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converting to a 6 speed.

Forum: C3 Engines, Driveline and Handling

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converting to a 6 speed.

Posted: 5/31/05 11:40amMessage 1 of 9
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BELLE RIVER, Canada
Joined: 1/5/2003
Posts: 25
Vette(s): 1972 LT1 coupe 2003 conv. 6speed aniv.
Has anyone converted a C3 4 to 6 speed. I have been trying to get as much info as I can before taking the leap. I am looking at the  Tremec T-56. What I have is a 72 LT and I don't want to do any major modifications to the car. It's all original and I want to keep it that way. I understand about changing the driveshaft and having a new cross member made. What I have been told is that some cross members were welded and some bolted. I will have to look at what mine it but I thought it was bolted.  What I don't know is the modifications to the tunnel etc. I was told by some that there are no mods to the car itself and that I can just go back to the muncie at anytime and no one would know that I had a 6 speed in it. Also I want to see if I can get a repo look alike shifter to keep the same appearance. Can anyone give me some knowledge about this or has anyone done this and can give me some tips on what I'm in for.  
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converting to a 6 speed.

Posted: 5/31/05 2:59pmMessage 2 of 9
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Tucson, AZ - USA
Joined: 8/31/2004
Posts: 19
Vette(s): 68 Roadster
I have read both good and bad about these guys, but they claim to do what you want to do ----   http://www.keislerauto.com/gm/transmissions/corvette_68-82_6 spd.asp
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converting to a 6 speed.

Posted: 5/31/05 3:45pmMessage 3 of 9
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CUYAHOGA FALLS, OH - USA
Joined: 12/2/2003
Posts: 6424
Vette(s): 1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!
The automatics are bolted, the manuals are welded.
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converting to a 6 speed.

Posted: 5/31/05 5:45pmMessage 4 of 9
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Frederick, MD - USA
Joined: 9/8/2003
Posts: 3398
Vette(s): 1969 convertible L71 427/435 4-speed black interior
I've given some consideration to installing the Keisler 5-speed in my '69, but haven't really been serious about it. From what I've found out, Keisler's 5-speed is essentially a bolt-in installation while the 6-speed requires modifying the transmission tunnel...something I'm not willing to do.

There's a lot of good and bad things said about Keisler. I've heard good things from the Corvette crowd and the Mopar people hate him. The magazine reviews are usually very good, but when you identify yourself as a magazine writer doing a review on their product, I would think you would get good service and carefully gone over parts.
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converting to a 6 speed.

Posted: 6/1/05 4:49amMessage 5 of 9
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SOUTHWICK, MA - USA
Joined: 6/26/2003
Posts: 336
Vette(s): 1975, L-48 coupe, 4-speed, light mods

One of my hot rod friends was telling me the other day that the best one to put in was the Nash or Richmond tranny. He said that this was because it was a true one for one gear change. I don't know if this is true but thought I would tell you.

I personnally like the info and links that Ben has on his site about this http://www.vetteprojects.com/cthulhu/trasmission_search.html

I was thinking about the TKO-600 but it will have to wait now that I spent all my money on the new offset t-arms and steeroids

Glenn's Bright Blue 75 T-Top
L48, 4 Speed, Dual Exhaust
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converting to a 6 speed.

Posted: 6/1/05 3:49pmMessage 6 of 9
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Encinitas, CA - USA
Joined: 9/9/2004
Posts: 17
Vette(s): 1968 Roadster with Tremec TKO500.

You can find detailed info here about a TKO 5-speed swap.

http://www.classicchevy5speed.com/tremec_transmission_1968_c orvette_wu.htm.

6- speed swap will require mods to the tunnel and is generally a more difficult install.

Feel free to call with questions.

Jeff Mortenson |
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converting to a 6 speed.

Posted: 6/6/05 8:45amMessage 7 of 9
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BELLE RIVER, Canada
Joined: 1/5/2003
Posts: 25
Vette(s): 1972 LT1 coupe 2003 conv. 6speed aniv.

Sorry for not responding last week, I had to go out of town and had no internet access.

Thanks Guys for the input. I really don't want to do any modifications to the car. It's all original and I want to keep it that way. It looks like the 5 speed is the way to go. I just want to keep the RPM's low due to I only use it for going to meets out of town. Does any one know how to figure the RPM's for the 5 speed vrs. the 6 speed with a 3.08 gear and stock tire size. Right now at 70 mph I'm doing about 2750 rpm with the stock tranny.

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converting to a 6 speed.

Posted: 6/6/05 8:52amMessage 8 of 9
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Frederick, MD - USA
Joined: 9/8/2003
Posts: 3398
Vette(s): 1969 convertible L71 427/435 4-speed black interior
Go to http://www.keislerauto.com/tools/gm_analyzer_5sp.html ; (made link clickable - Norsky)

It's at the Keisler Auto website and is the calculator for rpm's and speed with their 5- and 6-speeds transmissions. Norsky38509.3990856481
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converting to a 6 speed.

Posted: 6/6/05 9:44amMessage 9 of 9
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BELLE RIVER, Canada
Joined: 1/5/2003
Posts: 25
Vette(s): 1972 LT1 coupe 2003 conv. 6speed aniv.

Thanks,  I take a look.

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