Jump to content

Recommended Posts

Does anyone have the schematic for the air lines on a twelve speed?

Share this post


Link to post
Share on other sites

How many times has this come up in the last few months, we may need to send out a group email of the schematic.

Share this post


Link to post
Share on other sites

What up with the air line that comes from the tranny to the aneroid valve, we heard it was to reduce power when to muchtorque?

Share this post


Link to post
Share on other sites

Um that's a new one on me, I can't say I remember seeing that line on my 84.

Share this post


Link to post
Share on other sites

Um that's a new one on me, I can't say I remember seeing that line on my 84.

Thats the problem, my dad has been working on Macks for 35 years and hes never seen one besides our 93 RB had it but that was a 8LL. He was at mack one day and asked the service manger what it was and he didn't know either. We didn't notice it until today on our superliner when we the aneroid valve was leaking because of it. We just put another rebuilt 12 speed in it and we were trying to figure it out so my dad asked his friend who has a 12 speed in his R-model what it was and he said there was some torque valve on the tranny that went to the puff eliminator/aneroid. he never noticed it on his till his air ride cab broke and broke it off the transmission. he said he never put it back on so it cant be too important? :idunno:

Share this post


Link to post
Share on other sites

Ha puff eliminator, well since I remove those pesky air leakers I guess I wouldn't know about that air line. Good tip, find an 1/8" pipe plug and put it where the off limiter was.

Share this post


Link to post
Share on other sites

I thought it was to limit Torque when backing up...at least that what I was told back in the 80's when I worked on them often...

  • Like 1

Share this post


Link to post
Share on other sites

It limits full engine power. I would suspect it limits when in low low and reverse. Only?

  • Like 1

Share this post


Link to post
Share on other sites

My trucks have not had the valve you speak of I say remove it and thats one les air leak in the future, if you flat foot it in low or reverse under a load you dont need to be driving anyway.

Share this post


Link to post
Share on other sites

Its not pressurized in reverse only in neutral, direct, and high it goes into the manifold where it connects to aneroid valve.

Share this post


Link to post
Share on other sites

How many times has this come up in the last few months, we may need to send out a group email of the schematic.

Post it in the Wiki section

Share this post


Link to post
Share on other sites

can someone please Idendify these valves so I hook them up to the shifter correctly.

I guess starting at 12 and going clockwise...

Thanks

post-17-0-08527600-1361654297_thumb.jpg

Share this post


Link to post
Share on other sites

Its not pressurized in reverse only in neutral, direct, and high it goes into the manifold where it connects to aneroid valve.

well yeah that would make it a limiting valve if its got air in everything but low and reverse, I dont know how that works, seems it would be the other way around in my mind, oh well I always give em all the fuel they can get all the time anyway. I got no puff limiter, and the governor is turned up about 4 turns, of course they say turn it a half a turn and try it to keep the egt's low but I go about 1-2 turns then try it myself, makes it fun if you have someone driving in a diesel pickup trying to blow smoke and you can bump it thru a couple gears leaving a light then skip a couple and get the rpm down to about idle and just lay on the throttle, most of the time it will make automatic headlights come on behind me!

Share this post


Link to post
Share on other sites

well yeah that would make it a limiting valve if its got air in everything but low and reverse, I dont know how that works, seems it would be the other way around in my mind, oh well I always give em all the fuel they can get all the time anyway. I got no puff limiter, and the governor is turned up about 4 turns, of course they say turn it a half a turn and try it to keep the egt's low but I go about 1-2 turns then try it myself, makes it fun if you have someone driving in a diesel pickup trying to blow smoke and you can bump it thru a couple gears leaving a light then skip a couple and get the rpm down to about idle and just lay on the throttle, most of the time it will make automatic headlights come on behind me!

We have a switch hidden in the cab that turns it on and off that way if they want to check emissions its all good. My dad disconnected the line for tranny since hes the only one that drives it.

Share this post


Link to post
Share on other sites

Emissions! thats one of them thar dirty words in Truckin mister!

  • Like 1

Share this post


Link to post
Share on other sites

Valve on the far right is the reverse high low valve.

Valve on the bottom is for the front compound

Reference my post above to see how the valve on the far right is plumbed

The front compund is plumbed similarly to the reverse from the dash switch

The valves are inversion valves, they close the delivery port when the control port has air. The other port is supply.

Share this post


Link to post
Share on other sites

Emissions! thats one of them thar dirty words in Truckin mister!

CT has two guys that go around checking

Share this post


Link to post
Share on other sites

CT has two guys that go around checking

Time to move!

Share this post


Link to post
Share on other sites

I have a 95 rd with a 12 spd. The outside inversion valve is constantly leaking air from the botom of the valve, not from an air line or fitting(two bolted together on side of tranny, one closest to frame leaks)I replaced it and still acts the same. The only way to make it stop is if I flip the switch on the dash for low low, then i flip the switch back and the air leak is gone but will come back after driving.The transmission works fine, anyone have any ideas what's causing the air leak?

Share this post


Link to post
Share on other sites

I’m having the same issue with the inversion valve mounted closest to the transmission. I just replaced it with a new valve and it is still blowing air out the bottom. Did you ever figure out what your issue was or can anyone else point me in the right direction? I’m at a loss right now. The only thing I can figure is the pressure reducing valve is failing and there’s to much pressure? The supply line  for the inversion valve  that is leaking is the yellow line that comes down from the transmission shifter. 

Share this post


Link to post
Share on other sites
Posted (edited)

I had a Combination Cylinder crack on my 8LL trans a couple years ago. It's the disc that air pushes against to change from high to low and low to high. Easy part to change. Air would leak through the crack to the vented side. Switch range and it'd still leak, because you're just inverting which side of the disc is pressurized and which is vented. I'll bet thats where you'll find your problem.

Edited by JoeH

Share this post


Link to post
Share on other sites

Will likely be called Splitter Cylinder or Shift Cylinder on a 12 speed. 

Combination Cylinder is what it was called on my 8LL

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...