Auxilliary Transmission :MPG?

[DBelshee]

I have been searching this web site for info on auxilliary transmissions, and have gleaned a lot of information, but haven't seen any info on MPG gains by anyone. I have an 03 3500 DRW quadcab with HO cummins and 6 spd manual, with 4:11 gears. It gets fairly busy under the hood at 65 MPH, and have been toying with the idea of an overdrive aux transmission to both lower the rpm and increase fuel mileage. We currently get 20 MPG running empty, and 11-12 pulling a 13,000# 5'er. For those of you who actually have the aux transmission, has your running empty mileage changed? Also, currently while towing on the flats, we run 6th gear at about 1900 rpm, which doesn't seem to be taxing the engine. Would I be better to tow in 5th gear at a much higher rpm, or continue on as I am. I don't have an EGT or boost gauge, so don't know whats cookin' inside. Any thoughts or ideas? Does the Gear Vendors have problems with the use of an exhaust brake?

 

[DPKetchum]

20 running empty!!! darn. I've got friends with 3. 73 gears that hit that but NOT mine. More like mid teens. i get 11/12 pulling 10k but never ever hit 20 and I hardly EVER hit 70mph. I would LOVE a Gear Vendor Or ??? aux. trans. One works good with autos(Gear Vendor I think)and one works good with manuals. Can't for the life of me remember the vendor.

 

[TCDiesel]

You need to get gauges than you can tell more were the power band is when towing,Example pulling 13k in 6 and running 16 to 18 lbs of boost and egt"s are between 600&800*and between 1800&1900 RPM"s with a ambeint temp of 75 this is what I would consider the ideal power band of the ISB,Now if in 6 and running and 12lbs of boost pulling 13k your egt"s are going to clime to 1000, you need to increase you boost by increasing your RPM"s than your EGT"s will drop. Conditions effect everthing and it will take time to find the best power band and mileage.

 

[Sherman]

I also have spent a lot of time looking at aux boxes,first thing is, if you have an e-brake then you are limited to the US Gear aux trans,Gear Venders is not compatable with an e-brake. The mpg,according to Cummins should yield 5-10% increase,it's based on the amount of power used in relation to total power etc,the formula is long an complicated. At that rate the cost of the aux box at $3000. installed

 

[Sherman]

Buys a lot of fuel,You would need to drive the truck 150,000mi to pay for the transmission addon.

 

[jacqnbill]

Aux transmission

I also have spent a lot of time looking at aux boxes,first thing is, if you have an e-brake then you are limited to the US Gear aux trans,Gear Venders is not compatable with an e-brake. The mpg,according to Cummins should yield 5-10% increase,it's based on the amount of power used in relation to total power etc,the formula is long an complicated. At that rate the cost of the aux box at $3000. installed

Be careful. I have a US Gear on my 98 5 speed. It does a great job with the 410 but I lost fifth gear on the 5 speed and Dodge voided the warranty because of the US Gear.

Bill

 

[DPKetchum]

Why may I ask did they void warranty. There was some KNOWN problems with main gear nut problems on the 5 speed. Did they say undue stress with slowing?

 

[Snow man]

If your getting 20mpg,and happy cruising at 65mph, then id say leave it alone,the engine may sound busy,but there's no damage being done to it at 65mph, you should only be taching 2200-2300 tops,which is nothing. The fact that your getting 20mpg shows you are in the engines sweet spot,from that fuel mileage id say that dropping the rpms wont help much,If you want to to cruise at 80mph,and are doing lots of hi speed trips,Id say it may pay for itself faster. an add on aux gearbox is just one more thing to go wrong and leak,and another thing to generate more heat under the truck. I cruise at 80mph with 4. 10 all the time,no problems so far,and i do not get 20mph,more like 15-16

 

[NIsaacs]

At 20-miles to the gallon empty, I would be happy. That is about the best you can get with the Cummins. I have seen better, but you have to drive slow & who wants to do that The aux. trans. is a fun option and nice to have if you do a lot of towing. Who cares if you pay for it in fuel savings if you are having fun, most of our mods don't pay for themselves anyway. We buy them because we want them. However I don't think you will realize much of a fuel savings. What you gain in higher gears, you lose in one more gear box to turn. If you want a little higher gear, I would consider some bigger tires. This is someting you have to buy from time to time anyway. For every inch of tire diameter, you gain about 3%. So if you go up 3 inches for example, that is 9% or a new final drive ratio of 3. 73.





"NICK"

 

[DPKetchum]

I WANT some 19. 5s :{

 

[jacqnbill]

Why may I ask did they void warranty. There was some KNOWN problems with main gear nut problems on the 5 speed. Did they say undue stress with slowing?

I took the truck in for the fifth gear problem and they told me they had to order a bill of material for the problem and that it was covered under warranty. When they removed the transfer case and US Gear auxiliary transmission and discovered the damage to the transmission was more severe than the fifth gear they called me and informed me that the warranty was void due to the auxiliary transmission add on.



I questioned them and they refused to discuss the issue other than telling me to read my warranty and that it stated " any unauthorized modification to the truck would void the warranty"



I would be required to pay for disassembly and reassembly just to take the truck somewhere else. When I asked for this in writing they refused. When I told them I was recording the conversation he hung up on me.



On a later discussion they quoted me $5,000 to install a Dodge rebuilt transmission and I would be required to sign a waiver that there was no warranty on the replaced transmission.



By the way this was the second time the fifth gear went out and they fixed it under warranty the first time.



Bottom line I ordered a rebuilt transmission from Standard Transmission of Ft Worth for $1450 and the Dodge dealer installed it. Wendell at Standard was great to work with.

 

[DPKetchum]

Did Wendall at Standard trans have any comments on what caused the failure? I've seen the US gear used on a few and no problems including towing HEAVY like a 6 horse trailer with LARGE living qtrs. But I have seen MANY 5 speeds fail without TOWING also. Did YOU get a Factory Rep involed or was this all a DEALER that THOUGHT it caused the failure with no PROOF. Just curious.

 

[jacqnbill]

Did Wendall at Standard trans have any comments on what caused the failure? I've seen the US gear used on a few and no problems including towing HEAVY like a 6 horse trailer with LARGE living qtrs. But I have seen MANY 5 speeds fail without TOWING also. Did YOU get a Factory Rep involed or was this all a DEALER that THOUGHT it caused the failure with no PROOF. Just curious.

I didn't get Wendall involved in the problem. Only ordered from him the replacement unit.



I didn't get a factory rep involved, only the local yahos. I plan to escalate the problem to Chrysler and other channels.



The US Gear is a wonderful unit and I would buy one again. Lots of fun to split shift and like someone on this forum said "Bulletproof". The Dodge service manager didn't indicate the US Gear caused the problem with the fifth gear, only the presence of the unit voided the warranty.

 

[DPKetchum]

HUMMMM. The DEALER can't void warranty. Its the manufacture who does.