What is the difference in these two trucks?

[mrsilv04]

My folks have their own lake. We have two jet skis on a side by side trailer.

The ramp into the lake consists of packed gravel and has been there for about 20 years. Unfortunately, the ramp is a little steeper than what would be ideal.

Here's the two trucks that we use to put in/pull out the jet skis.

Dad's - 2000 GMC 2WD Ext. cab, 5.3 with a 3.73 posi.
Mine - 2004 Chevy 2WD Ext. cab, 5.3 with a 3.42 posi.

Dad's has a fiberglass topper, mine has a fiberglass lid.

Mine has the factory tow pack, Dad's doesn't.

Mine will pull the jet skis out without spinning the wheels, but Dad's will lose traction, spin, and dig in. Both trucks have similar tires with good tread.

The only obvious difference is the rear end gearing.

Is the 3.42 posi in mine allowing the engine to rev more into the torque band before it starts pulling forward... where as the 3.73 posi in Dad's starts pulling quicker off of idle?

Or is there something with my truck (since it is newer), that when I drop it into L1, that the rear end is automatically locking.... where Dad's older truck doesn't lock up until after there's wheel spin (and it's too late at that point).

I'm trying to figure this out. There's just not a lot of difference in these two trucks.

And honestly, he's a little flustered about it. It seems like when push comes to shove, the 3.73 should outperform the 3.42.

It sure seems to me that the 3.42 in mine is allowing the engine to get deeper into the torque band before moving forward, and that is making the difference.

Thoughts?

 

[firefighter]

Does your truck have electronic throttle??? I have noticed on the 04's there is a slight lag and slower take off I believe for economy reasons. This coulped with your numerically lower ratio gives you a little less torque on initial take off. Where as your dads truck would not have electronic throttle and with a little more torque from start with the higher # rear is probably just enough to start spinning then the rest is history once the tires break loose on gravel. As for getting deeper in the torque band if that was true you would be losing traction. Your traction is directly related to the torque your tires can handle and not spin, so with more torque you would spin faster.

 

[Johnny]

I may have this all wrong but, since yours is geared lower it takes less power to get things started, i.e. easy pull out of the gravel. His has higher gearing and more power has to be applied to get things moving and more power causes the tires to spin in the gravel.

 

[javacontour]

Gearing or driver, those are two most glaring. I'm not sure how much difference tires will make on gravel.

What happens if you put his truck in 2nd instead of L1?

His truck is geared lower, so it's going to pull harder. It's not much of a difference, but maybe it's enough in that circumstance.

So if you can run his truck in 2nd to try to pull out the trailer, about the only other experiment you can try is to swap the rear tires from truck to truck if you are really that curious about the issue.

 

[javacontour]

I should say assuming the gearing in the automatic transmission is the same.

If that's the case, then his truck is going to turn more RPMs for a single turn of the rear wheels compared to yours.

The ratios listed are turns of the drive shaft to turns of the wheel. So your truck will turn the drive shaft 3.42 turns for every revolution of the wheels, IIRC.

His truck will require 3.73 turns of the drive shaft to do that. If we assume his transmission has the same ratios as yours, he'll be producing more power during those 3.73 turns than you did in your 3.42 turns, making more power at the rear wheels.

Starting in 2nd, if he can do that, will reduce the engine power to turn the drive shaft those 3.73 turns, since the engine should be turning more slowly, therefore fewer power strokes from the engine, etc.

 

[rpn453]

Originally Posted By: mrsilv04
Both trucks have similar tires with good tread.


How similar?

 

[mrsilv04]

Originally Posted By: firefighter
Does your truck have electronic throttle??? I have noticed on the 04's there is a slight lag and slower take off I believe for economy reasons. This coulped with your numerically lower ratio gives you a little less torque on initial take off. Where as your dads truck would not have electronic throttle and with a little more torque from start with the higher # rear is probably just enough to start spinning then the rest is history once the tires break loose on gravel. As for getting deeper in the torque band if that was true you would be losing traction. Your traction is directly related to the torque your tires can handle and not spin, so with more torque you would spin faster.


Nope, mine still has a throttle cable. I won't yet own a vehicle without something that physically links the gas pedal to the engine.

