CAT 7155 Manifold rebuild

[R Racing]

Actually on this trans it was a 1992 rebuild but even so every O ring in the manifold was shot .You could see that about 15 were replaced. but the regulator O rings and quickfill unit O rings were so worn out that there was no tension left in them,and were worn thin, and they would fall thru the bore. All will have been replaced when done.

 

[NDT]

I guess the next question is, is it easier to pull the cab and do this repair in-frame?

 

[R Racing]

There is actually a access panel under the rubber mat in the floor. its tight but it can be lifted out from there. you want to remove the embilical cord. air feed.the head heater, and unplug the reverse switch and head temp censor.then remove only the outer 3/8 bolts all are about 3 3/4 inches long except for the 2 outer 1s towards the engine there shorter. when you find those screw them back in. they hold the layers together and dont hold it to the trans. its about 70 lbs or more. so you may even want to use a cherry picker to lift it off .

 

[R Racing]

Today was a Banner Day !!!! After finishing the rebuild at 4 am and back up at 8 am I have a tested and working manifold !!!!! I have close to 60 hrs of work between a hugh learning curve and making up the tooling and fixturing and the test bed . It has about 7 hrs of testing with not a missed shift or leak. I started testing Manifold #2 thats bad today its a rebuild thats dated 4-09-10 That I bought off of GL . You would not believe the rust inside !! here are some pictures of Manifold #2. It Goes to prove buyer beware on GL since they had such a pretty picture of the rebuild tag I assumed I was getting a working trans. Well The inside of the trans is very clean ! But when I applied air to the manifold it puked out gobs of rust ! And several of the shift pistons were rusted in place.

 

[NDT]

Next questions: How are you cleaning up the parts? Looks like bead blasting might leave too rough of a surface and tear up the new O-rings. Did you put the manifold back on the trans to test it? Is it OK to "dry shift" the trans (without it turning)?

I would hve never thought the manifold could come out of the hole in the floorboard.

 

[R Racing]

Agreed,I would not bead blast.I cleaned the parts a total of 4 times. I washed the whole manifold with dish soap and water first before disassembly. than after disassembly I used break cleaner. Than you have to sit down with TP and Q tips to remove the pasty stuff the brake cleaner didnt remove. then you stone all surfaces flat. then another washing of soap and water.

Ok The manifold is its own unit and with a shifter and umbilical cord. Air , Some fixture blocks, pressure gauges, and test spacers it can be ,and according to Cat should be bench tested. so its not in the trans when Im testing it. the way its designed, including testing clutch regulator pressure. all of that is internal to the manifold and can be adjusted by shims, and tested without being hooked to the trans. Cat does have a leak down test for the clutch itself for the trans , But that is to be done without the manifold on. I still need a 2 to 1 or 3 to 1 gearbox to fully test out a trans as a unit on the ground.Honestly what Im hearing and seeing myself is that about 95 percent of trans issues are in the manifold itself according to the local Cat GuRu .He said if thats right the trans mechanically should outlive the truck.

Its a tight fit, But have been told by 4 people thats how they do it ,LOL . I have to do my m917 soon and if I decide to do it that way, I'll take some pictures,lol. I can have the trans out in about 4 to 5 hrs if everything works right. It looks like it shoud come up on its side out.

Hope this helps !

 

[Hammer]

Are you thinking about doing this as a service for others?
Or is all this work basically to keep all of yours up and running?

 

[R Racing]

Well I started to do it out of nessesity ( Cat charges $115.00 per hr and said it could take up to 40 hrs Plus if you were to use all cat parts That came out to $3200.00 and some change for there parts ). But after finding out from Cat that they only have 1 Guy near by who they lean on to repair the manifolds, And he is retiring . I have decided that if others need it done That I could do it for them as well.It is very time consuming but I enjoyed the challange. I'm also able to source about 85% of the parts from other sources that are much less expensive! technology has greatly changed since it was designed, and there are now better O ring materials that will endure the higher temps of the trans better. Designs like double O rings that seal 200% better and have a greater life than original. I also found the trans was missing 2 key items that I hope to be doing a write up on next week. It will greatly extend the life of the trans

 

[Ord22]

Thanks for your effort R'. In the army, we always had issues with these. i've always wonder how these valve bodies work and being fixed. Thanks for the effort and keep us posted. Thanks a whole bunch!!

 

[R Racing]

Well I finnaly had time to tear into the 2nd maifold today. This is a recent rebuild unit that looked so beautiful if its wooden create, and fresh green paint and tags that I purchased from GL .This goes to show Buyer Beware and Beauty is only skin deep !!! LOL

 

[R Racing]

a few more pictures!

 

[DieselBob]

That almost looks like it was under water or something. Man what a lot of crud...

 

[R Racing]

You Know I was wondering if theses could have been flood damaged by Katrina ( was rebuilt in LA) but This 1s rebuild was 4-9-10 according to the tag and also the main trans inside is dry and clean as a whistle ??

 

[Hammer]

Wow, guess we know why so many have problems with these.

Is there some kind of external vent that allows moisture to enter the manifold when it's not running?
If not, these things need an air drier and a serious filter!

 

[EMD567]

That manifold spent some time in water. You don't get corrosion like that from moisture in the air.

 

[R Racing]

You mean like this setup here lol The trans has 12 vents that could let moisture in. The setup here is missing its filter ( its been on back order for 2 1/2 weeks but shipped friday) This I believe is a must for these transmissions ! This is what I have been testing . It a regulator/ filter/ oiler. The air tanks collect moister and send small spec's of rust into the trans that cut the O rings, and can gum up the inside. Also the seals and O rings can get dried out and wont hold air. The other thing that came to mind was the air pressure. My M920 and M917 shift better with 95 PSI of air than 120 PSI . Its a smoother shift (also less chance of breaking a gear) and it gives me more reserve for brakes and shifting .So I have it set at 95 PSI ( do not set below 95 PSI because the 1st thru 4th and both reverses need 90 PSI for the rear clutch ) the oiler gives about 1 to 2 drops of oil per shift . I think its a win win ! This setup was a upper range in price but NEMA 14 weather resistant . It also is good up to 175 degree temp. Its a 3/4 pipe inlet and out , But you could get away with a 1/2 inch pipe if nessary. I would not go any smaller as to starve the trans for air.

 

[Monkeyboyarmy]

Care to take a picture of the transmission test fixture thingy? I understand if it is top secret.

 

[R Racing]

That manifold spent some time in water. You don't get corrosion like that from moisture in the air.

I would agree.But when and were ? the trans was buttoned up pretty and had every hole plugged with plastic pipe plugs. Like I said it looked new in the crate and had all the paperwork with it ??

 

[R Racing]

Care to take a picture of the transmission test fixture thingy? I understand if it is top secret.

i can when I test the next. There is a lot of little stuff needed to test even some not listed in there manual. But there manual is full of info if you don't mind how they have it laid out.

 

[EMD567]

Who knows? Maybe they fished it off the bottom of a stack that sat in a puddle. Seeing that it was messed up, repainted it, and put all new plugs in the ports. What kind of material is the manifold milled from?