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3.08 to 3.73 gearing swap

Justin ratto

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Donstar Senior Enthusiast

Donstar

Posted
Posted
2 hours ago, jeffreydc said:

So according to this theory a 1 ton pickup rated to tow 15,000 should not tow more than around 9400?  

I didn't propose a theory but shared my comfort level.  The maximum payload of a 1/2 ton is so much easier to achieve than a 3/4 ton.  You would have much more difficulty reaching close to payload with a 9400 lb. trailer on a 2500 than adding a 6300 lb. (dry) trailer to a 1500. 

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Justin ratto Enthusiast

Justin ratto

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Ok so I get that the truck is rated. But what else is different beside axel ratio, I talked to dealership and mechanics and the said same frame same brakes and everything ect.... Just ratio, can u tell me please?? To get from 7k to 10k

Jon A Senior Enthusiast

Jon A

Posted
Posted

Justin, what year/model truck/transmission do you have?

 

Yes, your gears and gears alone are tanking your tow rating--but there was some confusion about how much on GM's part so some owners' manuals may not be accurate.  No, swapping gears won't give you the equivalent of the NHT ratings in the manual, as others have posted those trucks did get some different parts besides the rear gears.

 

However, it would be perfectly reasonable for you to use the non-NHT ratings for the non-3.08 ratio trucks (3.23, 3.42, etc, depending upon transmission) after swapping gears which should give you a couple thousand pound increase (depending upon exact model year, etc) and put your trailer well within your ratings.   For those numbers, the only difference was the rear gears.

 

More importantly, and why swapping gears is such a great idea for you, is that it will add a lot of real-world capability.  With 3.08's, your truck will struggle with that trailer up any sort of hills (especially if you have a 6-speed), staying in very low gears in order to maintain speeds which increases the tendency to overheat fluids and hunt back and forth between gears.  Your truck will be much better off towing with better gears.

 

As for "comfort level," the absolute best thing you can do to improve "comfort level" when towing with a 1/2 ton is to improve the truck's suspension because that is where it is lacking the most as far as "handling" a trailer.  Airbags, E rated tires and better shocks (in that order) are improvements you should also consider if you're going to be towing much.

willyr1er Enthusiast

willyr1er

Posted
Posted

Dropped my truck off this morning, hopping all goes well with the install.  I'll update when I get it back, hopefully today after work.

Bobaloo22 Enthusiast

Bobaloo22

Posted
Posted

I so want to do this to my truck. Please share all the details when you get it back.

Thanks,

 

Bob

willyr1er Enthusiast

willyr1er

Posted
Posted

Finally got the truck back!  Only driven home and to work so I dont have a good base line yet for MPG.  Expecting it to drop a little.

 

Only issue that came up was the wrong sized pinion bearings that came with the kit and caused a day delay.

 

Gears (Yukon 4.10)  are quite and the truck feels a lot better off the line, almost like prior to having the 35" tires.

 

The Kit used a ring spacer for the ring gear and I was able to keep my G80 carrier from the 3.08.

 

Looking forward to the ride home!

 

Lastly the shop couldn't diagnose the stabilitrak issue because it wouldn't kick on for them.  I even did the test drive with the mechanic, ohh well.

Grumpy Bear Senior Enthusiast

Grumpy Bear

Posted
Posted
18 hours ago, willyr1er said:

Finally got the truck back!  Only driven home and to work so I dont have a good base line yet for MPG.  Expecting it to drop a little.

How did the transmission react? ABS, Stabilitrac? 

EJPolaski Enthusiast

EJPolaski

Posted
Posted

Yes updates please!! Are you tuned to compensate for the change in speedo and possible trans learning?

willyr1er Enthusiast

willyr1er

Posted
Posted

Yes I do have a tuner to correct the speedo due to tires and gears.  Transmission feels no different smooth shifts.  No new issues/ problems from the ABS and stabilitrac.  I sill have an issue with the stabilitrac that started once I put the 35" tires on, but couldn't replicate.

 

I'll post up my MPG after some more miles.

Bobaloo22 Enthusiast

Bobaloo22

Posted
Posted

I need to find a shop to do this in central Virginia and soon. We want to buy a camper that weighs around 7k so 3:73 it is. Could you share the cost please to give me something to gauge it by? Also how long did it take from the time you set up install until they did it? I hope to find someone reputable in the Fredericksburg area. 

Thanks,

Bob

willyr1er Enthusiast

willyr1er

Posted
Posted

Bob,

 

It was $1350, broken down to:

416.82 Yukon Ring and Pinion 4.10

364.58 Master Install Kit

56.52 Valvoline SynPower

500 Labor

 

I know this is on the high end but I know that the shop and trust them when I cannot do something.

 

Time wise from ordering to install was about 2.5 weeks.  Installing was a day and half.

 

So far MPG seems to have dropped 1-2.  Also might help if I wasn't enjoying leaving stop lights now, lol.

Bobaloo22 Enthusiast

Bobaloo22

Posted
Posted

Thank you very much! I'm calling in the morning so I hope I can get it done soon.

 

bob

Doug_Scott Senior Enthusiast

Doug_Scott

Posted
Posted

When I went to 4.10 gears in my 2010 Sierra 2wd GM tech centre refused to support the dealers request for an updated bin file with the gears changed from 3.23 to 4.10 because on factory equipped 4.10 trucks had more than just a ring and pinion difference.  Since GM are the people that did the engineering, and also warranted that configuration I would trust their opinion over anyone else's.  I ended up getting Justin at blackbear to fix it.  

 

Since you had already swapped to tires that were at least 4 inches taller than stock, your 3.08 were more like 2.68, and your 4.10 gears are effectively 3.56 when using 35" tires in place of 31" tires. 

The move to 35s is what killed your trailering ability.  4.56 gears would have been somewhere between 3.73 and 4.10 gears with 4.88 gears being a bit higher at 4.25 when running 35s in place of stock 31s.  Note that none of this takes the increase in unsprung rotating weight of those larger tires. 

 

Just to avoid confusion, the reason I compare to original size tires is simply due to factory ratings being given with factory sized tires in place. 

 

When I was still doing the automatic transmissions at Chrysler dealership it was normal to have different clutch pack configurations for different engines or even some options in both the 904 and 727 transmissions, along with different torque converter stall speeds.  The differences in the clutch packs were the number of fibre disks and steel disks, plus different thickness retainer snap rings.  Intermediate band also came in different widths.  Would not surprise me if that continues to this day.  You may find the 6 speed has similar changes to allow higher tow capacity.  Same for radiator, trans cooler, and even addition of engine oil coolers.  NHT package gives heavier axle assembly and rear disk brakes as well to help deal with extra towing capacity. 

 

I changed my gears because the 4.8 with the 4l60 sucked for acceleration. I spent $500 including everything for the swap, back in 2010, and in Canada. 

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