1987 DM MACK X107

[TJ11404]

I HAVE RECENTLY CHANGED THE TRANNSMISSION IN MY 1987 DM MACK TRIAXLE IT IS THE 6 SPEED X107 REVERSE WAS BAD SO I HAVE FOUND ANOTHER X107 AND PUT IT BACK IN BEFORE THE TRUCK WOULD RUN AROUND 65-70 MPH NOW THE TRUCK WILL ONLY GO 55MPH I THOUGHT I DID ENOUGH RESEARCH TO KNOW THAT ALL THE 107 TRANNYS WERE 1 TO 1 IN HIGH GEAR BUT MUST BE WRONG ANY HELP WOULD BE GREATLY APPR IS THERE DIIFRENT RATIOS IN THE BACK BOX I COULD CHANGE TO HELP THIS

[67RModel]

I always thought the back box was the auxiliary which is an underdrive and direct (1:1). The overdrive gear is the 5th gear in the main box. If you change the direct gear in the auxillary to something faster (numerically smaller) you will make all the 5 gears in the main box faster which I don't think you want. You need an overdrive gear probably 0.6:1 in the 5th hole on the main box. It sounds like the one you have is direct in 5th not overdrive.

[Vladislav]

From what I learned about X107 they were 5th direct in the main box. And when that transmission gets high split added to the compound it becomes being T1070 10 speed. Or a 12 speed if the crawl gear added.  I doubt they had different set of wheels in the main box as an option and if yes I'd too like to know about that.

[doubleclutchinweasel]

I, too, thought the auxiliary was just low and direct.  I always thought the OD was in the main box.  In the "old" days, a "0" on the end of the model number indicated that 5th was overdrive.  I don''t know how the later stuff was numbered.  But, a TRXL-107 would have been direct, and a TRXL-1070 would have been overdrive, for example.  Don't pay any attention to the exact numbers, as I may have them wrong.  But, the "0" was the key...at least, it was at one time in history.

Was yours a two-stick 6-speed?  Or did it use air on the auxiliary?  If it is the 2-stick, and the reverse is on the compound stick, I wonder if the "new" auxiliary would mate to the "old" main.  Just thinking out loud.

[TJ11404]

Ya mine is a two stick

[67RModel]

Did you change the both transmissions or just the back box (auxiliary transmission)?

[TJ11404]

I changed both boxes reverse was bad in the back box in the original tranny

[67RModel]

16 minutes ago, TJ11404 said:

I changed both boxes reverse was bad in the back box in the original tranny

Well then from this statement it sounds like the main box of the replacement transmission is not an overdrive unit. Although I'm not sure on this I guess the easiest fix would be to put your original main box back in and the replacement auxiliary transmission on the back of it? Just a though if there was never any real problems with the main box. Since you have your original transmission out and on the floor you could do some real basic testing by placing paint marks on the input and output shafts and see what the ratio is when you have the main in 5th and the auxiliary in direct. If 5th is indeed an overdrive and assuming its 0.6:1 you should get about 1.7 turns of the output shaft for every one revolution of the input shaft.  In hind sight you should have done this once you got the old one out and before putting the new one in so you could make sure you had the same overall ratio......

[doubleclutchinweasel]

15 hours ago, TJ11404 said:

Ya mine is a two stick

Then I would definitely see if I could use the "new" rear box on the "old" front box.  Since reverse is in the rear box, the front box is probably fine.

Of course, I would like to hear from JoJo or one of the other pros about any issues one might encounter first.

Edited October 27, 2021 by doubleclutchinweasel

[TJ11404]

I wasn’t sure if the change happened in the auxiliary box or the main box that’s something I am trying to figure out if all the auxiliary boxes are the same or if that is where the ratio change happened

 

[terry]

Are you sure you are getting the numbers off the transmission case correct? A X107 is a direct transmission. with 4.17's it will top out about 60MPH. depending on your top RPM's.   terry

[TJ11404]

YA THATS WHAT I THOUGHT THAT THE 107 TRANNY IS A DIRECT DRIVE ALSO BUT THERE IS SOME PEOPLE SAYING THAT THERE IS AN OVERDRIVE ONE WITH A .68 RATIO IN HIGH GEAR I THINK I AM JUST GOING TO LOOK FOR A 2090 OR A 2100 SERIES TO PUT IN I GOT TO DO A LITTLE LOOKING AROUND TO SEE WHAT ALL I WOULD HAVE TO CHANGE LIKE DRIVESHAFT PTO THAT KIND OF STUFF

 

[67RModel]

51 minutes ago, TJ11404 said:

I THINK I AM JUST GOING TO LOOK FOR A 2090 OR A 2100

Be careful doing this. The 2090 and 2100 series have a 0.71 overdrive ratio. If your truck originally had a 6 speed lo hole transmission it almost certainly has a maxidyne engine and very slow rears (somewhere between 5.55 and 6.32:1, or even slower sometimes). With these rear ratios you need the 0.6:1 overdrive ratio to achieve a reasonable cruising speed. From what it sounds like you have 1:1 in top gear now so I guess 0.71 is "better", but still wont cruise as fast as it had before you swapped transmissions. Do you know what rear end ratio you have, what tire size, and what rpm your engine is governed at?

