available ratios between 3.08 and 3.73

[luvbowties]

What ratio differentials were available, thru 1972, between 3.08 and 3.73 that will work in a 1966 pickup? I cannot find a precise response, only approximations.

I want something lower, numerically, than the 3.73 now in my '66 stock differential--running with a 700R4. Mine is stock '66, but with the longer, later model 5-lug axles(using home-made spacers behind later, wider backing plates).

I've got a complete 3.08 diff'l. from a '72, but don't want to jump that far down. I'd ideally like to have something close to 3.42-3.50 range.

I'm almost certain I've seen reliable info from CaptainFab, but can't find it now. BTW: I don't ever come close to doing burnouts!
Thanks, all.
Sam

[Clyde65]

I have the 4l60e (same as 700 but electronic) I had the 3.08 and it was sort of a slug. Did fine over 70mph, but how often do you go 70+? So I put a 3.73 in my 12 bolt. This works great for me, I drive about 50/50 hey and city.

The 12 bolt 3 series has 3.08,3.42 and 3.73 iirc. Check summit for parts and rebuild kits.
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[luvbowties]

Thanks. I have an '87 S10 Blazer with your same 4L60E with close to a 3.42 (been 15 years since I checked it!) and it works great, town and hwy, with the '95 Z-28 LT1--even consistent 23-24 mpg on hwy trips; hence my desire to experiment with a similar ratio in my '66 C-10 with a stock '96 Vortec with perfect q'jet carb, headers, etc.

I find myself running in what feels much too low a gear while around-town driving, which is 95% of my runs with the '66. Even minus the multi-port f/i the S-10 has, it seems to have lots of low end torque, even tho' noticeably less than the S-10.

My 3.73 does well enough that I'd never swap it for a 3.42 without trying one out first. I think I recall CapFab saying the 3.73-and-larger do not allow simply changing ring-and-pinion to go to the smaller numbers, like the 3.42???


Another great help would be to know which years pickups were more likely to have the 3.42 ratio? I'd prefer to get entire diff'l to install in my '66?
Thanks again,
Sam

[Captainfab]

I don't think the 3.42 gears came out until '73 and up. The set I have in my '66 Burb came out of a '74 C10. To use the 3.42 gears in your '66 housing you will need a 3 series carrier. The 3.73 gears use a 4 series carrier. If you choose to use another complete differential, keep in mind that the '71-'87 differentials are 1.5" wider than your '66 12 bolt, plus they are 5 lug. However, you could change the axles for a set from a K10.

[luvbowties]

Originally Posted by Captainfab

I don't think the 3.42 gears came out until '73 and up. The set I have in my '66 Burb came out of a '74 C10. To use the 3.42 gears in your '66 housing you will need a 3 series carrier. The 3.73 gears use a 4 series carrier. If you choose to use another complete differential, keep in mind that the '71-'87 differentials are 1.5" wider than your '66 12 bolt, plus they are 5 lug. However, you could change the axles for a set from a K10.

Thanks, Clyde65 and Captain. I already have the longer axles--in effect my diff'l with the longer axles & its spacers is the same width as the '71-'87 already, so no problem there.
I still have 3 questions: One, what is a 3-series vs. a 4-series?

Two, which of the Summit r-&-p-sets would work in my present diff'l--they show 3 Richmonds(not to mention the MOTION ones): one has no special name & is p/n 4900701 @ $203.95; 2nd is "Excel" p/n 12BT342 @ $165.99; 3rd is "Sportsman" p/n SGM12T03 @ $192.00. >> http://www.summitracing.com/search/p...20and%20pinion <<

And Three, do you know anything about quality of the MOTION brand?
Thank you again,
sam

[Captainfab]

The 3 series carrier is for the 3.42 gear and higher. The 4 series carrier is for the 3.73 and lower gears. The difference is in the position of the ring gear flange.

I don't know anything about the 3 different grades of the Richmond gears. I would suggest a call to Summit tomorrow.

I believe Motion gears are a cheaper quality than Richmond.

[Clyde65]

I bought the Richmond or a 3 series carrier and I also called Summit, they were extremely helpful and seemed to be wanting to make sure I got what I wanted and what would truely work for my application. Im very happy with my 3.73 gears, no I dont do burn outs but this allows me to tow with my truck, even though I dont do much towing, I can and will in the near future.