huntertownsen

ok I hope im posting to the correct forum
I have a new to me 89 1 ton 7.4 4x4 p/u
I am on my third transmission, all with similar problems. I am not sure if its tranny or a shift down control problem
the first tranny started slipping shift 2-3 at about a week after I got it, I had to get home , I was pulling a tractor. I smoked it, np
so I rebuilt the tranny, It started slipping at about 2-3 shift 200 miles, figured I did something wrong pulled it apart , I could find nothing wrong , once again pulling a load. So I decided, I must have a bad casing (all seals looked perfect). tbh I didn't want to mess with it , I ran #s it was a 68
so I searched and found a core, he had a 2-3 shift slip when pulling a load uphill. It had a rebuild at about 20k back. that rebuild cost him 2500, when I pulled it apart 2-3 clutches were burnt but intact, he said it worked find w/o a load.
a lot of the parts looked new, whoever did it did a quality job.
I replaced the seals and clutches, and cleaned it of course.
so now its installed, I ran it for about 200 miles , no problems
I start pulling a load, it slipped on 3-2 kick down,
now when it starts im right on it and let off, and shifted down, only slipped for about 5 seconds. so im thinking bad shift down solenoid. I replaced, ran tranyy w/0 load, another 300 0r so miles , np. changed fluids and filter, I always do after break in
well today im driving no load , not on the pedal much , it slips, again. I let off , waited a few seconds . drove another 30 miles np, then just b4 I got home it did it again, once again let off, then its fine. but this time I stopped and ran it kind of hard on flat ground , it didn't want to seem to shift right from 1-2, I let off it shifted ok, did it again seemed ok.
I have rebult many trannys, 4l series th 350s c-6 etc, never had a problem
both trannys have had very similar issues, could it possibly be something to do with the shift down controls, or a clogged cooler line ??
i tested the 1st tranny after the failed rebuild and had proper line pressure, in forward and reverse gears. like i said both trannys having similar issues, no parts were interchanged between the 2
Im pulling my hair out , I can afford the down time , i make a living with this truck
thanks for any advice
rob

PBA

All TH400's have leaks between the case and center support and some more than others. This has been problem over the years when there is too much clearance caused from harmonics, and this creates wear and a lot of times when rebuilding these parts are switched from one case to another and the clearance can change slightly from one case to the next. Too much clearance and you can have 3rd gear clutch issues. On any TH400 rebuild or when you have the valve body off, add the TH200 low/reverse clutch housing seal cup plug. You will need two of them and install one on each side of the center support bolt. Industry part number is 54386A. "Always" add the support seals and this will fix all of the leaks at the center support. TransGo offers them in the 4L80E Shift kit for the above reasons. If you want to triple the 3rd gear capacity (excellent for towing) add the TransGo triple plate which comes in the 400-1-2 Performance Shift kits. I do not know if TransGo sells them anymore by themselves. Or you can make your own version of using both halves of the 3rd gear apply piston. Keep the apply hole in the separator plate on the smaller side when using both halves of the 3rd apply piston, as the firmness goes up quickly when you triple the 3rd apply area. If you do your own version of this, leave off the 2nd ring on the center support only, and "do not" take out the middle seal in the direct drum, as this will slow down the clutch release on the 3-2 downshift. Use the new Peek step cut sealing rings from the 4L80E on the center support and the front pump (GM started using them in 1998 & later units). They work very well and will not "knife edge" from higher pressure as easy as the cast iron rings did. Always use the Borg Warner Hi-Energy 4L80E clutches (GM started using them in 1996 & later units) in the 2nd and 3rd gear clutch packs, as they will out last any other clutch material out there. Once I started to add the center support seals back in the 1990's my 3rd gear problems went to just about zero. I hope this information will help some.

mrvedit

As always, thank you Dana for sharing your 25+ years of performance transmission rebuilding experience with us.

PBA

Try 36+ years....

mrvedit

I thought it was 30+, but when in doubt its better to say people are younger.
Congratulations on a long career!

I just turned 60 two weeks ago, 35 years in the computer software business.

huntertownsen

I have posted this question on every forum I could find that may have been of help. Not one response has made any sense. I have searched for hours on the web to no avail. You are the first person who has given me a explanation as to my quandary. I was ready to put a junkyard tranny in this truck, I will be using this truck for pulling my tractor on a daily basis, so a jy tranny was my last option. The truck is older, but I bought it for a specific reason, it will soon be a flat bed dump, It is going to be perfect for what I need. I have gone through every bit of this truck from front to rear to make it reliable, it runs like a top. I wont go into all the mickey mouse items I have found. For now I have put the truck to the side and am just finishing up a engine rebuild on my main truck. Tbh , I have been putting in 15 hour days for about a month now with no days off, im running on fumes. I need to re-read your information, and fully understand it, at this time I am unable to, I understand the answer , I just need to sit down and make sure I have the solution clear in my head. I may have a few more questions for u, if u don't mind. It will be a few days, since I don't do this professionally I want to have my books in front of me , I cant afford to make another mistake.

Once again I cannot thank you enough for solving this mystery for me. I hope in the future I can repay u somehow, Although I can turn wrenches better than your average guy, My specialty is home trouble shooting , I hope I may be of assistance to u in that aspect , Please if you have any questions about anything , I may be of help to u.

ty again
Rob