gearing question

[gmcman]

My uncle has an 84 1/2ton pickup with a 350 engine,700r4 tranny,3.08 axle gears and 30x9.50x15 tires. Does anyone here or has anyone run a 700r4 with 3.08 gears. I told him this setup would not work well. He says it will not stay in od on the highway. Any hill and it drops out of od. He says thats what was in it when he bought it. Did GM ever put a 700r4 with 3.08's?

 

[4xcrazy]

a bunch of them out there, yes

 

[gmcman]

That's a crazy setup. You would want pretty small tires for that to work well.

 

[4X4HIGH]

700R4 + 31" tires + 3.73's works real good and was a factory set-up for at least an 89 blazer. That's how mine came originally.

 

[b454rat]

You think that is bad, my 84 is originally a 2.73, 700r4, 31s and a 305. Talk about gutless. I regeared to 4.10s and is still a slug. I don't even use OD inless I'm on the highway....

 

[gmcman]

He uses it mostly as his DD and it sees mostly 55 mph and some 65 mph highway use. If he was to regear,what would be a good engine RPM to shoot for for highway use? The speed limit there is about 65-70 mph.

 

[4X4HIGH]

He uses it mostly as his DD and it sees mostly 55 mph and some 65 mph highway use. If he was to regear,what would be a good engine RPM to shoot for for highway use? The speed limit there is about 65-70 mph.

700R4 + 31" tires + 3.73's works real good and was a factory set-up for at least an 89 blazer. That's how mine came originally

This would be my suggestion even with his 30" tires, a little more RPM never hurt which is what will happen with a shorter tire.

 

[apache]

My 84 K5 had 3.08`s BFG 33`s, 350 and a 700 trans. I never ran in OD oherwise it would just lug the thing and got worst gas mileage than running in "3rd". Ran it that way for some time.

 

[4xcrazy]

another agreement for running 3.73's with a 30" tire, my Burb came stock with 350/700r4, 31" tires and 3.42's it was fine driving, always in OD at higher speeds, had no real trouble holding it either. did pretty well on highway between Phoenix and San Diego when i used to go there alot.

 

[dyeager535]

It's not really a problem for them to drop out of OD. They are an "automatic transmission".

GM probably knew that any hill would require the transmission to drop out of gear, and with the weight/gearing/power that the 3.08 trucks typically had (my K5 had a 305/3.08/700R4/31's) they probably assumed the transmission would STAY out of OD on the hills.

The only problem with shifting is when they "hunt" for gear. If it keeps shifting between OD and third, it's a problem.

The way many people drive anymore (and I don't know your uncle) I can see the constant shifting being a problem. If you are consistent with the throttle (or use cruise!) then it shouldn't hunt except maybe in very specific instances.

My 350/700R4/3.73/31" tired '87 moves much better than the truck mentioned above ever did, however if I manually shifted the transmission I could get on the freeway going 60-65 without issue. If I anticipated it hunting gears (like in town) I downshifted.

 

[gmcman]

Thanks guys for the info. This helps a lot. He's been talking about changing gears for some time now so maybe now I can convince him to get on it and get'r done!