Edited October 28, 2021 by 67RModel

[TJ11404]

YES IT IS A MAXIDYNE 300 WITH 417 REARS AND 22.5 TIRES NOT SURE WHAT IT IS GOVERNED AT 

[TJ11404]

THE INFORMATION ON THE SIDE OF THE TRANSMISSION I PUT IN IS X-107 THEN UNDER THAT T-755 THEN AT THE LEFT REAR SAME SIDE 284KB5175

[67RModel]

If you assume it is governed at 2100 and the replacement transmission is a direct drive (1:1) unit the math checks out. Maxed out at 2100rpm you will only be able to achieve 60-61mph. If you install a T2090 or any 2100 series transmission with your rears and running on 11R22.5 tires you will be turning 1716 rpm at 70mph, and will top out at 85mph.

[TJ11404]

Ya I would be happy with that it’s only really for local hauling but gotta go more faster than it does I would say it would go about 60 now but I didn’t want to push it the truck sat for 20 years before I got it

 

[terry]

6 hours ago, TJ11404 said:

YA THATS WHAT I THOUGHT THAT THE 107 TRANNY IS A DIRECT DRIVE ALSO BUT THERE IS SOME PEOPLE SAYING THAT THERE IS AN OVERDRIVE ONE WITH A .68 RATIO IN HIGH GEAR I THINK I AM JUST GOING TO LOOK FOR A 2090 OR A 2100 SERIES TO PUT IN I GOT TO DO A LITTLE LOOKING AROUND TO SEE WHAT ALL I WOULD HAVE TO CHANGE LIKE DRIVESHAFT PTO THAT KIND OF STUFF

 

That .68 overdrive trans is a 2060,2070 or 2080 series transmission, too much overdrive for 4.17 rears, the 2090 would be a real good trans for you.   terry

[Vladislav]

52 minutes ago, terry said:

That .68 overdrive trans is a 2060,2070 or 2080 series transmission, too much overdrive for 4.17 rears, the 2090 would be a real good trans for you.   terry

Those mentioned and also including T2050 have even 0.60 OD. And they seem fine for a 300 Maxidyne but with 5.32 or so rears I belive.

[TJ11404]

From what I am coming up with I would like to go with a 2090 I really ain’t coming up with much info on what all would be different like the overall length to know if the driveshaft would work and the pto 

[mrsmackpaul]

Are you sure your speed is different, as in have you had someone following you down the road or used a GPS

 

The reason I ask is no matter which overdrive Maxitorque Mack made I dont think you will get the speed increase your saying 

I wonder if the gears that drive the speedo are different as the diff ratios might well be different in the truck you got the gearbox from compared to yours 

Did you change the speedo gears when you changed the transmission ? 

 

Paul

[Quickfarms]

Also did the speedometer gear box, get changed or forgotten?

the speedometer on my 1975 did not work until I removed this from the side of the trans and found the drive tang was broken

 

 

[TJ11404]

YA I USED GPS TO CHECK THE SPEEDO IT IS RIGHT ON 

[mrsmackpaul]

Okay then

 

Well the maths doesn't  match the information, so if it was mine and its not so probably disregard

Its time start sorting the fact from the fiction 

Correct me when Im wrong, you have two transmissions plated the same and looking the same on the out side  ?

What I would do is try to find out exactly whats going on and take all the guess work out of this

The transmission thats out and sitting on the floor I would put it in each gear and count revolutions of the input shaft to do one output shaft turn 

This will give you a really good indication of whats i  your original box

The one in the truck is a little trickier, jack up the ass end and with the help of couple of people, one underneath counting the tail shaft and one counting the motor turns on the harmonic balancer and the last joker sitting in the cab turn the key 

Mark the tail shaft and the balancer with a paint pen and do the same, wind it over until the tail shaft has done on turn and count the revolutions ojf the motor

 

This will give a really good indication of whats going on as all any of us are doing is guessing at the moment 

 

Paul 

[TJ11404]

The whole problem started when I took the tranny out and took it to a guy who said he could fix it and tore the aux box all apart and then said he couldn’t find the parts to fix it so I bought a complete setup and put it in so as for checking the tranny that is out I can spin it over but the second box ain’t together so I am sure the ratio changes from the output shaft in the first box to the output shaft in the second box