Gear Ratio Advice - 1996 K3500 Dually with 7.4 Vortec & Automatic Transmisson

[52weekbreak]

Looking for some thoughts on best gear ratio for the truck above. I acquired this from the original owner (my Uncle) with 67,000 KMS in 2011. After 3 years of use, I have only managed to put 8,000 KM's per year as I use it mostly for towing my fifth wheel (33 feet overall and 10,000 lbs when loaded with gear and water).

Truck is a little sluggish off the line but pulls well at 90 KPH OR 120 KPH. In between, you are either gaining or losing speed or transmission is shifting into or out of overdrive. According to the codes, the truck has the 4.10 gears (GT5). I am wondering if it is worth changing to the 4.56 gearing (HC4) or does it just make more sense to just put the transmission into 3rd to cruise between 100 - 110 KPH.

I really like the truck overall and would just like to fine tune it a bit.

Any thoughts?

 

[Summitric]

4:56 would make big difference... But if it's 4x4, you would have to do both diffs..... Will get expensive

 

[52weekbreak]

I would source used diff's but that might still be pricey. Annual depreciation on a newer diesel isn't cheap either so that is the trade off. Truck also has considerable sentimental value.

 

[Bnorth]

I would source used diff's but that might still be pricey. Annual depreciation on a newer diesel isn't cheap either so that is the trade off. Truck also has considerable sentimental value.

I'd keep it for sure, it is super clean and I love those alcoas on it.

 

[sirkdev]

Maybe look into a gear vendors over/under drive deal... On second thought maybe smaller diameter tires when the time comes would have to do math to see if worthwhile..

 

[tex78]

If u leave it in 3rd, it will lock up in 3rd too... If it comes out of lock up then tranny temps go way up

I have a 97 sw 1 ton with diesel and a tranny temp gauge.... I try to keep it in lock up as much as possible , not in lock up converter is working and heating up

sent while I should be drinking tea's

 

[Bnorth]

If u leave it in 3rd, it will lock up in 3rd too... If it comes out of lock up then tranny temps go way up

I have a 97 sw 1 ton with diesel and a tranny temp gauge.... I try to keep it in lock up as much as possible , not in lock up converter is working and heating up

sent while I should be drinking tea's

Can you just put a lockup switch in them?

 

[tex78]

Not sure .... Biggest problem with that is if u forget and slow do

sent while I should be drinking tea's

 

[tex78]

Oh and 52.... If ur doing any pulling at all, put the deep b and m pan on ur trans..... Makes 30 degrees cooler fluid temps with 4 litres extra oil

And also the b and m shift enhancer... All 4l80e trans are adapt trans so a shift kit is not working after 10 min... The shift enhancer made a huge difference in my truck

sent while I should be drinking tea's

 

[bobsledder]

Oh and 52.... If ur doing any pulling at all, put the deep b and m pan on ur trans..... Makes 30 degrees cooler fluid temps with 4 litres extra oil

And also the b and m shift enhancer... All 4l80e trans are adapt trans so a shift kit is not working after 10 min... The shift enhancer made a huge difference in my truck

sent while I should be drinking tea's

Tex, can you explain what adapt trans is?

 

[52weekbreak]

Maybe look into a gear vendors over/under drive deal... On second thought maybe smaller diameter tires when the time comes would have to do math to see if worthwhile..

At about $3,100 not a cheap fix (he said still having no idea if reliable reasonably priced front and rear dif's are even available) but in some ways even a better solution then a gear swap. I'll check the tire idea but have found low profile tires expensive.

Thanks for the great input

 

[sirkdev]

Or you could get a supercharger.... then a transmission...

 

[52weekbreak]

Or you could get a supercharger.... then a transmission...

Heehee At some point just going with a newer diesel just makes sense. Surprisingly not much available for 454's that actually improve performance. The GV over/under is best I've seen. Do you know anyone who has one?

 

[tex78]

Buddy g.m tech I used to work with had his 454 working good, different fuel injectors , programing , ect

He's in Rocky I could give ya his phone #.....

Smaller tire size would be the way to do it, if u have 235-85-16 ( would be like 3.73 gears with them on) go back to 215-85-16 and get ur ratio back...

sent while I should be drinking tea's

 

[tex78]

Tex, can you explain what adapt trans is?

The trans will adapt to the way u drive and change..

So if u put a shift kit in, it see's shift psi too high and detuned them, taking the shift kit away via electronics...

sent while I should be drinking tea's

 

[sirkdev]

Heehee At some point just going with a newer diesel just makes sense. Surprisingly not much available for 454's that actually improve performance. The GV over/under is best I've seen. Do you know anyone who has one?

No I do not I just read about them... they maybe getting close to be a thing of the past with the amount gears in modern transmissions.

 

[brian h]

if i knew the tire size and trans model could figure out your rpm to let you know what your running at and changine ratio would do.but from 4.10 to 4.56 would be approx 250rpm at 100kmh. difference . dont recomend gear vender box have not heard alot of good and yes i have seen them in trucks.also under heavy loads its not recomended to tow in overdrive.no you cannot put a toggle switch on your lock up.recomend ratio change both diffs,cost of ratio change to purchasing used diffs would not be much difference in price and buying used diffs you dont know what you are getting at least with getting a ratio change you get warranty

 

[52weekbreak]

if i knew the tire size and trans model could figure out your rpm to let you know what your running at and changine ratio would do.but from 4.10 to 4.56 would be approx 250rpm at 100kmh. difference . dont recomend gear vender box have not heard alot of good and yes i have seen them in trucks.also under heavy loads its not recomended to tow in overdrive.no you cannot put a toggle switch on your lock up.recomend ratio change both diffs,cost of ratio change to purchasing used diffs would not be much difference in price and buying used diffs you dont know what you are getting at least with getting a ratio change you get warranty

Hey Brian
Tire size is 215/8R16 (Tex already knew this - I actually had to double check on the truck itself)
Transmission is the 4L80E

An update for those following this thread:
I have spent a lot of time searching for negative feedback on the GV unit and there has been very little and most of that from those who don't own one and never have. Transmissions have been getting more gears not less with 5 and 6 gears becoming common. I drove a friend's 69 Camaro with a 502 originally equipped with a 4 speed and later upgraded to a 6 speed. Believe me the 6 speed is more fun. Also have an Audi S4 (340 HP V8) in my shop (my brother's) with a 6 speed. 0 to 280 KPH and back to 0 in 1.2 kilometers with the top down is a gas. Point here is more gear options are better than less.

Take a look at this link Gear Vendors Under/Overdrive Chevrolet/GMC Truck-Car-Van 4-Wheel Drive 4-Speed Automatics.
You will note the chart showing the gearing for the 4L80E at the bottom of the page. Check out the final drive ratios for the 4:10 gears and you will see that with the GV unit engaged and the transmission in third I would have final drive ratio of 3.20. This would be slightly lower than the 3.08 that the stock O/D provides. I think this is effectively what I am looking for ratio-wise - a slightly lower final gearing without the gear hunting and transmission heating. Having 2 extra gears (1st and 2nd OD) would be extremely useful in keeping the engine in its power band and changing the diffs alone would not achieve a similar result.

The more I look at this, the more sense it makes to me. I have sent an email to GV and will be checking this out further.

 

[tex78]

One thing that I just thought of, these are for 2wd only are they not, cause it seems to me that they bolt in place where t case would go

Now I see in the listing some with 4x4, but the parts in the pics won't work for a 4x4

sent while I should be drinking tea's

 

[52weekbreak]

The way I read it is that you can't use it in 4WD which is not a problem. You got me thinking though and I will now go lay under the truck for a look see.