4.10's to 3.55's - Should I do it?

[Carl_F350]

I just did a 4.10 to 3.55 switch this past summer. You'll have to buy a spedometer recalibrator to adjust your shift points. (4-wheel parts)

I get a constant 19mpg with city/highway mix.

 

[bikepilot]

Sounds good - how fast do you generally drive on the highway?

 

[Carl_F350]

Sounds good - how fast do you generally drive on the highway?

Usually two over the speed limit 62,67 and 72 depending where I'm at.

 

[bikepilot]

Not bad at all. I'd be lucky to average 14-15mpg at those speeds.

 

[beretzs]

3.55's are probably your best bet.. I imagine, I just always thing the worst case. You will be fine pulling about any amount of weight with your truck, just may have lock out OD.. Pretty easy deal to gain a few MPG. Plus you are going to be able to do it so cheap, it is worthwhile. Scotty

 

[bikepilot]

Sounds good - and if it makes it sluggish, then perhaps that'll motivate me to goahead and do the turbo housing/down pipe upgrade and turn the boost up a bit :Sly

 

[beretzs]

You'll be fine.. You can always make up for a little sluggishness with MORE POWER.. Pretty easy deal. Scotty

 

[bikepilot]

Well I'm pretty happy with the 3.55's - don't have enough time on them to get a good feel for the mileage though. First tank was 15.5mpg - most of that was towing a trailer and there was a lot of idling and plunking around on dirt roads involved as well.

Carl, I'm a little confused over your comment about the spedo re-calibration gizmo. Best I can tell the spedo sensor measures carrier rpm which seems unreleated to gearing. Whatever the case, my spedo seems to be correct without any adjustments - do I still need the gizmo for some other reason?

thanks,

Josh

 

[Carl_F350]

Josh,
That carrier that I think you're refering to is the sensor on the axle which is actually the sensor for your anti-lock brakes.

Just about every vehicle made since 1992 is equipped with an electronic speedometer that uses a sensor to read the vehicle speed rather than a mechanical cable. These electronic speedometers are sensitive to changes in tire diameter and axle ratio, resulting in speed, odometer and shift point changes.

Goto:

http://www.superlift.com/accessories/truspeed.asp

for more info.

 

[The Warden]

That carrier that I think you're refering to is the sensor on the axle which is actually the sensor for your anti-lock brakes.

Yes, but on '92+ trucks, I think the ABS sensor also serves as the speedo sensor. So, you're probably fine...

Just wondering, have you noticed any power differences with the different gears on a truck that otherwise hasn't changed? Is acceleration slower?

 

[bikepilot]

Acceleration is very noticeably slower, especially off the line. Its not terrible, but not as quick as it was. Much more relaxed on the highway though

The speed sensor I was talking about is a magnetic type sensor in the top of the rear that gets signal from an exciter ring bolted to the diff carrier near the ring gear.
The exciter ring speed isn't affected by gearing. I don't know if the trans ecm is programed differently for vehicles with 4.10's vs 3.55's but its basically ok - doesn't seem to get above 2.5k rpm very often but it could just be that the gaps between the gears are so bit that for the speed I was driving the next lowest gear would have been too low.

 

[dbarilow]

I run 70 all the time empty with 3.55 right at 2000 19-21Mpg and thats on an IP& injectors with 180k on it. If i wanted tire roasting power I'd buy a Power Choke and dump thousands in it just to have it blow up my tranny or fry the motor. 20Mpg and smooth easy riding thats for me

 

[The Warden]

Thank you for reminding me why I want an overdrive unit I can get 20mpg out of my truck, if I can keep the speed to 55mph. 17's more "average"...

 

[bikepilot]

Yeah if I did a lot of city driving or really heavy towing I'd much perfer the 4.10's. Ideally, this truck should really have a 10spd close raito box or something of that nature - it just seems like the gaps between the gears are huge and there still isn't enough range.

An OD unit with 4.10's would be quite a good setup imo, but I didn't have the $$ for an OD unit and this was super cheep (free or better if I sell the old parts).

It sure is nice getting about the same mileage at 65-70mph as I used to get at 55mph though

I use the truck pretty much exclusively to get bikes to races and riding areas so nearly all my driving is on interstates or highways.

 

[beretzs]

Glad to see you got the gear swap done and it worked out well for you. Scotty