Servicing GM THM400: Seal?

tom p. · 08-23-07, 08:14

The subject transmission is a 4T 60E. My question is about this component. I think the dealer calls it a "seal". The parts guy and the technician have told me to ignore it and don't try to change it. They suggest it's extremely difficult to remove it and highly likely that you'll crack the new one when installing it. In previous years I've heeded their warnings. Now, I get my new kit and see the design has changed and don't know if I need to be concerned about this plastic seal. Anybody have experience with this?

Thanks.

Setec Astronomy · 08-23-07, 09:08

Yeah, boy does that design suck. I understand why they told you to not try to remove the seal, I had one stuck that I just could not get out, I would pull on it with vise grips and just break off small pieces of metal. I finally had to get a screwdriver up behind it and pry it out, scoring some of the bore.

So if I understand your question, you're saying that the old one was a rubberized metal part while the new one seems to be molded plastic? I believe I bought a newer kit for my '90 that had the newer seal, but I traded it before I changed the filter again.

I threw out my kit, so I can't look at the seal. IMO and working from memory on these parts, I think they went to the plastic so it wouldn't weld itself in there over time like the rubber ones. In any case, it isn't much of a "seal"; I'm not sure why they didn't use a straight bore with an o-ring instead of that crazy tapered seal.

Hope that helped.

tom p. · 08-23-07, 09:49

Quote:

Originally Posted by Setec Astronomy

So if I understand your question, you're saying that the old one was a rubberized metal part while the new one seems to be molded plastic? I believe I bought a newer kit for my '90 that had the newer seal, but I traded it before I changed the filter again.

Thanks, I really don't recall what the earlier seals looked like. I change the fluid annually, filter + fluid every other year.

Based upon your comments, I'm thinkin' I'd better not try to remove it and re-install the new seal. (IIRC, they all appear to be a hard plastic with a thin wall. Part of my concern is whether the change in design of the filter necessitates the use of this new seal

)

Setec Astronomy · 08-23-07, 10:02

Wow, that's a wicked change regimen. I think I did my '90 at 25K with Mobil 1 fluid and then went till 100K or more before I changed it again. I only got it up to about 125K in 16 years. As I said, they used to be rubber coated metal. Does your plastic one seem to have any metal in it?

Do you always use the AC/Delco? I changed the fluid in a family member's '88 a couple times too, and when they were newer, I used the "dealer" parts, but at one point I used some $10 off-brand filter kits (with Fel-Pro gasket) that a local parts store recommended, and developed a hard/delayed 1-2 shift in my '90, which only happened when the trans was hot, which was weird. I had bought a Purolator kit (of course Purolator doesn't make their own stuff anymore, it had some other name on the actual filter) for a lot more which I wound up never putting in, and I think it had the plastic seal.

I feel your pain, you want to trust the guys (at the dealer) who do this every day, but of course, with the level of factory training so minimal, they could be doing it WRONG every day. I still think you're changing way too often. What year is the car and how many miles do you put on it a year? I can't see changing more often than every 25K unless you are burning the fluid.

tom p. · 08-23-07, 10:18

Quote:

Originally Posted by Setec Astronomy

Wow, that's a wicked change regimen. I think I did my '90 at 25K with Mobil 1 fluid and then went till 100K or more before I changed it again. I only got it up to about 125K in 16 years. As I said, they used to be rubber coated metal. Does your plastic one seem to have any metal in it?

Do you always use the AC/Delco? I changed the fluid in a family member's '88 a couple times too, and when they were newer, I used the "dealer" parts, but at one point I used some $10 off-brand filter kits (with Fel-Pro gasket) that a local parts store recommended, and developed a hard/delayed 1-2 shift in my '90, which only happened when the trans was hot, which was weird. I had bought a Purolator kit (of course Purolator doesn't make their own stuff anymore, it had some other name on the actual filter) for a lot more which I wound up never putting in, and I think it had the plastic seal.

On semi-critical applications, I typically get the OE parts. I never have issues.

I feel your pain, you want to trust the guys (at the dealer) who do this every day, but of course, with the level of factory training so minimal, they could be doing it WRONG every day. I still think you're changing way too often. What year is the car and how many miles do you put on it a year? I can't see changing more often than every 25K unless you are burning the fluid.

<< AIO + #845

it's the 1995 Buick, rapidly approaching 160k, gearbox/engine never apart. I change the fluid annualy 'cause it's definitely showing strong discoloration (no burnt odor, however) after a year. IMO, it's super-cheap insurance. I paid less than $13 for the fluid yesterday. Filter kit was $28. Transmission works flawlessly. Don't know how much life is left in it. I know it'll be the end of the car when it barfs. There's no way I'd repair it.

We've had other H body cars...they've been super-durable apart from the transmission which failed around 125k miles.

I'm told I drive the car "hard"

. It's used almost exclusively for local trips that rarely exceed 40mph. Some trips are very short. There's a lot of stop 'n' go traffic - - that seems to take its toll on the trans fluid. Believe me, if the fluid wasn't so dis-colored, I woulnd't bother.

Setec Astronomy · 08-23-07, 10:33

Tom, you're a very reasonable man! I just get tired of crawling under the car...although over my lifetime I have gotten much better at getting the trans fluid in the drain pan and not in a puddle that I'm lying in

tom p. · 08-23-07, 11:24

Believe me, I don't look forward to doing it. The only job I dis-like more is CV joints.

I bought a trans pan drain plug kit last year. I may attempt to install it now.

tom p. · 09-04-07, 08:38

(The trans is really a 4T 60E, not THM400 as originally stated)

Next issue:

I'm still working on the trans fluid change/topping off routine on the old Buick I cannot get the fluid up to what I believe is the approriate operating range which I think is 70C - 80C. I've been able to get it up to 70C in previous years.

I was out yesterday and took a 100 mile round trip and air temp was around 80F. I got home and checked the fluid temp figuring I'd be able to finalize my topping off! No such luck

fluid temp was reading only 40C after a long drive on the highway. I couldn't believe my eyes.

Do you think these cars have a thermostat in the transmission cooler? I can't envision what else might be going on. Have you ever seen a temperature referenced when checking the fluid level? The books just say 'drive for 15 miles and you're all set'.

The Benzes give two reference points on their dipstick tool: 25C and 80C. It's no big deal to get those units up to 80C and top off.

Somebody else has suggested putting in 6.5 quarts and forgetting about it. I've already put in 6 cuz that's all I purchased. I'm not even to the bottom of the cross-hatched area yet.

Thanks for any clues.

Setec Astronomy · 09-04-07, 08:56

Hmmm...I always just put in the 6, IIRC, but I'm sure I checked that it was near the proper level. Again, IIRC, unless I'm thinking of my much older GM, there are a couple of dimples further down the dipstick which represent the cold fluid level.

tom p. · 09-04-07, 09:23

"cold" would be 70F or thereabout?? Yeah, I think there are two holes thru the very bottom end of the dipstick. I'll double-check that.

itb76 · 09-04-07, 10:49

Sorry to go off topic, but I had to say I've never seen a 12 year old Buick sedan that looks that good. Just goes to show what a little TLC will do.

tom p. · 09-04-07, 04:28

Quote:

Originally Posted by itb76

Sorry to go off topic, but I had to say I've never seen a 12 year old Buick sedan that looks that good. Just goes to show what a little TLC will do.

Thanks for the compliment. I've always been taught to take care of the things you have or lose them.

OTOH, I'm not sure why I spend the time I do on it. It's certainly nothing special. It does provide for an excellent rolling test bed for the new potions and chems we all enjoy. It still looks quite decent when puffed up...assuming you don't get closer than 10 feet