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custom transmission
Posted by: 1967vair500 ()
Date: July 08, 2019 11:56PM

so I was looking at swapping my 3 speed transmission with a 4 speed for quieter highway cruising, but then I found out that both transmissions in their highest gear are a 1:1 ratio. I had an idea to take the gears out of a 3 speed and put them in a 4 speed shell and then make a custom gear to replace the 4th gear with to make a sort of overdrive for highway cruising. any thoughts or opinions?

Alexander levi
SE Portland, Oregon
1967 corvair 500 95hp 3spd coupe

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Re: custom transmission
Posted by: American Mel ()
Date: July 09, 2019 12:02AM

What size tires are you running?
Diameter can make a HUGE difference in mileage, and cruising RPM.
Going to taller rear tires is much cheaper, and easier than trying to create a "New Transmission".
Are you a member of CORSA Oregon?
If not, then JOIN NOW ! ! !
CORSA Oregon has some of the BEST Corvair guys in the Nation ! ! !
They meet at the Stamp Society building in Northwest Portland, first Weds. of the month.

WA. state, 1 mile south of the Canadian border,
I am not at the end of the world, but you can see it from here.
Have; '66 Monza Coupe - 140, 4-spd. Daily driver beater
'67 Monza Vert. - 140, 4-spd. Daily driver beater
'67 A/C Moredoor Monza - Sale pending
Have had; '61 Monza coupe, '62 Monza Wagon, '63 Spyder, '65 Corsa
'04 Dodge Cummins Quad Dualy, approaching 400K

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Re: custom transmission
Posted by: vairmech ()
Date: July 09, 2019 04:49AM

It could be done but you would have a weird shift pattern. If you take a 4 spd third would have to be the overdrive. So your shift pattern would be 1-2-4-3. I forget what number you can get for an overdrive but the cost is somewhat prohibitive. I can easily see $1500-$1800 for a trans, maybe more as it would all be custom.

Ken Hand
Handy Car Care
248 613 8586

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Re: custom transmission
Posted by: steve c goodman ()
Date: July 09, 2019 05:07AM

What is your r/p ratio in diff? If you
have typical 3.55-1 it can be swapped to
3.27-1 or 3.08-1 if you can find one.

best wishes, Steve
Rear Engine Spec. Inc. Golden, Colo.

1962 spyder 3.0L turbo---1965 Crown V8
1967 monza 110/4---1968 monza 110/4
1971 amante gt 110/4

Edited 1 time(s). Last edit at 07/09/2019 05:12AM by steve c goodman.

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Re: custom transmission
Posted by: cnicol ()
Date: July 09, 2019 06:56AM

Years ago I put a "custom" transaxle in my '67.

The combination used a 3.08 axle ratio combined with an early-model, wide-ratio 4-speed. The low, 3.65:1 first gear (vs 3.11 in a '66-9 4sp) yielded a perfectly normal take-off and a relaxed highway cruise.

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe (sold, sniff sniff)
66 Sprint Corsa convt - First car! Re-purchased 43 years later
2+2 gnatsuM 5691

+17 Tons of parts

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Re: custom transmission
Posted by: scottymac ()
Date: July 09, 2019 10:04AM

I know in the Seventies after the first gas crisis, Ford and Chrysler took their four speed transmissions, juggled the ratios, and like your idea, third gear became a 1:1 ratio and added an overdrive gear. Honestly don't know if Saginaw did the same.

My old '66 Galaxie was originally a three on the tree. Found one of the overdrive trans in a Granada and replaced the three speed with it. In the late Seventies, Ford eliminated the external linkage and came out with the SROD transmissions. I found one with an aluminum case in a Mercury Zephyr, and swapped the Granada gears into the Zephyr (longer input shaft) case. With the .70 overdrive top gear and a 3.00:1 axle ratio, the old boat will cruise at 80mph @ 2,700 rpm (289 V-8 mostly stock), and knock down 20 mpg. Don't think about acceleration, though, gaps between gears are WIDE.

Danville, In.
'65 Corsa basket case
'66 Monza coupe

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Re: custom transmission
Posted by: caroseiii ()
Date: July 09, 2019 10:06AM

You have to do the 3.08 for that, like Craig wrote. It has some negatives if you don't have enough torque with the 3.1 first gear.

Crawford Rose

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Re: custom transmission
Posted by: RCSmith ()
Date: July 09, 2019 11:19AM

I believe Bob Coffin has built
a 4spd overdrive in the past.

In ‘86 chevy had one available in the Cavalier
with 2.8 6 cylinder.
3rd gear was 1:1 and 4th was around
a .7 overdrive. It worked out fine.

Ray C. Smith
'66 Corsa

Bergen County ,NJ

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Re: custom transmission
Posted by: vairchet ()
Date: July 09, 2019 11:22AM

So.... you like shifting? Check this out: []

Chet in Ramona

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Re: custom transmission
Posted by: 66vairman ()
Date: July 09, 2019 12:33PM

Compared to today's O.D. cars the Corvair does sound busy on the highway, but keep in mind a Covair engine was not built to run at low RPM under highway loads like modern engines with advanced lubrication systems.

I run a 66 four speed with a 3:27 diff. gear and it's a good compromise for nice starts in 1st and quieter cruising vs. a 3:55 ring and pinion.

I found adding sound deadening (including inside on the roof) and the engine compartment fiberglass mats (Clark's sells them) reduced the highway noise level.

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Re: custom transmission
Posted by: joelsplace ()
Date: July 09, 2019 12:52PM

For the OP's question - 4th isn't a "gear" as such. It is just the input locked to the output so you can't shuffle different gears around to change it. That will hopefully help you understand Ken's correct answer.

Northlake, TX
5 Ultravans, Lost count at 100 Corvairs...

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