3 speed to Muncie 4 speed conversion - Chevelle Tech
Transmission & Driveline Transmissions and Differentials

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post #1 of 14 (permalink) Old Jan 19th, 20, 6:21 PM Thread Starter
 
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3 speed to Muncie 4 speed conversion

Hi all,

I am doing a lot of research and I cannot find a lot of data on a 3 speed to 4 speed swap. Are these transmissions very similar and can I swap from a 3 speed to 4 speed pretty painlessly or what do I need to look out for when doing this sort of swap. also if any one has done this what rear gear would you recommend. I have a bone stock 327 on my 1968 Chevelle. Thanks!
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post #2 of 14 (permalink) Old Jan 19th, 20, 7:49 PM
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Re: 3 speed to Muncie 4 speed conversion

If you have a 68 Chevelle with a factory 3 speed the transmissions are very similar. You should be able to remove the 3 speed and replace it with a 4 speed. Obviously you will need a 4 speed shifter.

In 1968 there was a regular and HD 3 speed. They had about the same first gear ratios as the 4 speed. The final drive ratios on all were 1:1. The only advantage you would pick up by changing to a 4 speed would be to keep the car in a more favorable operating rpm at certain speeds.

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post #3 of 14 (permalink) Old Jan 19th, 20, 7:54 PM
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Re: 3 speed to Muncie 4 speed conversion

I would be looking for an m-20 trans. It has a lower first gear than the m21 close ratio. It will help get you rolling in first gear more easily.
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post #4 of 14 (permalink) Old Jan 19th, 20, 7:57 PM
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If your 4 speed is close ratio or 2:20 first, at least 3:73 or lower, higher numerically.

If M-20 wide ratio 2:54 first, at least 3:55 or lower.

Be sure to spring for Hurst Competition Plus shifter with metal rod bushings.

Get ready for Way More Fun. !


Edit: One of the best sleeper muscle cars ever was the 68 Chevelle, close ratio Muncie and L-79 327/350 option. It sent a lot of SS 396 owners home, very sad
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post #5 of 14 (permalink) Old Jan 19th, 20, 8:12 PM
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Re: 3 speed to Muncie 4 speed conversion

How much parts for the swap do you already have? What's your budget? Would you consider a swap to a 5 speed (or even a 6 speed) over drive trans?

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post #6 of 14 (permalink) Old Jan 19th, 20, 9:00 PM
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Re: 3 speed to Muncie 4 speed conversion

Look at which side the speedometer cable is on. It would be easier to hook up if the Muncie had it on the same side as your 3-speed. Also check overall length as Muncies from different makes an models can have different length tail housings.
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post #7 of 14 (permalink) Old Jan 20th, 20, 12:45 AM Thread Starter
 
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Re: 3 speed to Muncie 4 speed conversion

all really good replies. Thanks guys!
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post #8 of 14 (permalink) Old Jan 20th, 20, 12:50 PM
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Re: 3 speed to Muncie 4 speed conversion

Now, with all the above said, to be really trick and fool people, you COULD retain the 3sp column shifter. I would require a little bit of linkage fabrication. I did this MANY years ago on two cars, a 54 Chevy and a 55 Chevy. The reverse position on the column becomes the 1st gear position on the 4sp, 1st gear position becomes the 2nd gear position on the 4sp, then 2nd gear position for 3rd and 3rd gear position for 4th.
For shifting the 4sp into reverse, we used an Overdrive handle/cable from a 3spOD transmission (back in those days a 3spOD handle/cable was fairly common in salvage yards).

Other wise, your option is cutting a hole in the floor for a floor shifter. Hurst has an excellent shifter made specifically for the 68 Chevelle. From the factory, with a bench seat, Chevelles had a boot/bezel and hump for the shifter handle. These 3 parts are readily reproduction from the Chevelle vendors. Here is what it looks like. This is my son's 68 4dr that we converted from a Powerglide to a Muncie (of course, we had to locate and install clutch linkage).

Also, I would suggest placing a Wanted ad and checking the
For Sale adds here to see if anyone may have these parts for sale.
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post #9 of 14 (permalink) Old Jan 20th, 20, 1:23 PM
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Quote:
Originally Posted by DZAUTO View Post
Now, with all the above said, to be really trick and fool people, you COULD retain the 3sp column shifter. I would require a little bit of linkage fabrication. I did this MANY years ago on two cars, a 54 Chevy and a 55 Chevy. The reverse position on the column becomes the 1st gear position on the 4sp, 1st gear position becomes the 2nd gear position on the 4sp, then 2nd gear position for 3rd and 3rd gear position for 4th.
For shifting the 4sp into reverse, we used an Overdrive handle/cable from a 3spOD transmission (back in those days a 3spOD handle/cable was fairly common in salvage yards).

