Rear ratio and T10

[Donald H.]

Sorry to revisit this, but I am getting ready to order the rebuild kit for my T10. It is a 1960 which means close ratio. The car had a 3.70 non-posi, but originally was posi based on the axle housing and vent line.

Here is the story so far, I am in the process of rebuilding the rear with a correct P case carrier that I was able to locate and Eaton posi unit per Tom Parson's article. I have decided to go with 3.36 gears. Simple reason is that I want to be able to cruise at 60-65 mph without taching at 3,000 or near for extended cruising.

Since this is my first restoration and I don't know what I don't know, I think I have researched all the issues, i.e. buring out clutches, etc. When I took it apart it had an 11" clutch, so I assume that will help with the close ratio first gear and clutch burn out issues.

So my question is, should I convert the T10 to wide ratio? I know with wide ratio and the 3.36, the overall ratio in first is about the same as a close ratio and 3.70 rear. But if there is experience that says the 11" clutch will solve the issue of having 3.36 rear, then I will save my money.

I also know, or think I know, that converting to wide ratio will not affect flight judging, which I am pursue, but will likely fail if I were to pursue Duntov, which I am not considering.

Thanks in advance

Don

[John H.]

Re: Rear ratio and T10

I know with wide ratio and the 3.36, the overall ratio in first is about the same as a close ratio and 3.70 rear. But if there is experience that says the 11" clutch will solve the issue of having 3.36 rear, then I will save my money.

Don -

Having been through something similar, I'll offer an opinion (which is worth what you're paying for it) .

I have a '69 Z/28 that was built with an M-21 close ratio and the optional 4.10 axle; the first year I had it, I put a lot of freeway miles on it, and 3900 rpm at 70 finally got to me, and I swapped out the 4.10 for a 3.55. BIG mistake in terms of normal around-town driving/cruising and starts from a dead stop, especially on an incline. If I had it to do over again, I wouldn't go any lower (numerically) than a 3.73, which was the standard axle.

You will NOT like 3.36 gears with a 283 and a close-ratio transmission, except on a freeway. Others' opinions may differ.

[Joel T.]

Re: Rear ratio and T10

Don..

I had a similar situation with my '63 which I did a mechanical restoration on... My rear was stamped 3.70 however someone along the line installed 3.36 gears with a steel case T10. I installed a correct aluminum case T10 close ratio and drove the car for a while before I figured out that the rear was not what I thought it was... I would agree that around town driving was not all that great. Starting off in 1st required a fairly long clutch slip to get it moving with some bucking tossed in for good measure. As you drive it, you know something is not right... I finally got under the car and counted wheel/shaft revolutions.. and then went out and bought the correct 3.70 gears. With the 3.70's in there it is like night and day... 1st gear start are just fine and highway cruising is just fine. If you stick with the 3.70's (which I would recommend), get your driveshaft and yolk balanced.. makes a big difference.. My car will cruise at 70 all day... with zero vibration..

Good luck,

Joel

[Terry D.]

Re: Rear ratio and T10

Donald
If you want to cruise 60-65 without turning 3000 rpm you need to go lower than 3:70 gears. But I agree with the above posts that you will not like it around town. I think the wide ratio would suit your needs in this situation, and nobody is going to know if you don't tell them. Just my 2 cents. If you go to www.keislerauto.com on the right side is a like to "Speed Analyzer" then click on GM 5 speed. A window comes up with options for different transmissions, doesn'yt matter which one you pick, then you can chose the size tire and rpm you are running and it will give the cruising speed for both their new transmission and your old 4 speed, for the different rear end ratios. Should help you determine which gear you want.
Terry

[Donald H.]

Re: Rear ratio and T10

I was hoping there was an easy answer to provide both good in town driving, i.e. no lugging at stop lights and easy on the clutch and provide lower RPMs at cruising. That's why I was considering converting the close ratio transmission to wide ratio. But I am also torn with keeping the drive train "stock".

Since this is my first old vette I don't really have a point of reference. My last similar car was in 1965 and was a new Chevelle SS with 300hp/327 and 4 speed. So it has been 45 years since I really drove any Chevy with a small block and 4 speed.

I assume that I will be doing mostly in town, so that is obviously important.

Duke Williams provided a formula in another thread, and if I did the math correctly, 65mph with a 3.70 is around 3,100rpm and with a 3.36 it would be 2,800rpm.

I was hoping some C1 guys with stock 3.70 would chime in and let me know if crusing at 65 or so is not torture on the car or drive.

