Need advice on C-1 rear carrier assembly...

[Patrick T.]

I have a '57 (below) that I restored from the ground up in the early 90's. It has a close ratio M-22 transmission which I have to keep. I made a mistake of ordering a rebuilt 4:11 rear from Chicago Corvette, the gears are just too high. It has great take off from a standstill but the engine is screaming at 60 mph. I want to lower the rear gears to maybe 3:55 or 3:70 but not a 3:08. I want to drive a maximum of 75 mph and keep the engine revs @ 3000 rpm+/-. Also is there a vendor that sells a used rear carrier that I can trade my 4:11 in?

Thanks for any advice. PT

[Bruce B.]

Re: Need advice on C-1 rear carrier assembly...

How about a 3.36 : 1 gear?
I have one in my 62.
But my choice today would be a 3.55.

[Duke W.]

Re: Need advice on C-1 rear carrier assembly...

If you have MS Excel, search for a thread started by me - "gear chart", and try different ratios. Most are in increments of about ten percent, but 3.55 splits the 10 percent difference between 3.36 and 3.70.

Assuming OE equivalent 760 rev/mile tires a 3.36 would yield about 3200 at 75, but it will be pretty sluggish off the line and not a good choice for hilly country, especially with a Duntov cam.

Duke

[Terry D.]

Re: Need advice on C-1 rear carrier assembly...

with 3.73 gear at 3000 rpm, assuming a 27 inch tall tire, you will be going 64, with a 3:55 going 68 and with a 3:36 you will be going 72. In my opinion 3000 rpm is way too high for long range cruising, and you will have a hard time passing up a gas station. Running a taller tire will help a little, but an inch in tire height only gets you 2 mph more, but if you really want the best of both worlds you might consider a tremec 5 speed conversion. I did this to my 62 and I run 70mph at 2100 rpm, and get 24 mpg on the highway with a 383 crate motor!

[Patrick T.]

Re: Need advice on C-1 rear carrier assembly...

Thanks to everyone for their comments. I forgot to mention that I have a 350/345 Chevy crate engine with aluminum heads and a roller cam, with 23K miles on it. Not sure if you can still buy those anymore. Based on your posts, I think I will have to narrow my search to 3:55, 3:70 or a 3:73 as long as they are for a 4-speed.

When I bought the 4:11 from Chicago Corvette, you could trade in your old carrier assembly and get a $300 credit but it doesn't look like they do that anymore. Thanks again. PT

[Tom P.]

Re: Need advice on C-1 rear carrier assembly...

If you want to drive 75mph and keep the rpm at 3000 (and your tranny final gear is 1:1, such as a Muncie or T10), then your ONLY option is a 3.08 gear. Sorry.
I have a SB400 with FI in the 56 with a wide ratio (M20) Muncie and 3.08 posi and P225/75R15 tires and at 76mph both tachs (yes, that's right, I have 2 tachs) are at 3000.

[Patrick T.]

Re: Need advice on C-1 rear carrier assembly...

If you want to drive 75mph and keep the rpm at 3000 (and your tranny final gear is 1:1, such as a Muncie or T10), then your ONLY option is a 3.08 gear. Sorry.
I have a SB400 with FI in the 56 with a wide ratio (M20) Muncie and 3.08 posi and P225/75R15 tires and at 76mph both tachs (yes, that's right, I have 2 tachs) are at 3000.

Thanks Tom, that sounds good to me. I'll see what kind of deal I can work out. Will a 3:08 posi carrier assembly fit into my current 4:11 posi setup? What I'd like to do is have someone just switch out the ring and pinion.

[Tom B.]

Re: Need advice on C-1 rear carrier assembly...

