Cat 7155 tranny

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NDT

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Quote of the year: "I'm not a military truck nut , but i probably know an M715 more intimately then i do my wife"


RRacing will tell you the control manifold on the 7155 is complex beyond belief. How Cat managed to make air pressure do what normally is done by hydraulic pressure is beyond me. What I am getting at, is that trying to rethink the control of the transmission is a can of worms best not opened.
 

Floridianson

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Quote of the year: "I'm not a military truck nut , but i probably know an M715 more intimately then i do my wife"


RRacing will tell you the control manifold on the 7155 is complex beyond belief. How Cat managed to make air pressure do what normally is done by hydraulic pressure is beyond me. What I am getting at, is that trying to rethink the control of the transmission is a can of worms best not opened.
It's just a manual transmission with air shift and a little extra for the clutches. Bad AZZ transmissions when working correct.
 

Warden

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More Trans questions and a few other wonderments

It's just a manual transmission with air shift and a little extra for the clutches. Bad AZZ transmissions when working correct.

question , > does the fact that the gear changes are positive and lightening fast and have Zero resistance or drag , imply that clutches are not warped at all ? with ZERO Grinding ~! my road rangers have much more drag with cool oil with clutch in gear change or from neutral into the first chosen gear , ! Question 2 > are the clutches wet ? question 3) > do the clutches have a drainable reservoir at a low spot on each where i can drain and view , smell , taste ( assuming they are wet ) ? My son said he seen some plugs under that would appear to fill level or inspection possibly ?
In my mind ( and i know nothing at all about these yet ) what i hear and feel is everything working perfect , with not a bad clutch but if there was a air piston or follower plate that pushes on the clutch pack to engage / lock , that would be my uneducated guess , as to the problem , if both clutch packs are needed for full lock in all gears including 1, 2, 3, 4, then i assume one clutch pack is working , i don't understand the 2 clutch purpose , but if i allowed this to slip in the first 5 gears , then Bad action and heat would have to surface , in upper gears , i think there is not enough attempt to even make heat / load . and hopefully not hurt anything , i can drive this all day keeping it connected , (empty ) the people behind me on the hills don't seem too happy about it tho ! i go from 50 to 20 to find enough lock , ! i will do as R Racing
had instructed asap prob this weekend , ! but it helps to keep my mind working on the system , in the mean time can anyone tell me what the large twist lock outlet on the passenger side is for and the box with a keyed lock under it , ? there is a cord in the trunk that fits it , ?
and , any other tidbits that may be worth knowing , , as i said before i wanted one since 1979 but i never researched them at all , it is probably one of the trucks in the world i know the least about , it was kinda like winning the lottery , for me , you may dream about it but do you
research the options on a Bell jet ranger in anticipation of being able to win the lottery to purchase one ! i did not , more so i kept away from the disappointment and frustration of not being able to have one ! i would love to hear anything that is part of these trucks , just assume I'm the dumbest SOB you ever talked to ( give me enough time and i can probably prove it lol ) thanks for the help ,
 

Floridianson

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Warden was reading your thread and did you say something about comming disconnected. You know that the motor and Trans. do disconnect at about 2100rpm right.
 

Artisan

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Warden,


I sent you a PM, no reply.

I asked several questions, no reply, UNLESS you included a response
in your monster paragraph replies w/o CAPITALIZATIONS and proper
grammar, like paragraphs etc. No one likes to try to read that.

Still no pictures... For all's we know you are driving a massive piece of junk
that could contribute many issues to your problems.

One last try to reach you, here ya go, CLICK HERE, study in detail.

You still may want to address my questions. if not. Okeydoekey.
 

Warden

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i did not know about 2200 rpm disconnect

Warden was reading your thread and did you say something about comming disconnected. You know that the motor and Trans. do disconnect at about 2100rpm right.
No i did not know they disconnect @2100 .... Snap on mag Tach verifies the Gage to be close/to fairly correct , the gage actually reads shy in this temp by about 50 RPM+- So I'm banging approx 2300 in my upper gears and that would explain the lack of heat and the feeling of the clutch pedal being depressed , Artisan was kind enough to send me a schematic of the trans and i have a much better understanding of it , Now i need to know what part and how much of a part the centrifugal engage plays ? it may be all that works on my unit ! Keep in mind that a person
that did not Know That PM meant private message is trying to make this trans operate ! **** every time b4 that there has been a "PM" in my life , its been followed by an ''S" and i avoid that action like the plague !
 

