Explantion of transmission/overdrive behavior?

[kerrye]

Been driving from Denver to Flagstaff the last couple of days pulling my Sea Pearl Trimaran (1500lbs) with the 80. I've noticed some things about the transmission and I wonder if someone can give me a little tutorial on how it functions. If I'm in overdrive and it downshifts going up a grade, I assumed it was downshifting into third. However, if, once it has downshifted, I turn off the overdrive, the rpm's will drop 200. Also when in overdrive, if it shifts back up from third (?) to overdrive, the rpm's will momentarily stop at X and then a second later, drop down another 200 rpms. So it looks to me as if when in overdrive and downshifting automatically, it unlocks the torque converter. Is that correct? So, when I turn off the overdrive when it has downshifted, it re-engages the convertor lock up hence the 200 rpm drop. It also re-engages the lock up in overdrive once it upshifts again.
Knowing this fact is important because if the 4 spd Allison in my Bluebird Wanderlodge is any indication, an unlocked torque convertor produces a lot more heat. So, when doing a lot of climbing, disengaging the overdrive and allowing the transmission to lock up which it appears to do in all gears when the overdrive is off will keep things cooler.
Can anyone shed light on this interpretation of transmission behavior?

 

[muddinmetal]

I can't help with everything here, but I can tell you that a 80s transmissions lockup is controlled Mechanically, not electronically. I believe it is hydraulic at that. Thus meaning when you hit you od button, it immediately responds to that electric signal, but the mechanical lockup has to have certain hydraulic parameters met before it will lock/unlock

 

[rove_mcanus]

The torque convertor is electronically controlled in all electronic transmissions - so excluding the a440.

The behaviour is to go from 4th locked, to 4th unlocked, to 3rd in electronic models. Bit stupid if you ask me, i'd rather it just go straight back to 3rd

Going up the gears is the same. It goes from 3rd to 4th. and then momentarily later it locks the converter. That's why you get that last drop in rpm.

An unlocked convertor does produce more heat. However transmissions are programmed to unlock at full throttle to avoid damage to the lock up clutch. So with that in mind, under normal operating conditions there will not be a damaging build up of heat. However under towing conditions or other heavy load conditions the oil change interval drops to account for the higher running temps.

 

[kerrye]

It's a 94 if that makes a difference.

 

[SiRaDuDe]

It's a 94 if that makes a difference.

From '93 to '94 you have an Electronic Controlled A442F with mechanical lockup converter (From slee web, but could be wrong, but he is a reliable resource...)

I have a '94 also with 35's, when going up steep inclines I always take off the O/D button for better lockup.


Refrence: http://www.sleeoffroad.com/newbie/newbie100.htm

 

[kerrye]

If the lockup is mechanically controlled, why does it lock up once I disengage the overdrive after it has downshifted from overdrive on an incline? I tried it a number of times and there was no variation. OD on. Tranny downshifts by itself. Click off OD and it locks up. Click OD back on and it unlocks.

 

[Ebag333]

If the lockup is mechanically controlled, why does it lock up once I disengage the overdrive after it has downshifted from overdrive on an incline? I tried it a number of times and there was no variation. OD on. Tranny downshifts by itself. Click off OD and it locks up. Click OD back on and it unlocks.

The TC is electronically controlled and tied to the O/D button. You can see the same behavior if you are basically coasting in 1st or 2nd gear, click off the O/D button and the TC will unlock (and RPM will change by about 200). No O/D in 1st or 2nd gear......

 

[kerrye]

The TC is electronically controlled and tied to the O/D button. You can see the same behavior if you are basically coasting in 1st or 2nd gear, click off the O/D button and the TC will unlock (and RPM will change by about 200). No O/D in 1st or 2nd gear......

It's doing the opposite. Click off the OD and it locks. (at least in third). click OD on and it unlocks.

 

[Stylo07]

Do you have your ECT button engaged? Doing so will drastically effect when the torque converter locks/unlocks relative to throttle input.

 

[Ebag333]

It's doing the opposite. Click off the OD and it locks. (at least in third). click OD on and it unlocks.

I may have it backwards, it's been almost 3 weeks since I've driven the 80 and I'm about 1,000 miles away from it. (Plus I don't play with the O/D button too often.)

Regardless, I know that the lockup behavior is different with the O/D off than on.

 

[SiRaDuDe]

It's doing the opposite. Click off the OD and it locks. (at least in third). click OD on and it unlocks.

That's exactly what mine does. (ECT ALWAYS ON).

When I'm on a steep incline with O/D button ON and in 3rd, I can see the rpms are a bit higher , If I turn O/D off the rpms go down about 200 or so. (While in third, I can never get to 4th gear on a steep incline! IF it does go to 4th I will just loose power and slow down, making have to step on gas and down to third we go again)) We are talking steep right?