Thanks,

Don

[Terry D.]

Re: Rear ratio and T10

Donald
There is no easy solution. I've had several 62's. This last one had a 340hp and 3:70 gears. Great around town but I like to get out on the highway and go places with my car. I put 7800 miles on my car this summer. At 65 it was over 3000 rpm. So I pulled the engine and tranny and put in a 383 crate motor and a Tremec 5-speed. Like having 4:11 gears in town and at 70mph I'm taching under 2000. If you want to stay stock and get judged you have to pick the happy medium that works for you. If most of driving is in town then leave the rear end alone. If you want to cruise a lot then change gears and see how that works. I agree with John, I don't think you will like a 283 with 3:36 gears. There was a reason the General only let you order 3:70 and up in that year. The difference between 3:70 gears and 3:36 is 5 mph. Not much gain for the money and time and wear and tear on the clutch.
Hope this helps, I know you were looking for an easy answer but if owning these old cars was easy everybody would have one. Good Luck
Terry

[Domenic T.]

Re: Rear ratio and T10

Donald,
I went thru this a number of times and found that the wide ratio and the 3:36 worked fine for in town & road driving. The only time I wanted the close ratio was for the drag strip when I needed to top out in 4th gear with a 4:11 or 4:56. If you just want to blow off from a stop sign in town you can do just fine with a 3:36 and a wide ratio because your not going to reach a speed where 4th gear would hurt you.

DOM

[John H.]

Re: Rear ratio and T10

I'll add that my '67 300hp has the wide-ratio M20 and a 3.36 axle, and it's delightful, in town or on the highway.

[Barry H.]

Re: Rear ratio and T10

Don, I have had this problem several times in the past, plus I live in Western Pa. with lots of hills. In my 62 327/360 HP FI car I ended with a 3.36 Posi & a wide ratio T10 trans. Has been great for the past 7 years. Good highway RPM's & easy to start out on a hill.
I am in the process of converting my 65 327/350 HP Coupe to a wide ratio muncie, then I will change diff to a 3.36 Posi. (With the close ratio & stock 3.55 Posi it is difficult to start on a hill).
The transmission change is easy, all you have to swap is the Main Drive Gear (Clutch Gear) & the Cluster Gear, with ones from a wide ratio trans. Good Luck, But a (SHARP) PV Judge could probably tell the diffrence between a W/R & a C/R trans during the driving portion of the test. I know, I can! I also have a 66 327/300 HP Coupe with Wide Ratio & 3.36 Posi, & it is a great combination.
Barry Holmes

[Donald H.]

Re: Rear ratio and T10

I'll add that my '67 300hp has the wide-ratio M20 and a 3.36 axle, and it's delightful, in town or on the highway.

Thanks John, this is encouraging.

[Donald H.]

Re: Rear ratio and T10

Don, I have had this problem several times in the past, plus I live in Western Pa. with lots of hills. In my 62 327/360 HP FI car I ended with a 3.36 Posi & a wide ratio T10 trans. Has been great for the past 7 years. Good highway RPM's & easy to start out on a hill.
I am in the process of converting my 65 327/350 HP Coupe to a wide ratio muncie, then I will change diff to a 3.36 Posi. (With the close ratio & stock 3.55 Posi it is difficult to start on a hill).
The transmission change is easy, all you have to swap is the Main Drive Gear (Clutch Gear) & the Cluster Gear, with ones from a wide ratio trans. Good Luck, But a (SHARP) PV Judge could probably tell the diffrence between a W/R & a C/R trans during the driving portion of the test. I know, I can! I also have a 66 327/300 HP Coupe with Wide Ratio & 3.36 Posi, & it is a great combination.
Barry Holmes

I really appreciate your commenting. I now feel more comfortable with the approach I am taking. I am going to call D&L today and speak to Larry about what I need to convert my close ratio T10 to wide ratio.

Thanks,

Don Harris

[Jeff M.]

Re: Rear ratio and T10

I have tried both the close and wide with 3 different rear ends from 4.11,4.33 and 4.56. I can assure you that the wide ratio is the only way to go for the street and even more so for the drag strip. With a 4.11, the difference between a wide and close was 3/10ths an nearly 3mph in the quarter behind a 71 ls6, I can even feel the diff between the wide and close with the 4.33. I would not even consider a close with anything below a 3.70, 4.11 is really better. Wide and 3.70 is really zippy off the line and your clutch will like it longer