Question about re-gearing for daily driving

C

Camhabib

TJ Enthusiast
Joined
Mar 30, 2019
Messages
273
Location
Boston, MA
98 Sahara 4.0L 32RH w/ 31" tires running on a Dana 30 / 35 with I believe 3.07 in the back and ~120k on the clock. Yet another day, another thing that needs replacing. Going to be doing very little rock crawling, mostly just a weekend car that will see city and highway use. Went to replace the diff fluid front and back for what looks like the first time in just about forever and along with the oil was a good amount of tiny metal flakes. Gears seem... less than pristine. They haven't been making any unusual noise but, given the state of them, I can't imagine they have too much life left in them.

I've read up a bit and it seems like a lot of people recommend putting a Super 35 in the rear, especially if there is any plan on going with a larger tire at some point (there isn't at the moment). Most of the gearing guides I've seen are based on larger tires and rock crawling, so I'm wondering what people would consider an appropriate gear size for the rear, and what I should do about the front, since those need replacing as well? What can I expect to pay for parts + labor to do this (since this is outside of my comfort zone)? Thanks!
 
If you're going to stick with 31" tires, 3.73 is probably your best option with the 3-speed transmission.
 
  • Like
Reactions: Chris
As long as they aren't complaining I wouldn't worry to much about it. You'll probably get many more trouble free miles out of them. Maybe check them again in 10K miles and do some research between now and then. Re-gearing is expensive and and for small tires and city driving isn't a huge deal.
 
Only thing that concerns me some is that the car jerks a bit when going from drive to reverse. Don't know if this is because there is some play in the gears and it's just taking that up, or if that's just the nature of these transmissions. When I looked at my gloves after changing the front, they were covered in tiny specs of silver metal. That said, I've had it on the highway for a few hours and I don't hear anything abnormal from them.

Called a shop just to get an idea of price and they said $500 / axel + parts (outside Boston). Don't know how this price stacks up against others.
 
I wouldn't be worried about what looks like glitter. The play could be allot of stuff, u-joints, trans, who knows? Start looking at each part. My opinion is diffs go quick and angry.
 
Gears and bearings wear. There will always be some sort of metallic debris in the oil. A silvery sheen to the oil is perfectly normal, small flecks is probably bearings going away. The gear set itself is hardened and lapped and will provide thousands and thousands of miles if properly maintained. 120k is nothing on a properly lubed gear set.

If you never plan on bigger than the 31 or maybe a 32, 3.73 is recommended. If you plan on 33's or larger, then you'll need to re-think your ratio choice.

"Rock crawling" does not require a different ratio than a daily driver, generally. If you are running a rig that won't see the highway, ever, then sure, gear that sucker low. If you are doing very little hwy and more off road, then a bit lower is the way to go. Most are driving a combination of hwy and off road with hwy being the majority of use.
 
Rob5589 said:
Gears and bearings wear. There will always be some sort of metallic debris in the oil. A silvery sheen to the oil is perfectly normal, small flecks is probably bearings going away. The gear set itself is hardened and lapped and will provide thousands and thousands of miles if properly maintained. 120k is nothing on a properly lubed gear set.
Click to expand...
I should have taken some pictures before I stepped away for the weekend. I'll update on Tuesday with a few.

The front had no silver sheen to the oil, but there were metal particles in there. The teeth of the gears themselves looked to be in good shape.

The rear had no sheen and no flakes, but a couple of the teeth had some scratches on them (deeper than just surface) in what a reference picture I have calls the "drive" and "coast."
 
Post #6 Wins.

Rob's posts are considered a
shop manual in many countries.

His blood has the faint smell of 75 w - 140.
 
  • Haha
Reactions: Rob5589
My garage still stinks like gear oil from Toms re-gear months ago. I smelled like that 5 days a week for nearly 5 years. And shockingly, still had a girlfriend :ROFLMAO:
 
  • Haha
  • Like
Reactions: AndyG and JMT
Top Bottom
Back