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It's my understanding that some of the B.M. Corvettes had a lever one could pull that would add an overdrive gear and change the rear end gear ratio from 4.88 to 3.42, effectively changing it from a street/strip setup to a highway setup with the pull of a lever.
Does anyone know how this was achieved? How did they modify rear diff ratios on the fly? Or did they? I've been searching the ol Interwebz and cannot find any specs or tech info about how they did that.
Those are really cool...but these days it's easier to install a 5 speed. I've got 3.07 rear gears.....and with my current trans gearing in 4th gear I'm at a final drive ratio of 4.08. Then I click into 5th which is 1 to 1 with no O/D and cruise.
There can’t be much length for one. I would be curious about driveshaft angle issues in a c3. My driveshaft with my 5 speed is very short. 23”-24” if memory serves?
My buddy had one with electric engagement. The older ones had a lever sticking out of the passenger console. There was not much room for a driveshaft, it wasn't much longer then a 1/2 shaft if I recall. It bolted on the back of the trans in place of the tailhousing. It is old school technology that works better with cars with more room under the car. OD trans are a much better option today.
Those are really cool...but these days it's easier to install a 5 speed. I've got 3.07 rear gears.....and with my current trans gearing in 4th gear I'm at a final drive ratio of 4.08. Then I click into 5th which is 1 to 1 with no O/D and cruise.
JIM
Just curious. What is your 1st gear ratio? Thanks.
Just curious. What is your 1st gear ratio? Thanks.
3.49. Only gets me a 10.71 overall first gear. Equals somewhere between having a wide ratio Muncie and 4.10-.4.33 rear gears. Or about the same as 4.88's and a close ratio. Sounds like a lot...but a little more would help me get this thing rolling when the slicks are mounted.
JIM
Last edited by 427Hotrod; Dec 9, 2020 at 10:05 PM.
The hone over drive was a neat unit that lever. Probably made it slightly more compact than the gear vendors unit. But maybe less useful. The gear vendors unit can actually make a 3 speed automatic a 6 speed by allowing the overdrive function in every gear
I was looking into installing a Gear Vender unit in my 73 behind my TH400.
A friend of mine has one in his Chevelle and he loves it.
I talked with Gear Vendors customer service several times and found there was a large amount of tunnel modifications necessary for a Corvette.
Because of the modified tunnel width the seats had to be squished into place and in a few instances needed to be hard mounted with no adjustable slides.
The owner of Gear Vendors has a C3 which they did install their unit into which took them a lot on work to get it to fit.
Like mentioned above it will be easier to install a five or six speed unit.
Baldwin-Motion Switchable Rear Diff
Hone Overdrive. Basically the same as a Gear Vendor Overdrive. No modifications to the differential.
