daddy mopar

I have an automatic, 3:55 front and rear and I run 315,s. After my transmission went, the shop told me to lower my gears to ease the trans wear and tear.

3:55 have the small carrier
+ 4:10 have a larger carrier
= about $3500 shop labor and parts

For money and time what is the lowest gear I can put in my 3:55 carrier?
3:73, 3:9x, . . . .



I live in southern Oregon

8UPRACIN

I bet the tranny was just getting weak. If you tow a lot in OD it is going to stress it a lot more though. I ran 40s with the 3:54s in my truck for 2 years and then 38's for another 2 years. I found that high HP and big tires don't get along but now I run 35's on 20s and 315s when I drag race. You might want to look into a BD Pressure lock and some transmission upgrades if its just a stock rebuild cause stock tires will kill a stock tranny. Where in Southern Oregon are you at

high bid

Get a good rebuild w/TC & VB and you should have no issues as long as the weight is under 10k. I tow <10k pretty regularly from May-Sept. Starting out w/OD off till I get to 55mph works well and I pretty much have the same setup as you do. - the XZT+.

sheriffav8r

Basically, the transmission doesn't like to be pulling low rpms and when the TC locks and tranny goes into OD at 50-55mph it heats up because the rpms are so low. I would get a better tranny and take it out of OD if below 60mph and towing. The truck and tranny like about 1900-2100 rpm and that's where you will find lower temperatures for both....

ellerman

If you decide to go with re-gearing you should go to a different shop. $3,500 is way high, parts and labor should be just over 2k. As stated above if you beef up your tranny you should be fine with the 315's and 3:55's.

Tate

You should be able to find 4.10's that go on a 3.55 carrier. They make gear sets with a thicker ring gear to run the lower ratio carriers. Not sure if Spicer makes them, but I'm pretty sure Yukon does.

diggerfan99

You guys must have read my mind, Earlier today I was thinking of posting a question almost identical. My truck also has 3.55 gears and I am currently running 285 tires but want to convert to 315's. My concern is that I am losing power off the line. The truck had 265's on it when I bought it and sometimes I feel like it doesn't have the power that it should have. The truck is also an automatic and it seems like the tranny locks the converter too soon. So you are saying that it would be ok to keep the 3.55 gears with 315 tires?

sheriffav8r

For me, I like the 315s cuz it looks good on the truck. That is as big as I'm going to go, though. I think driveability is at the limit with these 315s. Mine is a daily driver so I want to keep it a "one hand on the wheel" rig. Or else I might spill my drink.... coffee....

I'm looking at 1500rpm at 60mph and 2000rpm at 80mph so I just keep it somewhere in between. Actually, at 110 it's loping along pretty nicely, but that's only when passing a Ford....

diggerfan99

I also don't want to kill my fuel milage because I drive 35 miles one way to work everyday. If the gear ratio goes lower when bigger tires are installed then the truck should think that you are running stock tires and thus keeping optimal fuel milage, am I correct?

Tate

You are turning heavier tires on a larger radius, it takes more power to get them up to speed. And depending on the tread, will take more power to keep it at speed. There is more to mileage than just bare minimum rpm. Otherwise we'd all be driving around at an idle.

sheriffav8r

Amen to that. But bigger tires look cool and can run over little cars easier....

daddy mopar

My truck with 315 75 r16 and 3.54 is gutless off of the line. I am not looking to tow all of the time or run at 100 mph. however I would like the power to chirp the tires if I wanted to. Does anybody know of any web sites I can visit to find my carrier and gear ratio information.

daddy mopar

I live in southern oregon

diggerfan99

Check out Richmond Gear, I haven't looked at much info for my Diesel but they were very helpful when I built my mud truck. Also, I am a big fan of anything produced by Eaton. Had a carrier that worked very well and was bulletproof.

Western Rammer

Probably not as close as you'd like but Randy's Ring & Pinion in Everett Wash. http://www.ringpinion.com/ has a great reputation.

Randy. (No relation...Honest!)