Now we come to the reason I actually came to this forum - and it was not to talk about speeding tickets and Cadillac "trucks" :)
Has anyone here "retrofitted" an older Vette with a modern 6 speed overdrive tranny? Yes, I remember form doing the clutch (years ago) that getting the tranny in and out is a royal PITA but I'm willing to go through it again.
I'm thinking of doing this "refit" to my '68 roadster (a driver painted AMC "fresh Plum",with no matching numbers anyway) to increase fuel economy, and of course it can't hurt performance. My syncros are worn (and have been for years) so it's another excuse to pull it.
I have a friend working at Borg-Warner so he can get me a real good deal on it. :)
Not to difficult but like you said getting it out is difficult. Best to start off with the engine loose. Many sites on the web that show step by step instructions for the change. Most are for 5 speed changes as the 6 speed has a bad shifter location if I remember correctly. GM in the early 80s had a 4 speed over drive in their pickup that is a fit for your car. Most are worn out and are expensive to rebuild. Take a look at
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If you take a good look at this change there is one small item that they did not mention. The exhaust pipe is close enough to the speedometer cable, now made from plastic, then it doesn't take long to melt it and then twist the cable off.
Even with a 35% reduction in RPMs you won't see that much in gasoline savings. You will still be running a inefficient V8 of yesteryear that may save you 15/20% at best. I'm having lunch with a friend that made this change and an upgrade on his fuel deliver management (injection) and I'll let you know how his worked out.
Yes, I'm curious. If I'm gonna do the work, I kind of want a new 6 speed - at least until that becomes impossible.
Again... this is still "out there" a bit. I plan to "rescue" the car from long term storage and move it to my SC home next month. Then I'll see where it's at and what it "needs" - then comes what I "want".
When he installed the 5 speed Tremac it was before they had started modifying them to fit the Corvette shifter location. Consequently he had to modify his floor pan. That is my thought on the Borg 6 speed also, the shifter location is back to far to fit the existing shifter location. He nor I have any on hands experience with that transmission so further actual location data would be needed. Just looking at old data I have of the Tremac top mounted shifter is 19.5 from shifter center line to mounting face, and 26.4 to bell housing face of the T56. Be aware that on the T56 that the bell housing is part of the transmission. In any case you're talking .68:1 versus .62:1 between the 5 or 6 speed. Also the back (top) of the T56 is higher than the shifter mount which will require a tunnel alteration. On the other hand an economical purchase of a 5 speed Tremac, new clutch, engine removal to install, plus the shortened drive shaft required, new speedometer cable, and shifter will produce a really neat "cool" factor.
He is still in the process of updating that Corvette and is going to a
3.08:1 differential to get better mileage. His mileage savings was in the 3 to 5 miles per gallon range which included TPI injection. That may give you a .03¢ per mile savings for a $2,500 transmission swap, or an 84,000 mile payback. I've looked at this a number of times for my '64 but always come back to the old 4 speed and keep my foot out of it, yeah, right. ;-)
On the other hand if you can find an early '80 MY6 GM 4 speed over drive they fit right in, 1st 3.09, 2nd 1.67, 3rd 1 to 1, and 4th .73. The later models changed the mounting pattern so choose the year wisely.
As long as we got your head working take a look at this.....
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They are quoting $1795, less ship/taxes on a new unit with this set of gears. I'm only 60 miles from them and if I can make an unmodified swap I might just do that. Not a big ratio change but I have had a bearing singing in third gear for the last 2 years. Failure will happen when I least need it, so I thought I'd give this outfit a try. Also comparing their price to the Tremac 5 speed at a bit higher price and a lot more parts to change. Haven't heard from them yet but expect it will be close to $2800.
What was your connection to South Carolina? My son lives down there, just got back from hog hunting with my sons down by Estell.
Sorry for the long delay. I was up in NH, amongst other things checking out the Vette for rescue. I moved to SC, 5 years ago - but the car got left behind in storage.
I plan to get it down here in 2-6 weeks and start taking stuff apart. It needs a LOT of work now to get healthy. This before any modifications etc. Started right up though!
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