Rear diff gear options for 3/4 ton
 

Hello all, I just picked up a 78 3/4 crew cab. Im wanting to swap gears in the rear diff due to them turning high rpm's at highway speeds. What are my options w/out installing a 700r4 for overdrive?

Thanks

Re: Rear diff gear options for 3/4 ton
 

My 86 3/4 ton has 3.23s in it.

Re: Rear diff gear options for 3/4 ton
 

I think GMC91 has the highest gears available... I was looking at that a while back for my 78 c20 and the highest I could find was 3.2x gear set.

Re: Rear diff gear options for 3/4 ton
 

With that being said, how will this truck do with a TH350 on the intersate? Or would my best bet be to find a TH700r and have it rebuilt?

Re: Rear diff gear options for 3/4 ton
 

Where did you find them at? or what in?

Re: Rear diff gear options for 3/4 ton
 

My 86 came with it when I bought it.

Re: Rear diff gear options for 3/4 ton
 

Best luck is to check a local wrecking yards and start counting teeth in the rear diff. Also, trucks with the smaller brake drums usually have a numerically lower gear ratio, thats what I was told. I am going to just change out my rear diff. Maybe I will be lucky and find a 3:23!!! I have a couple of them already. Just gotta start counting.

Re: Rear diff gear options for 3/4 ton
 

diesels usualy came with the high gears in them.

Re: Rear diff gear options for 3/4 ton
 

I found it on a web site that sells ring gear/pinion sets. I tried to find it again and I can't find it right now. It was hard to find and I think I only found 1 or 2. Seems anything higher than a 3.73 is uncommon and hard to find.

There's stuff for a 14 bolt 9.5 semi floater axle but you should have a 10.5" 14 bolt full floater in a '78.

Keep hunting, it's out there somewhere.


If i was going to swap trannys at all, I'd put a 700r4 in it. But I wouldn't use a 700r4 with just a stock rebuild if you are going to do much hauling or any towing with it.

Re: Rear diff gear options for 3/4 ton
 

swap to a 700r4 youd like it better a 3 to 1 first gear and od and it has four gears instead of 3 itd be better in the long run

Re: Rear diff gear options for 3/4 ton
 

When I get this truck finished, it aint gonna haul or tow nothing, never gonna see mud either, its strickly a daily driven show truck.

Re: Rear diff gear options for 3/4 ton
 

look in flat bed trucks too, i had a 80's flat bed that was a 454/465 and it had 3.23. granny was good till about 10mph.

i just built a rear with 3.23s for my 70, can wait to get it rolling to see how everything reacts.

Re: Rear diff gear options for 3/4 ton
 

why did they put such low ratios on the 3/4? because according to my SPID my 1/2 comes with 3.73's!