Everything else, I agree with. I think his truck is developing more power to the wheels faster, and that is turning into a DISadvantage on the gravel. If we were using a concrete ramp, that would be an advantage.

My truck seems to respond slower and more gradually, and that is giving my truck an advantage on the gravel.

However, out on the open road, his truck pulls the camper better than mine. That's the advantage of the 3.73.

I bought mine with the 3.42 to try and get 20-21mpg highway, which it does. Dad's truck tops out at 18mpg highway with that 3.73.

 

[IndyIan]

Assuming your Dad doesn't have more lead in his boots, I'll bet his tire pressure is higher than yours.
Or his truck has a more aggressive throttle tip in setup than yours. Have a look at the throttle cable guide profile on the two trucks, maybe his opens the throttle more with less pedal movement. A sticky gas pedal will also be a problem.
Probably dropping his tire pressure down to like 15 psi will help in any case. We almost got stuck on a snowmobile trail with the tracker digging in and chattering in 4wd, but dropping the air pressure way down got us going again.

 

[mrsilv04]

Originally Posted By: rpn453
Originally Posted By: mrsilv04
Both trucks have similar tires with good tread.


How similar?


There's not enough difference that I'd think that it matters. Remember that this is on gravel, and after a point, gravel is going to move under any tire that you use.

They're both all-season truck tires, both are "A" traction rated P255/70R-16's.

 

[mrsilv04]

Originally Posted By: javacontour
I should say assuming the gearing in the automatic transmission is the same.

If that's the case, then his truck is going to turn more RPMs for a single turn of the rear wheels compared to yours.

The ratios listed are turns of the drive shaft to turns of the wheel. So your truck will turn the drive shaft 3.42 turns for every revolution of the wheels, IIRC.

His truck will require 3.73 turns of the drive shaft to do that. If we assume his transmission has the same ratios as yours, he'll be producing more power during those 3.73 turns than you did in your 3.42 turns, making more power at the rear wheels.

Starting in 2nd, if he can do that, will reduce the engine power to turn the drive shaft those 3.73 turns, since the engine should be turning more slowly, therefore fewer power strokes from the engine, etc.


I know that on my neighbor's 2009 Silverado, that when you put it in L2, that it will starts from a dead stop in 2nd gear.

I see what you're getting at. However, I don't think either truck would make it up the ramp from a dead stop in second, due to the angle of the ramp and the load from the jet skis. (at least, I wouldn't try it without having a tow strap already hooked up to the front end first...)

It just appears to be a fluke that the 3.42 is better in these conditions.

Now... my truck has the factory tow package, and his doesn't.

Is it possible that my transmission is slightly different due to the factory tow pack? I do know that the factory tow pack includes different shocks and a transmission and power steering cooler, but none of that would matter here.

 

[LS2JSTS]

Originally Posted By: IndyIan
Assuming your Dad doesn't have more lead in his boots, I'll bet his tire pressure is higher than yours.



Thats my "guess". A large difference in tire pressures would make a bigger difference than the taller/shorter gearing would IMO.

 

[endeavor to persevere]

GM went to drive by wire on the trucks in 2003. Your 04 will not have a cable.

The rear diff would be G80 Eaton locking diffs. Your fathers may not be locking as it should. they will lock both wheels together when one wheel spins 100 rpm faster than the other. They unlock over 20 MPH.

Some one mentioned taking off in 2nd gear. On the 4L60E taking off in 2 actually has the trans in 2nd gear. I do this a lot in the snow in the winter time.

Tow package has nothing to do with the transmission. All the 5.3s have a 4L60E with the same gearing. That is until recently when they went to the 6L80 six speed.

 

[Ben99GT]

Originally Posted By: Johnny
I may have this all wrong but, since yours is geared lower it takes less power to get things started, i.e. easy pull out of the gravel. His has higher gearing and more power has to be applied to get things moving and more power causes the tires to spin in the gravel.


If I am understanding you correctly it should be just the opposite, as the 3.73:1 axle ratio should require less output/load from the engine to get the truck moving. The difference would be similar to starting off in 1st gear (a numerically higher ratio) versus 2nd gear (a numerically lower ratio). Though the difference won't be quite that drastic.

