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Mar
GenI
3/27/2001
09:46:28
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 Subject: Rear Ends
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Message:
I am going to buy a dakota and want to know about the rear ends. I know what a higher and lower rear end will do for you but just curious about what the dakota with 4.7 is like with them. Like what is the rpm at 70mph with the 3.91 and what is the rpm at 70 with the 3.55. Also how much preformance diffrence is there. Thanks.
MaRty
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Dan Gruber
GenIII
3/27/2001
11:36:20
| RE: Rear Ends
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I run about 2200 rpm at 70 mph with the 31" tires, 3.55 rear end and auto trans. The most annoying thing about the 3.55 gears is that between 45-60 mph, the slightest increase in throttle will cause the converter to unlock or drop into 3rd gear. The 3.92's should minimize that and increase your acceleration with a minimal decrease in gas mileage.
Dan
2000 CC/SLTplus/4X4/4.7/auto/3.55LSD
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intense99dak
*GenIII*
3/27/2001
14:39:20
| RE: Rear Ends
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My Dak started off with 3:55's, but now have 3:90's. The difference between the two is pleasantly noticeable. Take off from the line is quicker with the 3:90's as well as passing on the highway. There was very little difference in rpm's at highway speeds. Maybe 300 rpm difference at 80 mph.
I would definitely recommend the 3:90's.
Chuck Robbins
'99 Dakota Sport
www.intense99dak.com
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jsatter
GenI
3/28/2001
00:53:46
| RE: Rear Ends
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Chuck,
What'd it cost you for the rear end conversion?
Just bought my dak 3 weeks ago and never thought to check what kinda rear it had.
01 Quad Cab SLT Plus 2WD Auto 4.7L - Currently Stock
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Mar
GenI
3/28/2001
08:56:56
| RE: Rear Ends
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Message:
Chuck,
What is the diffrence in the gas milage. Also i thought that the higher rear end makes for slower passing on the highway if what you say is true then for sure i will get the 3.95 thanks.
MaRty
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mar
GenI
3/28/2001
08:58:17
| RE: Rear Ends
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Chuck,
What is the diffrence in the fuel milage between the two. Also i thought that the 3.95 rear end would make passing on the highway harder but if what you say is true then for sure i will get the 3.95
MaRty
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mar
GenI
3/28/2001
09:04:20
| RE: Rear Ends
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Jsatter
My money would go on you having the 3.55 because if you don't mention it they will give you the standerd and standerd for the dakota is 3.55.
MaRty
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intense99dak
*GenIII*
3/28/2001
09:20:27
| RE: Rear Ends
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I haven't really paid attention to gas mileage that much since most of my driving is in city and my right foot has a lot of lead in it ;-) But based on the rpm difference I would conclude that the mpg difference is very nominal.
The cost to have my 3:55 one wheel beast converted to 3:90 posi was a lot more than expected ... about $1200. My wife still to this day regrets talking me out of getting limited slip from the factory ;-) Parts were about $400 and labor was $800. Remember though that I had new gears and a LSD unit installed. Just gears would be a lot cheaper.
As for passing on the highway, yes I really do notice the difference. I'm trying to think of a way to explain why the difference, but the coffee hasn't kicked in yet ;-)
Think of it this way. The rear tire(s) spin once with 3:90 gears. With the 3:55 gears, it would only turn about 3/4 the distance the 3:90 tire did in the same distance. What this (very) roughly translates to is that the 3:90 tires will spin faster and therefore gets your Dak moving faster/quicker.
Hey, Bernd ... You want to give it a try ;-)
jsatter - Inside your glovebox, there should be a white sticker telling what your rear end ratio is. Also, look on the pass. side of the rear axle and there should be a sticker saying if your rear end is LSD or not. If you have any question about it being posi, just do a burn out and count the rubber strips ;-)
Chuck Robbins
'99 Dakota Sport
www.intense99dak.com
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CyberWolf
GenIII
3/28/2001
10:50:43
| RE: Rear Ends
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Message:
I disagree with just one thing Chuck. The tires with 3.90 will spin less times than a tire with 3.55. That is where you get the extra power.
