TH 400 forward gears give out

[wallew]

OK, Ive done a lot searching and reading on the TH400 and what happens to it with age.

Mine is an excellent example.

My b1985 M1009 Blazer has a little over 66k miles on it. I bought it with 58k miles on it about four years ago.

About the only thing I've had to do is replace the tires and change the oil and lubricate the chassis. EVERYTHING SEEMED GREAT.

But I knew, deep down that the tranny needed to be rebuilt. I could feel it. Then as I was taking it out to our static display at the end of August it started to whine a little bit.

Well, this started me on the road that will end with me rebuilding the tranny.

What I believe happened was that because mine had not had any service for at least four years - probably at LOT longer than that, the tranny fluid was very, very dirty.

By changing the fluid a couple of times I think I actually removed the 'friction the current clutch pack needed to work properly.

By flushing this all out, I now have a fairly clean tranny. And no forward gears. I still have revers and I'd bet if I look I will see not much wear on that portion of the transmission.

So after reading more than a dozen accounts that basically are the same as mine, I can tell you this.

If your tranny starts making noise and a fluid change fixes the problem, chances are high that it's a temporary fix. Invariably the fluid change will help for a while, generally a few days to a few weeks. But once it sits for a while, then the new filter 'cleans' any and all dirt and boom, you have no forward gears.

So, if you start 'messing' with your tranny and you think you are helping it, you may not be.

But a fluid change may be more of a problem that it fixes.

So, I have a spare TH400.

My next move will be to buy the DVD and the rebuild manual. And the parts kit.

I will not only keep you informed but will take pix as I go.

 

[jpekarek]

The worst thing you can do to a transmission is NOT use it. The rubber parts and the friction surfaces dry out and deteriorate. The T-400 is one of the very strongest transmissions avaliable, but parts do dry up and rot like anything else. All automatics would be the same.

I have a T-400 in my '31 ford. It was professionally rebuilt in 2007, then driven about 200-300 miles. It was then stored in my shop and not run at all for about 3 years. When I got it out to drive it last June, it would not shift properly and developed a huge puddle of fluid under the front seal after I shut it down. I had to remove it and rebuild it again.

Other than that, I would still use the T-400 for any and all heavy duty GM applications. There is no better tranny for GMs.

 

[mcmullag]

keep your seals wet with fluids

Interesting stuff fellas. I make sure I at least drive my deuce about 10 miles every two weeks for similar reasons, to keep all the rubber seals in the drivetrain, etc. more supple and pliable for less leakage and better sealing.
**************************** The GM THM 400 was used by Rolls Royce in their cars from 1965 to 1992, it's a smooth shifting, strong transmission.

 

[rickf]

I can tell you that if the fluid is dirty then the trans is toast. An automatic transmission is a sealed unit so there is no way for dirt or contaminates to get in there, short of running it underwater and that will end the same way. If the fluid is dark it is from burnt clutch material. There is no reversing that situation. You can flush it all you want but the burnt clutches are still burnt. Whenever I rebuild a transmission I ALWAYS put a Trans-Go shift kit in it. The kit has several stages available and I usually go for a towing stage. That will give a little more pump pressure and volume for the shift without making it too harsh. It will also prevent the clutches from slipping as much. ALWAYS replace the torque converter! You will never get all of the crap out of the old one.

Rick

 

[OL AG '89]

o.k. guys here's my approach based on common sense. These vehicles are 25 years olds. FACT
If they were owned by a national guard unit, which I believe most of them were, they were once a month, during drill and then they sat up for the rest of the month. FACT
When they were turned over to a govt. agency they were also driven on occassion, but not as daily drivers.
The maintenance on these vehicles was performed by competent soldiers on the weekends and by competent soldiers when they got an "annual" service by the full timers at the units.FACT
The vehicles spent more time sitting than being driven.

SO common sense says if you buy one these vehicles, in great condition, it has had a "hard" life, not because it was abused, but because it was rarely used. I purchased a M1009 last spring in great condition, but I know that I will enventually have to rebuil or replace the transmission. I could do it now or just drive it until it breaks...... my choice.
I really enjoy working on it an appreiate the fact that the military has the MOST comprehensive repair manuals..... No deling with the Chilton "assemble in reverse" statements....
I try to do the PMCS everytime I drive the vehicle, at least once a week. I have learned many of the quirks of the vehicle, that I can then keep an eye on and repair as needed.
I wouldn't trade my M1009 for anything.

