Any other gear ratios available????

[1970SWB]

My '84 3/4ton GMC suburban started out as a 6.2 diesel and has the 700R4 trans with a 4:10 rear axle(semi-floating). It now has a 454 with the 700R4 trans, I use it mainly for pulling a trailer, but it still has more gear then I need, what other ratios were available in this rear end? Was a 3:73 available or even lower/higher? Has anybody swapped and noticed a mileage or power difference??

[Rubble]

Semi float was available in 3.73,so was 3.42, not sure how much lower than that.

[D13]

There was a rare 3.23, I've only seen 1 and it was for sale here IIRC. 3.42's are very common in light 3/4 tons, both my 81 and 99 have that.

[79Betty]

3.42's people say are best of both worlds. Personall i'd go to them. My k10 did have them but i swapped for 4.10's. 3.42's and 38" baja clawz didn't get along too well...

[wilkin250r]

4.10 and 38" tires still sounds awful. I've got 3.73 and 40" radials and my truck can't even get out of it's own way. It will drive, but I'm thinking I'll be switching to 5.13 this summer.

To keep on topic, my truck (as stated above) has 3.73 gear ratio, and I believe it's stock. With the size tires on this truck, I can't possibly imagine anybody switching to 3.73 on purpose, they have got to be original.

How big/heavy is this trailer you're hauling? 3.42 gearing sounds to me more like daily driver gearing, with occasional towing. If towing is your primary task, I'm thinking 3.73 might suit you a little better. What size tires?

[Mattchu60]

I don't have a diesel, but have the TBI 350 in my 87'. I had 33" tires with 3.42 gears and hated it. Truck was on the verge of worthless for daily driving, constantly shifting between D/OD on the highway and could hardly pull itself empty on the interstate, towing was a total nightmare (max speed was around 35mph usually with a trailer, it just could not do it). I hated it.

I put a SF 14 bolt in with 4.10 gears and it made a massive difference. I actually get better mileage now and drive-ability increased by a large margin with the 4.10's.

[1970SWB]

I think I have 245/75/16's on it now. Just curious if it would be worth it mileage wise to swap in a milder gear. The 454 has more then enuf power to pull my trailer with drag car. My enclosed trailer is 8k plus loaded, & if I haul my open trailer its about half that. While I don't expect great fuel mileage from a Big Block Suburban, it'd be nice if i could squeeze a few more miles out of a 40 gallon tank.....probably just wishful thinking on my part.

[donut]

What rpm range are you running now?
You don't want the motor screaming, but you don't want it lugging either.

Thought OD may be the answer for my C-30, but with 4.10's and semi-stock size tires, I'm running about 2400 rpm @ 60 mph. For me, not worth the expense to change.

You could play with one of the online gear ratio calculators and see what you'd like.

[1970SWB]

Originally Posted by donut

What rpm range are you running now?
You don't want the motor screaming, but you don't want it lugging either

At 70-75mph its right at 2,800(if I am remembering correctly, Its been a bit since I drove it) That's in overdrive...........

Originally Posted by wilkin250r

So you're hauling a pretty big load. We're not talking about a little aluminum fishing boat or a trailer made from a truck bed. You're doing fairly serious towing.

245/75r16 is right about 30.5 inches tall. My calculations, at 60mph, puts you 2700rpm in drive, 1900 rpm in overdrive. I am assuming that you're not towing in overdrive, correct?

I don't have solid advice for you, but I have numbers. Looking at the numbers, I retract my previous statement. 3.42 gearing would put you at 2300 rpm at 60mph (in drive), which is perfectly reasonable for a big block. If you were towing 2k lbs, I would say a gearing change would suit you well. But for the kind of weight you're towing, I'm not so sure.

Towing 8k, my gut tells me 3.73 gearing is your best bet, but since it's only a small jump from the 4.10 you're running now, I don't think it's worth the cost and hassle to change. In reality, what might be more beneficial to you would be to look at a transmission upgrade. There are a few companies out there that offer heavy-duty 700R4 transmissions that they claim can handle the stress of towing in overdrive. That not only gives you the taller gearing and milage you're looking for, but also retains your get-up-and-go ability you have right now with your 4.10

Yea, its a 26' enclosed car trailer or open car trailer. I do "click it into overdrive" when at speed on flat/level roads. But keep it in drive if it try's shifting back and forth. My trans was built 8-9 years ago & the builder said this would be fine. I understand its heavy. I understand it's a carburated Big Block, I was just wondering if anybody had real world experiences with other ratio's and if a swap would be worth it. Honestly, for the amount of driving this vehicle gets it's probably not. I was just looking for somebody that had "been there done that".......THANKS GUYS!!

[wilkin250r]

So you're hauling a pretty big load. We're not talking about a little aluminum fishing boat or a trailer made from a truck bed. You're doing fairly serious towing.

245/75r16 is right about 30.5 inches tall. My calculations, at 60mph, puts you 2700rpm in drive, 1900 rpm in overdrive. I am assuming that you're not towing in overdrive, correct?

I don't have solid advice for you, but I have numbers. Looking at the numbers, I retract my previous statement. 3.42 gearing would put you at 2300 rpm at 60mph (in drive), which is perfectly reasonable for a big block. If you were towing 2k lbs, I would say a gearing change would suit you well. But for the kind of weight you're towing, I'm not so sure.

Towing 8k, my gut tells me 3.73 gearing is your best bet, but since it's only a small jump from the 4.10 you're running now, I don't think it's worth the cost and hassle to change. In reality, what might be more beneficial to you would be to look at a transmission upgrade. There are a few companies out there that offer heavy-duty 700R4 transmissions that they claim can handle the stress of towing in overdrive. That not only gives you the taller gearing and milage you're looking for, but also retains your get-up-and-go ability you have right now with your 4.10