I Can't Drive 70!
 

Hi All,

I have a '79 Corvette Coupe with a 4-speed manual transmission. The engine rpm is 3500 at 70 mph. Is there a transmission with overdrive that would bolt in? I'm thinking a Richmond 6-speed or would changing the rearend gear ratio do the trick? I enjoy driving this car around town but on the freeway for extended periods of time is unbearable and I curse the idiots who created this defect in design.

Thanks for any responses.

Steve

RE: I Can't Drive 70!
 

Kinda sounds to me like somebody changed rear-ends. That seems to be geared low. Check to see what your rear-end ratio is. Most tranys are 1-1 in high gear so I don't think that is your prob. As I said before, check rear-end ratio. I have a 3.08-1 in my '80 Vette w/M22 4-sp.

RE: I Can't Drive 70!
 

Changing the trans would be expensive and difficult, although there are good kits. I'd suggest just changing to a different rear end ratio, although you would lose some low end acceleration.

I did a little calculation based on typical tire sizes for C3s (tire diameter 25.6 inches) and came up with a 3.80 axle ratio to give 70 mph at 3500 rpm; I'm estimatd tire sizes so its likly you have something between 3.73 and 3.90, rather high for a non overdirve trans, but common among people who intended the car for 1/4-mile contests. A 3.23 would drop it back to just below 3K at 70 and a 3.08 to around 2650.

One thing to check before you do anything else is if your speedo is correct. Are you sure its accurate? It could be old and tired and indicating 70 when you are really doing, say, 80. I'd go out where you have a series of mile markers and drive a steady 60 with a passenger holding a stop watch - 60 mph is a mile a minute: easy to check.

RE: I Can't Drive 70!
 

a TKO500 trany would sute yoou well[&:]

http://www.keislerauto.com/gm/g_body.html

RE: I Can't Drive 70!
 

Nice '80. It looks just like mine. Black on Black?
Now how exactly do you check the rear end ratio?

Steve

RE: I Can't Drive 70!
 

Thanks for the calculation. Yeah my speedometer is correct.
I've got people passing me all the time when my speedo says 70.

Steve

RE: I Can't Drive 70!
 

What is a TKO500?

Steve

RE: I Can't Drive 70!
 

Reguarding your axle ratio.
See the posting: 71 LT1, what's my axle ratio? It's spelled out for you there.

RE: I Can't Drive 70!
 

Lee sounds correct, my old 81 in the end had 3:73's and I was in the same boat but you can't beat the acceleration. Initially it had something like 1:2.87 or 1:2.73 and in second gear 70 was easy. Changing the diff is the correct way to go, cheap , easy enough to do yourself. Your can buy them cheap enough , maybe around $200 to $300 for one in good shape. Try 3:08 ' 3:23 or 3:55's if you don't want to give up all the pep of the line. Remember , you get what you pay for and you only want to change this once....lol. Another thing, how tall are your tires, if their not around 26inches then you will go slower and your speedo will read high.

RE: I Can't Drive 70!
 

A tko500 is a 5 speed overdrive trany rated up to 500 foot lbs of TQ.

heres a kit link to a kit... http://www.keislerauto.com/gm/corvette-c3-kits.html

gears would be cheeper but not as fun[:'(]