Rear End Gear Change

[Calicajun]

Having a shop change out the rear end 3:08 to 3:73 gears. He is now on his fourth gear swap out as the first three sets of gears had a whine when driving. Today he said he going to put in another new set of 3:73 gears three cut instead of the five cut set he was installing.
Question, what is a three cut set of gears as to a five cut set of gears. Is one set of gears better than the other, stronger?

 

[TheFuzz]

You have 3.08 gears stock, so is it safe to assume that you've got a six speed trans? If so, why are you going w/ 3.73s? I think that with the six speeds, 3.42 is more than enough to really get it scooting while still keeping some semblance of economy in high gear. 3.73's in a six speed is the equivalent of 4.10 or better in a four speed.

"Becuase f*** you, that's why" is a perfectly acceptable answer, I'm just curious why you chose that ratio.

As to the cut, I'm not familiar enough w/ gears to have a clue what he's talking about. Pinion gear cut, maybe? Do you know what brand of gears he's using? If he's on the fourth set, there are some serious red flags flying. He either doesn't know WTF he's doing, or he's using shit parts. There's no reason why a competent tech shouldn't be able to get it right after three attempts.

 

[Calicajun]

Tried 3:42 gears and didn't seem to help with towing our 28' 5,800 lbs travel trailer. So when the shop couldn't get the whine out and said he was going to put a new set of gears in I up the gears to the 3:73. Hoping the 3:73 gears and the 6 speed trans will handle the load better with less strain on the engine.

 

[Dave01]

I'm surprised you need the 3.73 for that load, but they should pull very well. The tradeoff will be highway rpm that are very high if you drive 70 plus and some loss of mpg. Are you running stock tire size? If your tires are at all oversized it might explain the need for the gear swap.

I think the different cut numbers refer to gear profile, not sure if it's tooth depth or angle. I know the setup is different for the different cuts, and if I had to guess I'd say your guy isn't setting up the gear clearance correctly. Guys who do differential gears have a knack for it, and you want to go to a shop that does hundreds of gear swaps so they get the setup done right.

 

[jdpber]

remember with a camper it is not so much the physical weight it is the drag that the hugh freaking box creates. It's dragging a wall and an anchor. The weight is relevant it is the non existent aerodynamics and horrible turbulent drag created that generates the strain. Makes 5,500 feel like 8k+

I pull a 20' and know all about the drag. Camper drag and windage sucks.

 

[Dave01]

Definitely a big factor, I guess a lot depends on whether you are towing at 55-60 or trying to push it up to 70, that wind drag really becomes the major issue.

Those 35's really look nice on your rig! Without doing the math, I'm assuming you've got 3.73's, but with those tires you must be equivalent to more like 3.42 or less. Or did you do a 4.10 swap?

 

[Calicajun]

I'm running 17" tires on the Tahoe and tow at speeds between 55-65 only. The shop is one of the highest rated drive line shop in the LA county, he has done custom work for a number of big name race drivers. Maybe that is my problem, I'm not a big name.

 

[Dave01]

No, sounds like the right place to be! Also glad to hear that they are willing to work at it to get things right.

Your 17" tires - what exactly are the sizes, 265/75-17 for example? Then we can see if they are stock diameter or not.

 

[Calicajun]

The tires are suppose to be stock 265/75-17 I think but will have to check them when I get the Tahoe back later today (I hope). Need to make sure of the tire size before I buy some snow chains for our trip to Klamath Falls, OR.

 

[jdpber]

To clarify something that drives me insane (seller of wheels and tires) you have 17" WHEELS

Tires are rubber.
Wheels/rims are metal or wood.