33in tires and stock gearing?

[AJMBLAZER]

I'm running 33's with the stock 3.73, and it works like a charm. I do stay out of OD unless I hit the interstate. I never tow 2000lbs or more in OD. I do have the heavy duty engine oil cooler, but not one for the tranny yet.
I would definitely recommend modifying your DRAC to adjust speedometer for the 33's. Mine was off by 12%, but is now only 0.5% off. Not sure about '89 but my '91 its tied to ABS, Cruise and who knows what else.

No DRAC in a '89. Speedo cable.

How do I tell what gears I have now? Are all 89 gmc jimmy the same from factory? I dont see anything on the rear diff that says or in the glovebox. I also have a tranny cooler rated to tow 10,000 lbs.(I dont tow near that just small fishing boat) and stock engine oil cooler so I guess I should be ok with the 33,s. I do however have to climb alot of hills.

Are the 3 digit RPO codes still on the sticker in your glovebox. They can be decoded online. Gearing is all Gxx if I recall correctly.

 

[COCHEV]

All this talk about counting drive shaft revolutions, RPOs, build sheets.

Pull the covers, count the teeth, know for sure. Couldn't hurt to have some fresh gear oil in there anyways. who knows, the gear oil could be as stock as the gearing.

 

[shovelbill80]

by all means crack the pumpkin open, clean it out and refill it with good stuff.......

but i'll still stick with sayin that pblaze has 3.73's. he can't be that far off in his count on the shaft and math don't lie .

 

[pblaze725]

Yes sir,
I understand the complicated part, just not the easy stuff.
It has been said several times & I will say it again,
"The best way to determine the gear ratio is to take the cover off & read the numbers stamped on the gears. You know you are due for a gear oil change anyway, so why not?"

 

[89 jimmy]

I had the fluid changed not to long ago and at that time I never thought to check the gearing(should have though) at that time I wasnt thinking about bigger tires the 32'in bfg at tires have been great but you know how it goes now thinking about 33 in bfg km2s. Gonna stick with the stock alloys (15x7) as I dont like to wide a rim. Anyway acording to RPO sheet I have 3.42 gears (stock). So should I be ok with 33's and that gear ratio? Its been taking me a long time to decide 32,s or 33,s. I just cant decide!

 

[89 jimmy]

Update: Decided to stick with 32 in tires(bfg km2)on my stock rims. Thought about it for along time and the 32,s just make more sense for what I use the truck for(long trips,towing small fishing boat,gas mileage, gearing and so on. I had to set aside looks for practicality.

 

[chalet2506]

I had to set aside looks for practicality.

Looks good to me. Now you just need to pull the top off that sucker.

 

[AJMBLAZER]

Looks good man.

350 engine? If so then you made the right choice even if it has 3.73 gears.

 

[89 jimmy]

Thanks, 350 with 3:42 gears.

 

[tRustyK5]

My 90 has the same 3.42's currently, and I run 35's. It's 100% fine...I just never use OD anymore.

I tried OD on the freeway and it was pointless and killed my fuel mileage with all the lugging and hunting the tranny did.

Rene

 

[shovelbill80]

your truck looks real good.....you made a good choice for what you're going to do with her imo. i'm having trouble waiting to do my lift, tires and rims, but my Cooper ATR's are great tires and practically new. i have other issues before i really need the new stance.............cheers.