4.10 to 3.54

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I have a 2001 QC with a Cummins and a 4. 10 LSD automatic. I'm currently getting aout 20 mpg consistently. I want to improve my fuel economy (even though 20 ain't too bad). I recently checked with a Dana dealer about switching over to a 3. 54. He told me all I would need is the ring and pinion gear and would not need a different carrier. He gave me the part number and told me the price would be $367. 00. The only problem was that even though it was a good part number there are no 3. 54's anywhere to be found in the Dana network and he didn't know why... does anybody know what's going on and if I did switch to a 3. 54 what could I expect for mileage and do I have to change something to correct my speedometer?

 

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You might post an ad in the Classifieds area and see if you can find somebody with a 3. 54 rear end that wants to do an even trade of the entire axles. That way you save money and labor, and you can do the swap yourselves in a couple of hours.

Just have to be sure both trucks are 2wd.

Rob

 

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Bigfig-

Check these people out. As far as I know they are the Guru's and have a very large inventory.
http://www.ring-pinion.com

Dave

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99 QC SB 4x4 Auto
Factory Ordered
Most Options

 

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Bigfig, I dont have much experience with the "overvalved" cummins, but they say it likes to rev. You might not save as much MPG's as you might think.
I'd post the question over at the 24 valve area to see if it's a worth while swap before I'd go through all that.
Just my thoughts... .
PS welcome aboard.

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98 Quad cab 4X4 2500 12 valve,5 speed,3. 54 rears, 8' bed. Boost and egt gauges but basicly stock except for a "properly adjusted" AFC. Uniden HR 2510, Texas Star 1200 amp. 55,000 Mi as of 8/21/00.
NRA life member. High power/IDPA.

 

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Also, Bigfig, If you are pulling much, you may want to stay with the 4. 10 unless you are all interstate. On the two lanes at 55 you may be at the bottom of the safe area for not lugging the engine.

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2001 HO 6 spd 2500, 4. 10 LSD, Towing Package, Electric Brakes, SPA EGT/Boost Gauges, Running Boards, Fog Lights, Real Backup Lights, Running Boards

 

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Be careful on the price you get. Does that price include the labor to install it? My understanding is that Dana axles are one of the hardest to set up. Spacing (like backlash) is critical on these axles. They have to be basically put together before measurements are taken. If it's wrong, tear it back down and try again. I'm not trying to deter you as I have a 5 spd. with 4. 10's and at times wish I had gotten the 3. 54's. All I'm saying was an authorized Eaton/Dana shop told me the labor could be between $100. 00 and $400. 00 per axle.

Kinda costly for a couple MPG's.

Any other's have thoughts or experience on this topic?

Correct me if I'm wrong here.....


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2000 RAM 4x4 2500HD Reg cab. Properly valved 5. 9 Cummins. 5 spd. 4. 10 LSD. Stock except for K&N Air Filter.

 

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Diesel Doug, I think you are right on the mark. It is not just a simple case of pulling out the ring and pinion and putting in a new one. It is a tedious job at best to get the preload/backlash adjustments correct.

 

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What you report is different from what I was told, but I have the Dana 80 (manual trans) while you have the Dana 70 (auto). On the Dana 80 I understand that the 4. 10 is installed on a large carrier and the 3. 54 on a small carrier. I was told this when asking about limited slip differentials and gear options from a rear-end shop. I would get a second opinion on this before buying any gears as a new carrier will boost your gear-change costs way up.

If I had the auto, with its high overdrive ratio (0. 69), and I had my choice of rear-end ratios, I would not pick the 3. 54 as I think it's a little too tall. I would go with the 3. 72 (think that's the Dana number) as the tallest, and in fact would have used that ratio on my truck (with manual) if it was a factory option. The 3. 54 is quite tall a ratio for the 24 valve engine, especially with the auto trans. Note however that that's how I ordered my truck, and I am happy with it, but would have gotten 3. 72 if it had been offered.

Fuel mileage savings will depend how you drive. If you drive empty, and over 70 mph you should see some savings with a taller gear. If you drive at 60 to 65 mph your mileage will probably not change, even though you are at lower engine RPM. In any case, any savings in fuel mileage would be slight and it might take more miles driven to recover your gear change cost than you plan to put on your truck.

Check the previous issue of the TDR that has the graph with the ISB engine Brake Specific Efficency (right term?) shown. Best efficency is at about 2,000 RPM and does not change much between 1,800 and 2,300 RPM. If you currently cruise with the engine in that RPM range a gear change is probabily a waste of time and money.

To figure your new RPM at a constant cruise speed, multiply the RPM by a ratio of the gear ratio. For example if you are currently at 2300 RPM at 70 MPH your new RPM would be 2300 x 3. 54/4. 10 = 1986 RPM (at 70 MPH with new gears).

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Just got my 2001 2500 QC, SB, 4x4, ETH 6-sp, 3. 54 LSD, SLT++ (everything but those lights on top of the roof), White over Silver, Tan leather. Picked it up 8/31/00.

 

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Ski Bum is spot on! The gearing inside the auto and manual boxes is different... therefore the 4:10 works well with the automatic and the 3:54 goes with the stick shift. If you want some more MPG's you have 2 ways to go: buy taller tires, or a gear splitter overdrive. Just my $. 02

 

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What I was reporting on was based on a 94' gasser with the Dana 60. I don't know about the Dana 80 which my truck has. You are right about the 5 spd. and the 4. 10 though. If I run 70-75 MPH. I get around 17-17. 5 MPG. This is running around 2300-2500 RPM's. If I back it off to 60-65 MPH, I seem to gain a couple of MPG's. This drops the tack to around 2k. My only problem is driving that slow. I JUST CAN'T DO IT!!! (LOL)

 

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Bigfig: You also did not tell us how many miles are on your truck. As it breaks in your mileage should increase. I wished I were getting the kind of mileage you are. Also, with the advent of the 285 tires, that would be the cheapest thing to lower rpm. I had a 2000/3500 with the 3:54s and it would not pull well. My 2001/2500 is a Bear. Good luck!

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2001 2500 QC, ETH/DEE,4:10s, LSD, VA Magic Box, Boost/Pyro Guages, 4" Turbo back, BD Brake,Mag- Hytec Cover, Kleen Wheels, Energy Release, 70 gal. fuel, 20K Reese. (RV Dealer)

 

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My truck has 2600 miles on it. It's been getting around 20 mpg from day one, the electronic fuel monitor gauge above the mirror has never been accurate, sometimes it would read 19 average then suddenly drop to 10 or 11 mpg and after we would reset the thing it would climb back up to 19. +. But we have been checking it by filling up, driving until the low fuel warning light came on and then filling it up... each time it has gone around 540 miles and has taken around 26 gallons of fuel at each fill up. Also, the vehicle is a 2 wheel drive and has the Michelin 265/70/16 tires and I run the psi at 65 in the front and 60 in the rear, it states on the tire max of 80. I rarely tow, maybe once a year, the rest of my driving is interstate at about 70 mph. The engine feels smoothest between 1500 and 2100 rpm.

[This message has been edited by bigfig (edited 10-18-2000). ]