Simp's Cat 7155 Swap into a M923A1

simp5782

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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.
Thanks man and will do.

I thought about adding shut off valves on my heat exchanger and running the trans oil thru that in the winter time to keep it warm. My air to air cooler for the trans is about 5x bigger than what comes on the truck. That thing is surprisingly small for the gvw of a 920. I am going to run the 939 series hoses and spin on filter since the 915s dont have one. So that helps to keep the trans temp gauge set too.

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ponway

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Thanks man and will do.

I thought about adding shut off valves on my heat exchanger and running the trans oil thru that in the winter time to keep it warm. My air to air cooler for the trans is about 5x bigger than what comes on the truck. That thing is surprisingly small for the gvw of a 920. I am going to run the 939 series hoses and spin on filter since the 915s dont have one. So that helps to keep the trans temp gauge set too.

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I regularly gross 80,000 lbs. I still have the oil cooler lines shut off from the winter. The trans temp runs around 150 F and will get to 200 F when maneuvering or stop and go traffic. The 7155 Operation manual says 270 F is considered high and do not run there frequently or consistently. I'm pretty sure my temp is accurate, I just transferred the factory sender from the Roadranger to the 7155. I'm currently not running the mountains, but I wouldn't expect the the temp to change much unless the clutches were slipping. In fact, the 7155 literature says a cooler is not necessary but provisions have been made to connect one.

Have you taken a look at this booklet on the design and development of the 7155? An interesting read. http://www.plumbers.cc/images/m916/7155/Cat-7155.pdf
A 270 hp was used in some of the testing.

It was mentioned in another post that a special flywheel is necessary, however, this booklet states all that is necessary is a standard flywheel with the drive ring bolted to it and a SAE #1 flywheel housing. In my case with the Detroit Series 60, the 12 threaded holes were already there and the spacing of the drive ring and flywheel adapter (the part on the transmission that slides into the ring) was acceptable. You do want to check the runout on this assembly, the service manual details this procedure.

Another post asked about a engine where the RPM drops fast and shifting, if I understood correctly.
A smooth shift is all in the timing of the right foot. After a few hundred miles, you will instinctively know how to control your foot with the sound of the air passes. Your timing will vary depending on if you are skipping gears, what RPM your shifting at and even if the engine fan happens to come on. Same for down shifting. I modified my shifter to jump 2 ratios all the way to 16th. I like it better that way for jake braking on the downshifts.

The spin on filter you plan to use is probably not a bad idea, the 7155 only uses a screen and magnets.

Looking forward to following your conversion!
 

simp5782

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Well as far as top end goes. A 920 with the 7155 and 6.17 gears With 53s will run 65mph max. I dont think they have an overdrive transfer case. So basically with a 5ton having an overdrive Transfer case and 6.44s plus being on 395s i am hopeful for a 65mph max.

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patracy

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Honestly I'd love to go down to a 395 on my SEMTT. Tires can be had with a 67mph rated speed too. And it'd make trailers easier to deal with.

The 7155 has a .83 top gear. The 939's t-case is .732 in high range. And of course the 6.44 gears. (Saying tires are 47" tall)

According to my math, that works out to be a 75mph top speed with a engine speed of 2100rpm.
 

patracy

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Wanna hear something crazy? If it was a 8.3 powered truck, they can sustain 2800rpm easily. (They could go higher though) That works out to 100mph. Course I'm doubtful there's enough power on tap to make that happen.
 

simp5782

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I ran out of fingers to do all that math and my shoes are still on. I was just going off the 920 itself and its speed.

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simp5782

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Wanna hear something crazy? If it was a 8.3 powered truck, they can sustain 2800rpm easily. (They could go higher though) That works out to 100mph. Course I'm doubtful there's enough power on tap to make that happen.
Schoolbus' can fly like the magic one.

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patracy

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I ran out of fingers to do all that math and my shoes are still on. I was just going off the 920 itself and its speed.

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I'm weird. I enjoy working out things like that. I also work fractions in my head.
 

simp5782

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Parts day.

I got home from the road trip yesterday to a Christmas site in my hallway. Shifters, dryers, and other crap oh my. HA.

Well I acquired some parts today I had also ordered.

Was able to get some rear cab mounts from the swampdonkey. I believe I am going to use the old cab mounts for my transmission mount bushings.

The regulator and mister combo. I went this route as the mister was $75 and the regulator/filter from Fabco was $135.
I also picked up some muffler vents for the transmission since it has like 11 of those poppet things. I believe these will work fine.

Shifter showed up along from a guy in MI I traded with and the Air Dryer from Suprman. You can see a size comparison on the shifter. It is good size.

Bellhousing needs a little clean up but seems in good order.

Flywheel bolts came in. I know someone awhile back needed some flywheel bolts for the small cam and cummins had them but were costly. I was able to run the number thru Interstate McBee and my local diesel pump shop got them for $5.35 each. so that isn't bad at all.