You say that you have to keep the close ratio M22? I don't think you will like the 3.08 or even a 3.36 with that 2.20 low gear. Tom is right with using the wide ratio with the 2.56 low gear. Of course the extra cubic inches help too. It makes a lot of difference when moving away from a dead stop. My '59 270 has a 3.36 and a close ratio and it is not fun to get rolling. I had a 3.70 in it that I really loved until it ate it'self. The guy set it up wrong, so the 3.36 went back in. I have had several cars with 3.70s and they are not the best interstate gear unless you like to drive slower or listen to the engine scream. I have also had a '65 300 horse and a '67 390 horse with wide ratio and 3.36 rear and they were very nice cars to drive. 3000 at 70 doesn't bother me. I used to pull 19 mpg with the '65 300 horse. i don't think I ever checked the big block.

Tom

[Patrick T.]

Re: Need advice on C-1 rear carrier assembly...

You say that you have to keep the close ratio M22? I don't think you will like the 3.08 or even a 3.36 with that 2.20 low gear. Tom is right with using the wide ratio with the 2.56 low gear. Of course the extra cubic inches help too. It makes a lot of difference when moving away from a dead stop. My '59 270 has a 3.36 and a close ratio and it is not fun to get rolling. I had a 3.70 in it that I really loved until it ate itself. The guy set it up wrong, so the 3.36 went back in.

I have had several cars with 3.70s and they are not the best interstate gear unless you like to drive slower or listen to the engine scream. I have also had a '65 300 horse and a '67 390 horse with wide ratio and 3.36 rear and they were very nice cars to drive. 3000 at 70 doesn't bother me. I used to pull 19 mpg with the '65 300 horse. i don't think I ever checked the big block. Tom

Thanks for the advice Tom. For the most part, I'll be driving the car <60 mph. How did your guy set up the 3:70 wrong, just curious. I originally asked Chicago Corvette for a 3:70 rear and they said all they had available was the 4:11, so I took it. Big mistake but I've never had any mechanical problems with it. So are you basically saying a 3:55 might be a good choice?

[Tom P.]

Re: Need advice on C-1 rear carrier assembly...

Patrick,
I can't see the other side of your ring gear, BUUUUUUUUUUT, I'm presuming that your 4.11 ring gear is bolted to a 4-series posi unit (the outer cases are TOTALLY interchangeable regardless of what guts are in them). Thus, if your posi unit is in fact a 4-series, you CANNOT, repeat, CANNOT install a 3-series ring and pinion in it. It will require a 3-series posi unit. I have totally quit searching for good factory posi units since the introduction of the aftermarket Eaton or Nitro Power Loc posi units. Either of them are EXCELLENT posi units for these early rears--------------------------AND THEY CANNOT BE SEEN BY A JUDGE!!!!!!!!!!!!!!!!! I've been building these rears for early Chevys and Vettes for almost 50yrs, and since I've been installing the Eaton or Nitro units, I have not seen any issues with them. Back when gas was cheap (yes, I'm that old), 4.11 and 4.56 gears were the thing to have, but not today!
I'm sure you've noticed that the "in" way to go is with an OD tranny (lots more $$$$$$$$). The next best option is a higher geared rearend (ie 3.08, etc) and a WIDE ratio tranny. Once upon a time I had an M21 (close ratio Muncie) and a 3.36 rear in the 56, but that was behind a healthy 350, so it worked fine-----------------------until the day I tried to pull the jet boat up the ramp at the lake (yes, I have pulled a jet boat with the 56). Suddenly, the M20 replaced the M21. Now, with the SB400, M20 and 3.08 rear, the 56 is just right!
If you try to swap your 4.11 posi with someone for a 3.08 or 3.36 posi, I'm afraid you won't find a lot of takers. As I mentioned above, most people are looking for ways to gain lower rpm and better economy on the Interstate, and that takes a higher gear ratio, or, an OD tranny.

And last, this is an opinion input-----------take it for what it's worth. I'm not real fond of reducing rpm by using an OD tranny with a rear such as a 3.70, 4.11, 4.56. It's true, the OD will drop hiway rpm, BUUUUUUUUUUUUUT, you're still spinning that 4.11 ring gear (and the entire differential) at the same rate-------------still building up heat and friction which is tough on rearend gear oil.

[Patrick T.]

Re: Need advice on C-1 rear carrier assembly...

