transmission id
Thread Starter
Instructor
Joined: Feb 2006
Posts: 143
Likes: 0
From: floral city fl
transmission id
i need to replace my transmission pan seal on my 77 coupe due to it leaking badly. two questions
1. where do you drain the transmission from can't find a drain.
2. how do you tell if it is a turbo 400 or a turbo 350 auto tranmission
thanks scott
1. where do you drain the transmission from can't find a drain.
2. how do you tell if it is a turbo 400 or a turbo 350 auto tranmission
thanks scott
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
The only way to drain it is pull the pan off. Messy, but that's it.
A TH350 has the vacuum modulator at the rear, the governor is under a cover that has no bolts holdong it on, and the pan is nearly square with on corner cut odd.
A TH400 has the modulator on the side. the governor cover bolts on, the pan is straight on 2 sides, the front and the left.
A TH350 has the vacuum modulator at the rear, the governor is under a cover that has no bolts holdong it on, and the pan is nearly square with on corner cut odd.
A TH400 has the modulator on the side. the governor cover bolts on, the pan is straight on 2 sides, the front and the left.
Racer
Joined: May 2009
Posts: 295
Likes: 2
From: Columbus OH
To avoid getting tranny fluid all over you, start by loosening all the pan bolts, then take all the pan bolts out on one side (I usually choose the drivers side, I think there are four on that side) then work your way around the pan loosening the bolts but leaving them with a few threads in. This will tilt the pan to the open side and allow the fluid to drain out in one area. Once most of it is out you can drop the pan.
Burning Brakes
Joined: Sep 2005
Posts: 895
Likes: 4
From: whitman massachusetts
Draining Transmission
I have not tried this, but intend to in future. A forum member posted that he had inserted plastic tubing down transmission fill tube and attached to a small drill powered pump. He then drained pan fluid and removed pan with much less mess. Sounds reasonable!
7th Gear
Joined: May 2009
Posts: 7
Likes: 0
From: Franklin NC
The only way to drain it is pull the pan off. Messy, but that's it.
A TH350 has the vacuum modulator at the rear, the governor is under a cover that has no bolts holdong it on, and the pan is nearly square with on corner cut odd.
A TH400 has the modulator on the side. the governor cover bolts on, the pan is straight on 2 sides, the front and the left.
A TH350 has the vacuum modulator at the rear, the governor is under a cover that has no bolts holdong it on, and the pan is nearly square with on corner cut odd.
A TH400 has the modulator on the side. the governor cover bolts on, the pan is straight on 2 sides, the front and the left.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
I just pulled the tranny out of my '77 L48 today so that I can rebuild it with my b & M performance trans kit and I noticed that mine had a drain plug at the front of the pan. It looks like a TH350 (square pan with odd corner) But I don't see any plates or casting numbers on it. I'm hoping I bought the right trans kit. I bought one for a th350. I read somewhere about '77s coming with a t350 cbc or something like that? I always just thought it was either 400 or 350. Can anybody clue me in on automatic transmissions for the 77 sharks?
A 350C will have a the normal vacuum modulator at the rear, but on the left side of the case there's a wire connector. The pan is the key to determining it IS a 350 (cut off corner on the pan), but the 350C will also have the connector for the TCC. I'm thinking that the 350C didn't show until 78 or 79, but that may not be correct. The 700R4 was introduced in the early 80's and the 350C was just before that.
IIRC the 350 and 350C used the same filter and pan gasket
7th Gear
Joined: May 2009
Posts: 7
Likes: 0
From: Franklin NC
If there's a drain plug, somewhere, someone added it. None that I'm aware of came with a drain plug from the factory.
A 350C will have a the normal vacuum modulator at the rear, but on the left side of the case there's a wire connector. The pan is the key to determining it IS a 350 (cut off corner on the pan), but the 350C will also have the connector for the TCC. I'm thinking that the 350C didn't show until 78 or 79, but that may not be correct. The 700R4 was introduced in the early 80's and the 350C was just before that.
IIRC the 350 and 350C used the same filter and pan gasket
A 350C will have a the normal vacuum modulator at the rear, but on the left side of the case there's a wire connector. The pan is the key to determining it IS a 350 (cut off corner on the pan), but the 350C will also have the connector for the TCC. I'm thinking that the 350C didn't show until 78 or 79, but that may not be correct. The 700R4 was introduced in the early 80's and the 350C was just before that.
IIRC the 350 and 350C used the same filter and pan gasket
68-75 used only th400
76 used th350 or th400
77 used cbc350 or th400
78-81 used th350
82 used 7004r
And I read on another forum that the cbc350 (chevy/buick/combined) had a different 1st gear. My concern is that I don't know about the strength of these trannys compared to a th350 or a th400. As soon as I'm finished with the rebuild I'm going to be mating it with a built 383. I know a th350 will typically handle 400 hp but I don't know anything about these cbc transmissions. Today is actually the first time I'd even heard of it.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,113
From: Crossville TN
If you drop the pan for fluid/filter/gasket and don't add a drain plug, you're missing one great opportunity. I installed mine about halfway up on the backside of the pan [THM 400]. That location had nothing to interfere with the plug hardware on the inside, and it allows me to drain enough fluid out so that it doesn't slosh all over the place {and me} when I need to service it.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
The only difference in the "CBC" 350 is the case. It's a dual pattern bellhousing that will bolt to Chevy and BOP engines. Internals are the same.
400hp is very possible with a 350- I built a 350 for a friend that races a 67 GTO every weekend- 455 power, 4:11 gears and 9 inch slicks. Been running it for close to 10 years and hasn't broke it yet. Don't know why he hasn't broke it- he twisted the input shaft and broke an ear on the Muncie that was in the car before the 350.
And
with 7T1- if you have the pan off and don't install a drain plug you're missing a good chance.
400hp is very possible with a 350- I built a 350 for a friend that races a 67 GTO every weekend- 455 power, 4:11 gears and 9 inch slicks. Been running it for close to 10 years and hasn't broke it yet. Don't know why he hasn't broke it- he twisted the input shaft and broke an ear on the Muncie that was in the car before the 350.
And
with 7T1- if you have the pan off and don't install a drain plug you're missing a good chance.
