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Doug McCoach
Dodge Dakota
5/27/2001
01:02:13
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 Subject: 3.92 or 3.55 Gears?
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Message:
Gentlemen,
Like many of you, I too am spending more for hp than any married/with children person should, but I just can't stop. Assuming it will be a while before the 5.7L Hemi is offered in the Dakota QC 4X2 or 4X4 & all the kinks are ironed out, I think it is safe to say we have a few years to spend as much as possible to maximize hp in the 4.7L V8 magnum trucks. Besides, I just read a detailed description about the engine & it suggests that it was made for mods. Now to the point, I would like to swap out my 3.5 gears for 3.9's in my 4X4 for some more low end. A local dealer suggested the cost would be in the $2000 range-sounds way too high for a gear change doesn't it? Any thoughts on the prospect? Anyone done it yet, have cost info?
2000 QC 4X4 4.7L V8 Auto.
Mods: 3" Gibson Cat-back, Airaid intake, TB Spacer
Dreams: Better intake, Headers, larger TB, ECU programmer, Head Porting-etc, 17X9 rims with 1" lager tires.
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Shawn
Gen III
5/27/2001
01:12:04
| RE: 3.92 or 3.55 Gears?
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Message:
I'm debating the same thing. That sounds a bit high to me, I've been seeing $1200 or so around town. Not factory gear though, and that should easily cover both diff's unless I'm missing something. Check out your local 4x4 performance shops, they do these all day long. You get to keep your old gears, so if you trash the new ones you could always toss in the old ones.
my .02,
Shawn
98 5.2L 4x4 CC
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Hawkeye
Dakota Enthusiast
5/27/2001
09:19:34
|  RE: 3.92 or 3.55 Gears?
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Message:
I have been wanting to change to 3.92's from day 1. I have contacted every Ring & Pinion shop you can think of (Randy's, Genuine, Precision, etc). Dodge wants around $900 just for the front and rear R&P sets and the install kits. With labor it will total around $1200 to $1400. I can get aftermarket sets for about $500 to $600 for the front and rear. Labor is running around $500 for the install. Only problem with aftermarket is that the closest I could find was I believe Randy's and they could get me a 3.92 for the rear and a 3.91 for the front. The only other match available is 4.10's. I dont like haveing the odd setup, even though a 3.92 and 3.91 are close enough to not really matter, so I will probably just gripe and complain and spend the money to have Dodge do it. At least then it will be covered by their warranty.
'00 QC 4x4
4.7 3.55 LSD
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travis
Dodge Dakota
6/02/2001
00:19:09
|  RE: 3.92 or 3.55 Gears?
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Message:
It is very common to have 4.10's in front pulling 4.11's out back. The weight (F/R distribution on a truck) difference has as much effect on the tire diameter as the % difference in the gear ratio. As long as the front diff is pulling the rear ( 3.21 Front/3.23 Rear or 3.54/3.55, 3.91/3.92, 4.10/ 4.11) everything should work fine. If you check older Dodge/Chevy 4x4 specs you should see these types of gear ratio applications.
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lil red dak
Dodge Dakota
6/02/2001
09:29:26
| RE: 3.92 or 3.55 Gears?
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Hawkeye if you mix those 3.91 and 3.92 gears and run a closed center differential it will matter when it tears up on you . you will also have problems with an open center and the gear ratios being at all differnt, it will just take a little longer to bust the parts. You might not have much trouble on dusty or gravel roads or off roading , but you will on dry pavement. It would be the same as having 215-70-15's on one axel and 235-70-15's on the other and all offroad 4X4's know that is a no-no.
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Doug McCoach
Dodge Dakota
6/02/2001
11:26:19
| RE: 3.92 or 3.55 Gears?
