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Calling All Mack 12 Speed Experts!


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Gentlemen, i am in a pickle. In the the process of installing a rebuilt 12 speed in my r688 tractor, my "professional" mechanic cut and disconnected all of the air lines that go to the air shifter on the transmission. Thankfully, i marked on the end by the shifter handle, but the ends that connect to the tranny are not marked, so i am not sure where they go exactly. I am writing this with the hope that someone somewhere has a diagram of air lines for such a truck, God willing. My Mack dealership had nothing, so i am turing to the experts on this forum for help. Any help or leads will be greatly appreciated.

On a side note, through thorough cleaning, i have found that the bottom of the shifter knob/selector has numbers and letters for each air line and the same numbers are on the transmission. However, on the shifter selector knob, there is an "E" for one of the air lines, which has thrown me off. Otherwise, the 1-4 on the knob matches up with a 1-4 on the tranny, which im hoping is a light at the end of the tunnel. I hope there is someone on this forum that knows what i am talking about. If this doesnt make sense i can get pics

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Gentlemen, i am in a pickle. In the the process of installing a rebuilt 12 speed in my r688 tractor, my "professional" mechanic cut and disconnected all of the air lines that go to the air shifter on the transmission. Thankfully, i marked on the end by the shifter handle, but the ends that connect to the tranny are not marked, so i am not sure where they go exactly. I am writing this with the hope that someone somewhere has a diagram of air lines for such a truck, God willing. My Mack dealership had nothing, so i am turing to the experts on this forum for help. Any help or leads will be greatly appreciated.

On a side note, through thorough cleaning, i have found that the bottom of the shifter knob/selector has numbers and letters for each air line and the same numbers are on the transmission. However, on the shifter selector knob, there is an "E" for one of the air lines, which has thrown me off. Otherwise, the 1-4 on the knob matches up with a 1-4 on the tranny, which im hoping is a light at the end of the tunnel. I hope there is someone on this forum that knows what i am talking about. If this doesnt make sense i can get pics

taking a wild guess, i would say that E would stand for exhaust port.

GG2

We the unwilling, Lead by the unqualified, are doing the impossible, for the ungrateful.

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:SMOKIE-LFT: I've got the book right in front of me. Is it a TRTXL107 or a TRTXL1070 ? I'm not any good at sending this stuff on computer but I'll see if I can get my brother to scan it and post it for you in a little bit.
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Here's what i am talking about in the second paragraph:

P5120031.jpg

This is the bottom of the shifter knob, the numbers and letters are somewhat visible, 1,2,3,4, "S", and "E"

P5120026.jpg

This is the air shifter that goes on top of the tranny, it has 5 air line connections going to it, 4 of which are numbered

P5120030.jpg

This is a diagram i made up, which links 1-4 on the tranny with 1-4 on the shifter knob, "S" on the shifter knob is already connected, leaving "E" without a destination.

Does anyone know where "E" goes? and where does the extra connecter on the tranny labeled "4" go? any help would be greatly appreciated

By the way, the weird shape at the bottol of my diagram is supposed to be the top of the tranny shifter, as it appears in the picture above it

Edited by Warpman89
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Here's what i am talking about in the second paragraph:

P5120031.jpg

This is the bottom of the shifter knob, the numbers and letters are somewhat visible, 1,2,3,4, "S", and "E"

P5120026.jpg

This is the air shifter that goes on top of the tranny, it has 5 air line connections going to it, 4 of which are numbered

P5120030.jpg

This is a diagram i made up, which links 1-4 on the tranny with 1-4 on the shifter knob, "S" on the shifter knob is already connected, leaving "E" without a destination.

Does anyone know where "E" goes? and where does the extra connecter on the tranny labeled "4" go? any help would be greatly appreciated

By the way, the weird shape at the bottol of my diagram is supposed to be the top of the tranny shifter, as it appears in the picture above it

The "E" is for exhaust. The line terminates into free space under the truck cab. It does not connect to anything.

Cheap insurance is to rebuild that "Selectair" valve while you have the truck down. Parts are less than $20.00 from Mack.

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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:SMOKIE-LFT: Not having any luck posting the schematics for you but I followed your drawing and it matches my schematic in the book for the TRTXL1070 and the E on the shift knob is always the exhaust port on all 12 speeds I hope it works, I'm sorry I wasn't able to post the schematics I have for you .
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The "E" is for exhaust. The line terminates into free space under the truck cab. It does not connect to anything.

