Gear vendors etc towing fuel mileage

[RLDSL]

I'm studying up on the auxiliary transmission options , but am wondering if I'm going to really gain any fuel mileage while towing. I know I'll gain a bunch empty.

With the 4.10 rear and the zf5 as is, towing the fiver loaded out it weighs in around 10k pounds and I've found I have to stay in 4th to get 10 mpg but the thing is wound out, It will pull in 5th, but I have to keep the pedal floored and mileage goes straight in the toilet.
So assuming that I could get an aux tranny with a gear that would be about half way in between where the engine should be able to pull it just fine and even have a little boost going on with the turbo...... what kind of difference would be realistically forseeable in the fuel mileage department ?

If I could pick up 2 I'd be ecstatic.

Thanks--------Robert

 

[obinella]

us gear, much stronger, haul fat ass back down hill without breaking!

psiagreek&nsuck

 

[Agnem]

Ohhhhh Kaaaayyy...

Fuel milage, yea. You will definitely gain some. How much depends on what your towing and over what kind of ground. Empty, you definitely pick up milage. I'd say 3 to 4 MPG in some cases.

 

[RLDSL]

What I'm towing is an older 5th wheel camper, loaded out for the road with all our gear, about 10,000 pounds ( that includes the stuff poked in the bed and humans ) where would be average interstate driving figuring the mostly level stuff, obviously can't try to figure fuel mileage climbing divides etc )
Just anyones observations on average increases while towing heavy would be great

I wouldn't be getting an actual GV or USG unit, I'd be going with a regular truck aux tranny most likely with a .85od so where 4th puts final drive at 4.10 and 10mpg and wound up tight, and 5th puts milege in the toilet and low rpms with a final drive of 3.12 with 4th and over , I'd have a final drive of 3.49 which would be a pretty nice mid way split. Would probably do pretty close to a truck with 3.55 rear with turbo running in direct with that kind of load if anyone has a comparison.

 

[Full Monte]

You aren't likely to get an answer you can bank on. There's a lot of things that affect mileage. IP pump timing, gear ratio, tire height and width, tire pressures, cruising speed, rpm at cruising speed, just to name a few. At least you have a manual tranny, which will help. Most of the guys who are getting the best mpg are using ZF5 trannys and an additional overdrive to get the double-overdrive effect of 5th gear overdrive plus the GV or USGear overdrive. This can put your cruising rpms down into the 1400-1700 range, rather than the 2500 to 3000 rpm range that a lot of guys cruise at.

 

[tuckerd1]

The E40D in OD (4th) with 4.10 gears has a final drive ratio of 2.91. I cruise (60-70) at 1900-2200 rpm in OD. Towing 12000# 5'er (before turbo) I got 9-10 mpg depending upon terrain. This was running in OD with it downshifting as needed.

Since turbo I haven't towed the 5'er so I don't know the mpg yet. Towing a smaller load a couple weekends back I got less than 10 mpg. I suspect my IP timing is too far advanced. So my mpg should be down. Gotta check the timing.

I am still considering going to 225/70x19.5 or 245/70x19.5 tires and wheels. That should equate to slightly > 3.55 gears (3.60) with final OD ratio of 2.56. This will also add the capability to put disc brakes on the rear.

 

[Exekiel69]

The size of the camper also makes a big difference. I tow 10k+ often and the truck will handle it in every gear with out killing the fuel economy. The GV or aux tranny sure is on the list, some time ago I was asking another member about the benefits of a brownie box but space is a bit scarce with this option.

 

[RLDSL]

Well, I just pulled the trigger on a three speed Spicer brownie box on ebay with a .85 OD and a 2.35 UD so this summer I guess I'll find out. If nothing else, at least with that under drive, I won't be complaining about my clutch leg trying to get in and out of camp spots any more It'll be especially nice getting in and out at the house which is blind side at a pretty nasty steep angle and it's usually muddy.

Between that and the pair of new heated, motorized west coast mirror kits I scored yesterday for $280 I'm feeling pretty good this week

-----------Robert

 

[fx4wannabe]

Usually when I am backing my trailers around i grab 4lo and just don't lock the hubs in. Its the perfect gear for backing. Don't have to slip the clutch a bit.

 

[Whit]

here is one for sale if interested

http://www.dieselbombers.com/sale/11352-gear-vendors-ud-over-drive-sale.html