Simp's Cat 7155 Swap into a M923A1

fuzzytoaster

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I'm fascinated by the 7155... It's one of the reasons I've been looking to replace my current tractor with a M920. I have a 7155 question: How do you think it would behave behind a completely different engine than the Cummins 400? Let's say the Detroit 8V92TA from a HEMTT at 445 hp. Horsepower is similar, but the Detroit RPMs rise and fall more 'snappy' and it would have different torque characteristics. Would it still shift fine? Maybe the Cat's valve body would need to be tuned/recalibrated?

Jon
I can kind of answer this one: not great..or at least as great as the 400 in my opinion. With quicker RPM climb that shift window is shortened leading you to do some "racing" between the two. The 7155 has a minimum sustained RPM before the clutch disengages by itself to prevent damage and it's not a fast transmission anyway so you'd have to be more precise with timing and still be limited by the show shifting.
 

patracy

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So I guess a NHC250 (pretty much a 290 now, with a nudge more power) likewise isn't going to work well behind it?
 

simp5782

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So I guess a NHC250 (pretty much a 290 now, with a nudge more power) likewise isn't going to work well behind it?
I wonder how it would be without a transfer case. Especially an Od case

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patracy

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I'd imagine it wouldn't have a lot of effect until the higher gears. Maybe you'd have to start in 3rd unloaded instead of 4th? I just wondered about the operating rpm of the 250. I know the mentions earlier of being able to pull gears faster works behind it, but you'd be down nearly 100hp.
 

NDT

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The 7155 behaves like any manual transmission, except that clutch operation and movement of gears is done pneumatically, not with your feet and hands. The problem with other engines is finding the special flywheel.
 

patracy

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Oh, so it's not a torque converter? I honestly would be interested in this swap for the SEMTT, if it can fit in the area the 654 currently is at. My crane crossmember only has an inch or so clearance over the top of the transmission housing. Also, is there any means to installing a PTO onto the 7155? And would it fit in the frame rails?
 

simp5782

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Oh, so it's not a torque converter? I honestly would be interested in this swap for the SEMTT, if it can fit in the area the 654 currently is at. My crane crossmember only has an inch or so clearance over the top of the transmission housing. Also, is there any means to installing a PTO onto the 7155? And would it fit in the frame rails?
7155 can handle dual ptos. Its not much fatter than a 654 on the lower side. No pan to hang down either//cloud.tapatalk.com/s/596650afb0794/Screenshot_20170712-113828.png?
//cloud.tapatalk.com/s/596650c3157c5/Screenshot_20170712-113823.png?


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patracy

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I'm guessing that plate is on the top side? That might make this not work for my project at all.
 

simp5782

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I'm guessing that plate is on the top side? That might make this not work for my project at all.
That big plate is the manifold on the top side. Sits at an angle. The pto is below it. And sits at that slight angle on both sides. I can get an exact manifold height shortly. I know it wouldnt work in an 809 series cab but a 939 has alot of space above the allison.

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simp5782

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Updated parts list/cost. For those of you contemplating this swap.


Transmission - $350. New.
Shifter - $60 - NOS
Umbilical Line - $350- NOS - Hard to find
Air Tanks and brackets $60
Bellhousing $205
Splined Adapter $200 - Hard to Find
Flywheel/Spur gear - MAY have one. Otherwise $200.
Receiver Dryer $100
Oil Mister $80
Regulator/Filter $200.

So call it a $2000 mod once you fab up some brackets for the shifter tower and transmission brackets plus a driveshaft or two. I lucked out on that the transmission only costed me about $350
I have not found a dipstick or tube yet so I may be going to have to wing that and make one.
 
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simp5782

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So Wes will this be done before you swing by my way?
No. I am waiting for the splined spacer to still show up. Plus i dont want to do the swap and then go cross country loaded and not sure of the transmission characteristics nor its dependability

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ponway

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simp5782,
I put the 7155 behind a Detroit Series 60 430/470 hp, 1650 torque a year ago now. I have somewhere around 60,000 miles on it with no problems other than last winter when the temp dropped below 20 degrees, I believe the rear clutch would slip a little near peak torque in top gear. I increased the air pressure to the rear clutch which seemed to help. The transmission is rated at 1350. Think I will heat the oil with coolant to avoid the problem next winter.

I have posted pictures of the install in a album under my profile here on SS. A couple of them have measurements of the drive ring fitted to the standard flywheel (simply removed the clutch) and measurements of the adapter on the tranny. The flywheel and housing will need to be clean and all openings sealed as you will now have oil in the housing with this tranny.