Other wise, your option is cutting a hole in the floor for a floor shifter. Hurst has an excellent shifter made specifically for the 68 Chevelle. From the factory, with a bench seat, Chevelles had a boot/bezel and hump for the shifter handle. These 3 parts are readily reproduction from the Chevelle vendors. Here is what it looks like. This is my son's 68 4dr that we converted from a Powerglide to a Muncie (of course, we had to locate and install clutch linkage).

Also, I would suggest placing a Wanted ad and checking the
For Sale adds here to see if anyone may have these parts for sale.
👍. Very cool Chevelle ! 4 dr HT ?

and very cool “4 On The Tree”
(although, I think I’ll stick w/Hurst on this one !)
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post #10 of 14 (permalink) Old Jan 20th, 20, 3:41 PM
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Re: 3 speed to Muncie 4 speed conversion

Quote:
Originally Posted by Reelysalty View Post
👍. Very cool Chevelle ! 4 dr HT ?

and very cool “4 On The Tree”
(although, I think I’ll stick w/Hurst on this one !)

It is a super plain jane 4dr 300. Standard drum brakes, pwr str, factory air cond, 307/PG, AM radio. It was literally a little old man's car (as opposed to little old lady).
We put 15x7 painted steel wheels on the rear, 14x6 on the front with the original 68 dog dish caps. A few years ago, I bought a new 10bolt Eaton posi for him (it has a 3.08 rear).
We were GIVEN a 68 SS hood/hinges which we had painted and installed. Some of the guys here donated driver quality hood vents.


He had wrecked it several years ago (rearended a UPS truck!!!), and we put it back together with misc parts that we rounded up and some were donated by members here. We even came up with a floor shift steering column, so that we could get rid of the knob for the column shift handle.
We replaced the 307 with a 350 with an early Z28 intake, Q-jet and a set of headers, all of which I had up in the attic.


The front side marker lights had 307 in them. We replaced those marker lights with the plain marker light from a 6cyl car (no engine size).
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post #11 of 14 (permalink) Old Jan 20th, 20, 4:33 PM
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“The front side marker lights had 307 in them. We replaced those marker lights with the plain marker light from a 6cyl car (no engine size).”

Hahaha, all the 60’s street racers I know did that ! Best was those early Chevy II ‘s with “I-6” emblems 😁

“Plain Jane”. All the better when messin’ with SS 396’s. They’re such bad losers. 😁
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post #12 of 14 (permalink) Old Jan 20th, 20, 7:32 PM
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Re: 3 speed to Muncie 4 speed conversion

to make it easier, find a 70 or earlier 10/27 spline muncie trans so you can keep the same clutch, pressure plate, driveshaft and yoke. jim

Jim

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post #13 of 14 (permalink) Old Jan 22nd, 20, 12:26 AM Thread Starter
 
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Re: 3 speed to Muncie 4 speed conversion

Quote:
Originally Posted by DZAUTO View Post
Now, with all the above said, to be really trick and fool people, you COULD retain the 3sp column shifter. I would require a little bit of linkage fabrication. I did this MANY years ago on two cars, a 54 Chevy and a 55 Chevy. The reverse position on the column becomes the 1st gear position on the 4sp, 1st gear position becomes the 2nd gear position on the 4sp, then 2nd gear position for 3rd and 3rd gear position for 4th.
For shifting the 4sp into reverse, we used an Overdrive handle/cable from a 3spOD transmission (back in those days a 3spOD handle/cable was fairly common in salvage yards).

Other wise, your option is cutting a hole in the floor for a floor shifter. Hurst has an excellent shifter made specifically for the 68 Chevelle. From the factory, with a bench seat, Chevelles had a boot/bezel and hump for the shifter handle. These 3 parts are readily reproduction from the Chevelle vendors. Here is what it looks like. This is my son's 68 4dr that we converted from a Powerglide to a Muncie (of course, we had to locate and install clutch linkage).

Also, I would suggest placing a Wanted ad and checking the
For Sale adds here to see if anyone may have these parts for sale.
Sorry I should have specified that this is a 3 speed floor shift car but cool idea though on the 4 speed column shift
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post #14 of 14 (permalink) Old Jan 22nd, 20, 11:08 AM
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Re: 3 speed to Muncie 4 speed conversion

Quote:
Originally Posted by Cfritz1968 View Post
Sorry I should have specified that this is a 3 speed floor shift car but cool idea though on the 4 speed column shift

Then it would seem that all you need is a 70-earlier Muncie and a Hurst shifter for a 68 Chevelle.

Also, there are REPLICA handles available from the Chevelle vendors which have M U N C I E stamped in the handle. This would give you the solid shifting of a Hurst plus the APPEARANCE of a factory shifter.
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