My new umbilical showed up so I have 2 of them now.

Gallon of Lizard skin and some heat shield material so I might as well get the cab the best sealed and insulated a I can while it is off.

Flywheel should be here tomorrow and the splined adapter on Wednesday. Then it is go time for the weekend.

Unfortunately the Allison I was running didn't make it home from the last trip. She finally gave out 300 miles from home. Rear output got to have so much play it and vibration that it broke the bellhousing to transmission bolts off and pulled the torque convertor from the front pump. I had been fighting that vibration for awhile but that is that for now. I am getting my stuff loaded up in my other 5 ton to go get it and bring her home.
 

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simp5782

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Today she got stripped down for the most part. Used the M4K forklift to pick the cab up. Yes that is an AC unit on top of it that is bigger than the cab. makes for easy work. You can see the bellhousing sitting there broken off. I just left the torque converter in for now. I will get it and the bellhousing swapped tomorrow. Also did the work and pulled the cross member rear cab support bracket. Whoever designed that thing was retarded. Making you pull one air tank to get it out. Stupid. Along with that little air line holder just behind the drivers side body/cab mount bracket. the other side of the bolt is INSIDE the mount and nothing I had nor my hands could fit in there to reach it.

Some parts I ordered from CAT showed up today. This included new Umbilical cord gaskets for both ends as well as new bolts and washers for both ends. Along with several of the giant O-Rings.

I do know that I will have to relocate the main air dryer for the truck somewhere else. Being that I am moving the transfer case back a few things may hit. Also have to work around the cross member in the frame there.

She got a bath with 4 gallons of ZEP degreaser and I think I sucked the hot water tank dry with the pressure washer a few times before bed.

Took me about 6 hours to have it down to this point.
 

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simp5782

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Ok well today was a non productive day. Being that I bought a bellhousing off ebay that was advertised as Cummins 3016637 for a Big Cam I and M915 and other trucks. Well it showed up and someone had scratched the main cummins number off the bottom of the housing right. Looks nothing like the one that came off the truck as far as how the bolt holes lined up. and behold they didn't scratched the other cummins number that is stamped on it. 3032267 is the number on it. for an L10 engine. I am having issues since the seller "doesn't accept returns" yet the idiot didn't know what he had. Or tried a bait and switch. So I ordered another one that is brand new. Was $550 shipped and will be here on Tuesday. This one has 3016637 all over it. I know I will have to use an angle iron type setup to hook the bellhousing to the stock frame mounts on the truck. I think it will be a 5" x 3" 3/8" angle. I will know more on Tuesday.

Got the old bellhousing off. Replaced the rear main seal while I had it off and got a new Oring for the rear of the crankshaft.

Did some measuring and bracket placement since I did not have a soldier B today. The 923 driveshaft is around 35" long compared to the 25" on a 931. This will not cause any clearance issues on the cross member or air dryer. It does require a loom to hold the brake light switch up or simply move it down the frame a few inches. Luckily the transfer case frame brackets sit flush against the bottom off the frame so placement and it being level is easy. I am also swapping the transfer case to a single line system. It will only have air going to the front actuation valve when the switch is engaged. Nothing else, not even the shifter lock. Looked into a case with swampdonkey last week and this should be easy. I will also be using the stock transfer case shift linkage as I am just going to use the same clevis and go with a piece of linger allthread. Should be simple enough.

As far as the rear mount goes. I may have run into a snag. After measuring off the bellhousing to the placement of the two studs on the transmission I am concerned it will be right under the rear cab mount cross member. After looking at the mounts on a 920. I acquired one. They aren't weird just well. I have never seen a mount that was not bolted to the vehicle. The plate bolts to the transmission. then it goes up and bends and bolts to a cross section piece of 3 pieces of steel. This piece has an arch to it and goes from frame rail to frame rail. There are 2 brackets bolted to the outside frame of the 920 that have a little 90 degree piece on top that the arch actually just sits on. Not welded, tacked or anything just sits on top of it. I guess that transmission needs to have some type of movement. WITH that being said, with that setup it will be directly under that stock crossmember. I wonder if it would hurt anything to flip the bracket over and have it go off to the front of the transmission and then run the holding bracket like the 920 has but its only reversed. If that makes since. I don't think it will hurt weight displacement on the transmission. But I am also unsure if the transmission needs to be able to move.


I posted a picture of the valve body off a removed 7155. I am having trouble figuring out what the 3 sensors are. I am assuming one is for reverse lights since it is pretty cheaply made. The other is a flat piece sensor, 2 prongs. My transmission does not have a place for it even though the bolts are there. I don't have a clue what it is and no numbers. The other is in the far right corner of the pic and I am going to assume this is the Neutral safety switch. I guess the transmission has one.

went by CAT this morning and picked up the two umbilical cord gaskets, bolts,washers, and 4 of the Transmission Orings for the bellhousing. My manual still hasn't showed up after 2 weeks.