Cheap insurance is to rebuild that "Selectair" valve while you have the truck down. Parts are less than $20.00 from Mack.

Rob

:SMOKIE-LFT: Yeah selectair kits are pretty cheap. I would also put an O-ring kit in the air shift cylinders on top of the transmission while I was at it too.

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:SMOKIE-LFT: Not having any luck posting the schematics for you but I followed your drawing and it matches my schematic in the book for the TRTXL1070 and the E on the shift knob is always the exhaust port on all 12 speeds I hope it works, I'm sorry I wasn't able to post the schematics I have for you .

Thank You! I am still unsure of one port on the top of the transmission part. On my diagram, I labeled it "5", although it had no number. It is actually part of the number "4" port. Do you have any idea what this is for and more importantly where it goes?

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:SMOKIE-LFT: I've got the book right in front of me. Is it a TRTXL107 or a TRTXL1070 ? I'm not any good at sending this stuff on computer but I'll see if I can get my brother to scan it and post it for you in a little bit.

TRTXL1070B

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TRTXL1070B

The line you have labled number five should go to a limiting valve on the intake manifold.

I hope this helps,

Phil

Edited by counterman6

Thanks,

Phil

phil@globaltrucktraders.com

www.globaltrucktraders.com

603-239-7008

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  • 2 years later...

HI !

Is it normal for the E port (exhaust) to leak all the time when the tranny is on neutral and the selectair knob is also on neutral ( there is always a hiss of air under the cab , then if I select D or H or Reverse it stop hissing under the cab .

Makniac , collector and customizer of die-cast model in 1/50th scale

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Yeah E for exhaust, and no air shouldnt leak out of the exhaust in any position, your shifter needs to be recuilt and the kit at Mack was $26 when I got it for mine.

Warpman, make sure you supply clean dry air to that trans, it will save you some issues down the road like sticky shift solenoids and slow or erratic shifting. Mine had a spin on air filter on the trans that I changed every time I changed the oil, I also added an Air dryer (bendix AD-9 $175) it makes the whole air system happier and it cost you about $140 to get a new purge valve and a dessicant cartridge to rebuild it so I did mine once a year, Bendix recommends once a year or every 100k mi. I wish you luck thats the best transmission Makc ever built in my mind you always have the right gear with that one.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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Hi !

84 Superdog , so what you are saying is that you are adding another air dryer over and above the one on the truck only for the tranny ?

I search for the rebuilding kit for that tranny and I can't find any p/n anywhere , anyone knows the p/n please

Makniac , collector and customizer of die-cast model in 1/50th scale

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Hi !

84 Superdog , so what you are saying is that you are adding another air dryer over and above the one on the truck only for the tranny ?

I search for the rebuilding kit for that tranny and I can't find any p/n anywhere , anyone knows the p/n please

No my truck did not have any form of air dryer, most 80's trucks didnt have them, I added one in line from the compressor to the tank and it all but completely eliminated any moisture in my air system, and that is a good thing with a 12 spd. oh.... and air brakes!

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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post-12742-0-88415900-1350439147_thumb.j

TRTXL107 Prior to Serial Number 9G9071

1. Air Control Reference Locator

2. Air Control Select Lever

3. Gear Select Lever

4. Quick Release Valve

5. Exhaust

6. Reverse Shift Cylinder

7. Port No. 4

8. Port No. 3

9. Back-Up Switch (normally open)

10. Amber Indicator Light (on in reverse)

11. Pressure Reducing Valve (60 psi delivery)

12. Port No. 2

post-12742-0-63604900-1350439156_thumb.j

TRTXL1070, Serial Number 8S6798 and later

12. Hi/Direct Shift Cylinder

13. Pressure Reducing Valve (70 psi delivery)

14. Air Filter

15. Air Supply

16. Selectair Valve

17. Exhaust

A. Section A - A

B. Piston Port

C. Pressure

D. Exhaust

11. Port No. 1

Hope this helps

post-12742-0-62753600-1350439165_thumb.j

Edited by turckster
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Hi !

is the reducing air valve is adjustable or are they are factory set ?

I see some tranny needs 60 psi some need 70 psi !

could be either, most are adjustable,put a guage in line adjust it then remove the guage, or just leave it there if you dont want to remove it, bendix has preset regulators you can get at most truck parts places for less than $20.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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