Rear end gear
Thread Starter
Burning Brakes
Joined: Feb 2022
Posts: 988
Likes: 183
From: South Carolina
Rear end gear
I have a 1981,and I’m doing some performance to this 190 hp engine,but I find out that the automatics this year had a 272,and think it was 287 I think in manual which blows my mind in a corvette,I do still have the Th350,and curious what gear to go up to and where to get it from,or can I use any c3 .
Team Owner
Joined: Jun 2001
Posts: 43,136
Likes: 155
From: Thomson Georgia
I removed my TH-400 and replaced w/ 700R4. Once I added another gear I removed my 3:08 and switched to a 3:73 gear. My 74 is now so much more user friendly. Even with my aggressive gear my gas mileage improved with that additional gear.
She is also pretty quick.
She is also pretty quick.
Le Mans Master
Joined: May 2007
Posts: 5,028
Likes: 1,120
From: North tonawanda NY
Golferdad,
you can find the gears at numerous places but they are no longer US made gears and the juries still out on how much tat matters for most as far as longevity. I found a whole rebuilt replacement rear end for $500 on facebook but had to drive from buffalo to clevland to get it. rebuilt trans -$900 from an acquaintance that works in a trans shop. I bought the shift kit and lockup kit. depending on year and drivshaft its easier for some than others.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
tthis is a dana 44. it has a lot of use in light trucks. our eaton rear from 79-back is near extinct except in corvette use. try talking to these guys or other suppliers. plus, many 4x4 shops redo the gears in trucks when they go to huge tires. so they may have a selection of good gearsets laying around after they change people from mid-3's to higher. https://eastcoastgearsupply.com/c-28...d-pinions.html
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Wow! If you have a 2.72:1 diff and a TH-350 tranny, with its 2.52:1 first gear ratio, that comes out to a final drive in first gear of 6.85:1, which is kinda pathetic. It keeps the revs down on the highway, though, to a certain degree. The old "rule of thumb" for final drive in first gear is 9:1 for a street car and 10:1 for a SERIOUS street car, so you're pretty far off the mark there. If you were to swap in a 700R4 tranny, with its 3.06:1 first gear ratio, it would be at 8.32:1, which is a little more like it. However, the final drive ratio in fourth gear would be 1.90:1, and that's in combination with a lock-up torque converter, which is, like, Bonneville Salt Flats territory!
If you really want to stick with the present TH-350 tranny, a 3.54:1 diff ratio would give you a final drive in first gear of 8.92:1, which would probably be about as high (numerically) as you'd want to go anyway. With no overdrive, you'd probably be buzzing along at over 3,000 rpm on the highway.
Rock Auto has a 3.54:1 ring and pinion set for $163.79:
More Information for DANA 2020428 (rockauto.com)
Scotty
If you really want to stick with the present TH-350 tranny, a 3.54:1 diff ratio would give you a final drive in first gear of 8.92:1, which would probably be about as high (numerically) as you'd want to go anyway. With no overdrive, you'd probably be buzzing along at over 3,000 rpm on the highway.
Rock Auto has a 3.54:1 ring and pinion set for $163.79:
More Information for DANA 2020428 (rockauto.com)
Scotty
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Scotty
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Thread Starter
Burning Brakes
Joined: Feb 2022
Posts: 988
Likes: 183
From: South Carolina
I have to do some more investigation but found a SS monte Carla 1980s but not sure what year this is if it is a late year 1984 and up has the 200 4R transmission,at a junk yard.do you have a picture of it,if I’m not mistaken the pan is different from the th350.
Race Director
Joined: Jul 2015
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From: SW Florida.
Melting Slicks
Joined: Dec 2015
Posts: 3,181
Likes: 732
From: Texas City, TX Texas
DEFINITELY ditch the weak-sauce rear gear. 355s do get up there in RPM on the freeway without overdrive. That's what I have, I don't like it but it's liveable. O.D. is for sure in my future. If you put in an overdrive, I would just go big and get 373s or 411s. Bigger rear gears are like (almost) free horsepower. 200-4R would be the perfect swap for you, it is the same overall length as the 350, but the mount is about two inches behind or in front, I dis-remember. Need to modify the crossmember but can keep the stock driveshaft. 81 didn't have much H.P. so a 200 will live behind it. Will want a higher stall converter and a shift kit, no big deal. If you ever put some guts under the hood, there are plenty of parts to beef up the 200-4R. The Grand National guys have been running them into the 9s on the strip for decades.
Le Mans Master
Joined: Apr 2011
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From: Hermosa
Pro
Joined: Mar 2022
Posts: 564
Likes: 185
It lopes along nicely at highway speeds and if you drop it down into drive (3rd) the rpm’s come up noticeably so that overdrive is definitely doing its job and the 3.73 gives plenty of torque. The 700R4 is also much stronger than the 200R4 transmissions too.
Thread Starter
Burning Brakes
Joined: Feb 2022
Posts: 988
Likes: 183
From: South Carolina
Rear gear
I will take some pictures,but looking at the back of my car,it appears someone in the last 5-10 years,just guessing though,but they replaced rear shocks and replaced the spring,I’m assuming that’s what that one thick bar is,but can also tell on the drivers side a spot the size of a footbal,just in front of the u joint on that side,so,appears leaking between u joint and differential,is that common?
