Worth it to swap gears?

ghunt · #1 (**permalink**) 10-23-2007, 12:00 AM

I'm picking up a '94 IDI turbo in probably a week or so. It's a 5 speed, with 4.10's (limited slip in rear). I would prefer 3.55's. I found 3.55's for the rear for $180, and some 3.54 reverse-cut gears for the front end (Dana 50 correct?) on ebay for a decent price. Then of course the "mini install" kits with shims and etc for $50 or so each.

I'm a little intimidated by gear swaps (and I also don't really have a garage to work in). I was told there's a place near here that will do a gear install for $120 if you supply the gears and parts kit. So I guess it'd probably cost around $500-600 to have it done at a shop. Would it be worth it? I suppose I could try it myself, but gear swaps seem so easy to screw up.

How likely is it to need to swap bearings? Truck only has 94K on it.

With the cost of diesel, I'd like the truck to get decent mileage, especially since I'd like to be able to take it on trips and such.

BTW, I see these leveling kits on ebay for the TTB F250's that consist of front add-a-leafs and that's it. Can you run just those without getting weird tire wear?

starmilt · #2 (**permalink**) 10-23-2007, 12:10 AM

I wouldn't swap ring and pinions without bearing kits I would look hard at a shop that says they would it for 120 labor shops around here would get that much for ujoints everybody has to make a living everwhere.

Dave Sponaugle · #3 (**permalink**) 10-23-2007, 12:57 AM

The TTB front axle is very sensitive to height changes.

I installed air bags on mine for when I have a snow plow on the front.
One time while it was on the alignment rack, we played with air pressure in the bags.
The bags take up to 100 PSI and can raise the front by about 3".
10 PSI is the minimum pressure, that raises it less that 1/2".
If I put 20 PSI in the air bags, raised the front bumper about 3/4", there was not enough adjustment to bring the front end back into alignment.

starmilt · #4 (**permalink**) 10-23-2007, 01:49 AM

how much room did you have under your bumpstops.

ubahd00d · #5 (**permalink**) 10-23-2007, 01:53 AM

Having a 3.54 ratio in the front and a 3.55 in the back wouldn't be a problem?

starmilt · #6 (**permalink**) 10-23-2007, 01:58 AM

ford set lots of them like that

ghunt · #7 (**permalink**) 10-23-2007, 10:38 AM

Quote:

Originally Posted by starmilt

I wouldn't swap ring and pinions without bearing kits I would look hard at a shop that says they would it for 120 labor shops around here would get that much for ujoints everybody has to make a living everwhere.

A guy told me he supplied gears and an install kit to this shop for his Mach 1 and they did it for $120, and that they did a good job. That's all I know about it.

So how hard is it to install gears yourself? Right now I'm planning to keep the truck off the road for a bit while I do some other work, so I could probably do gears in there too.

Dave Sponaugle · #8 (**permalink**) 10-23-2007, 09:00 PM

About 3/4" setting on level ground with no air in the air bags.

Since I installed the 60 and four leaf front springs I have lots of room now.

You are going to be looking at more to install a gear set in a Sterling axle.
And don't forget you also have to do the front axle, which takes more time than the rear does.

axe_handle · #9 (**permalink**) 10-24-2007, 12:31 PM

I have a 1994 IDI Turbo E4OD with 4.10 gears and I'm constantly getting 14 mpg or so. At 60 MPH I'm turning 1900 RPM with stock 235/85/16 tire

According to my calculations, changing to 3.55 gears will provide 13% better fuel economy (at best). Assuming this is the case, and that changing the gearing is $1000 by the time you get done, it will take you about 35,000 miles to pay for the gear change by diesel savings alone (assuming $3.50/gallon).

These are rather rough estimates, but they lead me to leave my 4.10 gears alone.

However, it would be nice to be able to cruise at a lower engine speed on the highway.

Hope this helps. I'm curious what you end up deciding to do.

David85 · #10 (**permalink**) 10-24-2007, 03:58 PM

Quote:

Originally Posted by axe_handle

I have a 1994 IDI Turbo E4OD with 4.10 gears and I'm constantly getting 14 mpg or so. At 60 MPH I'm turning 1900 RPM with stock 235/85/16 tire

According to my calculations, changing to 3.55 gears will provide 13% better fuel economy (at best). Assuming this is the case, and that changing the gearing is $1000 by the time you get done, it will take you about 35,000 miles to pay for the gear change by diesel savings alone (assuming $3.50/gallon).

These are rather rough estimates, but they lead me to leave my 4.10 gears alone.

However, it would be nice to be able to cruise at a lower engine speed on the highway.

Hope this helps. I'm curious what you end up deciding to do.

I went from 4.10s to 3.08s, but I had a 3 speed auto, so leaving in the 4.10s was not an option, since I needed the truck for hauling at freeway speeds.

Swapping the gears myself, I spent a grand total of $400 CAD for the gears delivered to my door (back then it would have been less than $250 USD). I broke even in a few of months, but I only had the one differential to change.

EDIT: ghunt, the labor cost you list is very good, just make sure it isn't too good and the shop is trustworthy. But for under $600, I would do it, fuel prices can only go up, as dictated by the laws of physics.....