Gear Ratio for Rear End ??

[Chip327]

Hi everyone ,

I just broke a pinion gear in my pickup and need to fix the rear end. Currently I have 41 teeth on the ring gear and 11 teeth on the pinion gear which translates into a 3.73 gear ratio. The cover is a 12 bolt irregular bolt pattern cover .

I dont know much about rear ends. I have always done all the work on my truck. I would like to fix this issue myself if it is possible . Before I start anything though , I am considering changing the gear ratio in my rear end and would like to get some input from anyone who has done this before....

I have a 327 engine and a 3 speed Saginaw tranny ( I thought it was a Muncie but after doing some searches on the internet I now believe it is a Saginaw) My original owners manual says that the Saginaw tranny has the following ratios.

1st - 2.85:1
2nd - 1.68:1
3rd - 1:1

With my existing rear end ratio of 3.73 I was cranking about 2700rpm doing 60 mph on the highway. I have a 28" tire diameter right now. Obviously not the best gas mileage so I was thinking of going to a 3.42 or a 3.08 rear end since Im replacing it anyways..... Im not worried about snap or racing off the line anymore and would rather get some better gas mileage . I am concerned with my 1st gear ratio and I dont want to be too low that Im always chattering the clutch . I do have plans to eventually put an automatic into the truck but that is still a few years away yet. Also note that I am pulling a small travel trailer once in a while ( not super heavy )....

Also, Im not sure whether my existing rear end will fit the higher gears. I dont want to change the whole thing out if possible.

Any help on this would be greatly appreciated....

Next step will be to find someone close by who has the necessary parts.

THANKS !!

[Stocker]

With your trans (and considering some light towing), I don't think I'd go to 3.08s. I had 3.08s in my '68 Camaro (327, 4-speed) and it seemed fairly tall... I'm thinking 3.42s would be a better choice -- and as you said, easier on the clutch too.

[cdowns]

well if you go to a much higher rear gear you're going to have to change out the carrier too . i dont suggest using used parts on a rear rebuild about everything you'll need is available at most autoparts stores if you want to do the work yourself you need a factory service manual and some specialized tools // long story short to really get the most for your money i suggest finding a shop that rebuilds and taking it there to have it done cost depends but figure 5-8hundred

[Green Machine]

Got that same tranny and a 3.07 rear gear with 29 inch tires in our 1968 with a 307 with a small cam. Motor is not super torquey right off idle with the small cam, but it works just fine. It might require a hair more clutch slip at a stop light but nothing you really notice and your legs train themselves for the gas and clutch anyway. Short of getting an overdrive tranny, I would surely use those 3.07's behind a 327 anyday.

Best to get an entire rear end and swap. Changing the carrier and gears in your housing takes some experience to do right but if you keep everything in order from the donor rear you may get close enough to work but I couldn't suggest that is the right way. I have done it a few times and got lucky but your luck may vary.

[Chip327]

Hmmm, not sure which way to go now , lol...

I am starting to think that it may be best for someone at a shop to do this. $800 isn't bad if its done right !

My biggest struggle is what to do with the gears and how much taller I should go ....

[lilred67]

with your set up,,,,, 3.42's would be great!

[grayw0lf]

Sure you don't want a 4.56!?. Its been rebuilt & is rock solid. I'll make you a deal.... just as long as you don't ever want to go over 60mph.

[Chip327]

Went with the 3.42's

Cost me $1700 to have it completely rebuilt with the near gear ratio but it feels like a new truck. No more howl from the back end and it runs at a nice 2100-2300 RPM on the highway. Should have done this years ago.

[Stocker]

Thanks for the update, and glad to hear you're happy with your choice!

[67 cst swb]

I say 3.42 or stay with 3.73... I have owned a few vehicles with 3.07/3.08's. I personally never liked them. I will alway run at least 3.42 or 3.73's in my rides.
My fav was a '65 Chevelle 327/TH350 with 27" tall tires with 3.42's... Perfect set up for me...