C1 3speed to 4 Speed Conversion

[Mark P.]

I am trying to find out some info for someone. I appreciate any advice on this.

What is involved with replacing a stock 3 speed tranny in a 1960 with a correct 1960 Corvette wide ratio T-10 ?

Do I need to buy a new slip yoke, linkage, etc ?

Any modifications needed ?

Are original Corvette 4 speed shifters any better than a repro ?

What will this do to improve freeway driving ? What rear ends were typical with 3 speeds ?

Will probably replace the clutch while I am at it and balance the drive shaft.

[John H.]

Re: C1 3speed to 4 Speed Conversion

I am trying to find out some info for someone. I appreciate any advice on this.

What is involved with replacing a stock 3 speed tranny in a 1960 with a correct 1960 Corvette wide ratio T-10 ?

Do I need to buy a new slip yoke, linkage, etc ?

Any modifications needed ?

Are original Corvette 4 speed shifters any better than a repro ?

What will this do to improve freeway driving ? What rear ends were typical with 3 speeds ?

Will probably replace the clutch while I am at it and balance the drive shaft.

Mark -

Easy swap - everything is a bolt-in; all you need is the transmission, shifter, linkage rods, and shift pattern plate.

Freeway driving won't change - all 3 and 4-speed transmissions are 1:1 in high gear. Manual transmissions in 60's came with 3.70 axles as standard, with 4.11 and 4.56 optional.

[Mark P.]

Re: C1 3speed to 4 Speed Conversion

John - thanks for the advice. Would a wide ratio 4 sp be quicker off the line than the speed and overall more ennjoyable ?

In your opinion is the switch worth it ?

Mark

[Edward B.]

Re: C1 3speed to 4 Speed Conversion

My memory is a little hazy since it has been over 20 years since I last made such a swap, but I believe it also requires a different rear mounting bracket which bolts between the frame "X" members. "Off-line" acceleration might be marginally less due to the difference between 1st gear ratios of the two transmissions, but your driveability at speed will be greatly improved. An additional plus for the swap is the synchronized 1st gear of the T-10.

[Stuart F.]

Re: C1 3speed to 4 Speed Conversion

Be sure to check/replace the pilot bushing in the end of the crankshaft. On the linkage, make sure it is an all Corvette linkage and not one from or mixed with a passenger car linkage - of which there are many more out there. If you use the right shifter with the wrong side plate levers your throws will be all screwed up.

As far as the low end performance, you simple have to compare on paper what ratios you are dealing with and that will tell you the story about what to expect. The ratios are printed in service manuals and other sources.

[Bill M.]

Re: C1 3speed to 4 Speed Conversion

What is involved with replacing a stock 3 speed tranny in a 1960 with a correct 1960 Corvette wide ratio T-10 ?

No such animal. Wide ratios weren't available in 1960, but I think you could stuff wide-ratio guts in a correctly-dated close-ratio box. I haven't done it, but a previous post said you just replace the clutch gear and the countershaft.

That said, I replaced the close-ratio 4spd in my '65 with a wide-ratio. It gives me the same gear spacing as the close-ratio in 1st, 2nd, 3rd with an "overdrive" 4th. I love it.

[Tom P.]

Re: C1 3speed to 4 Speed Conversion

A 57-61 T-10 will be a bolt-in fit. But, a 62-later 4sp will require the 62 style tranny mount plate-------------which is available at all the vendors for about $20.
Furthermore, if you should install a Muncie in a 55-62 Vette, it will require not only the 62 mount plate, but also the driveshaft yoke will need to be changed to the finer 27-spline yoke for the driveshaft, plus spacers will need to be installed between the tranny cross member and the frame X-member to lower the rear of the tranny. From the factory, the 62s had about a 1/8in spacer on each side. On my 56, I have installed about 1in spacers.

[Mark P.]

Re: C1 3speed to 4 Speed Conversion

Bill - I was confused with C2's. The 1960 T-10 transmission he is looking to install has a "close ratio 220 first gear".

Thanks,

Mark

[Stewart A.]

Re: C1 3speed to 4 Speed Conversion

The proper shifter will be an expensive buy as well. An exact service replacement with the correct linkages will be around $600 keep that in mind. The car will be more fun to drive with 4 forward gears. Stewy

[Roger W.]

Re: C1 3speed to 4 Speed Conversion

Tom,
I have a Muncie in my 59. A previous owner made his own adaptor plate and after reading your post I checked and there are spacers about an inch thick between the cross member and the X-frame.
I have purchased the correct 62 adaptor plate. When I install the correct plate, what is criterion for determining the correct thickness of the cross member spacer?

[Tom P.]

Re: C1 3speed to 4 Speed Conversion

Tom,
I have a Muncie in my 59. A previous owner made his own adaptor plate and after reading your post I checked and there are spacers about an inch thick between the cross member and the X-frame.
I have purchased the correct 62 adaptor plate. When I install the correct plate, what is criterion for determining the correct thickness of the cross member spacer?

Roger,
The spacers on 62 Vettes w/4sp are about 1/8in thick, and that's with a T-10.
I've had my 56 with a Muncie since 73 with 1in spacers--------ZERO problems. If it ain't borke, don't fix it----------that's my criteria for the 1in spacers. Also, the early Vettes have (in my semi-expert opinion) have somewhat severe U-joint angles to begin with, thus the 1in spacers have GOT TO HELP reduce those angles.
Here is the Muncie installed in the 56 with both the 62 mount plate and the 1in spacers (1in square tubing).

[Roger W.]

Re: C1 3speed to 4 Speed Conversion

Tom,
Thanks for your reply. You have a beautiful clean transmission setup on your 56.

Roger