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Change rear axle ratio


Well-known member
Oct 23, 2001
Oconomowoc, WI
1989 Medium Blue Metalic Convertible
I have an 89 convertble with the L98, 700R4 auto trans and 2:59 rear axle ratio.

I would like to change to the 3:07 or 3:31 rear gears for a little better punch from the hole. I still need a good highway cruiser so I don't want to go way up in ratios.

Has anyone tried this change?

I know that a change to the speedometer transmission tailshaft gears is needed. How difficult is it to change these speedometer gears? Is it necessary to pull the tail shaft off the 700R4 to change both gears or can you just change the plastic gear?

I know, lets get this over with so I only one more question. Does the 700R4 need any changes internally or will the shift points match up to the new axle ratios okay?

I can't wait for spring to get the Vette out and get this change installed.

Best Regards,
:xmas :confused
thanks for sending Radar in the right direction.
I'm going to add some more info to the post I already opened on this because I'm not completely done yet. That way my whole experience stays in one thread and can be used for others thinking of the change. Yours is only slightly different.
I'm adding some more info now and will again later this week.
Hey thanks Graham. I will stay tuned.


I read the threads you posted. I see what you mean. They almost answer my questions. It sounds like Graham will have a few more comments but I think I am squared away.

I don't want to sound stupid, and I think I may have seen this somewhere, but where can I buy a Dana 36 series gearset?

Does anyone know of a shop in the Milwaukee, Wisconsin area that can do this work? I could do the speddo gears but I won't touch the rearend!

Radar :xmas
You need to decide what brand gear you want to use. I went with Strange, but you can pick Richmond, Precision Gear, Yukon, Dana, and I'm sure there are others. We tried to get a Dana part for mine but it was discontinued.

Here are a few websites to keep you busy:


Also visit the actual gear makers website for info.

Don't do the speedo gears yourself. In order to get the R&P changed they'll have so much taken apart it will take them all of 15min to put the speedo stuff in.

I know of a great shop, but it's in the Chicago area. Actually, there is a guy from your neck of the woods that brought his C5 to my buddies shop to have ARE's heads and cam package installed, along with a Carroll Supercharger installed. 526 RWHP!!!!

Anyway, if you are interested, check out www.vettewrench.com for the phone number. I'm the webmaster and haven't had time to update the site with more information.

Also, this is where I had my Dana 44 conversion done. Excellent work and great prices.

One more thing you may want to consider. You could pick up a rebuilt rearend with the gears you want from Mid America or Ecklers. I know one of them sells a complete rearend, but not sure if they both do. I think Zip products also offers these rebuilt diffs.

This route would leave you to do the labor yourself and avoid the hassle of rebuilding your own rear diff. All you have to do is send in your old diff as a core. You would save a little on labor.
Hey Thanks for all of theinformation!!!!!!!!!!!

I have been gone a few days and just found these replies.

Regrads and Thanks,

Radar :SANTA
Boy, spelling leaves a little to be desired! Where is a spell checker when you need one!

Radar said:
Boy, spelling leaves a little to be desired! Where is a spell checker when you need one!


:L :L :L We all have our days. What's even worse is when you spell a word right and it just looks wrong.

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