I got a 1998 wrangler tj 2.5. The 30RH transmission is hesitant to upshift and i usually have to release the throttle at high revs which allows it to up shift. It shifts up fine when going downhill. The transmission slips and randomly gears down while at cruising speed. I also noticed the transmission most of the time stops slipping only while at full throttle accelerating uphill. The transmission was also recently rebuilt to try and fix the problem but its still there. Any possible causes?
30RH transmission slipping after rebuild
- Thread starter Maiik767
- Start date
The easiest first thing to look at is the fluid level. Get things warm & on level ground, then put it in N and check the level with the engine running. A little over the line is better than under the line.
I'm 99.9999% sure ATF+4 is required, but I've never done any work on the 30RH so I'll defer to @Jerry Bransford for the specific fluid recommendation.
I'm 99.9999% sure ATF+4 is required, but I've never done any work on the 30RH so I'll defer to @Jerry Bransford for the specific fluid recommendation.
X2, a slipping automatic transmission normally means its ATF level is low. Start the engine and shift the transmission to Neutral then check its ATF level. The engine MUST be running and the transmission MUST be in Neutral while checking its ATF level. If it's not completely up to the full mark insert a small funnel and add enough ATF+4 until it measures full. And as above, it's better for an automatic transmission to be slightly overfilled than slightly underfilled. If the bottle of ATF doesn't say ATF+4 in big letters on the front label it's the wrong stuff.
Hey Jerry, just for my own knowledge, again not familiar with the 30, doesn’t the throttle valve affect line pressure and in theory could cause a slip by not allowing enough pressure to secure the bands or clutches completely? Or is that not an issue on these transmissions?
I believe they are virtually identical save some smaller/weaker parts in the drivetrain. Given that the problems started on the heels of a rebuild I would guess either a line pressure problem or too much clearance on the clutches. Seems like they would've checked that at assembly since it's easy to do, whereas the pressure check is harder. What I don't understand, even after having rebuilt a couple of these, is how an overhaul can affect the line pressure even if you don't touch the pressure screw on the valve body. But it definitely seems like it does.
You sound like you’ve never seen expert screwing up. At this stage of life, I would not be shocked if I opened it up and found a Twinkie stuffed in the valve body. I think you’re barking up the right tree if his fluid level is good. It would have to be bleeding off inside. The next question is all gears or just one? I’ve seen people think that this transmission will work fine only missing one of the clutch plates
In regard to your wondering about the pressure changing on rebuild, you think it’s attributable to just variations in parts tolerances? That’s about all I can come up with. Provided everything else is on par.
You sound like you’ve never seen expert screwing up. At this stage of life, I would not be shocked if I opened it up and found a Twinkie stuffed in the valve body. I think you’re barking up the right tree if his fluid level is good. It would have to be bleeding off inside. The next question is all gears or just one? I’ve seen people think that this transmission will work fine only missing one of the clutch plates
In regard to your wondering about the pressure changing on rebuild, you think it’s attributable to just variations in parts tolerances? That’s about all I can come up with. Provided everything else is on par.
yeah, depending on the slip it could just be a band adjustment.
on the pressure changing after a rebuild, I really don't know. But mine definitely shifts differently after the rebuild, and I didn't do a pressure test at any point along the way, but I absolutely want do understand how to do it, and then how to use the data to correct any issues.
You’re supposed to adjust those after rebuild?! Crap
That’s the real challenge. Having to start off with, was it built right in the first place, or are we just diagnosing a simple part failure.
That’s me. I can’t let questions lay. I need answers. I’ve played with pressure testing when viable. Sometimes the ports are inside the trans and customers won’t pay the additional diag time. I hate my industry just checks fluid and then just throws a trans in it. I like to sleep well at night.
I just had an idea! Have a get together and compare what we’ve learned about trannys! Wait, that doesn’t sound right. Scratch that idea.
Check your ATF level as described above before worrying about anything else like that.
I totally agree. I was was making a joke to hear about having to adjust the bands when the trans was just built and should have been adjusted then.
Good, next time be sure to let us know you're kidding with our vast assortment of avatars.
etc. 
Good, next time be sure to let us know you're kidding with our vast assortment of avatars.
Vast! Ha! Wise guy!
Will do Jerry
Thanks, turns out i was checking the fluid level wrong all the time. It was basically empty when i checked while the engine was running and in neutral. Filled it up and the problem was fixed.
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