 

[rnd-motorsports]

Wan't to add a little something here that alot of peaple overlook I deal with it becouse I own a Motorsports shop and deal with a lot of older motors and trans. oils for one do not have the additives needed in the older engines like flat tappet cams. Now days everything is roller so the oils do not need alot of the additives needed for the older engines and the older stuff still needs them the average person with the 70's or 80's engine do not think about the oil and what its not doing anymore for there older engines the same is true with trans fliud the grit if you will is being done away with. Try finding type f or even dextron you find dextrol 3 or simular less additives and more failers in the older stuff with the modern lubricants! when you guys change the trans fluid put in the correct oil dextron not the dextron 3 if you can get type f bye all means get it. Its like the bm trick shift perfomance oil the dif is its a little more grity rub some in your fingers you will feel the dif. Check it out and your older stuff will live longer

 

[wallew]

Thanks for the 'type f' tip. I CAN get it. Right around the corner. It was cheap. I'll go back and buy several.

If I'm going to run these trucks, I might as well get the correct fluid in them.

I had to have the M1028A2 tranny rebuilt last year. I don't remember what fluid they put in it. Could I drain it and replace it with 'type f'? Or should I leave it with what I believe to be Dex III? I've put about 5k miles on it since the rebuild. I drive it fairly often. But I am retired and have two M1009's I also drive. But there are times I'll hop in and run a freeway route I have. Takes about an hour. Allows me time to blow the cobwebs out and get each truck out several times a month. Plus the wife has errands and I have other things to keep me busy and in my trucks.

 

[Crash_AF]

Type F transmission fluid is for FORD vehicles (Hence Type F for FORD), it is not designed or formulated to work with GM (DEXRON) vehicles. The type F fluid does not have the friction modifiers that the Dexron fluid does because the friction materials used in the Ford transmissions was paper based and the stuff used in the GM applications was compound carbon materials.

While I don't trust this new 'one size fits all' stuff in my 66 Mustang, I do trust it in my 1008/9 GM stuff.

Later,
Joe

 

[baddy3]

My 1009 has 46k miles, I changed the transmission oil with Valvoline dextron III, replaced the filter at the same time. Drained oil was clean and no metal particles in the pan. Now, I might imagining it, but it’s developed a slight whine, especially under light throttle. the whine gets quieter, almost unnoticeable once the vehicle warms up. all shifts are ok and it pulls strong in all gears. I had the similar gear whine in my LR Discovery, but that was considered normal for that vehicle. Should I start worrying and prepare for the rebuild?

 

[MuleMac01]

i got my blazer with 64,000 miles on it frist thing i did was change all the fuilds


tranny was fine changed the fuild, cleaned the pan and the magnet on the pan nothing has happend sence then . it shifts smooth .. i also run Lucas Oil Automatic Transmission Fluid Conditioner in it. Lucas Oil Automatic Transmission Fluid Conditioner : Lucas Oil

 

[rnd-motorsports]

Yes crash_af type f trans fluid is for ford it is a little dif than Dex but if you will check it is about the same as what B&M trickshift performance trans fluid is and a lot cheaper. I run it in everything I have and build Mud trucks , drag cars anything with an older trans You don,t have to beleive me it makes no dif to me just passing on some info! anybody that whats to check it out ask an older transmission builder or somebody that does performance transmissions and when you buy a shift improver kit for a trans the older stuff It always recomends if you read the directions a performance trans fluid like B&M trick shift ask any true performance shop about the oils today they will all tell you the same thing thats why you here about lucas and other proprietary friction reduing additives for race and older engines . Not telling anybody they have to use it just passing on some info. wallew if you just rebuilt the trans the change is up to you, Myself as stated run type f in everything I own and build its your call! its just like todays fuels not having the same additives they had in the past now you have to run oils or additives for the older trucks or cars or change valve guides becouse of the lack of leaded gas no lubricating propertys for the older guides so you need bronze guids to make them last but thats another thing altogether just like todays deisel and lack of lubricating propertys but hay its just oil or fuel no big deal till you have to pay to have it fixed