I assume this is because the TC is locking when I turn OFF O/D. ( in other words tranny is in 3rd, OD is off so why would it try to shift up more? instead it locks TC and stays there)

So whenever I about to go up a steep incline I always turn OFF the O/D to limit my TC slip, and stay in 3rd. (In my mind the tranny will lock up better with OD OFF) I might be wrong, but thats just the way i see it while I drive.

 

[SiRaDuDe]

Some search found related posts...

One thing to remember is that with the O/D OFF, torque converter lockup in 3rd gear is allowed. If you simply downshift from 4th to 3rd with O/D ON, you're just in 3rd gear and the TC won't lock up.

What I do, is if I'm in 4th gear and deep throttle, say enough to unlock the TC, I decrease the throttle and turn O/D off and let the TC lockup in 3rd gear. You can see the RPM increase and then drop as it goes from 4th --> 3rd --> 3rd L/U.

The difference between 4th with TC unlocked and 3rd gear with TC locked is about 200 RPM (higher). That way the transmission runs much (much) cooler as the TC isn't creating heat as it does when it's multiplying torque.

Dan.

I agree with CreeperSleeper.

I leave mine on unless I'm about to climb a steep pass on the freeway, or my tranny is hunting for a gear. I can usually hold my speed up the passes with the OD off. Another great time to turn the OD off is coming down a steep pass, as you can lay off of your brakes in order to heating up your rotors, or even worse, warping them (ask me how I know). I have better control with the OD off coming down the pass, and then I can drop down into D2 from there to slow down further if necessary, all the while staying off the brakes, yet remaining in control.

by the end of 2005, I'll have over 9000 miles of towing with my 80...all hauling my 3800ish# FJ40 around on a 1500ish# trailer.

I hit the ECT switch to change the shift points, and generally pick either OD or 3rd with the selector switch...as soon as the tranny begins to "hunt", it gets manually put in 3rd. The RPM's drop by 2-300 and it goes into lockup mode. Once I crest the hill and my speeds have resumed, I manually push the button to put it back into OD.

If you watch your tach while in OD, you'll occasionally see your RPM's increase by 2-300, meaning it's kicked out of lockup....when I catch those, I immediately shift into 3rd.

I tend to avoid cruise control if the terrain is at all hilly....while I lose speed on the hills, it's less likely to drop hard into 3rd...

my "last" towing trip for 2005 is this coming weekend, 300 miles each way to Attica. The prior trip was 1000 each way to Oklahoma, and the 80 performed excellent as a tow vehicle. It's NOT a hill climber, but get a decent draft and it will hold it's own.

I am pretty sure that it locks up when you have the OD off. If it kicks down automatically, then it is not locked....well on my rig anyhow. I have no clue about what tranny the JDM rigs have.

 

[SiRaDuDe]

More related quotes....

Many threads on this. Nay and I have done this at altitude. Just keep the OD off so the torque converter stays locked, to prolong the life of the tranny by keeping the heat down from slippage.

It is not bad running 35's with stock gears. I would not do it permanently, though.

 

[d0ubledown]

so third would be...D with OD off? been wondering the shift points as well and whether TC locks when OD is off.

 

[SiRaDuDe]

More quotes...

Nice tires, thinking about getting the same.

Just make sure your torque converter is locked in OD so you don't get unnecessary heat build up in the tranny and wear things a little quicker.. May be worth while running OD off, in 3rd gear, so the TC stays locked.

Sounds pretty close. Depends on if torque converter is locked. Out West we generally have bigger hills and have the opportunity to see the T/C lock and unlock by watching the tach on a long grade. With Cruise Control set, you can watch this real clear. Try some experimenting with the O/D button if you suspect O/D not working. T/C should lock up in both 3rd and O/D. Seems like with throttle applied, there's a couple of hundred RPMs difference between T/C locked and unlocked. RPMs will be higher with T/C unlocked. HTH!

Well that is news to me! So if I understand correctly:

- the '94 version of the A442F has L, 2, and D but no 3 but it has an overdrive button instead. Am I correct to assume the third gear in this transmission is directly conneceted thus locked, as well as the overdrive?

- the A440F has 3 gears plus Drive like the '91 A442F in my HDJ81, and does not lock in 3rd gear when you set it in 3rd, just like mine would seem to do.

- My interpretation of the A442F locking in 3rd when D is selected would be consistent with the behaviour of the A442F in your '94, but it automatically shifts in OD as well.

Assuming my interpretation is correct, you have to admit this is a bit confusing. The reason I asked in the Diesel forum first was that I thought the Canadians with JDM import knowledge would understanhd my question and clarify, but it would seem I'm the only one with this particular situation. Hmmm! Maybe the trnasmission was updated/overhauled/ is not the original one after all!

aim, thank you for your kind answer!

hey, fellow cannucks, I thought only JDM Land Cruisers with the extreme valve body option had this 3rd gear lock... What gives?

(thinking to self: I think I'm going to rephrase and repost the question innthe JDM alliance forum)

Chris

 

[SiRaDuDe]

I will stop quoting now...

so third would be...D with OD off? been wondering the shift points as well and whether TC locks when OD is off.

