Audiophobe

Thanks!
2600rpm should work for me @60mph. I'd prefer 2200 but most of my driving is around town so that should do. I got a really good deal on the 3.55 so that's how I settled on it.

toms silver 60

Congrats. Here's a thread on speedo plastic gears:
http://forums.corvetteforum.com/c1-a...to-3-36-a.html
Don't know if this applies to your transmission, but it's good info. You may have problems getting a correct plastic gear to work. But if you don't swap plastic gears, your speedo and odometer will be reading low by about 1/6. So if you're showing 60, add 10 mph. (4.11/3.55=1.16). The 3.55 gears are a good compromise and are reported to be sought after by people going to OD transmissions.

toms silver 60

just sayin' that a 3.08 is actually more like 3.076923 etc ( or 40/13) but I'm sure that was incredibly obvious......

I do note that, on slick roads, my car gets a lot more unintentional wheel spin on starting to move with the 3.70 rear than it ever used to get with the 3.36. So, in snow, it should be better starting to move with the lower numerical ratio.

PG99

Ok so now that we have the math staightend out.. ....

I would still love to get any one of your 4.11 posi with full case for my 59. I want to go from my 3.70's to the 4.11. I did have the 3.55's
(there in my garage)

I might be in the minority here, but, I still believe an old corvette should be loud, fast and have attitude. So .. damn the gas milage I want to run in the 12's

PG.

NOM61

And if you want to sell that complete 3.70 pumpkin, let me know! (also would be very interested in the 4.11 posi for my 61, but if you bought the 4.11 and I bought your 3.70 everyone would be happy!).

DT

INMYBLOOD

PG99

Just curious any one swap out the 4.11's yet?

Frankie the Fink

I agree that is what I run, but with a Tremec TKO-600 now...its a hard-to-beat combo. And yes the generator tachs can be 'iffy'...which is why I have the rev limiter in the '61 set to 5,500 RPM

Audiophobe

An update for those who asked:
Just had the swap done, 4.11 to 3.55 close ratio. Drove a while yesterday on street and highway.
Overall I much prefer the street drivability.
At 60 rpm I'm 2700ish from 3400. The speedo is off so I used a speedo app on my phone.
I'll have to give the season but I think I'd prefer the highway rpm was closer to 2300-2400 but it's still a great improvement and around town I don't have to shift as quickly which I love.
Overall I'm happy after a a few miles of testing.
Again, I'll drive it a while before the final verdict is in.
I was holding off til this swap I am happy enough to know that I'm selling the 4.11 rear though. If anything I'd go lower.

Ironcross

Both are Fuel Injected cars as you can see as new, both with 670-15 tires.... the Black 360 1962 is a 4.56 gear and the 315 1961 White car is a 4.11 gear .........Speeds at 70 MPH, the 4,11 car is at 3500 RPM`s and the Black is 4000 RPM`s ...... both were pure stock factory ordered Vettes no aftermarket substitutions....

By the way or BTW for the initial types, mileage for the 61 was exactly 20 MPG at I-75 speeds.....but the 62 was not as generous with only 16......

.....Miami

Blacksburg Hokie

I know this is an old thread but I have been contemplating switching gears in my '61. I have 4.11 with posi-traction and have been thinking about going to 3.55 or 3.70. In all the reading I have done, I am confused if I need to change the carrier or not to make the switch with my rear gears. I would appreciate any input.

Thanks!

jim lockwood

Maybe. Maybe not.

Years ago I had a shop convert a 4-series carrier from 4.11 to 3.55. I'm pretty sure a special gear set was needed. Whether or not you could still do this conversion would depend on the current availability of a similar gear set.

Tom (DZAUTO) is the expert on such matters. Check with him.

Jim

DZAUTO

First of all, I THINK I have two 4.11 posi center sections ready to go. I'm sure I'll never use either of them again. Both are virtually perfect and one (if I remember correctly) has new gears.

Second, if the intent is just to change the gears (that is, replace ONLY the ring and pinion gears), you CANNOT, repeat, CANNOT install a 3-series ring gear on a 4-series carrier-------------------WILL NOT WORK!
If a 4-series rear (such as a 4.11) is in the car, and the goal is to switch to a 3-series gear, such as a 3.55, 3.70, then there are two choices. Either round up a 3-series carrier to install the ring gear on, or, locate a complete 3-series center section and swap the complete center section.
If a car has it's ORIGINAL center section with a 4-series ratio, and the owner wants to change over to a 3-series ratio----------------BUT YET RETAIN THE ORIGINAL CASE---------------------then the change will require BOTH a set of 3-series gears and a 3-series posi unit (such as the Eaton or the Nitro). When everything is swapped into the original case, ONLY EXTERNAL appearance and codes will be visible. Unless some EXTREMELY knowledgeable judge rides in the car (such as during an NCRS Performance verification), no one will know what is inside the case.

Last, if the goal is to go the other way, that is, from a 3-series gear to a 4-series gear, then a 4-series gear can be bolted to a 3-series carrier by using a spacer between the ring gear and the flange.

MaineDoc

Next week I'm pulling my 3.36 non-posi out and putting in a 3.70 posi for my 62 with a 327/360. Anyone interested in a 3.36? The poor low end torque of these motors made starts a struggle. Obviously a previous owner decided that highway mileage was more important than around town fun. GM knew what they were doing putting in 3.70 as a standard ratio.

DZAUTO

Profile information provides a "real" name and geographical location.

Blacksburg Hokie

The rear section is not original. The casting number is 3707306 which I believe is from a '56. My goal is to go from a 4-series to a 3. I am wondering if the previous owner went from a 3-series to a 4-series and bolted the gear to the 3-series carrier by using a spacer between the ring gear and the flange as Tom stated above. I guess I will have to look into it and see. If that is the case, then I can just unbolt it, correct?

DZAUTO

If the current rear is in fact a 3707306, I would really encourage you to get it replaced with a later center section. The 306 rears (case, gears and carrier) are in fact a 55-56 style, which is a thinner/weaker rear and a posi was not available in those early rears. For sure, someone has changed it with an earlier rear (probably from a 55-56 pass car).
To change the center section simply requires pulling the axles and unbolting the center section. If there is a need for a quick swap, I can change out a center section in 45min--------------------maybe faster with a helper---------------------but these days I no longer get in a hurry.

Blacksburg Hokie

Great information and advice. Thank you!

jimh_1962

deleted... But I do like having 4.11' with positraction and a 4 speed.

jimh_1962

Yep...