Other than that we got rain this afternoon and suppose to rain all day tomorrow but if not I will get the transfer case put in and maybe some Lizard skin sprayed on the cab.

Also posted a picture of the adapter spacer ring and the flywheel. Standard clutch flywheel but the splined adapter is the key. It ONLY GOES ON ONE WAY. it can go either way but the lip and recessed side should go down inside the lip on the outside of the flywheel. Putting it in backwards will give you a nasty vibration.
 

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ponway

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Your transmission has a valve body heater on it. There is a guy in France that has a couple brand new surplus heater kits for sale, but I'm guessing you won't need the heater with a good air dryer. Pretty sure that is what the diamond shape sensor is for.

The one between the umbilical line and supply line is for the reverse lights.

The one at the back by the regulator is a switch to cut the jakes off while the transmission is shifting. Don't think your going to need that one either.

The neutral safety is in the shifting console.


As far as the rear mount, get everything mounted and in place and see what will work then. In my case, it's not holding a whole lot but stabilizing it. I put some nice heavy Freightliner mounts on the flywheel housing and ran a bead of Permatex Ultra Black between the housing and trany with the o-ring. The first transmission tore up after 100 mi because it wasn't getting oil to the rear output. Anyway, I had a **** of a time getting it pulled back off. I jacked it up, let it down and all that weight wouldn't break the seal! ended up pulling it off with a chain and ratchet binder. As I said before, the flywheel will be running in the oil, that area does stay dry though.

My splined adapter came with the grade 8 bolts and hardened washers.
 

simp5782

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Your transmission has a valve body heater on it. There is a guy in France that has a couple brand new surplus heater kits for sale, but I'm guessing you won't need the heater with a good air dryer. Pretty sure that is what the diamond shape sensor is for.

The one between the umbilical line and supply line is for the reverse lights.

The one at the back by the regulator is a switch to cut the jakes off while the transmission is shifting. Don't think your going to need that one either.

The neutral safety is in the shifting console.


As far as the rear mount, get everything mounted and in place and see what will work then. In my case, it's not holding a whole lot but stabilizing it. I put some nice heavy Freightliner mounts on the flywheel housing and ran a bead of Permatex Ultra Black between the housing and trany with the o-ring. The first transmission tore up after 100 mi because it wasn't getting oil to the rear output. Anyway, I had a **** of a time getting it pulled back off. I jacked it up, let it down and all that weight wouldn't break the seal! ended up pulling it off with a chain and ratchet binder. As I said before, the flywheel will be running in the oil, that area does stay dry though.

My splined adapter came with the grade 8 bolts and hardened washers.

I figured it didnt have a neutral safety switch but i wasnt for sure cause of the chance The truck left in gear and turned off and the air switch still depressed. So basically it is sensorless.

It will have its own air dryer that has a heater on it.

My adapter was second hand so ill have to come up with bolts and washers tor everything

Luckily ive got a spare trans if it doesnt work right.

Im gonna run it with the cab off for a few hours letting it shift thru the gears to make sure everything works properly.

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simp5782

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Got the transfer case installed today along with the brackets it moved back a total of 8.5" I am going to shorten the driveshaft going to the front tandem by about an inch or so. I just don't like it's current situation at being at the base of the slip. Redrilled the frame. I had a tough go at the drivers side, just didn't want to drill thru the frame. Even with a 200rpm 1/2" drill it just kept eating bits up. So I had to get the plasma out and pop the holes fairly quickly. Installed the Companion flange in place of the stock jackshaft flange. Pulled the cover on the transfer case and went thru the shifting linkage on it to make sure it was kosher. I don't think I am going to need low range much if at all. I did have to cut the rear stock transfer case bracket off to put the new one in. Actually I could have left it there and just added the 2nd one 6 inches behind it. but I was not sure on the front driveshaft length. BTW I hate cold rivets, and that's all I have to say about that.

Was able to keep the air dryer in it's raised spot. The spot light switch may have some interference but I can probably work around that. Pulled the fittings on the wet tank and cleaned it out and reinstalled them with thread sealer. Try to fix some leaks someplaces.

As measured from the back of the engine block to the front of the flange is 69 inches. I believe the bellhousing overall's thickness is 6.5". The same as the stock housing. All difference is a 1 vs 2 bellhousing. Transmission overall is 36inches. Plus the flange so say 40 inches total. Still leaves about a 21 to 23inch jackshaft give or take.

Got the lizardskin sprayed on the firewall of the cab. Also ran a bead of silicone around the crack for the dog house. I will add the stick on insulation stuff before I put the cab back on.

I might have an issue with the rear head on the engine. I snagged the dual fuel line coming off with the cab and snapped the fitting off in the head. I hopefully can get it out tomorrow. I didn't really even notice it was broke off till today.
 

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