3.73 & Z71 Question... Again -- Sorry!

piscator · January 25, 2009

Sorry to ask about a 'well-worn' topic, but I don't want to start negotiations on a 2009 Sierra when I still don't understand 'rear differential gearing'! This Sierra I found is a 5.3, crew cab, with 3.73 rear end.

If I read the achive threads correctly, 3.43 is the standard ratio, while 3.73 & 4.10 are optional. I've also learned that:

Higher number = easier towing

Lower number = better gas mileage

Yes? No? And if so, WHY?? I really don't understand what the trade-offs are -- help!

I tow a 24' fishing boat on weekends and plan to take it up to Maine for vacation. Aside from that, my truck is a 'daily driver' that is used to haul my daughters' kayaks, bicycles, etc.

My Silverado 5.3 with 3.42 seems to do the job, but "what do I know?"

The 'sticker' on the Sierra I found reads:

SIERRA 1500 4WD EXT CAB SLT

VORTEC 5.3L V8 SFI ENGINE W/ACTIVE FUEL MANAGEMENT

4-SPEED AUTOMATIC TRANSMISSION

7,000 LBS GVWR

3.73 REAR AXLE RATIO

HEAVY DUTY TRAILERING EQUIPMENT

LOCKING REAR DIFFERENTIAL

AUTOTRAC TRANSFER CASE.

So is all of this good? Is it 'way better' than my 2000 Silvy with 3.42?

The 09 Sierra under discussion has the Z85 suspension package. My Silvy has the Z71. Did I read correctly that the only difference between Z71 and Z85 is shocks, skid plates, and 'high output' decals?

Am I correct that I can uprgrade the 09 Sierra to Z71? If it's 'just shocks', should I let the dealer do this now, or wait a while?

I really appreciate everyone's help. You've gotten me this far! I'll probably start negotiating on the 09 Sierra next week!

Thanks! piscator

BuckFeverZ · January 25, 2009

IMO 3.73's is the best compromise if your just towing occasionally. You still have some down low power to get the load moving, but you still have better MPG's than if you had 4.10's.

J-man67 · January 25, 2009

IMO 3.73's is the best compromise if your just towing occasionally. You still have some down low power to get the load moving, but you still have better MPG's than if you had 4.10's.

Agreed!

Ryan00TJ · January 25, 2009

X3, I like my 3.73 gears along with the 5.3L. I tow a 5Klbs boat in the summer and it seems to work very well.

4.10's = lower gearing than say 3.42's despite the number being higher. The lower the gearing the more torque and rpms. The faster your engine will rev and get in the powerband. Tradeoffs are less MPG and more engine rpms.

3.42's = higher gearing than say 4.10's despite the number being lower. Generally the higher the gearing the truck will achieve better MPG but rev slower and stay low in the powerband.

The options on the 09 are nice. Same as mine. Test drive the truck. I beleive you will find its a better powertrain with 315hp and 3.73 gearing vs your 5.3 and 3.42's.

If the 09 is not a Z71 from the factory and not a Z60 its a Z85. I've never heard of a dealer doing a Z71 upconvert but its possible I guess. '

Good luck on the new truck.

mjb929rr · January 25, 2009

I tow a 22' boat regularly and if I did it over again I would get the 4.10s. I have the 3.73s and the vortecmax 6.0.

VMax2007 · January 26, 2009

I tow a 22' boat regularly and if I did it over again I would get the 4.10s. I have the 3.73s and the vortecmax 6.0.

+1

MarkD · January 26, 2009

I would stick with the 3.73's, especially if you are happy with the 3.42's.

If you could find a truck w/ a 6-speed, I think their 1st gear is lower and offers the best of both worlds.

Maybe this will help...

What the gear ratio means is that what ever number is posted as the gear ratio is the number of turns of the driveshaft for every one turn of the rear axle.

The higher the number, the more turns of the driveshaft per turn of the rear axle. The more turns of the driveshaft per turn of the rear axle, the easier it is for the driveshaft to turn.

If you ever rode a 10-speed bike in first gear you peddle like crazy, it is real easy to peddle but you don't go very far for all that work. The more steps you take up in gearing, the harder it is to peddle, but you go further with each gear for the same amount of peddle revolutions.

First gear is like 10:1 real easy, 10th gear is like 1:1 really hard if you aren't already moving, but not so bad if you have built up momentum.

The gearing in your transmission works with the gear in your rear differential to tailor the power produced by the engine to the demands of moving your truck.

The lower the gear (larger numerically) in your rear differential, the easier it is to move your truck forward in all gears.

3.42:1, 3.73:1, and 4.1:1 are numerically pretty close, but if you do the math, your engine will turn 20% more rpm in every gear with a 4.10:1 compared to a 3:42:1 differential gear. 3.73:1 is seen as a pretty good compromise.

If you are planning on replacing your tires with taller tires, then by all means get the 4:10 gear.

Hope all of this wasn't too basic.

piscator · January 26, 2009

Thanks guys! I've got two trucks to call on tomorrow and your help is invaluable.

MarkD, That's just a terrific exposition and deserves to be 'stickied' somewhere into perpetuity!! Your 'ten speed bike' analogies are not, 'too basic' -- they're basically clear and well done!

Ryan, You and MarkD have 'put the lights on' for me' and I appreciate it. I'm glad you mentioned the gearing in relation to the extra-horsepower, I hadn't considered it.

I found a few Sierras with 6 speeds, but the better deals seem to be 4 speeds. Everything's gotta stop somewhere!

Buck, Jman, I won't be towing often, so maybe 3.73 is the best compromise.

MJB, Vmax, my local launch ramp is 3 miles from my house, so it's not 'long haul' The trip up to Maine is, but we only do that a few times a year. I'm not sure it'd be worth gearing the 'daily driver' just for those trips.

I haven't taken the bigger boat very far... yet! With a little more boat and and a new truck, I'm hoping to expand my fishing horizons!

piscator

BuckFeverZ · January 26, 2009

Thanks guys! I've got two trucks to call on tomorrow and your help is invaluable.

MarkD, That's just a terrific exposition and deserves to be 'stickied' somewhere into perpetuity!! Your 'ten speed bike' analogies are not, 'too basic' -- they're basically clear and well done!

Ryan, You and MarkD have 'put the lights on' for me' and I appreciate it. I'm glad you mentioned the gearing in relation to the extra-horsepower, I hadn't considered it.

I found a few Sierras with 6 speeds, but the better deals seem to be 4 speeds. Everything's gotta stop somewhere!

Buck, Jman, I won't be towing often, so maybe 3.73 is the best compromise.

MJB, Vmax, my local launch ramp is 3 miles from my house, so it's not 'long haul' The trip up to Maine is, but we only do that a few times a year. I'm not sure it'd be worth gearing the 'daily driver' just for those trips.

I haven't taken the bigger boat very far... yet! With a little more boat and and a new truck, I'm hoping to expand my fishing horizons!

piscator

You gotta remember Brain will probably read this post, so next time use simpler terms so he can understand what you're trying to convey...oops I mean say.