With 3.90 gears, that means that the driveshaft will spin 3.90 times while the tires spin only once.
With 3.55 gears, that means that for every 1 time the tires spins the driveshaft will spin 3.55 times.
That means that tires with the 3.55 gears are actually spinning faster than the 3.90 gears. This doesn't mean that with lower gears (higher number) your vehicle will be slower, it just means that you will have more rpm's wrapped up at the same speed thus increasing power. The difference between 3.90 and 3.55 gears is small compared to what I'm used to. I am an avid 4 wheeler. Our gears are more like in the 5.13 or 6.13 area. The only problem is our top speed is only around 60 mph. Oh well, the things people will do for power.
'01 4.7 CC, 5 speed, Sport , 3.92 limited slip, Intense
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intense99dak
*GenIII*
3/28/2001
15:00:25
| RE: Rear Ends
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Great explanation, CyberWolf ;-) I knew something equaled something, but I hadn't woken up enough yet to think straight.
Thanks for your praise on the other post. I try ;-)
Chuck Robbins
'99 Dakota Sport
www.intense99dak.com
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RonW
Gen III
3/28/2001
16:36:48
| RE: Rear Ends
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The cost to just do the gearing is approx. $550. I made that costly mistake also of not getting it from the factory. The 3.92 vs the 3.55 from the factory is $35. The LSD from the factory is $285. $800 seems like a lot of labor if you're doing both at the same time. I'd have to check with my shop. Parts wise, the gears are $275 and the LSD is ~$200.
Ron
00 PB SLT QC 4X2 5.9 46RE 3.92 LSD
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intense99dak
*GenIII*
3/28/2001
17:13:51
| RE: Rear Ends
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Yea, my jaw dropped when I was told $800 ;-) The only thing that makes feel better is that the guy who did the job works mostly on high performance stuff. He gave me a year warranty and that's knowing that I'd be adding a supercharger and other go fast goodies. Plus he knows how heavy my foot is ;-)
Chuck Robbins
'99 Dakota Sport
www.intense99dak.com
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Russ
GenIII
3/28/2001
20:38:26
| RE: Rear Ends
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How does this sound?-A LOW numerical rear axle such as a 3.55:1 is also referred to as a high ratio,because the road speed is relatively fast for any given engine speed.The characteristics of this ratio are lower engine rpm, reduced power output,and higher fuel economy.A HIGH numerical rear axle ratio such as a 3.92:1 is referred to as a low ratio because the road speed is slow relative to the engine speed.the charateristics of this ratio are higher engine rpm,more easily available power output,and lower fuel economy.But you have to consider tire size also.A 3.55 ratio with the smaller P235 Tires is going to rev about the same at 55 mph as a 3.92 ratio with 31x10.5 tires.My cheap personality is happy with my 3.55 ratio but my Boyish But Dyno Personality (BBDP) is wishing he had 3.92 (lower et)gears.
2000 CC SLT 4X4 4.7 L-SLIP AUTO 3.55
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jsatter
GenI
3/29/2001
00:51:32
| RE: Rear Ends
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Message:
Could someone define LSD (Nothing smart-ass, please) and posi?
01 Quad Cab SLT Plus 2WD Auto 4.7L - Currently Stock
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Broeheem
GenIII
3/29/2001
03:24:14
| RE: Rear Ends
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Here's my "spin" on the matter... LSD (limited-slip differential) and Posi (positive traction) are essentially the same, but not to be confused with a full locking rear end. An open diff (standard on most) will allow the rear wheels to turn at different speeds, keeping your tires from excessive wear and UNWANTED tire-squealing from normal cornering, but mash the throttle, and one wheel will melt the tire to the steel belts while the other tire does nothing. An LSD will allow the same cornering advantages, but under spirited acceleration - :) - after one wheel begins to spin faster than the other, the second wheel will kick in, providing considerably more traction. A full locking rear is just that : fully locked - both wheels turn at the same speed - no matter what, and is intended only for drag-strip use... helpful in keeping you going in a straight line when your front wheels are in the air.
As far as 3.55 vs 3.92... absolutely opt for the 3.92's if you plan on doing any racing. The differences in acceleration far outweigh the loss of MPG. I went with the 3.55's because in real life (for me anyway), they offer a near-perfect balance between MPG and power.
Final thought : I can't think of a single plausible reason NOT to get the LSD if you haven't already bought the truck. If you have, the cost would make me think twice.
Patriot Blue '01 CC SLTplus, 4.7/multi-spd auto/3.55:1 LS
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RonW
Gen III
3/29/2001
12:45:13
| RE: Rear Ends
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Message:
Very well put, Broeheem. I couldn't agree more. The only difference is if I was racing a lot, I would probably opt for 410's. Those of you that want a streetable truck should not go for lockers, but a custom built valve body and torque converter wouldn't hurt. Ah, but that's a whole different subject.
Ron
00 PB SLT QC 4X2 5.9 46RE 3.92 LSD
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CyberWolf
GenIII
3/29/2001
13:44:56
| RE: Rear Ends
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Message:
I just finished buidling a ford 9" with 5.13 gears and a spool for a Blazer. Talk about steep gearing. You can't beat the feel though.
'01 4.7 CC, 5 speed, Sport , 3.92 limited slip, Intense
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Doug
GenIII
3/29/2001
14:22:11
| RE: Rear Ends
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for what it's worth; checked RPM today. 70 @ 2125, 80 @2425 and 100 @ 3000. 31x10.50x15, 3.9 gears. (S.W.A.G. on 25 RPM using factory tach)
Doug
99 Dakota Sport, 4X4, Auto, 3.9
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Jonas Janek
Unregistered
3/30/2001
11:14:15
| RE: Rear Ends
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Message:
Ok what is the diffrence in 0-60 or quarter mile times of the same truck, say CC 4.7, same size tires, and only a diffrence of gears between, the 355 and 392's. (estimate if you have to) and What will be the MPG diffrence between the two? Guestimates are fine, but if anyone has any actual stats that would be great. Also where can you find out if you have lsd or posi on the truck?
While discussing traction, does anyone know if the addition of say Lakewood universal traction bars help at all? And if they have any negative effects on the truck or driving?
Jonas
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Bernd
GenIII
3/30/2001
19:34:10
| RE: Rear Ends
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Message:
Doug, are those RPM's in 1:1 (4th gear or no OD on automatics) or in overdrive. If it's in OD, you'll have to calculate in the OD ratio in the final drive as well.
5-Speed = 0.79 in 5th Gear
Automatic = 0.69 in OD
Anytime you have shorter gears (3.90, 4.10, 4.56:1) you'll (most of the time) be quicker off the line and in the 1/4 mile. With taller gears (3.55, 3.20:1, and lower) you'll be slightly slower off the start but may have higher trap speeds. Now that also depends on the HP and TQ that the engine is putting out.
But in this case, 4.7 vs. 4.7 (one with 3.55 and the other with 3.92:1)...i'll put my money on 3.92:1.
Bernd D. Ratsch
1997 Dodge Dakota SLT
Supercharged w/Nitrous
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Doug
GenIII
3/31/2001
03:35:52
| RE: Rear Ends
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Message:
Bernd, RPM's were for info only for comparrsion between 3.5 & 3.9 gears however overdrive was on. standard driving configuration. still not sure how fast it will go before governer cut in. need no traffic on road. safety thing.
Doug
99 Dakota Sport, 4X4, Auto, 3.9
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mar
GenI
4/05/2001
10:42:23
| RE: Rear Ends
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Message:
Do the Dodges have a diffrent limited slip then the GM's because my friends Gm doesn't have that locked feeling and i saw him spinning on ice with one tire not spinning but he does have the limited slip.
MaRty
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