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Message:
Thanks for the replies. I got a quote from a local 4x4 shop who said they have done a couple of Dakota's & recently a Durango & they strongly recommend going with 4.11's front & back since some people haven't been totally happy with the little change that occurs when going from 3.55 to 3.91's. They also mentioned that I wouldn't need a new carrier & yet the cost is still pretty high - approx $1450 plus tax. I have 15x8" rims with 255x75xr15(31x10.5xr15)tires & eventualy want to upgrade to either 16" or 17" rims with an overall tire diameter about 1" larger to fill in the wheel well a little more & have it retain the "useable" look of a 4x4. A larger tire diameter decreases the gear ratio, ie. if I go with 4.11's & then increase the tire diameter 1", my gearing is now less than 4.11's, maybe 4.00's or so. I have the formulas that would give me the exact ratio but you get the idea! Another way to improve the bottom end torque/hp is to get a programmer that can change the shift points. These can run $400-$500 but is a much cheaper way, however, nobody makes any yet & the custom flashes available for $400 or so don't change the shift points. I talked to a few Dodge dealers about Mopar holding back on the high performance stuff for the 4.7L V8 & the consensus is that Mopar doesn't want to rush out with new products since it increases the odds of people using the 3/36,000 mile warranty. In other words, they sell you a high performance ECU/PCM & it really rips but it also increases engine wear & thus causes more waranty claims. Based on this info, whether valid or not, it may be another year or so before we see any major high performance stuff available from Mopar for the 4.7L. Oh, I just hate waiting!
2000 QC 4X4 Auto 4.7L V8 3.55's
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travis
Dodge Dakota
6/03/2001
16:14:45
| RE: 3.92 or 3.55 Gears?
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Message:
Doug: It sounds like you've gathered the right information.
Lil red Dak: Not to be a smart ass, but look at it this way.
Gears 3.92-3.91= .01, .01/3.91=.0025 or 0.25% different.
Tires: 31.0"dia. x 3.1416(pi)=97.38"circumference. If you measure the tires on any vehicle you will see at least 1" manufactured( or 3/8ths in. tread wear) variance in circumfence 1"/97.38= 0.01 or 1.0%
Translation: Unless you are measuring and matching your tires to mix them for proper ratio per axle (the factory does not, racers do), the odds are every 4x4 out there is operating with more ratio difference than 3.91's w/ 3.92's. Any difference will waste power and put stress on components, but anything mass produced has to tolerate some variation. Mass produced tires are headaches for auto manufacturers.
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Hawkeye
Dakota Enthusiast
6/03/2001
18:35:32
| RE: 3.92 or 3.55 Gears?
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Message:
I would go to the 4.10's if I were going to 35 inch tires. But I am only going to 33's when I lift the truck. Right now I am running 32's stock.
My friend has the same truck as me only he has the 3.92's. He has 32's as well. Other may not be able to tell much difference between the 3.55 and the 3.92 but we can. He had 4.10's in his last truck and I had them in one of my older trucks. Rpm's ran way to high on the highway and ate a lot of gas. But both trucks pulled like crazy though. I have always owned 4x4's. I have seen guys run gear combinations like 3.91 in front and 3.92 in the rear. Some had no problems, others broke all the time. I would just rather play it safe and go with the 3.92's from dodge that way I wont always be wondering in the back of my head.
'00 QC 4x4
4.7 3.55 LSD
Jet Power
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Matt Barret
Dodge Dakota
6/04/2001
07:48:51
| RE: 3.92 or 3.55 Gears?
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Message:
Have any of you checked the price on a "complete assembly" rear from Chrysler? It comes with the case, gears, posi unit, spider gears, everything except for the axles, you just slide your old axles into the new housing. I did this with my truck after I destroyed the rear end at the drag strip, I got the entire assembly, minus axles for $1050.00, then all I had to do was bolt it in!!You might check on it, especially if you have a good parts connection, you may come out cheaper.
Matt Y2K-HEMI
'00 RC 4.7L 5spd 217 RWHP
14.23@ 94.49
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