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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Garrcus on July 17, 2012, 05:43:04 pm

Title: Proper Gear Ratio?
Post by: Garrcus on July 17, 2012, 05:43:04 pm

Hey Guys,
Here is my current setup:

1985 K10
5.0L 305
SM465 Manual Tranny
208 T Case
3.73 Gear Ratio
31'' stock tires

I am planning on adding a full-leaf 4'' lift with 35'' tires. This truck is mainly used as my hunting, fishing and camping rig so off-road capability is highly valued. However, I will have to travel on the highway every once in a while and out here in Western Colorado the Speed Limit is 75mph and I don't want to burn up my engine trying to maintain that speed. Should I keep the 3.73 gears or go lower to 4.10's or even lower? What would be the best ratio to maintain the low end torque for offroad use but allow me to adequately (just adequately) get down the highway without blowing up my engine? Any advice is greatly appreciated.

Title: Re: Proper Gear Ratio?
Post by: Da67goatman on July 17, 2012, 05:59:11 pm

I say leave it, with 35s and 3.73 you MIGHT actually be able to use that creeper gear.

Title: Re: Proper Gear Ratio?
Post by: Edahall on July 17, 2012, 08:05:45 pm

You would probably be better off with an overdrive.  You would either have to change transmissions or install an overdrive unit.

Title: Re: Proper Gear Ratio?
Post by: ehjorten on July 18, 2012, 10:00:08 am

You say off-road capability is highly valued...so...you aren't going to get 35's to fit under a 4" lift without trimming.  If you don't want to trim wheel-wells (and I don't blame you) you are going to be looking at 33's with a 4" lift or 35's with a 6" lift.

Title: Re: Proper Gear Ratio?
Post by: Captkaos on July 18, 2012, 04:21:31 pm

And if you aren't going to trim the wheel wells and go with 35's (even if you did) I would stay with the 3.73's, it isn't enough change to make a difference on a Granny gear manual.

Title: Re: Proper Gear Ratio?
Post by: bluecrew on July 18, 2012, 06:48:06 pm

I'd leave them gears alone.  That creeper gear will be useful, finally.  And yeah, 35's would fit with a 4" for mall crawling, but off camber, actual off road, they will "self-clearance" themselves on your front fenders.  6" will be needed to "no worries" fit them 35's.  I ran a sm465 with 4.10's on 31's, 33's, 35's and even 38.5's.  No need to change gears.  I never used the granny (creeper) gear until I slid my 38's under there, and that was with 4.10 gears.  You have the 3.73's, which'll help you out on the highway without an overdrive, and the granny gear will help that little 305 get your 35's going.  I'd rock that combo!

Also, that sm465 tends to jump out of 3rd.  Just FYI...

Title: Re: Proper Gear Ratio?
Post by: Garrcus on July 19, 2012, 07:54:23 pm

Thanks for the advice guys, looks like I will probably just keep those 3.73 gears and actually get to use that creeper gear, I always wondered when I'd be able to use it.

I've actually seen some 4" lifts that claim 35" tires will fit, perhaps thats just wishful thinking though and I'll have to just go with 33"s.

Title: Re: Proper Gear Ratio?
Post by: slammed79 on July 20, 2012, 11:15:30 am

In my experience, the 4" lift will clear the rear fine, but you'll want to go 6" up front to clear. These trucks had a 2" rake from the factory