posi rear end gears
 

My 87 Silverado is finished except for the posi rear end. I have the 350 engine with the 4 speed (overdrive) transmission that came in it. The right rear tire will light up but the drivers side doesn't. Some tech lines say 373 is best all round.I'm not racing it. Just a cruiser but would like both tires to spin and get reasonable mileage. What are other 350 guys installing that fits the bill.
Thanks,
Eric
my project can be viewed at :
https://www.fuelcurve.com/1987-chevy-c10-pickup/

Re: posi rear end gears
 

If you have a true posi differential than I would think both tires should lay down the rubber....if you dont, you can add the posi carrier without replacing the gears...Good luck on smokin both tires !!!!!

Re: posi rear end gears
 

Beautiful truck!

What gears will partly depend on what the diameter is of your rear tires and what you want out of a gear change. Are you looking for better performance or lower RPM's at highway speeds? Lower rpm's don't always mean better MPG's. The engine needs to run in it's 'sweet spot' for best efficiency.

Re: posi rear end gears
 

I have 20” Mickey Thompson tires ! All I want to do is spin both tires. I can live with current gears. Thanks !!!

Re: posi rear end gears
 

20" diameter tires..........what are those on 13" wheels?

If you want a posi, then you will have to either install one or have it installed.

Re: posi rear end gears
 

Sorry !!! My wheels are 20’s on rear and 18’s on front!

Re: posi rear end gears
 

Get a Detroit True Track...Eaton brand.

Re: posi rear end gears
 

Thank you very much !!

Re: posi rear end gears
 

The OUTSIDE diameter of the rear tires is what is needed to determine the optimum gear ratio for the desired usage, not the wheel diameter. Your original post sounded like you were wanting a gear change also.

Re: posi rear end gears
 

I’m open to change gear size if it would help but if I can posi what I have, that’s fine too. I’m trying to determine whats the best approach at this point.
Thank you for helping !

Re: posi rear end gears
 

I’d say 3.73s maybe 4.10s. With either gear the drivetrain won’t be working as hard, so tho seems backwards but would get better mileage, while having fun at the same time lol...

Re: posi rear end gears
 

Thank you !!

Re: posi rear end gears
 

What gear ratio do you currently have?

Re: posi rear end gears
 

I’m not sure. The label in the glove compartment door indicates GU2

Re: posi rear end gears
 

Believe that is 3.23.....

Re: posi rear end gears
 

Wow, it’s 2.73s.....

Re: posi rear end gears
 

Thank you b454rat ! Should I just do the locker on those gears or change. If change to what & why ?

Re: posi rear end gears
 

Change the gears for sure!!!! At least 3.73s. Any posi that isn't the grenade lock.

Re: posi rear end gears
 

If you go from 2.73 to 3.73 gears your going to kill any mileage you got from that thing. It would dramatically change they way they whole drivetrain responds to the engine. I would bet that thing is a dog right now with those gears.

Re: posi rear end gears
 

That is a very nice looking square body right there! If you really do have 2.73 out back and a standard 700r, 1st gear off the line is probably OK, but 2nd gear must be a let down ( I'm thinking WOT here ).

If you don't want to change your current mileage/driving characteristics, don't change the gear ratio.

If you want to change the way your truck gets down the road and/or increase the fun factor stop light to stop light, change the gear ratio.

I would first make sure you know what you have currently. Determine that for certain then decide what you want to do with respect to the ratio.

-klb

Re: posi rear end gears
 

The glove compartment sticker is: