THM400 Rebuild Options in SWO

LandShark68_2+2 · Guru

THM400 Rebuild Options in SWO

Canadian Poncho · A Poncho Legend!

Try Hutch's Transmission service on First street in London. John Hutchinson was a tech at Eastown Chev Olds when I worked there back in the 80's. He raced a stock looking 68-9 Roadrunner with a 383 and a built trans that ran 12's. He now just does transmissions. Was a straight shooter back then.

https://hutchtrans.com/

65 SD L79 · Canadian Poncho Superstar!

Scott, how many miles on tranny and what was it doing?

LandShark68_2+2 · Guru

65 SD L79 wrote:
Scott, how many miles on tranny and what was it doing?

The tranny has 120,000 miles on it and has had nothing done to it, up until now.

The shift from 1st to 2nd is really delayed and when it does shift, it is either hard or stuttered.
The shift from 2nd to 3rd is perfect.

The tranny is also whining now. The pitch of the whine changes as the gears shift.

One shop suggested it might not need a full rebuild, but definitely internal work.
If I'm going that far, I figured I should just get a total rebuild.

Regards, Scott (LandShark ...)

73SC · A Poncho Legend!

May or may not be relevant, Something to keep in mind, I've got a 28,000 mile unit sitting in my garage, I got it out of a running hearse that the drivetrain was harvested from. Was keeping the THM 400 for the 454 but its surplus now.

Its a 1975 THM 400 bolted to Cadillac 500. .

65 SD L79 · Canadian Poncho Superstar!

i have 96,000 on the 66 Lords car and it shifts fine, no winn but if i put my foot into it it shutters. Maybe torque converter? when it comes out it will get a full rebuild and new gaskets on the motor and a rear main seal

65 SD L79 · Canadian Poncho Superstar!

73SC wrote:
May or may not be relevant, Something to keep in mind, I've got a 28,000 mile unit sitting in my garage, I got it out of a running hearse that the drivetrain was harvested from. Was keeping the THM 400 for the 454 but its surplus now.
Its a 1975 THM 400 bolted to Cadillac 500. .

Ray, is a caddilac bell housing the same as Chevy? what year did they start that lock up converter thing?

i

73SC · A Poncho Legend!

65 SD L79 wrote:
73SC wrote:
May or may not be relevant, Something to keep in mind, I've got a 28,000 mile unit sitting in my garage, I got it out of a running hearse that the drivetrain was harvested from. Was keeping the THM 400 for the 454 but its surplus now.
Its a 1975 THM 400 bolted to Cadillac 500. .
Ray, is a caddilac bell housing the same as Chevy? what year did they start that lock up converter thing?
i

Quick look at Wiki shows Lock up Converters introduced in 1979 so this one does not have that.

Also Cadillac 500 adheres to B-O-P pattern for bellhousing but four bolt holes and two locator pins are common to the Chevrolet and B-O-P patterns plus Cadillac starter is on right side as is Chevrolet.

4SPEED427 · A Poncho Legend!

There are no lock up torque converters ever on a TH400 regardless of year.

65 SD L79 · Canadian Poncho Superstar!

4SPEED427 wrote:
There are no lock up torque converters ever on a TH400 regardless of year.

always learning something new, thanx Carl

4SPEED427 · A Poncho Legend!

They should have because they really screwed up on the pickup trucks. There was a few years, late 80's where they had a TH400 in the 2 wheel drive pickups. Those trucks were notorious for horrendous fuel mileage. They even used the TH400 behind the 4.3 V6 in those trucks.

Back to the initial topic here, I'm surprised to hear the 400 is giving issues. Those things were almost bulletproof on a daily driver, even with a big block in front of them.

seventy2plus2 · Canadian Poncho Superstar!

I'm very surprised your local tranny shops don't want to take it on. I can think of a few here on Calgary who'd tackle it without hesitation.

-- Edited by seventy2plus2 on Wednesday 18th of September 2024 10:39:23 PM

Canadian Poncho · A Poncho Legend!

Is my post about Hutchisons transmission invisible? lol
They build performance 400's and are in London

LandShark68_2+2 · Guru

Canadian Poncho wrote:
Is my post about Hutchisons transmission invisible? lol
They build performance 400's and are in London

I reached out to them and left a message. No reply yet.
Looking at their website and talking to a few guys, it looks like he exclusively does racing transmissions and is
very busy with a long queue of projects to do.

