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Old 07-14-2008, 08:24 AM
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gear ratios

I pull with a chev silverado 2008 4.3 6 cyl w 323 rear, this thing pulls to much RPM at speeds of 65 on highway, around 3800 to 4000, never gets in OD. stock auto trans.

I want to change the rear to pull 4800 to 5000lbs@65 mph. What would be the best ratio to run 3.73, 4.10 etc.

trying to kill some of that high rpm for a small engine. can't afford a bigger eng. TIA

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Old 07-14-2008, 09:49 AM
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Even if you are not in OD those RPMs don't seem right for the ratio that you say you have.Drive is 1 to 1 ratio.Go to a site with a ratio, RPM computation like Randys ring and pinion and plug in your tire diameter and rear ratio and 1 to 1 as if you were in drive and I think you will see what I mean. I think you might have a trans problem.JMHO.Hope this helps.
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Old 07-14-2008, 10:00 AM
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I went to Randy's ring and pinion.I don't know your tire height so I guessed 29".With a 3.23 rear ratio and a 29" tire in drive at 65 MPH you should be turning 2498 RPM's and in OD 1703 RPM's according to their calculator.Unless I got the tire height wrong you have other problems or you don't have a 3.23 ratio.

Last edited by speedydeedy; 07-14-2008 at 10:08 AM.
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Old 07-14-2008, 10:09 AM
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I agree Speedy. I checked with the same 29" tire size. If he's in 2nd gear, 1.62:1 ratio running 3800rpm it will be 62mph.
http://hotrodworks.net/hotrodmath/quarter.html
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Old 07-14-2008, 10:31 AM
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I could be wrong, but doesn't the owners manual specifically warn you NOT to tow anything in overdrive? Especially with that kind of weight and that small an engine, it will "hunt" in and out of overdrive constantly. Truck with a V8 is the only real solution, beside the mentioned trans problem/rpm discrepancy.
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Old 07-14-2008, 12:26 PM
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your truck wont shift in to od because the calculated load is to high.In other words your trying to tow to much weight with it.
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Old 07-14-2008, 01:13 PM
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Quote:
Originally Posted by 84 Monte Carlo
your truck wont shift in to od because the calculated load is to high.In other words your trying to tow to much weight with it.
I agree.But there is still the problem of RPM versus rear ratio even in drive just doesn't add up. Something else is wrong here.I also agree about no OD when pulling that heavy of a load.
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Old 07-14-2008, 03:29 PM
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It may be in second.5000# is a lot of weight for 4.3 1500.

1/2 ton=1000#. There should be a spec. for tounge weight.

You also have to think about stopping it.
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Old 07-14-2008, 04:39 PM
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gear ratios

Without towing everything works fine, shifts are properly achieved. When towing the trailer on flat ground, every thing works ok, normaly in tow haul mode, were running around 2400. While pulling the hills near danville, Va and in the hills of NC is when I had problems. Most GM's with tow package has a 373 and light duty has a 323. I don't use od unless its on flat ground and not bumping in and out like someone stated. I was wondering if I changed to a 373 wether I would benefit on the hills and if the difference is worth the expense. GM says able to tow 4800 in my manual. Thanks
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Old 07-14-2008, 05:16 PM
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I wouln't try to pull the skin off of rice pudding with a 4.3. You really need a V8 to tow that kind of load.
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Old 07-14-2008, 09:48 PM
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The 3.73 will help, but the 4.3 just really isn't powerful enough for that big a load if you are towing frequently.
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Old 07-15-2008, 07:15 AM
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The 3.73 will give you a little more grunt when pulling the trailer but your rpm will be up there so gas mileage will still go down the tubes.

I was in the same situation as you... pulling 3500 lbs. Finally gave up and put a rebuilt 5.7 in my truck a couple of weeks ago. Haven't tried pulling with it yet but the power is sure there.
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Old 07-16-2008, 03:27 AM
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Quote:
Originally Posted by 84 Monte Carlo
It may be in second.5000# is a lot of weight for 4.3 1500.

1/2 ton=1000#. There should be a spec. for tounge weight.

You also have to think about stopping it.


i've got a 2000 4X4 with a 5.3 (shortbox), weighs 5100ish with me in it.
IF his has 4 wheel disc, it'll stop just fine.
had mine 3 years now, still need to hook up trailer brakes.....
DISCLAIMER!!!!
DO NOT TRY THIS AT HOME!!!!
you're trying to haul a 5000# trailer, correct?
with a 4.3, correct?
guess they must run better where YOU live
i'm at 5000 ft....

you're asking A LOT out of a 4.3......of COURSE it's going to want to run in 2nd gear!.....
how about slapping a turbo on it?
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Old 07-27-2008, 06:11 AM
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gear ratios

Thanks for the help: I fixed it with a 2008 Siverado 1500 5.3 V8 and 373 rear w/towing package in a new truck,
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