The Western Star has a AD-9 air dryer on it - a very good dryer. I did not install an oiler or a filter system nor a valve body heater and had zero problems with that part of the tranny. However, this truck is operated weekly and does not sit.

Got to get back to work, If I can be of any assistance, just ask and I will try and help you out.
 

patracy

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Updated parts list/cost. For those of you contemplating this swap.


Transmission - $350. New.
Shifter - $60 - NOS
Umbilical Line - $350- NOS - Hard to find
Air Tanks and brackets $60
Bellhousing $205
Splined Adapter $200 - Hard to Find
Flywheel/Spur gear - MAY have one. Otherwise $200.
Receiver Dryer $100
Oil Mister $80
Regulator/Filter $200.

So call it a $2000 mod once you fab up some brackets for the shifter tower and transmission brackets plus a driveshaft or two. I lucked out on that the transmission only costed me about $350
I have not found a dipstick or tube yet so I may be going to have to wing that and make one.
Where did you order all this? I'm game. Even if I have to redo the crane mount.
 

simp5782

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Where did you order all this? I'm game. Even if I have to redo the crane mount.
-Shifter from ebay.
-Bellhousing from ebay cummins # 3016697
-Splined adapter from member RR racing.
Vintage iron may have some splined adapters.
-mister and regulator from ebay
-upper trans bracket mount, neutral safety switch, air switch, output yoke from memphis equipment.
- flywheel is with the splined adapter hopefully if not. Jatonkas can get them for $375 new
-umbilical is from militarytrucks.com but i have another source for them.

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simp5782

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My plan for the driveline is this.

Move the transfer case back. Use the the spicer style output yoke off the 915. Remove the 7c mechanics style input yoke and install thr companion type flange that the rest of.the truck then the driveline can bolt in that way. Move the transfer case back far enough that a 931 driveshaft or a between the tandem driveshaft would work.

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patracy

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-Shifter from ebay.
-Bellhousing from ebay cummins # 3016697
-Splined adapter from member RR racing.
Vintage iron may have some splined adapters.
-mister and regulator from ebay
-upper trans bracket mount, neutral safety switch, air switch, output yoke from memphis equipment.
- flywheel is with the splined adapter hopefully if not. Jatonkas can get them for $375 new
-umbilical is from militarytrucks.com but i have another source for them.

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I went ahead and posted up a WTB for the transmission, but I had hoped there was somewhere with them on closeout/surplus you lucked up on.
 

NDT

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simp5782,
I put the 7155 behind a Detroit Series 60 430/470 hp, 1650 torque a year ago now. I have somewhere around 60,000 miles on it with no problems other than last winter when the temp dropped below 20 degrees, I believe the rear clutch would slip a little near peak torque in top gear. I increased the air pressure to the rear clutch which seemed to help. The transmission is rated at 1350. Think I will heat the oil with coolant to avoid the problem next winter.

I have posted pictures of the install in a album under my profile here on SS. A couple of them have measurements of the drive ring fitted to the standard flywheel (simply removed the clutch) and measurements of the adapter on the tranny. The flywheel and housing will need to be clean and all openings sealed as you will now have oil in the housing with this tranny.

The Western Star has a AD-9 air dryer on it - a very good dryer. I did not install an oiler or a filter system nor a valve body heater and had zero problems with that part of the tranny. However, this truck is operated weekly and does not sit.

Got to get back to work, If I can be of any assistance, just ask and I will try and help you out.
Ponway, thanks for this post and the pictures you posted in your album, they are one of a kind. What is your opinion of what simp is going for here, specifically, the 7155 behind 250 hp not 400+?
 

simp5782

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Ok sports fans. I employed the donkey in a little engineering mission. He came back to find that the companion flange. The one that goes to the front output on the transfer case is the same flange overall as the jackput input flange. So That solves that. Go to a companion style flange on that and use the spicer side output flange on the transmission. Just sucks having to beat the joints in with the shaft in the truck. but oh well. Since I am moving the transfer case back it will allow for a cheaper driveshaft to be made being that all spicer is being used rather than the 9c and 7c series meritor joints.

I was able to score a used umbilical today. I thought about maybe taking it apart to see how the connectors are set up. Get some new blocks machined and attempt to reproduce it as a spare. Just a thought.

I also dropped the parker air/filter regulator since they were having some order problems and went over to a Fabco Air unit. Was also $120 cheaper than parker as well.
 

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