Improving Transmission Shifting (2 Viewers)

[Tools R Us]

IMHO the auto trans is tuned more on the smooth shift side than I prefer. As lift, weight, larger tires, etc, have been added, it has moved more towards a slip shift end of performance. So, did a bunch of reading, talked to a trans tech buddy and have tried a few tweaks with good results. Wasn’t comfortable posting until I had some trail days on it, over the holidays ran 7 days and 287 trail miles and very happy with the improvement.

The disclaimer: I’m not a trans expert, so try at your own risk. I have only researched the A343F, this probably wont work on the earlier transmissions?

System line pressure has a direct effect on the holding force of the clutches and brakes. Lower line pressure makes for smoother shifts by allowing more slip, more slip increases wear and running temps. Higher pressure makes for firmer shifts, less slip, wear and IMHO better trail feel/response.

There are two relatively easy adjustments that change the line pressure, first the primary regulator valve. Its job is to regulate the main pump output. It is in the lower valve body, so requires removing the pan.

 

[Tools R Us]

Mine was set to the middle setting, moved it to the highest position. Adjusting is easy, using a screwdriver in the slot, push in and turn to the desired setting. The retainer pin just slips into the slot in the valve body, so hold it in place when you push the valve in.

Before and after adjustment pictures.

 

[Tools R Us]

Next is the transmission throttle cable, often called the kick down cable. On older type transmissions it played a roll in shift timing, on the A343F shift timing is controlled by the ECU. Its purpose is to increase system pressure as more throttle/engine torque is delivered. When adjusted tighter shifts are firmer, when looser shifts are smoother.

The first step is to confirm proper throttle cable adjustment. Remove floor mats, gummy bears and any other debris from under the throttle pedal. Under the hood loosen the adjustment nuts on the throttle cable. Have a helper hold the throttle pedal to the floor, pull on the cable housing (the larger black part) hard enough to fully open the throttle plate, turn the outer nut (on the cable housing side) until it touches the bracket, then tighten the other nut (on the cable/linkage side). The goal is to have the throttle butterfly fully open when the pedal hits the stop. If adjusted too tight the cable will stretch/fail.

Now adjust the transmission cable tighter, finding where it works best for your setup and preference takes experimenting. I first had it tighter, almost pushing the boot off, worked well on the road. When in low range, on dirt, would get brief wheel spin when shifting 1st to 2nd, not the best for smooth wheeling? Moved the adjustment several times until I found the happy spot for my setup/use.

It’s not a modified valve body or shift kit, but made a noticeable difference, especially on the trail. Feels more hooked up, solid, better climbing and compression braking over rocks, etc. The 2nd gearshift is still very firm in low range, but I run 2nd start when in low, except when on obstacles that require 1st gear, so not an issue for me. IMHO for the cost was some RTV sealer for the pan install, ATF to refill the trans and time, it’s a good improvement.

This is where the adjustment on my trans cable ended up.

 

[Michael Hanson]

Is this the same on the 1991 fj80? MIke

 

[tblume]

and on the '93?


subscribed for the eventual "bus trans" write up.

 

[Tools R Us]

Is this the same on the 1991 fj80? MIke

Nope, the A343F trans is only in the '95-'97 rigs. I don't have trans repair documentation on the earlier rigs, but IIRC the '91-'92 trans are mechanical/governor controlled, so would be different.

 

[Eicca]

If there is a valve-style trick like mentioned above for the A440F I would love ever so much to know

 

[NKP Garage]

Very good information. I'll have to try this out.

 

[OGBeno]

Very interesting Kevin.

Might have some fun with this....

 

[Cattledog]

Thanks for the great tip! When I drain the trans next I will do this mod.

Thanks!

 

[ShawnTRD]

Keep us updated.. Do you have a tranny temp gauge? Would like to know if it's running cooler.

 

[sledge916]

Great job Kevin, I am going to give this a try

Sethro

 

[UCBerzerkeley]

possible downsides?

 

[jibber]

possible downsides?

x2,

'95 DD ?

 

[azrider]

I remember hearing over the radio on one of our trail runs, you mentioning something about testing the tranny. Now I know.

 

[spdwaver]

I am also interested in knowing how this will work/if this will work on the A442F transmission.

 

[medtro]

and on the '93?


subscribed for the eventual "bus trans" write up.

Line pressure adjustment for A442F is not as easy as the A343F. For A442F, line pressure is changed according to the number of the adjusting rings installed on the primary regulator valve assembly.

 

[Tools R Us]

possible downsides?

Yep, it shifts more firmly, some prefer luxury smooth shifts.

x2,

'95 DD ?

Mine is a DD.

 

[Tools R Us]

Keep us updated.. Do you have a tranny temp gauge? Would like to know if it's running cooler.

I don't have a gauge, haven't seen the need. Have carried an IR thermometer on several runs, taken lots measurements and never seen anything to worry about, even in very hot ambient temps. In my experience the stock US cooler works great, so don't see the point of a gauge?

On one side, pumping the fluid at a higher pressure will slightly warm it. On the other, less clutch/brake slip will make for cooler running. If I had to guess, it would probably run slightly cooler on an average, but probably not by much. It would greatly depend on the conditions, so would be hard to tell? When lightly loaded, normal driving it may run very slightly warmer due to higher pressure. When flogged hard would probably run slightly cooler due to less clutch/brake slip.

 

[dnp]

I need to try this. My transmission is already in 3rd by the time I reach 20 mph, and MAN does it "slide" into gear. I'm going to try your suggestions in hopes that it firms up the shifts. It drives me crazy the way it shifts right now. In fact, I usually s*** it manually................does anyone make a shift kit for the 343?