rpm and pump output. You can modify stuff to get it lock slightly slower, however the pressure is lower and at a certain point you wont have the pressure to get a positive torque converter lock up. I did quite a bit of research on the ZF before I gave up on it. Just not alot of info out there, and even less aftermarket stuff or mods to do anything besides a stock rebuild.

Jason

[Aidan]

Very true Jason, ZF info does seem to be very hard to find. Any idea's where I might find info on the governer, if I could tweak it enough to get it to lock at 50, I could live with that.

[ian2000t]

Aidan, from your comments about hopeless drivers and speeding up/slowing down on 60mph limit roads causing lock up/lock down, I assume you are also from UK??

My D24TIC with ZF is exactly the same - locks up/down at 57mph exactly! Frustrating for 2 reasons:

- On light throttle driving (60mph roads just following others) it would be nice if it was locked or fuel economy, but no one actually does 60 - so it's always lock up/lock down/lock up/etc...

- When driving it hard in fourth you can be at the right revs for good boost so accelerating quite well, then at eactly 57mph it locks up, boost falls off because of lower revs, and the acceleration becomes embarassing... and if you're really unlucky the person you're overtaking on dual carriageway finds their power and pulls back past you.

[Aidan]

Aidan, from your comments about hopeless drivers and speeding up/slowing down on 60mph limit roads causing lock up/lock down, I assume you are also from UK??

My D24TIC with ZF is exactly the same - locks up/down at 57mph exactly! Frustrating for 2 reasons:

- On light throttle driving (60mph roads just following others) it would be nice if it was locked or fuel economy, but no one actually does 60 - so it's always lock up/lock down/lock up/etc...

- When driving it hard in fourth you can be at the right revs for good boost so accelerating quite well, then at eactly 57mph it locks up, boost falls off because of lower revs, and the acceleration becomes embarassing... and if you're really unlucky the person you're overtaking on dual carriageway finds their power and pulls back past you.

Hi Ian, how did you guess mate, yep I'm origionally from Essex. Sounds like you have driven on Irish roads as well, honestly, it's really frustrating plus it cant be doing the convertor any good constantly locking/unlocking. The factory spec for the D24TDic is 46 mph lock up (different specs apply to different engines) but over time something obviously wears out/goes weak as most 940 owners with the same engine as us report a lock up at about mid 50's. I found an old post on here where someone "changed a diagphram in the autobox" and got his convertor to lock at 48 mph. Obviously the lock up point must be adjustable in order to suit different engine applications, but finding out the relevant info is proving a nightmare. A couple of years ago a friend of mine who has a 940 with the same engine bought a brand new autobox for it and it locked bang on 46 mph so it confirms something in our boxes is worn or weakened. I read some info on a Blingmobile site (Beemer, yuk, vomit) that gave some info about the ZF box and refered to small check balls that wore out and caused various problems including late lock up but it gave no usefull info on how to deal with it. I had a night run up to Dublin recently and filled the tank just before the start of the M8, zero'd the trip meter and for curiosity I decided to keep at 55 mph so that the convertor did not lock. As soon as I reached Dublin I filled up again, noted the milage and fuel used. Did excactly the same on the run home but drove at 60 mph with the convertor locked,, 8 mpg better with the convertor locked, so it is a big difference and with the milage I do I could really use a lower lock speed.

[Aidan]

forgot to add this to my last post.

[heavyequipment]

There is a listserv (emailing list) dedicated to d24's and d24t's. Write to it at <d24@elist.tufts.edu> to post your question on the list. Some of the members have experience repairing ZF automatics, and there has been repeated mention of problems from wear in the governors.

[Aidan]

There is a listserv (emailing list) dedicated to d24's and d24t's. Write to it at <d24@elist.tufts.edu> to post your question on the list. Some of the members have experience repairing ZF automatics, and there has been repeated mention of problems from wear in the governors.

thanks h e, I'll give that a try.

[m-reg]

Hi Aiden there is a post on here from `fudge` who has used the parts from a petrol `gasser ` 900 zf which locks up at a lower speed ,I say 900 but probly 740/760 as later gas ones had aw auto boxes , I want to try this too but not done it yet so cant say how much it improves things i think the post is `some mods to my 940 tic`.

[Aidan]

thanks m, I'll have a look at that and see whats what

[m-reg]

yeh never noticed before someone else already posted up the table from the greenbook with the shift speeds -I just found my books & the same table so what we need is a valve body for d24t USA/Canada @ 46 mph lockup , i always wondered how they got on in the days of 50 mph speed limits

[indestruktable]

I have a Range Rover which has the same ZF box, I think (4hp22) and it locks up at 52mph unless I have the throttle on or near the floor. The transmission is in good health. I've just accepted it as how it is, as every other LR with the same trans does the same thing...