When to re-gear?

[HarrisonTX]

Whats up guys..
My 31''s just arnt cuttin it anymore.
I would like to jump up to 33''s or 35''s, my only problem is the previour owner JUST had the entire rear-end rebuilt, with brand new 3.42's.
35''s would probably demand some steeper gears?

 

[throttleissues]

If you've got overdrive, then 31s would demand more gearing. 3.42s are great on my s-10 commuter with tiny little tires, but my K20 has 4.56s with 36" tires w/o OD. Let's hear what your drivetrain is before the recommendations start flying all over the place.

 

[toomany]

Let's hear what your drivetrain is before the recommendations start flying all over the place.

X2, and what your plans are for the truck. A daily driver could get away with a more conservative gear. On the other hand, a rocks only rig would need more gear.

 

[jonathon]

I'm planning on 4.56's for Suburban, and that'll only be with 33"ish tires. Should keep it in the power band perfectly for 70mph(2400 rpms), and tow in 3rd at 60mph(around 2700rpms)

 

[HarrisonTX]

Grr... i dont like those people who post, with not enough info. Sorry folks.

Its got a 700r4 in it, and yes, its going to be my daily driver, its just out of state now.
This truck will see off road use, just minor climbing for now.

throttle issues- you think its already under geared? It does seem gutless as hell, and this with this 325HP crate motor.

 

[throttleissues]

Yes, I think it's already undergeared. I've got a 2wd '87 'burb with a TBI 350/700r4/3.73 gears with 31x10.50 tires, and it downshifts on almost every hill unless I'm doing over 85mph. I'm thinking about 4.10s if I keep the 31s on it. I'd go to more gear if I was putting bigger tires on it.
You've got more power than I do, but if you're gonna run 35s, I'd probably go to a 4.56 gear. Not everybody agrees with me, so inevitably it's up to your preferences.

 

[brooks294x4]

4.10's or 4.56's definately, juste depends what you wanna sacrafice on a DD
4.56's - be better for your offroad use, but worse fuel milage
4.10's - better fuel milage, but use a lil more throttle offraod

IMO, if you have a 325hp crate motor, go 4.10's, it should turn 35's easy. my 90TBI 350 has 95k on it and turns 42's fine with 4.10's

 

[HarrisonTX]

I think im going to find an online calculator, and let that decide for me. I want to be able to drive 70MPH, and not spin the hell outa the motor. If 4.56's have me spinning 3000 RPM, i will go with something numerically lower.
I just need to find the 4th gear ratio of the 700r4

 

[onetonbb74]

.70 is 4th gear in a 700r4

 

[onetonbb74]

w/ 35's, id go 4.56 if your keeping the 700r4

 

[oakknight]

http://accuautoparts.com/calculatorfin.jsp
here a nice calculator shows axle torque etc
I put 4.56 gears with 35s

 

[HarrisonTX]

Yea, with 4.56's, and if my 700r4's 4th gear is in fact .7, at 70MPH i will be turning 2150 RPMS. Thats about perfect.

Anyone know what the stock rear end is? 10 bolt, 8.5''?

 

[oakknight]

My old 85 had 3.73 factory gears. you said he had the rear end rebuilt with 3.42? did he work on the front as well? they have to be the same so if he put 3.42 in the back your front is probably a 3.42 as well if he did the job correctly.

 

[HarrisonTX]

Right, i saw somewhere that it had 3.42's from the factory. I think it was on the door seal, or maybe the VIN.
simply putting on some larger tires now is gonna run a 4'' lift, new tires, and some new damn gears, which i estimate will run me about $500

 

[oakknight]

if you go lift and tires first the 3.42 might be ok for a short time. Have to watch the 700r4 short cycling in OD back to third .. might eat up the 700r4 over time .. if you watch the cycling it should be fine on the road and run low rpm at highway speed. I ran 35s for a year on my 3.21/3.23 set.. wouldnt stay in OD unless i was doing 80 on flat lands. lol