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3/19/13 10:36am - Reply: 'Re: change differential ratio'
tonytheroofer
Former Member
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Rochester, NY - USA

Vette(s):
1980 L- 82 fully restored and upgraded.

Joined: 6/12/2012
Posts: 95
Resurrection of a thread :):) 

Someone said they have a 3.08 rear , if you do , you can not run an OD transmission because your carb is unable to regulate the fuel mixture for the high load low rpm situation you will encounter, Your motor will kick and buck like a steer at a rodeo ..  


My best guess for rear gears would be no less then 3.36 ,,, however a 3.55 up to a 4.11 would be a perfect range for all driving even if your in OD as early as 40mph. So if you have a really low rear and no fuel injection you can not run the OD units. 


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1980 , ZZ430 , 3.92 rear , 700R4 2400 stall NEW EZ EFI 
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3/19/13 12:32pm - Reply: 'Re: change differential ratio'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19449
F4Gary said: 3.36 would be perfect.  I wish I had done that.

So can I put a 2.64 first gear in my tranny if it doesn't already have one?  I assume the LT-1 came with a close ratio tranny.

As far as originality in your rear end.  Wink  I don't think the NCRS checks the actual rear end ratio.  I assume they just check the numbers stamped on the rear end housing.  Kinda like changing the internals of an original engine.  What they can't see they can't check.

Go for it.

Why, coitainly....all ya gotta do is change the cluster gear, and the 1st, 2nd, and 3rd gears on the mainshaft....or just swap the trans for a wide ratio and be done with it. Thumbs Up

As far as NCRS stuff on the gear ratios, it wouldn't matter at all unless you were going for a P/V(performance verification). They check the rpm vs speed, and mileage on that, so you wouldn't be able to get away with a rear ratio change.


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6/17/13 8:20am - Reply: 'Re: change differential ratio'
thallow
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Brownstown, IN - USA

Vette(s):
1969 Red Convertible

Joined: 10/3/2007
Posts: 24

dan did you get the ratio changed. I am considering a change also and was wondering how it came out.  My 69 has 3.7 with a tremic 5 in it and I agree 1st gear is way to low, I start in 2nd most of the time but it is a bit tall. 70 in 5th is about 2360. The engine pulls good at the low rpm, and we use it for long trips.



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6/17/13 9:43am - Reply: 'Re: change differential ratio'
dapperdan
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COLUMBUS, NC - USA

Vette(s):
2011 Grand Sport Coupe, 6-speed 1977 Coupe L82, 4-speed

Joined: 8/19/2012
Posts: 42
I have decided not to change the rear end, mostly to keep the car in its original configuration.  I just learned the it has the "Rockcrusher" transmission, so I am going to keep that too.  Had the U-joints replaced; the rear strut rods and the 4 shocks.  Also, had the inside rear wheel bearings  lubricated with a device that I got from Zip Corvette.  I am just going to live with the 3.70 rear end, since the car really runs great with the setup that the Chevy engineers thought was a good compromise at the time.  The car is a "trip" to drive, but it is just my toy, since I have a 2011 Grand Sport as my daily driver.

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8/9/13 9:00pm - Reply: 'Re: change differential ratio'
RalphTil Lifetime Member
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Summerville, SC - USA

Vette(s):
1977 Silver Coupe; built on March 15, 1977. Every option except towing package and roof rack! Just turned 61,000 original miles!

Joined: 9/23/2009
Posts: 24
Sorry but a move to a 3:53 rear is not worth it.  If you want to get your gas mileage up say, above 20 MPG, you will need to go to a Tremec 5-Speed trans and a 3:07 rear.  We have tried every variety above that (ie 3:36, 3:55)  and you struggle to get to 20 MPG.  I, too, have a '77 and all that numbers matching stuff is nice but doesn't really move the $ needle.  I would make the changes that improve driveability and save the original parts.  Gas was under $1/gallon when these Vettes were new and the big gears helped with the smogged engine performance.  I have a Turbo 400 automatic, L82 with a 3:55 rear and it races at 70 MPH.  I'm going to a 2:87 rear with an engine rebuild over this winter.  Only has 61,000 miles but valve seals and guides are leaking.

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6/11/15 6:35pm - Reply: 'Re: change differential ratio'
dwa175 Gold Member
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oakville, CT - USA

Vette(s):
1979 coupe and now 2007 c-6

Joined: 7/19/2014
Posts: 183
hi  I know on this site the fellas  don't like overdrives  I have used overdrive in my 49 ford to 73 chevy p/u  easy to do  takes up no room   little bit      nobody likes them.my 79 runs 3200 rpms at 60 mph hour  50 to 60 miles cost a half of tank of fuel,i have looked high and low  for a overdrive unit   no luck   contact a company that's sales overdrive  they want me to buy a new 5 speed   at 5,000 $  not going to happen,going to calf  this mouth  I will find a overdrive unit if I do  I will tell you  and you can do as you wish  good luck  dwa     p/s  can stand using that mush gas for short trip.Beer

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