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2001 Trooper Trans slipping after rebuild

1K views 3 replies 2 participants last post by  Buster28 
#1 ·
My son and I just finished our first ever transmission rebuild on his 2001 Trooper, and while it went really well and we are quite confident that we did things correctly, we still have some slipping/shudder in 1st gear under load (hill or quick accel), so the band adjustment may not be quite right. I'll summarize as much as possible, but here's the backstory that will explain how we got here:
* He purchased the Trooper in the fall of 2019, and it drove well for a year as a daily driver locally.
* He'd purchased a Casita camper last summer (2500 lbs), and he towed it without any problems on one 200 mile trip last August.
* We went to FL panhandle together last Oct, and he towed the camper while my wife and I took our Class C RV.
* As we arrived at the site in FL he lost 1st gear drive. Next morning it could barely get moving, so we limped it to Miramar Beach and I towed his camper the rest of the trip.
* We drained and changed the fluid, and I researched and discovered the Winter Mode and band adjustment info, but we were only there for 1 night.
* Next day we found that Winter mode was sufficient to get us to Panama City Beach, where we were able to drop the pan, change the filter, and adjust the band. That didn't fix it perfectly, but being gentle with it he was able to get home to TN. (What a trip! But we still had fun in between!)
* After copious research we dove into a rebuild of the trans in March, and finished it up in early April. We took our time to do a thorough and careful job, and we were excited when it drove well after reassembly on a couple local test drives. We were pushing to get it done before a local camping trip, so he was able to tow his camper again... until it wouldn't! Again. :(
* It towed fine the 3 miles to the expressway, and when we came to stop at the first off ramp (almost exactly 20 miles from home), there was zero 1st gear. I had my strap so I towed him off the ramp and we assessed things and found that Winter mode still worked, so we limped it home and I ended up towing his camper for our trip.
* We have redone the band adjustment again, and we carefully counted rotations to see how much different it would be. It ended up adjusting over 2 full turns tighter the last time. But... it still slips/shudders a little on an uphill grade from a stop, or when punched from a stop. It's still not right.

We've seen disparity in the band adjustment instructions different places, so we've done them a little different each time. In FL I think we did 39 or 40 in-lb tight and 4-1/2 turns back. During the rebuild the manual and most advice we saw said it should be 5 turns back, so that's what we did (which was probably too loose after it warmed up). The last time, we only went 4 turns back. But it's still slipping. We need advice from someone who really knows these 4L30E's: How tight can we adjust this freaking band? Is it possible that we burned up the band in a 20 mile (mostly 4th gear) trip? What else could cause the slipping if the band is adjusted correctly? If we adjust it too tight, how will we know (short of burning it up)?

I know it'll be needed to know, so here's the details of our rebuild: Full rebuild kit with all new clutches, steels, band, gaskets, seals, bushings, etc. The works; Put in Superior K4L30E kit; Sonnax Thrust Washer Kit (54701-03K); Replaced the low band drum (old one was scored as the center of the band had lost it's friction material); Rebuilt torque converter; added an additional aux trans cooler in front of radiator and in series with factory cooler (flushed stock cooler!); new 1-2/3-4, 2-3 and TCC solenoids. New connector housings for both connectors. Cleaned and reconditioned the PRNDL switch. Due to cost and availability we did NOT replace the Bosch force motor or the band apply solenoid. Fluid fill was ACDelco 10-9240 Type III (H).

The last thing I did, after reading the suggestion somewhere here, was to disconnect the two electrical connectors and try it using only the mechanical manual shift. We only went up our fairly steep driveway and a hundred yards on the street, but it had no noticeable effect. Same slipping. We are ready to drop the pan again and tighten the band 1/4 to 1/2 turn and see if that fixes it, but if anyone has any better ideas or tests we can run, as Ross Perot would say: "I'm all ears!" (If you read all the way to this point, Thank-you!!)
 
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#2 ·
Not much magic involved in adjusting the Brake Band. However, a hydraulic leak involving the Brake Band Servo Piston can cause the Brake Band to burn up quickly.

To burn the Brake Band in 20 miles it would have to be partially applied in 3rd and 4th gear. To release the Brake Band for 3rd and 4th gear operation, 3rd clutch apply fluid is applied to the reverse side of the servo piston without releasing the apply side fluid, if the pressure on the reverse side is less than the apply side the piston will move to the apply position and apply the band. A leak involving the servo piston or a leak in the 3rd clutch apply fluid can cause the Brake Band to drag. The issue seems related to the kit you installed to "fix" this problem.
 
#3 ·
Thank you, Buster, for your reply. I was hoping you could provide some assistance after having read quite a few of your previous posts and coming away impressed with your expertise on these transmissions. If you would indulge me, I have a few follow up questions:

* Is there a conclusive way to test the Band Control solenoid? We would gladly replace if we knew it was at fault, but other than the resistance -- which I did check -- I don't see a way to validate that. If it was failed/stuck/etc what would happen?
* Is there a conclusive way to test for the leakage you mentioned. What you said makes sense, but I can't think of a way to know if that's happening.
* The Superior kit seems to have almost universal praise from the info I was able to research. I could remove the accumulator mods before adjusting the band next time if you really think that's a likely issue.
* I've read that the 1-2 accumulator pin is a failure point for leakage, but that showed virtually no wear and was in great shape. I know Sonnax made a retrofit for that, but it was more machining than we are capable of.
* Was my 'bypassed electronics' test worthwhile, or did that really not indicate anything useful (just curious)?
* Do you think the band is still too loose? Was 5 turns back on the band adjustment too much. My theory is that it was, and after warming up and expanding slightly, it wouldn't grab at all. But I'm admittedly a noob, and I'm guessing. ;)

Anyways, thanks in advance to Buster or anyone else who has experience with this and is willing to enlighten me!
 
#4 ·
The Brake Band solenoid is controlled by a 32Hz Pulse Width Modulated (PWM) signal. Equipment to bench test a PWM device costs a lot more than a new solenoid so buying a new one is the best option.

The Brake Band solenoid does not apply the Brake Band, it controls the rate that the servo piston operates to control the mechanical linkage that applies the Brake Band. It is basically a flow control device, the fluid port is normally open and by controlling the duty cycle of the PWM signal the hydraulic pressure acting on the apply side of Brake Band servo piston can be controlled. The Brake Band is a friction clutch and the reaction drum is the "disk" The Brake Band solenoid modulates the engagement of the clutch.

When you adjust the Brake Band mechanical linkage using the procedure and tighten the lock nut it should not need any further adjustment for at least 25K miles and usually considerably more. The FSM procedure is "Adjust the brake band by tightening the servo adjusting screw to 4.5 N·m torque. Be certain the lock nut is loose, then back-off the screw five turns exactly. Hold piston sleeve with wrench and tighten lock nut to 18.5 N·m torque. Be certain the adjusting screw does not turn."

I am unsure what your problem is but it is likely the Brake Band is dragging in 3rd or 4th gear causing the friction material to be burned away so that the Brake Band slips. If the reaction drum is not held stationary there is no Drive or Manual 1st gear, it will feel like your in Neutral.

This link addresses Brake Band failures starting on page 173:
https://atracom.blob.core.windows.net/m ... import.pdf
 
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