The Stovebolt Site Forums The Shop Area Engine Shop 4:10 rear end gear swap on a 69 3/4 question

I have a friend that has an original 69 Chevy 3/4 ton with 4:10 rear end. Is there a different ratio gear he can swap out without much trouble. He doesnt pull anything and wants a little more speed....more highway friendly.
Thanks
Ken

Depends on a few things.What engine he has,power,etc. With enough power he can get away with a 3:08 set of gears,or perhaps 3:42s.I am runnuing a 350 in my 55,with an OD 700R4 trans. and 3:90 gears. With the OD it works out just fine.It will run at freeway speeds and gets 20 MPG all day long.If I was using a standard shift,or perhaps a 350 or 400 Hydramatic. I would want a lot taller gear,around 3:08s.

4.10 is as high as you can find for the stock 3/4 ton rear end. The best way for him is to change trans. A 5 speed o-drive manual or a 700-4R auto o-drive.

OK, he has a 350 with a turbo 350 trans. So is there a gear swap that can be done to get away from the 4:10?
Thanks
Ken

Maybe someone else can explain it better then I can.
Spell better too.

what wrenchbender sez is no, there's no better gears available for the stock 3/4T rear, but an overdrive trans will give the same effect ... or find some other rear end that'll fit, with better gears

Bill

The problem is if you have the Eaton rear axle 4.10 is the best there is. The Eaton has a removable pumpkin, and is the most common rear axle 3/4T and up. My 68 3/4T had a Dana with 4.56 and leaf springs. I replaced it with another Dana that had 3.73 from a 73 that had a BB and auto. The biggest problem was shock mounts. The good news is that if indeed he has a Eaton 4.10, he can sell for what the used rear axle will cost. There are a few on this board that dearly love to get there hands on it. I have 4.10s with a A833 stick and 4th is an OD, I love it. I'd look for a 700r4.

Larry

OK, so basically he changes out the whole rear end, or at least the axles and gears? Right? Or would he have to change out the entire rear, housing and all? Or, find a 700r4? How hard are they to come by? Thanks in advance for all your help.
Ken

If he has the Eaton, he'll have to change the entire rear axle. The 700r4 was one of the first GM autos with overdrive. I've seen them for sale, not as many as the TH350/400.

Larry

Lets assume it is the Eaton axle and not a Dana (does it have a "third member" that pulls out from the pinion side?).

There is no lower ratio available for the Eaton axle to make it spin faster. It is stuck with the 4.10 gears for low speed. If you want a faster axle you must buy a different one. Consider the GM 14 bolt if you want to have a strong (i.e. 3/4+ ton) rear axle that is still GM. Lots of gears available (for $) for that axle and they can be found relatively cheap in junk yards. You can also put disk brakes on that axle. Lots of widths to chose from. Super strong, heavy axle. Make sure you get one with the carier that supports the lower ratio gears (4.57 and down I believe) and not the higher ratio gears (4.57 and up I believe).

If he's building a race truck, maybe get a Furd 9" rear, custom built. Lots of $'s but you'll get a good strong axle that is exactly the width you want.

If you chose to get rid of that Eaton axle, PLEASE!!!! put it for sale on this site. There are quite a few people (Denny are you listening) who would love to get there hands on that 4.10 Eaton gear to replace their 4.57 or 5.13 gear.