R-Model transmission upgrade?

[kahall82]

Hi all,

I have a 320 Cool power R-model. At the moment it has a two stick 5 speed transmission but I think the 2nd stick is just for lo-lo. And drives very slow...but has 354 welded on the diff housing.

I have the chance to grab a Eaton 18spd double overdrive from a 1994 International Transtar. Will this make my truck faster and more for highway travel?

I am just waiting on the model number of the box. Have read that double overdrives went out in the 80s but yet have had plenty of people tell me they are the go.

Thanks for any info

[Lmackattack]

Yes a double over will give you faster road speed. To be certain you need to check your rear end ratio and do the math with the 18 speed ratios.

[bullhusk]

Hi all,

I have a 320 Cool power R-model. At the moment it has a two stick 5 speed transmission but I think the 2nd stick is just for lo-lo. And drives very slow...but has 354 welded on the diff housing.

I have the chance to grab a Eaton 18spd double overdrive from a 1994 International Transtar. Will this make my truck faster and more for highway travel?

I am just waiting on the model number of the box. Have read that double overdrives went out in the 80s but yet have had plenty of people tell me they are the go.

Thanks for any info

Is it an older R model? Cause Mack also made a trans like that, with OD an could only shift the side stick in 5th for over drive

[oilburner]

Well like the other guy said find out your ratio, if it is slow it is not a 3.54, that thing would fly with that high of a gear, a double overdrive is a good tranny if you have alot of engine or just don't haul much. When you make a trans double over you losse you low ratio, because you flip the gears on the countershafts and it makes each gear higher. If it were me i love the 15 speed overdrive with a mack engine, you have a deep reduction in the trans giving you 5 low gears, but not as low as frist in a six speed mack, and tight ratio going up in the gears, but that's just me, some people like super 10's which to me are useless, but they do have the biggest overdrive you can get in a single over trans in a eaton that is. I would not recomend a double overdrive unless you ratio is in the 500 range or so, you would probley never get it in the big hole loaded.

[rsb502]

that thing might fly with a 3.54, if it has 11r 22.5's and a direct trans the 3.54 that only makes about 69mph at 2000rpm, with a .73 od it jumps to 94 @2000rpm all 18 spds have 2 od gears and most people consider that a double overdrive, the older eaton double od trans and flipping an eaton to get double od will get you a .64 od gear I think and you will have 4 od gears in a flipped 18spd.

[rsb502]

oh and with lo pro 22.5's that makes a mere 59mph @1800rpm go to a .73 you get 80

[oilburner]

Yeap that sounds about right, our international 9370 has 3.55 with low pro 24.5 and a 9 speed direct and it does about 82 mph at 2400, but that is a old big cam 4 400,

[oilburner]

Yeap that sounds about right, our international 9370 has 3.55 with low pro 24.5 and a 9 speed direct and it does about 82 mph at 2400, but that is a old big cam 4 400,

And i am pretty sure the maxi touqe 13 speed has two overdrive gears to, but not a double over, the 13 speeds when fliped actaully have 3 over drive ratio, to make it a double over because when you split 10th to go to 11th you were in direct in 10th then you split it with the back box and 11th 12th and 13th are overdrive ratios, i thank anway correct me some one if i am wrong.

[kahall82]

Hi,

OK now it has 354 welded on the housing. But I have always had in my mind that they are 5.17 in there. I will have to go to the yard and check. Thanks for the info

Gear Ratio

Eighth H 0.73

Eighth L 0.86

Seventh H 1.00

Seventh L 1.17

Sixth H 1.38

Sixth L 1.62

Fifth H 1.95

Fifth L 2.29

Fourth H 2.73

Fourth L 3.20

Third H 3.74

Third L 4.38

Second H 5.16

Second L 6.05

First H 7.30

First L 8.56

Lo H 12.29

Lo L 14.40

[rsb502]

And i am pretty sure the maxi touqe 13 speed has two overdrive gears to, but not a double over, the 13 speeds when fliped actaully have 3 over drive ratio, to make it a double over because when you split 10th to go to 11th you were in direct in 10th then you split it with the back box and 11th 12th and 13th are overdrive ratios, i thank anway correct me some one if i am wrong.

yeah 13 and 18 have two od gears they are both based on an od 9 speed main box with an underdrive rear box, so in the case of the 13 if you removed the back box it would be 1.1 in 8th and .73 in 9th and with the back box its 1.1 in 8th high and .73 in 9th high like the chart above, if you do a gear flip you actually give it 4 od gears as the 1.1 drops down one whole gear in the main box so it would be 1.1 in 7th high, .86 in 8th low .73 in 8th high .68 in 9th low and .62 or .64 somewhere in there in 9th high of course this is all from memory so I may be off a hair or two.

[fjh]

Just be awear you will need to buy a bell houseing! the binder housing will likly not have the mount ears for the mack install and the clutch fork for the mack is upside down for the cable clutch ,there are Quite a few conciderations to think on when doing one of these swaps also there are or were two shiftlid configs on an eaton trans a foward mount and a rear mount stick opening! A couple of inches can make the install easy or hard when dealing with the stick opening on the floor ! Been there done that!

Just some stuff to think on

[rsb502]

Just out of pure curiosity did you get any numbers off the trans in your truck? Im pretty sure one of us could give you a better idea of the rpm drop if any you would get out of the swap if we knew which trans you had, then we would know what your top gear ratio is. And have you thought obout keeping it all Makc and finding a Mack OD trans to drop in, it would make it an easier swap for sure, something like a t2090 or trtxl1070. the 2090 would give you a .68 od the trtxl makes it a .78od

[SLEEPER DOG]

Anyone know which RTO 13 was used on a mid 70s R712 ETAZ (300+). Was it a 9513 or a 12513?

Wayne