Something thats been bothering me.

[dodge man]

This is one of these things that been bothering me for over a year, I don't need an answer, I'm just curious.

My previous truck was a 2002 GMC 1/2 ton 4x4 regular cab with the 5.3 egnine and a 3.73 rear end. When I first got the truck, I posted a questions about what rear gears I had. I had jacked up the truck and counted wheel rotations compared to the drive shaft. It was a little less than 2 rotations. Someone said this was normal for Chevys, that you can't count the rotations, and gave me the code for the glove box sticker, which turned out to be 3.73 rear gears.

My question is, why can't you count the driveshaft rotation compared to the wheels? I've seen rear gears, and the ratio is determined by the number of teeth on the ring gear compared to the pinion gear. Whats different about a Chevy?

 

[RDrancher]

It's not a Chevy thing but an open differential thing.

Not sure of the technical way of explaining it...but if the differential is an open unit (no locker) you count the tire rotation compared to one rotation of the driveshaft and then multiply the tire rotation by two. If you had gone a smidge over two rotations the ring and pinion ratio would be a 4.10 or 4.11. About 2.25 rotations would be 4.56, etc.

 

[dodge man]

That just might make sense. The truck did not have a posi. If I think about it, the other tire is also spinning, but the opposite direction. Thanks for the answer. Another one of liefs great mystery's solved for me.

 

[RDrancher]

Yes, that's an "open" differential. If one slide slips (such as on ice) all of the power is transferred to that axle...and you just sit there spinning.

A limited slip diff-ratio can be found the same way. A limited-slip or "posi" (GM's terminology) acts just like an open diff until one tire slips to a certain degree and then the clutches create enough friction to drive the other side.

A "locker" is just that...both axles are locked together. Locking differentials will unlock in turns under deceleration, but lock right back up when the throttle is applied. That's not such a big deal in a longer wheelbase vehicle, but in a short wheelbase Jeep or Land Cruiser it takes some getting used to. Wears tires out quicker too. Sometimes lockers will let out a BANG!!! that sounds as if stuff is breaking but it's perfectly normal.

Check this out http://www.youtube.com/watch?v=K4JhruinbWc&noredirect=1#t=1m50s

 

[Diamondpilot]

If it has the G80 locker it will not work right.

I tell everyone to look at the code for all brands. Its too tough to count accurate these days. I see trucks with 2.93, 3.15, 3.33, 3.42, 3.55, 3.73, 3.92, 4.10, 4.30, 4.88, and a few more. Just too tough. Gone is the days with one or two gear sets.

This brings up another good point, know what the heck you are buying. Case in point, one of my customers Greg is a GMC guy. Last summer he came over to show off to me his brand new 1500 4x4. Pretty truck but with the 5.3 and the gear set it had the tow limit is 6500#. His old one with 3.73 gears was rated at 8500#. He now has a new truck that can not tow his camper

Chris

 

[flusher]

If it has the G80 locker it will not work right.

I tell everyone to look at the code for all brands. Its too tough to count accurate these days. I see trucks with 2.93, 3.15, 3.33, 3.42, 3.55, 3.73, 3.92, 4.10, 4.30, 4.88, and a few more. Just too tough. Gone is the days with one or two gear sets.

This brings up another good point, know what the heck you are buying. Case in point, one of my customers Greg is a GMC guy. Last summer he came over to show off to me his brand new 1500 4x4. Pretty truck but with the 5.3 and the gear set it had the tow limit is 6500#. His old one with 3.73 gears was rated at 8500#. He now has a new truck that can not tow his camper

Chris

Hmm--what was Greg's problem? The window sheet on that new 1500 should have had the rear end gear ratio called out. Didn't he realize that he had 3.73 gears on his old truck and probably should have the same on his new vehicle?

I was fortunate when I bought that 2004 Isuzu NPR/EFI truck last year since the window sheet was in the glove compartment so I knew that, at least out of the factory, it had 4.777 gears. My NPR has a GMC 6.0L LQ4 V-8 engine (truck was assembled in Janesville, WI).

 

[slowzuki]

Any truck you need to look at the spec sheet. Ford and GM have light and heavy 1/2 tons and different gvwr packages. I know the ford's better but you go from lighter 8.something axle to semi-float 9.75" sterling axle in the max gvwr models. Max tow or the off-road package gets you the lower gear ratios in the heavy axle to get the tow rating up.

 

[HHR]

I just picked up a used Ford Excursion and the space on the sticker for the axle code was blank. I looked at the tag on the rear differential and it said 4L10. I assume this means 4.10 gears with a limited slip differential.

 

[Diamondpilot]

Hmm--what was Greg's problem? The window sheet on that new 1500 should have had the rear end gear ratio called out. Didn't he realize that he had 3.73 gears on his old truck and probably should have the same on his new vehicle?

I was fortunate when I bought that 2004 Isuzu NPR/EFI truck last year since the window sheet was in the glove compartment so I knew that, at least out of the factory, it had 4.777 gears. My NPR has a GMC 6.0L LQ4 V-8 engine (truck was assembled in Janesville, WI).

The problem with Greg is like what I venture 75% of truck owners, they know nothing about them. He had no idea how gears work. He seen 1/2 ton V8. I have seen it through all ranges of trucks. All are not created equal.

Chris

 

[Diamondpilot]

I just picked up a used Ford Excursion and the space on the sticker for the axle code was blank. I looked at the tag on the rear differential and it said 4L10. I assume this means 4.10 gears with a limited slip differential.

That is suspicious that its blank. I have owned over a dozen Fords and all as a axle code. It something like 31 or B6. On Fords, if its two numbers its usually a open diff, but if its a letter then a number its a limited slip diff.

This is not right. A 4L10 axle is a Ford 8.8" axle used on Explorers and Rangers, not Expeditions. It is a 4.10 LS though.

Chris