Engine/Transmission (1998.5 - 2002) Swithching gear ratios

[FUL POWER]

I am getting a new Dana 80 for my rear end. So while i gpoing that i was wondering if it would be a good time to put a lower gears. Right how i have a set of 3. 55 in a 2001. 5 with 35inch tires with auto trans. I am truck pulling with it but im also driving it. I was wondering if i should go with 3. 73 or 4. 10. Also is it have to switch the old gears for new gears in the front axel. I want to put a locker up front anyways.

 

[Bob4x4]

I can tell you I am very happy with 4. 10's and 315's on the 05 amd my trailer is a light one. It still will run double the speed limit in most of Cali



Bob

 

[FUL POWER]

If going with the 4. 10 gears, will that hurt my MPG on the top end.

 

[LOtero]

personally i think 4:10 gear is too high for highway driving with an auto 3:73's will put you real near stock rpm range with the 35's. for a pulling truck only 4:10's will get them spinning real good.

and yes always match front and rear gears in the diffs, mismatched gears puts a huge strain on the diffs, driveshafts and t case. Highly recommended unless you like picking parts up off the ground of course

 

[FUL POWER]

With my set up right now,i pull in low range and third. I have not had a problem when i get down at the end of the track with my wheel stopping. I always spin out.

 

[Devil Black Diesel]

I agree with MOtero, 4. 10's with 315's are too high for freeway driving unless you drive 55mph. I usually drive 70-75mph and I wish my rpm's were about 200-300rpm's lower in the sweet spot (1800-2000)..... plus, when a ricer or another truck pulls up to you at 75-80mph and wants some you don't have much left before you're in the red and gearing out... . I think 3. 73's with 315's would be the perfect ratio for highway driving at 75mph. Can anyone do the math and tell me how much my rpm's would drop at freeway speeds going from 4. 10's to 3. 73's - say 75mph? Anyone have 3. 73's in their 2nd Gen? If yes, how much and where can I get them?

 

[FUL POWER]

My trucks run 1800 rps at 75 mph with 315s and 3. 55 gears

 

[Devil Black Diesel]

Using your speedo or GPS? Your speedo is probably 5mph off unless you recal'd it. Anyway, I think I'm at about 2200 at 75 so 3. 73's would be right at 2000 which would be perfect.

 

[OTRPU]

When I lost my second RR axle spindle I switched to a 4. 10, 2k used to net me 71. 5 MPH per GPS. This new ratio I get 61. 5 MPH at 2k. Only way I can bust 20 MPG now is to run 55 MPH. If I could have found a 3. 73 I'd have been happier. But when towing the 4. 10 is easier on the truck. Price of fuel these days has me slowing down lots anyway. Can't say it's having the same effect on anybody else though. Couple tanks, 140 gals, I'm averaging just under 16 combined mileage. I pay a higher price when empty, but doing better when loaded.



Cheers,

Steve J

 

[CCBrady]

A place to look for your 3:73 gears and use their ratio calculator for doing your what if questions, is West Coast Differentials. I am getting ready to change from 3:55s to 3

:73s and unless I find someone better, I plan to go to them for my parts. Their web is www.differentials.com

 

[Sixpack]

I'm also researching this project. I currently have 3. 55 and am looking to switch to 4. 10. Along with the install kit, oil, and ring and pinions for both ends is there anything else I will need? I've read the rear carrier will have to be changed as well????? Also what about the speedo? Thanks Phil

 

[K5IP]

Keep the 3:55. When it cost over $100 to fill the tank, squeek every mpg out of it.

 

[CCBrady]

Phil, what I've found is that we have two ways to go. With the 3:73 gear change I have been told that I can use standard 3:73 ring and pinion gears or what is called a lite set where the ring gear is a little thinner than the standard one. Both with out changing the carrier. I am not sure about the 4:10 gear, but I don't think you have to change the carrier.

K5IP, I'm with you on squeeking out every mpg, but when you live on and island where every mile is an up hill drive and you have to go through the mountains to get to any place you want to go, the 3:55s don't get that good of milage. I think 4:10s are too low, and 3:55s are too high, so I'll try the 3:73s and hope for the best.

Chris

 

[rweis]

I think I remember that 3. 73's use the same carriers as 3. 55's. The 4. 10's you have to have different carriers I am pretty sure. I have NO idea what the carriers would add $$$ if you went to 4. 10. I would be interested to know though.



I am going to change mine from 3. 55 to ?. ?? before I do extensive traveling in a couple of years.



Bob Weis

 

[Regcabguy]

I just switched to 3. 73's on my truck and with 285's I feel I've regained the stock gearing it came with. Stock tires in '99 were 245's. With my camper the shift points would bog initially and now are much better. Hopefully mpg's will increase and about 100,000 miles from now I'll break even on my investment. Driveability is much enhanced.

 

[pwerwagn]

On the D-60 and D-70 the carrier break is at 4. 10. you can put 4. 10's on a carrier that had 3. 55's. if you want to go lower than 4. 10 (i. e, 4. 56) you have to change carriers.

FWIW,

I PERSONALLY dont think the change from a 3. 55 to a 3. 73 will amount to beans.

3. 55's with 34" tires in 1:1 gear (3rd on autos, 4th in 5-speeds) @ 55mph should turn about 1930 rpm, give or take a few.

3. 73's, with same tires and gear and 55mph should turn about 2025 rpm.

thats not even 100rpm difference. I doubt it would even be noticeable in a 7,000lb truck.

--Jeff

 

[rivercat]

what about a d-80 PW

 

[pwerwagn]

Oh, sorry I forgot we were talking D-80. In that case, no. A d-80 4. 10 carrier is diff than a 3. 55 carrier.

HOWEVER, YUKON (randys ring-pinion) makes a thin 3. 73 that will fit on the 4. 10 carrier. thats the only exception I know of... . which doesnt help this situation since you have the 3. 55 carrier.

 

[CCBrady]

Jeff,

Good point on the RPM differance between the the 3:55s and 3:73s. But the problem I have is I can't put bigger tires on, because of my training wheels. I have to deal with the tire seperation on my rear wheels and in 99 they hadn't gone to the deeper wheels that the newer trucks have. Now if I could get a newer rear end with disk brakes that would be a different story altogather. But by the time I made the whole change over, rear end, 6 tires and wheels, plus what ever else is needed for the change over. Which will cost less, gear or rear end change? And one more thing, the only time me and the old girl ever see 55 MPH, is when we go through it heading for what ever speed I can get away with.