terrystrand

Would appreciate your help on this: Found a place called Vtech differentials in Stillwater, IL that has been swapping Corvette diffs for years. I got a price of about 800 for the part itself and 3-500 for their R&R labor to change my 3.36 gear for a 3.70 or higher gear. Before spending this total of around 1300 bucks I'd like to get some feedback from youse guys who have actually experienced a diff change on your car. Specifically I enjoy acceleration, and don't drive much on the highway. So how much do you notice in the take-off....for example, from a stoplight to about 30-40 MPH?
Thank you,

Terry S.
Chicago

Tumarr

auto or manual? what engine combo and hp?

Ganey

Yes it will make a diff. in accel. Sounds like you have a 4 spd. manual trans.
You should state yr., engine & trans.

Will's'74VetteL-82

Terry-

My 1974 L-82 4 speed came from the factory with 3.70s and it still has them. The car is very fast with them, and can do pretty "incredible" things. I have taken 90 degree turns slowing down to about 3 mph in 4th gear and it takes 'em. The shortness of the gear allows really slow creeping while in gear. For city driving it is fine, 25 mph in 4th. On the highway, however, it is at 3500 rpm at 70mph. With sidepipes is makes for a thundering journey! I'm sure its not the best for mpg or wear and tear, but it is a great thing to experience and it pulls like a beast. They allow for the power to be applied at all times, no matter what gear you're in.

I eventually want to put a 5 speed in, because its begging for another gear on the highway. Other than that, I love the gears.

Will

68sbcoupe

The main difference will you feeling $1,300 lighter. The torque multiplication factor improvement is only 10%. In a well sorted out car, we swapped a 3.54 rear for 4.10, and picked up .2 in the quarter. Should have gone to 4.56 or 4.88.

You can obtain a similar increase in acceleration potential by going to shorter tires. For a whole lot less $$.

Tumarr

yea I agree, its not going to be a huge seat of the pants feel difference. your better off looking for additional HP and tq to make a better difference.

LT1driver

disagree it will feel faster and you will notice it....how do I know, been there done that and best move I ever made good luck and happy motoring

AGVI

It'll feel harder on the gas bill?!?! Seriously, I hope you notice a difference in acceleration!

7T1vette

Spend the $1300 on heads and cam; it will give you a lot more 'kick' than a 10% change in gearing.

Vette5.5

I'd think long and hard about changing out that 3.36, as it's probably the best comprimise for street/highway, and certainly not worth $1300 bucks for 10% change. While a lot more money, a friend with a 79' L-82 4 speed 3.70, recently changed to a Keisler TKO 5 speed. Lower 1st gear, and .70 o.d. Pretty much transformed the car.

gkull

If your motor is a dog. Gearing makes it a slightly faster dog. Once you are in a gear it takes power to move mass

terrystrand

Thank you very much for the info.

It's a 75 base 350, four speed, tired, eighty k mileage, for those of you who asked.

Never thought about shorter tires, though that would affect the whole look of the car?

A five speed with OD is the way to go, but that's several grand for me. Ouch.

I don't need to highway drive, just city hops around Chicago, so maybe I can go to even a higher gear like a 4.11 or 4.56?

The car is such a dog that I miss the 'pull' at low speed or from a stop that I had in my old crate-engined 77 'Vette.

Also looking at cam/manifold/headers for next project. Man this thing is going to be a real gas guzzler, but if I get some great perfomance it could be worth it.

Any of your further thoughts on all this are much appreciated.

Ganey

Start thinking about a rebuild. You can get more perf. & better mileage w/ better exhaust like about +1 duals & +1 headers. See what many refer to as my Exhaust topic. http://www.corvettefaq.com/c3/ganeyexhaust.htm
Cam & al. intake can be done at same time. This will make a day & night diff.! Then heads can be replaced or rebuild w/ more compression.

63split63

I just swapped out my 4.11s for a 3.36 and I like it . I got tired of all that RPM . I,m going to try a 3.08 if I find one cheap .
I guess I'm getting old .

