changing rear ratio to get more mph

[puppydog1918]

I have a mack with mack 4.64 rears does anyone know if I change the ratio from 4.64 to 4.42 how much more mph will result?

[rsb502]

if you give me the tire size and transmission model I can get you pretty close to max mph @ whatever rpm, i swapped from 4.64 to 3.65 with an Eaton 9 spd so .73 OD and 11R24.5 tires, I went from wound out at 70 to 1400rpm @ 70. If ypou have an Eaton OD trans and 11 R 24.5 tires a 4.42 will make about 1600 rpm @ 65, 4.17 would do 1500@65mph

[Brandt]

I have 4.42's w 11R 22.5 tires. I run 1875rpm at 65mph. I have a .78 OD

I'd like to re-gear to run 1500 at 65mph

Edited March 25, 2014 by Brandt

[MACKS]

There was a mph calculator on here a while back does any one have the link for it or know where it could be found?

[Freightrain]

My guess is about 5% faster......you'll gain about 3 mph.

4.62/4.42= 1.045% faster

So 60 mph x 1.045 =62.7 mph

[Glensts]

4.64 divided by 4.42 is 1.049, so you will gain 4.9%. Not a big increase. YOu need about 3.71 to get what you want, 25% higher.

[puppydog1918]

i have a mack 6 speed with 4.64 runs at 2000 rpm about 65 now what would 4.42 do?

[Freightrain]

Using the math, about 68 mph. Not a big change for all the work.

[RowdyRebel]

Brandt: It'd be cheaper next time you need tires to get 24.5 rims and buy 11R24.5's for the truck. That'd get you CLOSE to where you want to be for only the cost of the rims (IF you time the upgrade to when you were buying tires anyway...)

[j hancock]

That is a good swap if you are running disc wheels.

If you are running spokes, then you have to change from 20 inch spokes to 22 inch spokes plus get new rims and tires.

[rsb502]

i have a mack 6 speed with 4.64 runs at 2000 rpm about 65 now what would 4.42 do?

what size tires?, like I said above I can do the math but not withou the tire size and the trans ratio.

[rsb502]

low pro 22.5 are 40" tall, 11R22.5 and low pro 24.5 are 42" tall, 11R24.5 are 44" tall use this and your info in this calculator.

http://www.powerblocktv.com/resources/

[puppydog1918]

the tires on it are 11 24.5 now. truck is triaxle dump, truck runs good but on the highway at 65 truck is screaming if i go to 4.17 will i have low end i need? or should i swap transmission instead

[BKrois]

If you swapped a 12 speed OD tranny in you'd probably gain some speed and have 2x the gears as current tranny. 12 speed in 5th gear direct is 1.00 ratio and .78 in High

[MACKTRUCKS4]

I too am looking at getting more speed out of my superliner since I changed the trans from a 9 sp. to a 12 sp. Does anyone know the high gear ratio on a 1070B? I also have 4.64 with 24.5" tires, looking at going to 4.17 but not sure of final ratio in the 12 sd. Is this trans also .78?

[j hancock]

A TRTXL1070B runs a .78

[Brandt]

I'm running 22.5" spokes. Rims and hubs will get expensive. I have 22.5 tires on my Western Star and trailer. I would rather stay with one tire size.

[rsb502]

Puppydog, Going from a 4.64 to a 4.17 would be ok for your overall gearing, youll lose a little torque but little, I doubt you would notice much difference in power from a 4.64 to a 4.17. I have run 4.64, 4.42 and 4.17 oin tri axles running 74,000+ pounds and they all ran fine for me, it really all depends on you, yes a trtxl1070 or 1070B would get you some more speed but even with that you would want to get up to a 4.42 to get the same cruise speed as a 4.17 with your trans. The math with a 1:1 trans and 11R24.5 tires comes out at 2300rpm@65 for a 4.64 and 2070 for 4.17 rears, a .78 OD will get you down to 1790rpm with 4.64 and 1600rpm @ 65mph with 4.17 rears. I would make the swap to a 4.17 if it was me, the 4.64, 4.42 and 4.17 are very common Mack rear ratios so finding a set and swapping your carriers shouldnt be an issue. You will need to know the carrier input splines on the driveline and axle splines, also if it is taper mount or saddle mount on the torque rod on top, taper looks like a drag link end with one big nut, saddle mount has two smaller bolts and a wishbone style bar.

[R.E.D]

I have 4.17 on my rd and im lookin for 4.64 ...if any on you guys would maybe like to swap let me know..only thing I need is for the rear axle to have or be drilled for a transverse torque rod bracket

[j hancock]

If swapping, remember that there are two style of mounts for the longitudinal torque rods between the trunion cross member and the carrier.

One has the tie rod taper mount in the top of the carrier with one nut or the style utilizing two bolts to attach to the carrier.

[puppydog1918]

ok

thanks jack

how bout this leave the 4/64 ratio and change trans to 14708ll what will that do for me?

by the way if anybody is looking for 4.64 ratio i have a parts truck here still in rolling chassis

[rsb502]

I have 4.17 on my rd and im lookin for 4.64 ...if any on you guys would maybe like to swap let me know..only thing I need is for the rear axle to have or be drilled for a transverse torque rod bracket

Looks like the perfect match here, you want 4.64's and he wants more road speed, dun deal!

[MACKTRUCKS4]

I want too know if I can change just the side gears on my rears to 4.17 from 4.64? I have the manuals and have rebuilt my transmissions, motors, but no rears. Do I need to change anything else? If possible, I think changing the side gears would be a lot easier than the unit.

[Vladislav]

I'm too afraid not.

When you talk about side gears do you mean an upper (bewel) gear set?

If yes you need to set the position of the gears to each other to get a correct contact area, also you have to set the bearings pre-load.

A lot of work, I'm going to get over it one day but I have no chances to find ready rears of the kind I need.

Much more easier to swat just diffs. You need to get them out for rebuilt anyway.

[hicrop10]

My B87 has a 9.10 rear ratio and she tops out at about 72 at 2100.