Regards, Scott (LandShark ...)

Big Bear · Addicted!

Sold my race car to a guy from Lambeth that runs a shop on Colonel Talbot rd. Shop is across from L'Arche London down a laneway to his shop. His name is Todd 519-652-9326. He works on older cars and my be able to help you out. Barry

CdnGMfan · Canadian Poncho Superstar!

FYI Scott, you should have a Turbo Hydramatic 375, which is a TH400 with a smaller output shaft & tailhousing. They were used on 327 / TH400 applications, plus Oldsmobile 88s with 350s through the mid-70s.
They are not to be confused with the TH375B, which is a TH350 for H.D. applications like 4x4 light duty pickups starting the mid-70s.

A "soft" rebuild shouldn't be a problem, I don't understand the hesitancy. Friction material breaks down & sludges things up, which is not good for anything in the valve body with all it's passages and check balls. A good disassembly, cleaning & replacement of friction material (clutches) should usually restore it to like new.

LandShark68_2+2 · Guru

CdnGMfan wrote:
FYI Scott, you should have a Turbo Hydramatic 375, which is a TH400 with a smaller output shaft & tailhousing. They were used on 327 / TH400 applications, plus Oldsmobile 88s with 350s through the mid-70s.
They are not to be confused with the TH375B, which is a TH350 for H.D. applications like 4x4 light duty pickups starting the mid-70s.

A "soft" rebuild shouldn't be a problem, I don't understand the hesitancy. Friction material breaks down & sludges things up, which is not good for anything in the valve body with all it's passages and check balls. A good disassembly, cleaning & replacement of friction material (clutches) should usually restore it to like new.

The engine I have is a 396 with an RV cam. I finally got through to a rebuilder, that Todd recommended, here in London and he is putting
together an estimate for me right now. Hoping for the best.

Regards, Scott (LandShark ....)

4SPEED427 · A Poncho Legend!

CdnGMfan wrote:
FYI Scott, you should have a Turbo Hydramatic 375, which is a TH400 with a smaller output shaft & tailhousing. They were used on 327 / TH400 applications, plus Oldsmobile 88s with 350s through the mid-70s.
They are not to be confused with the TH375B, which is a TH350 for H.D. applications like 4x4 light duty pickups starting the mid-70s.

A "soft" rebuild shouldn't be a problem, I don't understand the hesitancy. Friction material breaks down & sludges things up, which is not good for anything in the valve body with all it's passages and check balls. A good disassembly, cleaning & replacement of friction material (clutches) should usually restore it to like new.

I know better than to question you Cam but a TH375 behind a 396? I've parted out over a dozen 396 and 427 cars over the years and never yet have I seen anything but one size output shaft and tailhousing. I'm still not too old to learn but I'm getting close.

65 SD L79 · Canadian Poncho Superstar!

Ok here is another question, my 67 427 Caprice with TH400 would automatically shift into 2nd @ 5200 rpm with shifter in low. Did all of them do that?

4SPEED427 · A Poncho Legend!

65 SD L79 wrote:
Ok here is another question, my 67 427 Caprice with TH400 would automatically shift into 2nd @ 5200 rpm with shifter in low. Did all of them do that?

Yes, you can't keep a 400 in low even if the shifter is there. Just another reason to swap them out for a 4 speed!

CdnGMfan · Canadian Poncho Superstar!

4SPEED427 wrote:
CdnGMfan wrote:
FYI Scott, you should have a Turbo Hydramatic 375, which is a TH400 with a smaller output shaft & tailhousing. They were used on 327 / TH400 applications, plus Oldsmobile 88s with 350s through the mid-70s.
They are not to be confused with the TH375B, which is a TH350 for H.D. applications like 4x4 light duty pickups starting the mid-70s.

A "soft" rebuild shouldn't be a problem, I don't understand the hesitancy. Friction material breaks down & sludges things up, which is not good for anything in the valve body with all it's passages and check balls. A good disassembly, cleaning & replacement of friction material (clutches) should usually restore it to like new.
I know better than to question you Cam but a TH375 behind a 396? I've parted out over a dozen 396 and 427 cars over the years and never yet have I seen anything but one size output shaft and tailhousing. I'm still not too old to learn but I'm getting close.

OOPS! A 396. I was thinking 327 for some reason. hmm

In the words of Emily Litella, "Never mind!"