From all the threads I've read so far... (Im no tranny expert)

The '91 to '92 tranny will only lock the TC in 4th (OD) at about 47mph no button on these...

The '93 - '94 will lock up on 3rd or 4th (no 3rd gear selector on these) so you need to put it in D and swith off OD and you can lock up on 3rd to stop the hunting you might get while uphill or towing. With OD ON I will assume it will lock up on 4th on level surface?

'95 + tranny - Not sure here, should behave like the 93?

ASAIK - Yes, Turning OFF OD will restrict you to 3rd gear, ( and if correct, why would it not lock if this is as high as it will go?)
From what I've read so far it will only NOT lock on 3rd if you have a 3rd gear selector and you have selected it '91-'92 only?)

As quoted from this...

O/D (Overdrive). There are two buttons on the left side of the automatic transmission shifter. The big one lets the shifter move. There is a little tiny button under it about 5mm diameter. When pushed in this allows the truck to enter overdrive when the shifter is in D (drive). When this button is out it restricts D (drive) to 3 gears. When it is pushed in you have 4 gears.

NOTE: I'm only quoting whats on this forum...

 

[sleeoffroad]

Here it is from the repair manual. THE ECM and TCM is electric, but the lockup is still done mechanically inside the tranny with shift solenoids.

4. FUNCTION OF TCM

• Control of Shift Timing

The TCM has programmed into its memory the optimum shift pattern for each shift lever position
(D, 2, L positions) and driving mode (Normal or Power).
Based on the appropriate shift pattern, the TCM turns No.1, No.2 and timing solenoid valves on
or off in accordance with the vehicle speed signal from the vehicle speed sensor and the throttle
opening signal from the throttle position sensor. In this manner, the TCM operates each shift
valve, opening or closing the fluid passages to the clutches and brakes to permit up−shift or
down−shift of the transmission.
HINT: The electronic control system provides shift timing and lock−up control only while the
vehicle is traveling forward. In REVERSE, and NEUTRAL, the transmission is mechanically, not
electronically controlled.

• Control of Overdrive
Driving in overdrive is possible if the 0/D main switch is on and the shift lever is in the D position.
However, when the vehicle is being driven using the cruise control system (CCS), if the actual
vehicle speed drops to about 4 km/h (2mph) below the set speed while the vehicle is running in
overdrive, the CCS ECU sends a signal to the TCM to release the overdrive and prevent the
transmission from shifting back into overdrive until the actual vehicle speed reaches the speed
set in the CCS memory.
On this model, if the coolant temperature falls below 55* C (131 F), the ECM sends a signal to the
TCM, preventing the transmission from up−shifting into overdrive.

Control of Lock−Up System

The TCM has programmed in its memory a lock−up clutch operation pattern for each driving
mode (Normal or Power). Based on this lock−up pattern, the TCM turns lock−up solenoid valve
on or off in accordance with the vehicle speed signals received from the vehicle speed sensor and
the throttle opening signals from the throttle position sensor.
Depending on whether lock−up solenoid valve is on or off, the lock−up relay valve performs
changeover of the fluid passages for the converter pressure acting on the torque converter clutch
to engage or disengage the lock−up clutch.
Mandatory Cancellation of Lock−Up System:
If any of the following conditions exist, the TCM turns off lock−up solenoid valve to disengage
the lock−up clutch.
(1) The brake light switch comes on (during braking).
(2) The IDL points of the throttle position sensor close (throttle valve fully closed.).
(3) The vehicle speed drops 4 km/h (2mph) or more below the set speed while the cruise control
system is operating.
(4) The coolant temperature falls below 70C (158F).
The purpose of (1) and (2) above is to prevent the engine from stalling if the rear wheels lock up.
The purpose of (3) is to cause the torque converter clutch to operate to obtain torque multiplica−
tion. The purpose of (4) is both to improve general driveability, and to speed up engine warm −up.
Also, while the lock−up system is in operation, the TCM will temporarily turn it off during up−
shift or down−shift in order to decrease shifting shock.

 

[kerrye]

Thanks. It's far more complicated and sophisticated than I imagined. I think the advice to turn off the OD when faced with a lot of climbing is the best advice.

 

[SiRaDuDe]

Christo,

To what tranny does that wripe up apply to?

I will assume to the a442f and the a343f?

Or to just one in specific?

 

[rove_mcanus]

Christo,

To what tranny does that wripe up apply to?

I will assume to the a442f and the a343f?

Or to just one in specific?

That is typical behavior of any vehicle, not just land cruisers.

The lock up clutch is a hydraulic/mechanical device. It is controlled electronically via a solenoid. A solenoid is a device that converts an electric signal into a mechanical action. In this case an electric signal opens a valve which allows hydraulic fluid to pass. This fluid pressure is what engages the lockup clutch. It is three systems operating together, not just one single mechanical or electrical system.