rear ends swap

[tradr1]

has anyone swapped rear ends ? i have a 4.1 rear end thinking of swapping to 3.42 . what do you think? i don t tow. what do recommend swap gears in diff housing or replace both rear and front rear ends. who sells these gears. does any one know of a wreckers that has these rear ends

[john8662]

I've got a similar vehicle, and when I get it back on the road again (off for 7 months now) I'm seriously considering dropping in 3.42's to replace the current 4.10's. I just can't justify the 4.10's anymore, heck its the one vehicle that gets the worst mileage out of anything I've ever owned (but 2nd was a 97 5.7 gasser).

A source for gears is:

www.randysringandpinion.com (http://www.randysringandpinion.com)

They will be able to tell you what you have and what you need, make sure to get a shim kit with the gears.

[andro70]

I have a '96 6.5 that had 4.10's. I swapped 3.23's about 3 months ago hoping it would drastically increase my fuel efficiency. Prior to the swap I averaged 16 mpg (mostly freeway miles) Now I'm at about 17 / 18 (mostly freeway). Not much of an increase in fuel efficiency but a drastic reduction in freeway rpm. I think my engine likes me better but it hasn't repaid me with savings at the pump.

[Turbo Al]

andro70,
Over the years I have figured that for ever drop in range on the gears you would gain about 3/4 of a MPG (average). You dropped 3 ranges so you should expect about a 2.5 mpg increase. As you stated the real bonus is the lower rpm.
The only real way to get a lot of MPG at one time is to put in the 5 speed standard. Even back in 1993 Chev was claiming a 5 mpg increase over the auto trans. My truck got almost 24 mpg when it was new 3.43 with 5 speed, syn oil in everything -- except rear end. The only other mods were K&N and BD exhaust.
Al

[turbovair]

How long to get your money back in fuel? What else needs to be done to make it work(computer?)

[john8662]

For the gear swap you'll also need to re-calibrate the speedometer/odometer.

This is done by soldering connectors to re-program the VSSB (Vehicle Speed Sensor Buffer) to be calibrated for the Gear change. An article on this is available in print form over on the main TDP page here:

http://www.thedieselpage.com/65book.htm

Entitled "Vehicle Speed Sensor Buffer"

I bought this one and it has just the info you need to figure it out.

I'm going to wait to do mine, because I want to change my gearing from 4.10 to 3.42 and upgrade my tire size from 245/75 to 265/75. No sense in doing the manual reprogram twice.

[More Power]

Run your tires at (or close to) the max air pressure listed on the sidewall, get a front-end alignment, make sure your brakes aren't dragging, gear the 6.5L TD for 1800-rpm at 65-mph (combination of tire size & differential gearing).

Set the fuel injection TDC-Offset a little to the advanced side (i.e. -1.5xx to -1.9xx).

Recal the speedo/odo, or your fuel mileage calculations will be off.

Drive as though there's an egg under your accel pedal and your tank is nearly empty. The driver is a huge contributor to fuel economy.

Lastly, calculate the fuel economy over several tanks of fuel (more statistically accurate).

Jim