Cat 988H,

[fmatemberere]

I removed a transmission from 988H to change the mounts. I fitted back the transmission and all the oil lines.
I topped up the transmission oil using the quick fill but it took a while to show on the side glass to the full mark. I walked away to do something else but when I came back the oil level had dropped down but before the machine is started. I topped the oil again to the full mark.
I started the machine with someone on the ground checking the oil level .The oil level rose up to the overfull position instead of going down after just running the machine for less than a minute.I stopped the engine and removed the transmission oil filler cap but pressurized oil shot out of the transmission.
The oil level on the side glass dropped down to low but oil kept coming out of the oil filler tube.

I need your help please. I am thinking I might have overfilled oil in the transmission but why was it not showing on the side glass or maybe I might have interchanged oil lines.
Please help.

 

[kshansen]

My first thought would be a plugged breather not letting the air out of the transmission.

Here are a couple different views from parts book, note as you did not list S/N may not be 100% correct for your machine!



Appears the one breather is connected to both the torque converter and the range transmission.If you need more views of the lines for the transmission post the full S/N.

Been a few years since I was up inside that area but do recall a real rats nest of hoses. Think we replaced about half or more on the 988H at the quarry one day!

 

[fmatemberere]

My first thought would be a plugged breather not letting the air out of the transmission.

Thank you very much. I will check this tomorrow morning. I also noticed that the transmission case is overfull bur reading low on the sight glass.

 

[kshansen]

Thank you very much. I will check this tomorrow morning. I also noticed that the transmission case is overfull bur reading low on the sight glass.

Another thing if the sight gauge is not showing the oil level that is in the drop-box I would suspect a problem in the lines to and from it as it is, at least on the ones I'm familiar with, a remote mounted sight gauge.

In the picture below the sight gauge is in red and the "vent hose" for it is in green. My first thought would be to disconnect the line from the top of sight gauge and see if the oil starts going up in the gauge. If not I'd try disconnecting the line from the bottom and oil should start draining out if end of hose is below the level in the filler neck.

 

[fmatemberere]

Thank very much, can I ask something please. That green vent hose from top of the sight glass, where does it connect on the Transmission please?

 

[Nige]

One thing you have to be very careful with regarding the remote-mounted sight glasses is that the "air vent" hose (marked by KSH in green on his illustration) CANNOT turn downwards at any point between where it leaves the top of the sight glass and where it attaches to the transmission. If it does you'll get a slug of fluid in the hose and the sight glass will never read correctly.
Maybe this illustration might help regarding the routing of the hoses for the sight glass and where they connect to the transmission.......

 

[fmatemberere]

Thanks Nige, I will double check in the morning. Does this vent hose from the sight glass connect on top of the transfer case?

 

[Nige]

From what I can see from the Parts Manual (which is where I took the illustration) I assume so.
It looks suspiciously like hose #3 in the illustration below which is taken from the remove & install procedure for the transmission.

 

[fmatemberere]

Thanks Nige, I will double check tomorrow and will let everyone know of my findings

 

[kshansen]

One thing you have to be very careful with regarding the remote-mounted sight glasses is that the "air vent" hose (marked by KSH in green on his illustration) CANNOT turn downwards at any point between where it leaves the top of the sight glass and where it attaches to the transmission.

Never ran into that problem, but can easily see it happening. But that line possibly being plugged was the reason I suggested removing it from the top of sight gauge.

I have run into some strange things related to a dirty breather, most common was a transmission that would not drain when drain nipple was inserted in the drain valve. 980 G's had breathers in to worst place! I always relocated them and made cleaning easy.

 

[fmatemberere]

Thanks everyone, I removed the Transmission oil sight glass vent hose and found it blocked. I cleaned it and oil started showing on the sight glass. But I have another issue. I started the machine and ran for about 5 minutes in Neutral and I found that the Transmission case is pressurising because the oil pushed out the oil filler cap under pressure and just wondering what might be causing this.

 

[Nige]

Let me ask two questions. You said in your OP that you "removed a transmission from 988H to change the mounts".

1. Was the transmission & drop box disassembled in any way while you had it removed, or did it go back into the loader in the exact same state as it came out.?
2. Did it have this problem of internal pressurizing before it was removed..?

If the answer to both questions is NO then IMHO you have something in the transmission hydraulic lines connected incorrectly, or you have a similar problem to the one with the sight glass in that a hose that should be open is plugged by something.

 

[fmatemberere]

This machine was working fine before we removed the Transmission to do the mounts. All hoses were capped with the blue caps to prevent contamination. I am not sure if we left a cap in one of the hoses because it seems the Transmission pump is not pumping oil out of the Transmission case sump but at the same time the Scavenge pump is returning a little bit of oil to the Transmission case thereby pressurising the oil in the Transmission case. It's just my theory, I don't know if this is possible. I don't want to run this machine for long to do the tests otherwise I might do more harm, but don't know how best to check if the Transmission and Scavenge pumps are working please.

 

[fmatemberere]

The Transmission and the Dropbox were not repaired and were fitted just a they were. This machine did not have this problem of pressurising the Transmission, it only started after refitting the Transmission.

 

[Nige]

So the logical conclusion is that it was something during the remove/reinstall that led to the problem. I think I if it was me I'd be: -

1. Ensuring that each hose is connected to the correct points. Do you have a Parts Manual where you can see the hose setup..? Personally I wouldn't have touched the transmission without some sort of illustrations showing what went where, or maybe even a load of photos on my phone showing how everything connected.
2. Removing every hose one at a time and blowing through it to make sure it was not plugged, then reinstall before moving to the next hose.

if you want some Parts illustrations a Serial Number would be a good starting point.

 

[fmatemberere]

Thanks Nige, I will have to double check every hose when I go back to work. I don't have the serial number with me at the moment, but that illustration /diagram you sent me yesterday about the sight glass vent hose was perfect, just exactly the same setup on our machine.

 

[Nige]

Just on the off-chance that the pump was removed (or one or more lines connected to it were removed) I'd also be looking to make sure that a blue plug had not been left in a pump port when a hose was reconnected.

 

[fmatemberere]

Thanks Nige,I will check the hoses on Monday and will let everyone know of my findings

 

[kshansen]

Just on the off-chance that the pump was removed (or one or more lines connected to it were removed) I'd also be looking to make sure that a blue plug had not been left in a pump port when a hose was reconnected.

I won't say who did it but someone with over 6,200 posts on this site installed a new transmission pump suction pipe on a 988A Cat years ago and when nothing would work on start up had one of those DUH! moments. Was lucky and found the problem and removed the plastic plug in suction pipe and had it reconnected and machine moving before anyone knew what had happened.

And that was on a very simple machine compared to the rats nest of hoses like a 988H has up in there!

As Nige says post the S/N and one of us should be able to help with Parts illustrations if needed.

 

[fmatemberere]

Thanks Kshansen, I will post the serial number on Monday morning I am off work now.
I want to thank everyone on this Forum for all the contributions, they are very helpful and I am learning a lot.