Cat D8N transmission trouble part 2

[Mobilewrench]

9TC
Back in October I posted about weak first and second gear. Trans pump tested fine but P1 pressures for first and third were in the 100 to120 psi range.
Between that and all of the Teflon seal material I found in the screen on the trans, we decided that the trans was coming out.

The local Cat dealer made a really good offer on rebuilding it, so I took it to them. They can do it inside with full access to cat tools and cat info, I would be doing it in the gray outdoors with just a service manual. I don't think I got it to them until late December or early January. Got it back in March and then we had epic rain and flooding with a good portion of the damage right on my yards North fenceline. So I think I reinstalled it early this month.

While it was down I did some engine work that I had been putting off. Intake seals (post turbo), replaced the water pump and replaced the transmission oil cooler.

The day it went back into service the transmission started overheating. Operator said that it would cool right down when he just put it in neutral. The owner changed out the filter and said it ran fine, I cut up the filter and didn't find much other than a bit of dirt ( when I put the screen back in the trans I was a little surprised by how grimy the housing was. So I expected to find grime in the filter).

The next day the operator said it overheated again. Last week I checked the control linkages and barely adjusted anything. Waited while the operator ran for about an hour and then bounced out to fix a water truck. Again , overheated while I was gone.

Hooked up gauges to pump pressure, P1 and P2. Pump pressure is 500 psi, P1 (speed clutch) is 360 to 370 in all gears and both directions.

But, P2 (directional clutch) is sitting around 75 psi in all gears and directions.

But here is the next weird thing.
My P1 pressures are wildly different depending on which order I choose a gear. The numbers above are from when I chose a direction (forward or reverse) first and a gear second, which isn't the way I have ever operated a dozer. If I choose a gear first and direction second all of the numbers fall down to 150 psi.

I can't make any sense of that so we called the dealer out. Tech showed up this morning and was not one of the techs I was hoping to see. Not that I know anything about him, I just would have rather had the tech who worked on the trans, the tech that I hoped was going to work on the trans or the tech whose name I can't remember but has always impressed me when we chat.

I don't think he really knows much about it. I know he knows less than me, less than the owner and probably less that the operator.
At least the operator knows how to start a d8. "Well, yeah. You have to pull the throttle lever." And probably the operator knows that there is no point to finding your adapters and lugging your laptop up to the cab to try and diagnose a machine built in 1985.

He did check something that I hadn't checked. Transmission lube pressure. I didn't, because I don't think I have a gauge to read 3psi (from the service manual low idle. No number for high). What he printed out said .9 +- .8 psi at low idle and about 20psi at high.
And I could see the oil was flowing like a water fall when I put the last axle in (left side i think). His gauge read 0 both low and high. His gauge was digital, brand I didn't recognize and he said had a rang of 0 to 10,000psi.

So, I am left with low directional clutch pressure, really goofy pressure readings that depend on shifting sequence, possibly no lube pressure and a Dealer tech I currently have little faith in.
Thought I would offer it up to the forum.

 

[Shimmy1]

Sounds like you're going to have to have an uncomfortable discussion with a shop foreman.

 

[John C.]

I heard you guys had a stormy winter this year. I hope all the rain and flooding didn't affect you too much.

The dealership has earned the first strike in your eyes. I wouldn't talk to a dispatcher or shop forman at this point. Ask for the service manager and work your way up if you need to get to yes. Chances are they sent the first guy available to check out your problem. Let the service manager know that the person came out, didn't appear to be qualified and in fact didn't fix anything. Keep calm and let them know what you expect next. I would recommend that you want the guy who did the work or your own selection of wrench that you trust. Right now you are in the fact finding part of this. Should that request be rebuffed, start climbing over the manager to the next level.
I had an engineer tell me years ago to never accept no from anyone who can't say yes. It's a great premise to work from.

 

[pittsburgh cat man]

First thing i would tell you is 75 psi sounds like primary pressure. Did they change the load piston orifice? They are known for coming apart and plugging the orifice

 

[Mobilewrench]

Tech came back today. And he has risen quite substantially in my esteem, because he brought the tech that I wanted in the first place with him. Someone once asked me what I thought was the most important skill that a mechanic should have. "Knowing when he doesn't know enough."

So, yeah, they sent out just who was available yesterday. And now that I think about it, next day service from the dealer is a pretty good representation of the relationship that I and the owner have with them. The owner grew up with the management. And I have been doing this long enough that they know me pretty well. I actually took a position at the dealer a few years ago. Not because I was looking for a job, but because they asked me to. Also, I have enough respect for my preferred tech that I recognized that I had a pretty good chance of learning a lot from him. I didn't stay very long, maybe ten weeks. I couldn't really adjust to being a domestic mechanic after being feral for so long. Bit of red tape tries my patience. couldn't really stand having to ask permission to fix something that needs to be fixed and have to wait three days for an answer.

Anyway, talked to Martin (might as well call him by name) for about two minutes to let him know what I thought he needed to and then went to work on something else. He rechecked the other techs numbers, probably checked a couple of things else and then came to find me to chat. We bounced some theories back and forth and then I reminded him of the strange pressure differences with shift sequence.

So he went back to look at that a little and then the trans pump seized up and sheared the bolts from the pump driveline on the torque converter yoke. He said that he was going back to the shop to do some research and I said I was going to look at the suction screen.

When I pulled the cover off I found the screen was partially collapsed. I decided to not pull it out without witnesses. Found a little shade and a few minutes later the owner pulled up and said that the dealer was coming back. Ten minutes later they did. Not a tech, the management.

I let them pull the screen and I will post a pic of that in a second, sorry it is on a different device. I am pretty sure that they know this is now their problem. Well, that is exactly what they said.

I will probably pull the pump to see if it can be saved because factory ones seem to be getting pretty rare. But they are going to pull the trans on warranty.

 

[Mobilewrench]

 

[Nige]

But they are going to pull the trans on warranty.

In your position I would strongly suggest to them that at the same time they are pulling the transmission they should also pull the cooler.

 

[nicky 68a]

Little D8N story…..
Had an old 1988 D8N in yard that the trans was worn out.Had to build revs up fully to move it around the yard.Wouldn’t climb onto a lowloader in 1st or 2nd forward.Had to reverse on with it.
Anyway,no intention of spending money on it.The potential buyer of it employed Finnings to come and do and inspection on it.Young lad turned up with his lap top.Sat in it videoing it on his phone saying how vintage it was and spent the next few hours sat in his van doing nothing.
Asked us about plug in ports,we shrugged our shoulders and said nowt.
The D8N was subsequently sold to the buyer and I was interested to see the Finnings report on it that stated it was good in all functions,but suggested oil sampling.
What a complete load of BS!!
Never had a call back on it though.

 

[John C.]

Hey nicky, I kind of like those stories about the dealer wrenches doing a pour job of inspecting things. It's good advertising for my business. I hate to see it for the potential buyer though.

I spent twelve years at the Cat dealer as their used equipment appraiser. Worked for the sales department and they would never use a wrench out of the service department for what I had to do. It wasn't because service didn't have highly capable people to do the job. They just considered those guys should only work on revenue jobs.