Another 4HP22 question

[p m]

Every time you thing you've seen it all, life surprises you.
Just drove my friend's 95 LWB. It has a few quirks, and this is one of them:
- while coasting in Drive, at speeds about 30 mph, no throttle input, it would downshift (engine speed would go from 1200 to 2000 rpm @ 30 mph), then upshift a few seconds later, then repeat the pattern.
- it does not happen while coasting with the shifter in the 3rd gear.

This truck had been known to have other bizarre transmission issues (like no drive at all unless the fluid was at perfect level).

Any ideas?

 

[LRDONE]

Just a shot in the dark. Could the torque converter & lockup be causing some funky stuff?

 

[p m]

Just a shot in the dark. Could the torque converter & lockup be causing some funky stuff?

They could. But whatever happens seem to be related to the 4th gear.

 

[LRDONE]

Isn't 4th gear overdrive and torque converter lockup? I could be wrong, I'm just starting to learn about these transmissions.

 

[LRDONE]

Gear Ratios of the 4HP22/4HP24 Transmissions​

1st	2nd	3rd	4th	R
2.478:1	1.48:1	1.00:1	0.728:1	2:086:1

I think it could possibly be going from 4th gear to lock up back to 4th gear when it should or shouldn't be. If you're in 3rd I don't think the computer is going to let the torque converter lock up. With the various inputs that influence that lock up, that's the direction I would start looking.

Late ZF4HP22 and ZF4HP24 Transmission Control Using the COMPUSHIFT Spo

Find out about the history of the Late ZF4HP22 and ZF4HP24 transmissions along with specifications, problems, ratios and how they can be controlled using a stand alone transmission controller.

hgmelectronics.com

** The link I added could be something to think about as well if it's a company still in business, I don't know. Aftermarket transmission controller. Make it do whatever you want.

 

[mbrummal]

Early trucks like this are purely mechanical -- they don't have a computer to control lockup or shifting.

Could the kick-down cable need adjustment? Or maybe a worn out/gummed up governor?

 

[waveridin1959]

I'd check the kickdown cable adjustment or see if it is binding.

 

[LRDONE]

Yeah, if it doesn't have solenoids then everything I thought is out the window lol.

 

[waveridin1959]

I've been have shifting issues for the past month and it is all being caused by the kickdown cable binding and not retracting.

 

[Flyfish]

Check to make sure the cable moves freely inside the sheathing and retracts easy from the spring tension on the valve body it attaches to inside the tranny. I’ve seen the cable start to fray and catch on the inside of the sheathing.

 

[p m]

Kickdown cable was my first suggestion - couldn't check it easily with broken remnants of an inop cruise control on the way. I tried to feel where the crimped ferrule was - and found it "uncrimped" and floating freely on the cable.

 

[StangGT5]

I will third the kick-down cable. If it moves freely, adjust it out and see if it gets any better. I had to replace one on a Disco I forever ago and afterwards it would downshift with any amount of throttle.

 

[discostew]

Isn't 4th gear overdrive and torque converter lockup? I could be wrong, I'm just starting to learn about these transmissions.

I think the way these apply the torque converter is 1/2 shift then lockup,2/3 shift then lockup, 3/4 shift then lockup.
They told us that was to maximize engine braking no matter what gear your in.

 

[discostew]

Kickdown cable was my first suggestion - couldn't check it easily with broken remnants of an inop cruise control on the way. I tried to feel where the crimped ferrule was - and found it "uncrimped" and floating freely on the cable.

I agree. I like to get that last shift to happen at 52 mph under light load.
You might change the cable to make up for pressure changes inside the trans. Kind of compensating for wear.
In my younger days I did transmissions for GM till I’m sure I would have puked if I did another. I learned that pressure leaking off in a clutch will lower line pressure in general while that clutch is applied. So when line pressure is low the valves in the valve body will not operate properly and shift points change. Springs inside the valve body depend on the line pressure to be at spec. Also governed pressure might not be effected by a leaking clutch and mess up any shift dependent on line pressure overcoming governed pressure to move a valve.
We had a problem with some of the older transmissions having no drive after first cold start. It would come if you waited and be fine all day. Till the next overnight sit. The fix for that was a valve body. It was because the torque converter would drain down due to a leaking check valve

 

[p m]

I guess I'll have a go at it come Friday. Hope I'll fix the misfire my own 3.9 has by then.

 

[luckyjoe]

The 4HP22 shifts: 1, 2, 3, 4, TC-lockup. In a stock LR (standard size tires) the lockup should occur ~52mph. If you drive on a flat, straight road at 50mph and increase/decrease above/below 52mph, you should feel it lock/unlock consistently.

 

[LRDONE]

The 4HP22 shifts: 1, 2, 3, 4, TC-lockup. In a stock LR (standard size tires) the lockup should occur ~52mph. If you drive on a flat, straight road at 50mph and increase/decrease above/below 52mph, you should feel it lock/unlock consistently.

This is the reason I speed in a 45mph zone. lol about 50 mph on the dot. Coasting at 49/50mph my truck will unlock/lock repeatedly. Either way, it's about a 5-600rpm change.

 

[p m]

The 4HP22 shifts: 1, 2, 3, 4, TC-lockup. In a stock LR (standard size tires) the lockup should occur ~52mph. If you drive on a flat, straight road at 50mph and increase/decrease above/below 52mph, you should feel it lock/unlock consistently.

That's almost exactly what I noticed my truck doing - with caveats of 1.4:1 high range and 31.5" tires.
Tweaked the kickdown cable a little bit today, seemed to go away where it was noticeable.

 

[luckyjoe]

This is the reason I speed in a 45mph zone. lol about 50 mph on the dot. Coasting at 49/50mph my truck will unlock/lock repeatedly. Either way, it's about a 5-600rpm change.

Also the reason I went with stock tire size on my '95 LWB - I have a 10-mile, 50mph posted speed limit on my way to work.

 

[p m]

Every time you thing you've seen it all, life surprises you.
Just drove my friend's 95 LWB. It has a few quirks, and this is one of them:
- while coasting in Drive, at speeds about 30 mph, no throttle input, it would downshift (engine speed would go from 1200 to 2000 rpm @ 30 mph), then upshift a few seconds later, then repeat the pattern.
- it does not happen while coasting with the shifter in the 3rd gear.

This truck had been known to have other bizarre transmission issues (like no drive at all unless the fluid was at perfect level).

Any ideas?

I was just about to post that exact question, since that my friend's 95 LWB is now my 95 LWB, did a search and came across my own post from almost a year ago.
With a correction - it shoots from 1k to 1500 rpm @ 30mph, and also at 20 mph. Other than that, the transmission runs well.

Add a blurb: This behavior is very pronounced when the kickdown cable is adjusted nearly ideally. When I adjust it so it downshifts at much less of a throttle and keeps lower gears longer, this behavior is barely noticeable.