STX 425 transmission acting up

[vicegrip]

So I have a 2002 Model with 13500 hours I am having transmission issues with. I have noticed a slip in the 13th 14th and 15th gears. I did a pressure test and all of the clutch and lube pressures are within spec ,although there are only about three PSI in the range that the book specifies. It happens the easiest in the 13th gear so I hooked up gages on those three clutches that are engaged in that gear, and there was no difference when the slip happened. If I understand the book correctly I can turn up the pressure by removing shims somewhere and I'm wondering if maybe that could solve the issue. When the percent load gets over 80 I also hear a loud whistle More like a shrill really that I always thought was coming from the turbo But it seems to be Somewhat consistent with the slippage. I should also mention that I got a filter block error once and I cut it open and there Was fine black stuff in there, I'm assuming from the clutches? Am assuming I have to take out the transmission , I wondered if there was anything else I should check before doing that? I appreciate any input. Thanks!

[GaAgTech]

Does the transmission oil smell burnt or look discolored?

Based on the evidence when you cut the old filter open it’s a pretty sure bet that there is a burnt/damaged clutch pack. 
 

Not what anyone would want to hear. 
 

Upping the pressure if it is already in spec won’t help. The damage is done. 

[HydroTek]

Remove the cab and pull the transmission out the top

if you have a forklift and boom this is not a bad job -- or other lifting equipment
There is an "H" shaped frame that fits on the top of the cab for lifting 

also gonna need some 6x6 blocking to lay the transmission on it's back so you can split it 
Remove the speed sensors from the transmission before splitting the case -- no need to break those 

[vicegrip]

Yes the oil smelled burnt was a little darker than normal.I found the damaged clutch pack,and i see in the parts book there are 2 different thicknesses of disks ,and in the service book you measure the travel of the assembled pack depending on serial number so am i gonna have to buy both sizes and mix and match to get the correct distance or is it one size up to said serial number and the other size after that serial number? Appreciate your advice,thanks.

[HydroTek]

Measure the old metal disks with a mic and lay in separate piles or mark with a sharpie 

usually can reuse them 
mix and match to get the stack clearance
-- dial indicator is handy and use air to activate the clutch pack 

mostly what I see when there is a failure is a broken piston 

[vicegrip]

I didn't see anything on the piston, i wanted to take apart the master clutch to see how they look but i dont have a bearing splitter of that size and cant seem to locate one online either ,but i did see one at the dealer .I took apart one on the first shaft and the teeth are showing wear so i'm leaning towards replacing all the clutches and all the bearings as one of the tapered ones is in rough shape .It just seems a bit odd that they wouldn't specify which size disks to use if you put in all new ones.

[HydroTek]

Picked this one up a while back -- looks like a legit puller

you still need the long rods and the bridge piece 
I use a 20 ton short ram 

Split puller

[vicegrip]

• So I got the parts I need and a gasket kit #87432750 and the piston o-rings look to be rubber and the ones that were in there are of a solid material with hooks to hold it together. I'm wondering if the rubber one is an update? And the shaft seals seem to be teflon where the original are of the same stuff as the piston seals. I'm also wondering what the purpose is of the seal on the master clutch gear. There are 2 smaller ones that came with the kit that I didn't see when taking apart the clutches although in the parts diagram there is one on the 2r clutch gear with a serial number break after mine. Just wondering what their purpose is, maybe I should put it in?? 

[HydroTek]

The split teflon rings are for lube , to hold oil in the clutches -- as long as they look decent can reuse since lube is low pressure 

[vicegrip]

Since I had it off anyway I thought I'd check out the solenoids, so I hooked up 12 volts and air like the book says and they all seem to work good but i hear air escaping with no solenoid engaged . Is it normal for air to escape where oil would not? Thanks for your thoughts.

[HydroTek]

The pilot valve behind the solenoids will leak a little air

I suppose it depends on how much is a "little" that you are hearing 

There are no seals -- only the valves in the bores 

[vicegrip]

I filled the block with oil and then put air on it and it seemed to seal off fine but it then pushed oil out of the one of the circled ports. I'm don't know what those ports do they line up with the ports in other picture of housing. Parts book shows a spring and spool in the housing. Pressure relief??? Service book just doesn't say anything about plugging off those holes when testing. I'm assuming the valve block worked fine since I never saw any pressure in a clutch where it wasn't spossed to be. Curious what those ports do.