TH 400 Question
Thread Starter
Instructor
Joined: Dec 2009
Posts: 146
Likes: 4
From: Penville On.
TH 400 Question
I need to replace the transmission in my car. I have a 1987 TH 400 with 95000 km on it that has been sitting in my garage for about 7 years that I want to use. My question is, do the internals of the transmission degrade over time. I removed the pan and found it to be very clean and nothing on the magnet.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
First thing is to figure out what the trans problem is. As noted, the seals do degrade over time- the rubber seals will just kind of fall apart. No hard parts get damaged, but the clutches wear because of the low holding pressure. If it's shifting sloppy, it could be just the seals. Or low fluid level-check that, OR the modulator- check the vacuum lines first thing.
Pro
Joined: Jan 2010
Posts: 518
Likes: 12
From: Panhandle
My Thoughts!
I have a 400 out my 74 (went to a Muncie). The 400 has been sitting in the garage for about 8 years. If i had another Vette which needed a trans, I wouldn't hesitate to put that puppy in.
That trans didn't leak before it went inactive and wasn't abused under my care. Shifted and behaved very well. No burnt fluid smell. Front & Rear seals didn't leak.
If you don't have deep pockets, and you are sure the one in the car is Toast, the cheapest way to go is to "swap and pray".
If its your daily driver......get a reputable trans shop to do the R&R and road test....and go from there.
If you have the time, tools, garage, & health, do the R&R yourself. If the 2nd one has a problem, the 2nd time doing the R&R is a piece of cake. You just have to have the right temperament!
Couple of years ago (almost 20) daughter needed a Volvo auto trans, I got one on the internet cheap and with some of the saved $$$ paid a shop to do the R&R. Still proud of myself for that one. Would have been a PIA for me to change and correctly adjust.
Good Luck.
That trans didn't leak before it went inactive and wasn't abused under my care. Shifted and behaved very well. No burnt fluid smell. Front & Rear seals didn't leak.
If you don't have deep pockets, and you are sure the one in the car is Toast, the cheapest way to go is to "swap and pray".
If its your daily driver......get a reputable trans shop to do the R&R and road test....and go from there.
If you have the time, tools, garage, & health, do the R&R yourself. If the 2nd one has a problem, the 2nd time doing the R&R is a piece of cake. You just have to have the right temperament!
Couple of years ago (almost 20) daughter needed a Volvo auto trans, I got one on the internet cheap and with some of the saved $$$ paid a shop to do the R&R. Still proud of myself for that one. Would have been a PIA for me to change and correctly adjust.
Good Luck.
Thread Starter
Instructor
Joined: Dec 2009
Posts: 146
Likes: 4
From: Penville On.
I checked all the easy stuff first. Fluid, shifter adjustment, modulator and vac hose. The transmission has no reverse and the oil is very dark and smells burnt. Based on that I went ahead and pulled the transmission out. I'm thinking that doing a rebuild is the way to go, even though I'm tempted by the "swap and pray" method.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Change the fluid and filter, install a drain plug set into the pan while it is down, button it back up with a new pan gasket, and run it. The plates in your THM-400 were of better quality back then and should be fine. If you develop any leaks, you should be able to fix almost all of them with the trans still in the car.
Oil level should be somewhat 'high' on the stick with engine OFF. After you start the car, check trans oil level and it should be at the COLD mark on the stick.
Oil level should be somewhat 'high' on the stick with engine OFF. After you start the car, check trans oil level and it should be at the COLD mark on the stick.
Le Mans Master
Joined: Feb 2011
Posts: 5,943
Likes: 61
From: Southern NH
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Getting it out of the car is the tough part. The rebuild is pretty straight forward. If the fluid smells burned it's a good bet the clutches are toast. A good rebuild kit is between $100 and $150 depending on if it has steel plates and bands included.
You can cheat a little and use 4L80 steels and clutches- they are a little thinner than the TH400's so you can add a couple into each pack and gain some more holding power from increased surface area. All new seals and a convertor, you're back on the road.
You can cheat a little and use 4L80 steels and clutches- they are a little thinner than the TH400's so you can add a couple into each pack and gain some more holding power from increased surface area. All new seals and a convertor, you're back on the road.
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Thread Starter
Instructor
Joined: Dec 2009
Posts: 146
Likes: 4
From: Penville On.
Getting it out of the car is the tough part. The rebuild is pretty straight forward. If the fluid smells burned it's a good bet the clutches are toast. A good rebuild kit is between $100 and $150 depending on if it has steel plates and bands included.
You can cheat a little and use 4L80 steels and clutches- they are a little thinner than the TH400's so you can add a couple into each pack and gain some more holding power from increased surface area. All new seals and a convertor, you're back on the road.
You can cheat a little and use 4L80 steels and clutches- they are a little thinner than the TH400's so you can add a couple into each pack and gain some more holding power from increased surface area. All new seals and a convertor, you're back on the road.