Patrick,
I can't see the other side of your ring gear, BUUUUUUUUUUT, I'm presuming that your 4.11 ring gear is bolted to a 4-series posi unit (the outer cases are TOTALLY interchangeable regardless of what guts are in them). Thus, if your posi unit is in fact a 4-series, you CANNOT, repeat, CANNOT install a 3-series ring and pinion in it. It will require a 3-series posi unit. I have totally quit searching for good factory posi units since the introduction of the aftermarket Eaton or Nitro Power Loc posi units. Either of them are EXCELLENT posi units for these early rears--------------------------AND THEY CANNOT BE SEEN BY A JUDGE!!!!!!!!!!!!!!!!! I've been building these rears for early Chevys and Vettes for almost 50yrs, and since I've been installing the Eaton or Nitro units, I have not seen any issues with them. Back when gas was cheap (yes, I'm that old), 4.11 and 4.56 gears were the thing to have, but not today!
I'm sure you've noticed that the "in" way to go is with an OD tranny (lots more $$$$$$$$). The next best option is a higher geared rearend (ie 3.08, etc) and a WIDE ratio tranny. Once upon a time I had an M21 (close ratio Muncie) and a 3.36 rear in the 56, but that was behind a healthy 350, so it worked fine-----------------------until the day I tried to pull the jet boat up the ramp at the lake (yes, I have pulled a jet boat with the 56). Suddenly, the M20 replaced the M21. Now, with the SB400, M20 and 3.08 rear, the 56 is just right!
If you try to swap your 4.11 posi with someone for a 3.08 or 3.36 posi, I'm afraid you won't find a lot of takers. As I mentioned above, most people are looking for ways to gain lower rpm and better economy on the Interstate, and that takes a higher gear ratio, or, an OD tranny.

And last, this is an opinion input-----------take it for what it's worth. I'm not real fond of reducing rpm by using an OD tranny with a rear such as a 3.70, 4.11, 4.56. It's true, the OD will drop hiway rpm, BUUUUUUUUUUUUUT, you're still spinning that 4.11 ring gear (and the entire differential) at the same rate-------------still building up heat and friction which is tough on rearend gear oil.

Thanks again Tom, I have gathered all the information in this thread and will call the place where I bought originally it and see what they can or cannot do for me. This 4:11 is getting old on me.

[Tom P.]

Re: Need advice on C-1 rear carrier assembly...

Here is an article (55-64 Chevy rears/56-62 Vette rears) I put together a few years ago on another forum (wasn't any interest here). Scroll all the way through it and also click on the links in the first post. it may be of interest to you (and it may not).
http://www.chevytalk.org/fusionbb/sh...hp?tid/223912/

[Tom B.]

Re: Need advice on C-1 rear carrier assembly...

Thanks for the advice Tom. For the most part, I'll be driving the car <60 mph. How did your guy set up the 3:70 wrong, just curious. I originally asked Chicago Corvette for a 3:70 rear and they said all they had available was the 4:11, so I took it. Big mistake but I've never had any mechanical problems with it. So are you basically saying a 3:55 might be a good choice?

He set the backlash too tight. It started to whine after a couple of days and by the end of the week when I took it out you could shave with the ring gear or pinion gear teeth. I've never tried a 3.55 with a close ratio trans. It might be a good compromise considering you will be normally keeping it <60.

Tom

[Patrick T.]

Re: Need advice on C-1 rear carrier assembly...

Thanks Tom and Tom, will do.

[Chris S.]

Re: Need advice on C-1 rear carrier assembly...

I have a '57 (below) that I restored from the ground up in the early 90's. It has a close ratio M-22 transmission which I have to keep. I made a mistake of ordering a rebuilt 4:11 rear from Chicago Corvette, the gears are just too high. It has great take off from a standstill but the engine is screaming at 60 mph. I want to lower the rear gears to maybe 3:55 or 3:70 but not a 3:08. I want to drive a maximum of 75 mph and keep the engine revs @ 3000 rpm+/-. Also is there a vendor that sells a used rear carrier that I can trade my 4:11 in?

Thanks for any advice. PT

For a vendor check with Pipers - I bought 2 rear center sections from him recently