JMOP Bill 71LT1

Rally68

I guess I don't understand...Do you need a new differential housing and/or posi carrier & side yokes? Because $800 for gears and a rebuild kit is too much. US Gears (made in Chicago!) from Tom's are $270 for a 3.73 ring and pinion, and a rebuild kit with Timkin bearings & seals shouldn't cost more than $150 or so. Are you sure they didn't mean $800 all-in?

I am a big fan of the 3.73s but I went from a 3.08 so I could really feel the difference

Big Block 69

In my opinion, If you mostly drive in town and enjoy acceleration, you will appreciate the change to lower gears.
I changed mine to 4.11s and I'm thinking of changing them again to either 4.56s or 4.88s.
If you buy the rearend, there's plenty of people on here to walk you through changing it yourself.

Rally68

I have my old set of 3.08 gears that are in excellent shape; I'll sell cheap. PM me & I'll send pictures

fauxrs

A 75 base 350 is the absolute low point for a C3 in HP (165hp) - it was arguably a dog when new and a tired old one will be more so. A 10% change in gearing is really just a band-aid for that bigger problem, and not a particularly effective band-aid at that.

for $1300 you should be able to boost the power of that motor well in to the 200's if you can do some of the work yourself.

• If you still have the factory catalytic convertor, replace with a modern hi-flow unit
• Headers if you dont already have them
• Intake and rebuild the carb
• Find Lars' timing paper and use it - (there is a fair amount of power untapped in that motor just from timing)
• over time - replace the cam - replace the heads

terrystrand

Hey guys, that's a lot of great information for me on getting more performance out of my 75 Vette...and I really appreciate it.

Probably should have purchased a 'done' Vette instead of getting nickle and dimed with cam, heads, carb, headers, gear change, etc., but this is a nice car, and my third white mid-seventies Vette that I've owned in my life....I buy 'em because I like seventies c3's and they are relatively inexpensive.

I was told by Corvette City to avoid a crate engine if I didn't want to get involved with some simple but costly adaptations like throttle linkage and odds and ends. They said instead to do a top end rebuild with hi-perf heads, manifold, cam at least, if possible, headers. They've done nothng but Vettes for thirty years here and are the ultimate experts I've found in Chicago on the Corvette.
http://www.vetteconnect.com/
These guys are the Corvette gear gurus, and also have been around here forever.
http://www.vtechcorvette.com/

Keep those ideas coming...because I read every word, and thank you again.

7T1vette

If you just want to pep up the engine a bit, there are several inexpensive things to check/change which will make a significant difference in performance:

1) Verify that your secondary throttle plates are opening and doing so completely. You must do this by depressing the accel pedal--not using your hand to exercise the linkage on the carb. The pedal, pedal linkage, cable, etc. are all part of the system and this is a very common problem that folks neglect to check. There is also a secondary throttle lockout on the right side of the carb base which prevents secondary operation when engine is cold (it is released by an 'open' choke mechanism). If the choke is not working or not set correctly, the secondaries will not open. Now, if you hold the lockout lever away from that pin and hold the secondary air valve open, you can look down to see the secondary throttle plate action as someone else is depressing the pedal. If the throttle plates don't open or don't open fully (completely vertical), that is part (or most) of your problem.

2) Reset your ignition timing and recurve the distributor for performance...rather than "engine comfort" and minimum warranty expense (which is why GM set them up as they did from the factory). Lars Grimsrud has info on how to do this. It is relatively simple, nearly free, and makes a tremendous improvement in performance if your distributor has not had this done previously. Use the SEARCH function to find this info using search words like "timing", "distributor", "recurve", etc. If you can't locate the info, send an e-mail to Lars politely requesting his paper on modifying the distributor for performance. His e-mail address is V8FastCars@msn.com. All you need is a timing light and a screwdriver to remove the distributor cap and the rotor.

If your engine does not have any serious problems, and you have not previously implemented the items above, I can guarantee that you will be quite pleased with your car's performance when you've properly implemented/corrected just these items. Good luck.