Warden

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Unless you used some sort of thick oil. It didn't mess up your manifold. Most of these were made in 1980 ( 32 years ago) there all on borrowed time til they need a rebuild)
Is air brake anti freeze ( alch) with lube a bad idea to pour in the line of the rear of the outboard pass side air tank ? I'm just sitting here thinking that the temp has not been above 25F since i carried the truck home , and a few weeks back in SC i picked up a semi trailer with no brake action at all , it had sat for years and the
trailer protection valve was for sure stuck , and my mix of air brake juice freed that up and really worked like a charm ,,,, I'm not big on adding alcohol to a system , but i could be dealing with a freeze here , i have gotten Zero moisture out of any tank , Also i don't drive a truck that holds air pressure as well as this unit (i drive allot of different trucks ) im bringing the 916 in the shop now and will let it warm up for a couple of days ! thank you
 

R Racing

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No i did not know they disconnect @2100 .... Snap on mag Tach verifies the Gage to be close/to fairly correct , the gage actually reads shy in this temp by about 50 RPM+- So I'm banging approx 2300 in my upper gears and that would explain the lack of heat and the feeling of the clutch pedal being depressed , Artisan was kind enough to send me a schematic of the trans and i have a much better understanding of it , Now i need to know what part and how much of a part the centrifugal engage plays ? it may be all that works on my unit ! Keep in mind that a person
that did not Know That PM meant private message is trying to make this trans operate ! **** every time b4 that there has been a "PM" in my life , its been followed by an ''S" and i avoid that action like the plague !
See post 34. I told you about the disconnect.
 

Warden

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See post 34. I told you about the disconnect.
Yes you did , however I miss understood it the way you explained it . I assumed it as a trailing throttle over speed safety , I did not realize you could be under accelerating throttle and loose connection ! This is bassackwards from what I'm familiar with , where the eng. Gov. protects on the way up and then the jake would be next . A drive line disconnect on acceleration with proper inertia can lead to an over speed by itself . This engine may rev too much to stay connected , I will hold to 2000 and try it , I believe it will pull 2300 in any gear.
Thank u
 

Floridianson

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. A drive line disconnect on acceleration with proper inertia can lead to an over speed by itself .

Mine governer is set for 2400 on the PT and the motor wil not go over that because of the PT not the transmission over speed disconnect. I will look for my 7155 cat manual and give you a part number if you want one for yourself.
 

Warden

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Update, Today I called the kid where i picked up my truck from. I asked if it drove ok for him? He Exclaimed that he only drove it in their Lot (huge lot , my guess is 50 acres) and his superiors told him Don't try and shift it , "just put it in Drive " i asked him what was drive ? his reply was 12 in the front part of the lot
and 16 in the rear , " The Boss told me it automatically shifts up to the selected gear if driven that way" He said he only drove it 3 times for approx 30 minutes each and it drove great. He has only worked there 3 months and to drive this truck was like a little bonus for him , and practice for when he takes his class A.
I guess this explains my transmission woes !! thank you for all the advice !
 

NDT

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FWIW, I've been driving my 915 for going on 6 years now and I really like the 7155. When you get the hang of it you can get to 70 mph as fast as regular traffic when empty.
 

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simp5782

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Anyone kind enough to give me a spacer ring measurement? From engine bellhousing to the 7155. I assume it has one since the Allison does and the face of it looks like it does have to have one.
 

Artisan

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Anyone kind enough to give me a spacer ring measurement? From engine bellhousing to the 7155. I assume it has one since the Allison does and the face of it looks like it does have to have one.
Does the TM show a spacer?
I do not remember seeing one...
Do good research...measure twice, install once.
 

simp5782

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The problem is that the 915 book is half retarded and parts are pages over from where they should be. page 532 shows that section of the engine but the actual splined spacer that bolts TO the flywheel on the engine side is on page 170 of the transmission TM. So there is no telling if it has one or not from the parts books. the front of the transmission protrudes out. but I am not sure if the splined section will sit recessed enough. I do know that the 2piece splined spacer only goes one way onto a flywheel or it will vibrate
 

simp5782

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Going to add this to this thread. Member Ponway brought this up to me about his shifter. It is the 2 step modification that allows the shifter to jump 2 gears all the way to 16th without using the shifter interlock. Pretty simple. Took about 15mins. Also makes for a good time to spray lube everything as well.

The pictures to the procedure are in his album located here:
https://www.steelsoldiers.com/album.php?albumid=4428

https://youtu.be/3p2vVF2ybN8
 
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simp5782

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Adding this as Ponway shared this overdrive article from 1974 on the transmission.

Basically it cant burn up if you run it out of oil. I experienced this on Saturday as my heat exchanger failed and the end cap started leaking transmission oil. So it coasted in neutral. Bypassed the leak and refilled the transmission and it was fine. IMG_24371.jpgIMG_24191.jpgIMG_24341.jpgIMG_24311.jpg

Sent from my SM-G965U using Tapatalk
 
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