32RH and RPM fluctuations

[GA_Jeeper]

I'm looking for some advice on things to consider regarding an RPM fluctuation when going down the highway...The rig is a 2002 TJ 4.0 and 32RH automatic with about 167K miles on it. Recently it has had new plugs, fluids, trans fluid and filter. Shifts just fine though first second and third. TC seems to engage without any challenges. But when causing at a constant speed with light throttle I'll get a mild RPM up/down repeatedly, usually on some sort of incline mostly around 60-65 MPH Feels like repeated TC lockup/unlock because it is only a couple of hundred RPM if that. Figured I'll have to take it in to a transmission shop but thought I'd throw this out and hopefully gain some knowledge.

 

[Mitchrb1]

Is it making any noise? I believe mine had a similar issue years ago. It wasn't an issue with the 32RH transmission. it was my fan clutch going off and on constantly. once replaced I no longer had the issue. I had actually forgotten about this until I read your post.

 

[Jerry Bransford]

You're feeling your 32RH automatic transmission's torque converter locking and unlocking. When you reach cruising speed the torque converter locks to eliminate slippage. That allows the transmission to run cooler and at roughly 100-150 rpms lower when the torque converter is locked while cruising. But step on the gas a little and the PCM (computer) will unlock the torque converter which gives you slightly more rpms to accelerate at. Stop accelerating and the torque converter will lock back up again. To some it feels kinda like a 4th gear but it's not. Locking the torque converter also slightly improves the mpg since it eliminates slippage between the engine and transmission.

 

[JasterMereel42]

You're feeling your 32RH automatic transmission's torque converter locking and unlocking. When you reach cruising speed the torque converter locks to eliminate slippage. That allows the transmission to run cooler and at roughly 100-150 rpms lower when the torque converter is locked while cruising. But step on the gas a little and the PCM (computer) will unlock the torque converter which gives you slightly more rpms to accelerate at. Stop accelerating and the torque converter will lock back up again. To some it feels kinda like a 4th gear but it's not. Locking the torque converter also slightly improves the mpg since it eliminates slippage between the engine and transmission.

New to me TJ. Only 74k miles, but it sat in a garage for 3 years.

I'm driving it more and more and I think I'm feeling the slipping thing or the torque converter unlocking. I'll be doing city driving but at 45-50mph. I'll stomp on the gas to get around someone and the RPMs will jump up suddenly, as if it is in neutral. I let off the gas, step back on the gas, and it is engaged again. Is this normal behavior or is there something bigger wrong? I suspect the trans fluid is low because the gasket is leaking so I am planning on replacing the trans oil pan gasket this weekend.

 

[Jerry Bransford]

Check the ATF level after starting the engine and shifting to Neutral. Make sure it's all the way up to the hot full mark. It's better for it to be slightly overfilled than slightly underfilled. If it's low insert a small funnel into the dipstick tube and add enough ATF+4 (only!) to make it full or slightly overfilled.

The engine MUST be running and the transmission MUST be in Neutral while checking the ATF level.

 

[JasterMereel42]

Check the ATF level after starting the engine and shifting to Neutral. Make sure it's all the way up to the hot full mark. It's better for it to be slightly overfilled than slightly underfilled. If it's low insert a small funnel into the dipstick tube and add enough ATF+4 (only!) to make it full or slightly overfilled.

The engine MUST be running and the transmission MUST be in Neutral while checking the ATF level.

Its pretty much on the very bottom end of the OK section.

 

[Jerry Bransford]

Its pretty much on the very bottom end of the OK section.

Bring it all the way up to the hot full mark. Slightly over would be good

 

[JasterMereel42]

Bring it all the way up to the hot full mark. Slightly over would be good

I'll do that after I change out the fluid and replace the leaking gasket. I just hope that the trans oil pan is fine and not wavy.

 

[Vtx531]

Sounds like a vacuum leak to me.

 

[hear]

New to me TJ. Only 74k miles, but it sat in a garage for 3 years.

I'm driving it more and more and I think I'm feeling the slipping thing or the torque converter unlocking. I'll be doing city driving but at 45-50mph. I'll stomp on the gas to get around someone and the RPMs will jump up suddenly, as if it is in neutral. I let off the gas, step back on the gas, and it is engaged again. Is this normal behavior or is there something bigger wrong? I suspect the trans fluid is low because the gasket is leaking so I am planning on replacing the trans oil pan gasket this weekend.

First and foremost, get the fluid level correct. If it's still doing odd things, then the below may become relevant.

At 45mph I can't get mine to downshift, it will only unlock the torque converter. When you say the RPMs jump up, how high are we talking? You should film the jeep from a stop, showing us the tach so we can see the gear changes and know for certain if it's trying to downshift or just unlock.

Kicking down to 2nd uses the kick down band to hold the front drum. If it revs significantly on a kick down, I would be thinking about a band adjustment. Does it act at all funny when you go from 1st to 2nd? Maybe try it in Manual 1 and then shift to Manual 2 at higher rpm's? I would expect that if the band is slipping during kick down it would probably slip going into 2nd from 1st as well.

 

[JasterMereel42]

Sounds like a vacuum leak to me.

Other people have said the same thing. This was sitting in a garage untouched for 3 years. The first mechanic that took a look at it said the brake booster needed to be replaced. My friend drove it and it stalled out. The Jeep has stalled out on me twice in the last month and others have said vacuum leak. I am thinking about replacing the brake booster since I got one off of eBay.