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Old 01-14-2018, 01:26 AM   #1
Captainfab
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Gear Ratio Match Up

I'm helping a friend gather parts and install a 10 bolt front and 14 bolt rear under his Blazer. The 10 bolt front has 4.10 gears. The first 14 bolt we pulled has 3.73's so the search began for another with 4.10 gears. I found a early '80's G20 or G30 with a 14 bolt, but it has 4.09 gears. I had never heard of such gears for a 14 bolt, but in doing some research, it seems that is a common gear used in the G series vans. So my question is, has anyone used a 4.10 front gear with a 4.09 rear gear? I know that is backwards from the normal ratio match up, but I don't know how it will act with the rear wanting to push a little.
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Old 01-14-2018, 01:33 AM   #2
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Re: Gear Ratio Match Up

Match up is correct, won't hurt a thing
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Old 01-14-2018, 07:45 AM   #3
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Re: Gear Ratio Match Up

I've used 2 of the van rears now with no issues. But I thought when I checked they were 4.11.....either way not enough of a difference.
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Old 01-14-2018, 11:53 AM   #4
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Re: Gear Ratio Match Up

For off road it's fine as there's enough tire slip for the slight mismatch not to matter
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Old 01-15-2018, 01:01 AM   #5
Captainfab
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Re: Gear Ratio Match Up

Thanks for the replies guys. I thought it should be fine but since the ratios are the opposite of how they should be, I just wanted some input from those that may have done the same thing.
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Old 01-15-2018, 01:29 AM   #6
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Re: Gear Ratio Match Up

Pretty sure thats what I have in the '63 now with the Dana 44 and the 14B rear. Works great.
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Old 01-15-2018, 05:32 PM   #7
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Re: Gear Ratio Match Up

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Originally Posted by Bigdav160 View Post
For off road it's fine as there's enough tire slip for the slight mismatch not to matter
Agreed, and in fact I never engage the front axle on pavement anyway..... only when 4WD is called for, on a loose surface so the tires can slip.
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Old 01-15-2018, 06:23 PM   #8
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Re: Gear Ratio Match Up

The rule of gear matching is as long as they are within 4% of each other you're good.
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Old 01-15-2018, 06:58 PM   #9
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Re: Gear Ratio Match Up

4%?? Try 1%.
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Old 01-15-2018, 07:11 PM   #10
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Re: Gear Ratio Match Up

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4%?? Try 1%.
Well ideally rat yes, but industry standards from the '60's through the '90's, solid axle eras, had a 4% leeway.
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Old 01-15-2018, 09:17 PM   #11
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Re: Gear Ratio Match Up

Only vehicle I can recall that had a "major" difference was early Bronco's. I had a set of axles that were 3.54 front Dana 44, and 9" rear had 3.50s. Even that is 1% IIRC.
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Old 01-15-2018, 10:24 PM   #12
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Re: Gear Ratio Match Up

Yep, the spread wasn't big but they still said up to 4% was approved. Chev's had 4.09-4.11 difference in applications.. Jeeps had a 4.07-4.11 spread. Dodge had a few too that was 3 10th's difference. Heck tire pressure difference between the front and rear can create more than 1% ratio difference with just a couple psi. That's why tires can be considered as variable gearing devices.
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Old 01-15-2018, 10:35 PM   #13
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Re: Gear Ratio Match Up

A lot on here would be surprised by the difference in gearing on pulling trucks front to rear.
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Old 01-15-2018, 10:47 PM   #14
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Re: Gear Ratio Match Up

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A lot on here would be surprised by the difference in gearing on pulling trucks front to rear.
Yep, but that's purposely designed for under drive/over drive between the front and rear using either different size tires or major differences between the front and rear tire pressures for tracking issues through the pull.

Check out those mud pit runners and their gear and tire size differences. Super cool!
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Old 01-15-2018, 11:51 PM   #15
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Re: Gear Ratio Match Up

1% or 4% one thing is for sure... Its 100% harder to disengage 4wd on dry pavement for the unlucky moron that doesn't believe what everyone says about using 4wd for "4wd conditions". Its just as hard to do the second time since I didn't learn from the first

One thing I do miss about a couple of the last trucks that I did have was the ability to "shift on the fly" while driving in snow or ice. I think those trucks had Borg Warner t cases and there must have been some sort of "differential" type mechanism to them that allowed this?

I haven't tried it with my current 205. I always stop to shift. Does anyone here run with hubs locked and shift while moving at more than creep speed?
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Old 01-16-2018, 01:33 AM   #16
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Re: Gear Ratio Match Up

I was doing 4x conversions in the late 70s and early 80 where the rear was 3.64 ratio and the front we put in had 3.54. Never had any complaints about the difference of 3% 3.54/3.64= .972 or 2.8%
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Old 01-16-2018, 07:40 AM   #17
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Re: Gear Ratio Match Up

Quote:
I think those trucks had Borg Warner t cases and there must have been some sort of "differential" type mechanism to them that allowed this?
AWD drive or "full time" 4WD get a third differential.

Shift on the fly trucks have a transfer case with a synchronizer like a manual transmission. Many makers have them. I think some of the late NP205's were synchronized.
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Old 01-16-2018, 02:29 PM   #18
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Re: Gear Ratio Match Up

My 61 k10 has 3.38's rear and 3.31's in the ft dana 44. stock was 3.90 and 3.92 ft. No problems with this set-up on dirt/snow. Don't think i would run it on payment though.
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Old 01-17-2018, 01:21 AM   #19
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Re: Gear Ratio Match Up

Just to clarify, I am completely aware of the typical gear ratio split between the front and rear differential. I have dealt with several 4x4's over the past 40+ years. my concern was with having the 4.09 gears in the rear and 4.10's in the front instead of the 4.09 in the front and 4.10's in the rear.
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Old 01-27-2018, 03:02 PM   #20
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Re: Gear Ratio Match Up

That's perfectly fine. Easily close enough match. You have nothing to worry about.
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