ReGear 3.73 on 1984 Jimmy

[The_Lew_USA]

Finally pulled off the diff cover and found out that my Jimmy has a 3.73 gear ratio. It had 37s on it when I bought it a few weeks ago. You can really notice the lack of power with the 3.73 trying to turn those tires.

Does anyone know a respectable shop in the Phoenix area that can help me regear to 5.13 or something similar?

Thanks!

Kirk

 

[Fastereddie]

@Wes Harden @Babaganoosh
@JoshHefnerX might know?

 

[Babaganoosh]

Phoenix rack and axle or letzroll in mesa. Letzroll did mine, no issues other then user error.

 

[Bent77]

5.13s will work great, just not real highway friendly

 

[Blue85]

Hold on, are you about to put money into a rear 10-bolt?

 

[The_Lew_USA]

Hold on, are you about to put money into a rear 10-bolt?

It must have been redone previously cause I have a GM 12 bolt 8.875 in the rear and a Dana 44 10 bolt in the front.

 

[The_Lew_USA]

5.13s will work great, just not real highway friendly

Should I consider the 4.88s if there will be a good amount of pavement driving? My knowledge consists of browsing the forum info

 

[cheavyk10]

What transmission are you running? Having an overdrive will let you go to a deeper gear in the axles and still get you down the highway at a decent speed.

 

[The_Lew_USA]

What transmission are you running? Having an overdrive will let you go to a deeper gear in the axles and still get you down the highway at a decent speed.

Yes it has the 700r4 with overdrive

 

[Blue85]

It must have been redone previously cause I have a GM 12 bolt 8.875 in the rear and a Dana 44 10 bolt in the front.

Those are really no upgrade.

 

[tarussell]

Something to consider when choosing a gear ratio is the added resistance of air on a lifted truck and weight of larger tires/wheels combo.
Use a gear ratio/speed/RPM graph or calculator to find what you like and don’t be afraid to go a little higher to adjust for the added resistance.
A 3.73 combined with a 31” tall tire is a good base line example for a heavy K/5 that is as aerodynamic as a brick in stock form - use it as a starting point for RPM and match it to your desired tire size and gear.

 

[Chickntrk]

With 3.73s


With 5.13s



If you’re good with 2300 RPM at 70 mph it looks like 5.13s are for you….personally I’d rather have a few more RPMs than be under-geared, working a 700r4 too hard is a recipe for disaster

 

[Wes Harden]

4.88 with 700r4 is 3.42 final ratio in 4th. I have this combo on 33 in a heavy ass k20 burb. @2400 @65mph. Going to 35 next set of tires.

5.33 would equal 3.73 in 4th. Keep in mind the 700r4 has 3.0 1st gear.

I typed this 4 hours ago and forgot to post

 

[tarussell]

4.88 with 700r4 is 3.42 final ratio in 4th. I have this combo on 33 in a heavy ass k20 burb. @2400 @65mph. Going to 35 next set of tires.

5.33 would equal 3.73 in 4th. Keep in mind the 700r4 has 3.0 1st gear.

I typed this 4 hours ago and forgot to post

Keep in mind that Wes has a 400 SBC in his ride which has a fair amount of extra grunt that a mild 350 just ain’t got.
I would suggest to round up in the rev department - a few hundred more revs on a K/5 ain’t gonna hurt but will certainly help.

 

[The_Lew_USA]

Those are really no

4.88 with 700r4 is 3.42 final ratio in 4th. I have this combo on 33 in a heavy ass k20 burb. @2400 @65mph. Going to 35 next set of tires.

5.33 would equal 3.73 in 4th. Keep in mind the 700r4 has 3.0 1st gear.

I typed this 4 hours ago and forgot to post

A guy I know at a 4x4 mechanic shop told me the 5.13 would be too tall for the Jimmy and that I should do 4.88. I don’t intend on using it for hard core wheeling. just a camping and hunting rig as well as around town. I’m waiting for a quote from his gear guy. I still need to call this other shops that were recommended.

 

[The_Lew_USA]

Those are really no

4.88 with 700r4 is 3.42 final ratio in 4th. I have this combo on 33 in a heavy ass k20 burb. @2400 @65mph. Going to 35 next set of tires.

5.33 would equal 3.73 in 4th. Keep in mind the 700r4 has 3.0 1st gear.

I typed this 4 hours ago and forgot to post

A guy I know at a 4x4 mechanic shop told me the 5.13 would be too tall for the Jimmy and that I should do 4.88. I plan on using it for hunting and camping trips as well as around town.

 

[Wes Harden]

So what we really need to know is where does this engine like to sit rpm wise at cruise, and what highway speed you need to run. Even with 33's I limit mine to 3rd gear, it can and does shift into 4th just above 40mph. the rpm is to low, for cooling charging and ac. 45 mph and greater I will allow OD. With bigger diameter tires lowers the rpm at every speed.
Oh my memory failed me in earlier post, @2400 rpm I am doing 70ish mph. So when I switch to 35s 70mph will be 2200.

And @tarussell i wish I still had the SBC400, am running high compression 355. mild cam. 4v qjet

 

[imiceman44]

A guy I know at a 4x4 mechanic shop told me the 5.13 would be too tall for the Jimmy and that I should do 4.88. I don’t intend on using it for hard core wheeling. just a camping and hunting rig as well as around town. I’m waiting for a quote from his gear guy. I still need to call this other shops that were recommended.

I had the 4.88 with the 350sbc/ th350 and 37" tires.
I was running very high rims on the highway.
I ended up putting a 700r4 and things were great.
I wouldn't go more than 4.88 especially if you are not planning on rock crawling.

 

[6872xtc]

I personally wouldn't go lower than 4:88 because of the pinion to ring gear tooth engagement amount. Not that I have any proof of the 5:13 being more failure prone in a 12 bolt axle, it was what I determined in my research 20 years ago for mine.
And if you ever decide to drop down to a 35" tire for any reason, like ease of entering the truck, then it will be a very nice combination IMO.

 

[tarussell]

Wes, I guess I recalled reading that ya had a 400 in several post and never picked up on that it was old info - or it could be my ever fading memory…. most likely a combo of both.