The 3.73:1 truck should be easier to make spin due to greater torque multiplication from the shorter gearing though, if that's what you are saying.

I'm almost wondering if the taller geared 3.42:1 truck is just allowing more modulation of the throttle so it's able to pull the load without wheel-spin.

I also wonder if the posi in the 3.73 truck is in good working order.

 

[endeavor to persevere]

If his locking rear is not working the gear oil probably needs changing...

GM Bulletin..



LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION) #91-4-109
SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)
VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS
Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.
This condition of alternate engagement and disengagement of clutches in differential assembly is usually caused by contaminated axle lubricant.
To correct this condition, drain and refill the rear axle with SAE 75W-90 GL5 (P/N 12378261). The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life.VEHICLES/COMPONENTS INVOLVED: ----------------------------- Some light duty trucks equipped with locking rear axles, RPO G80.
SERVICE PARTS INFORMATION:
Part Number Description ----------- ------------------ 12678261 Lubricant, Rear Axle (1 litre)
Parts are currently available through CANSPO.
WARRANTY INFORMATION:
As specified in Light Duty Truck Maintenance Schedules, locking rear axle fluid drain and refill is required owner maintenance at the first engine oil change. Failure to drain and refill the rear axle as specified may contribute to a later axle chatter condition. Refer to the appropriate Light Duty Truck Maintenance Schedule or service manual, section OB, for further details on change intervals.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
© Copyright General Motors Corporation. All Rights Reserved.

 

[mrsilv04]

Originally Posted By: endeavor to persevere
GM went to drive by wire on the trucks in 2003. Your 04 will not have a cable.

The rear diff would be G80 Eaton locking diffs. Your fathers may not be locking as it should. they will lock both wheels together when one wheel spins 100 rpm faster than the other. They unlock over 20 MPH.

Some one mentioned taking off in 2nd gear. On the 4L60E taking off in 2 actually has the trans in 2nd gear. I do this a lot in the snow in the winter time.

Tow package has nothing to do with the transmission. All the 5.3s have a 4L60E with the same gearing. That is until recently when they went to the 6L80 six speed.


Well, I learned something today. I assumed that DBW was used sometime after '04. It was indeed added when they freshened up the GMT800 platform in 2003.

So, that's probably a fairly significant difference between the two trucks as well. I would assume that DBW has the advantage here as well.

With the steep gravel ramp, once there is wheel spin, it is all over anyway... as it will only dig ruts into the ramp. At that point, the rear end locking in already a lost cause. This is where having a 4x4 would be really handy.

The last time I noticed (last winter), the limited slip in both trucks was functioning properly.

 

[mrsilv04]

Originally Posted By: LS2JSTS
Originally Posted By: IndyIan
Assuming your Dad doesn't have more lead in his boots, I'll bet his tire pressure is higher than yours.



Thats my "guess". A large difference in tire pressures would make a bigger difference than the taller/shorter gearing would IMO.



It shouldn't be a huge difference, as I check/set the tire pressures each time that I change the oil or detail his truck.

 

[mrsilv04]

Originally Posted By: Ben99GT
I'm almost wondering if the taller geared 3.42:1 truck is just allowing more modulation of the throttle so it's able to pull the load without wheel-spin.


That... as well as the fact that the truck with the 3.42 is drive by wire, and is easier to "ease into the throttle" with.

 

[Bill in Utah]

Originally Posted By: endeavor to persevere
GM went to drive by wire on the trucks in 2003. Your 04 will not have a cable.


Interesting...

My 2004 GMC built in 6-04 has a throttle cable...

Cable is coming out of the firewall and direct to the throttle body...

Bill

 

[xxch4osxx]

My 2004 Silverado has drive by wire.

 

[01rangerxl]

Originally Posted By: Bill in Utah
Originally Posted By: endeavor to persevere
GM went to drive by wire on the trucks in 2003. Your 04 will not have a cable.


Interesting...

My 2004 GMC built in 6-04 has a throttle cable...

It's a 4.3 though. It probably didn't get all the retrofits and upgrades the V8s did.