D7F Transmission over heating after 3-4 hours

[.RC.]

Here are some scans. The speed and directional taps will be under a plate on top of the transmission. Probably 1/8NPT thread, and some others could be 9/16 UNO. Do not automatically think every pressure tap is going to use the same thread. The last lot of photo's show the location of the pressure taps and testing. Also shows the setting of the transmission controls. Also have included the troubleshooting guide from the manual. You could have air getting into the system when the oil is hot and hoses and seal soften causing low oil pressure.

I also scanned in parts manual pages in case you want to get the expensive silicone O-Rings and reseal the transmission control valve.Someone may be able to decipher what you need for that. My D6D had an issue where it would sometimes when the oil was hot would not engage properly, the transmission would slip and the dozer would barely move. I replaced the springs in the transmission control valve (had to come from singapore so took a couple of weeks) and the O-Rings and adjusted the control spool valves so far it seems good, but I have not given it a decent run yet.

 

[.RC.]

 

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[Wiggo]

Hello RC, thanks a lot for your help here, this will keep us progressing until the Manuel arrives.

 

[Wiggo]

Hello Nige, We finally got back out there to test some pressures, see below.

At cold Idle
Pump direct 500PSI
Pump Filter 400PSI
Torque Out 57PSI

Warm
Pump Direct 400PSI
Pump Filter 375PSI
Torque Out 37 PSI
Steering pump port 375PSI
Converter Inlet 85PSI high idle
Converter Inlet while in motion and high RPM 60 PSI

The converter inlet pressure is meant to be minimum 140 PSI. Considering the Touque converter is new and the tractor had the problem before the torque convertor was replaced, we have removed the pressure control valve to clean it and check internally for damage. There was a bit of hard black Debree in the valve, the rest looks ok. we are guessing that we need to add or remove the tensioning washers under the springs to adjust the pressure. We are still waiting for our manual to arrive so are just going off the information provided.

Are we on the right track?

 

[.RC.]

You seem to be missing the pressures for the speed and directional clutches.
What about pressures when it is playing up?

 

[Nige]

The converter inlet pressure is meant to be minimum 140 PSI.

Not so. T&A is not clear on this. 140psi converter inlet is MAX pressure with cold oil. You'd usually expect something around 100-110psi.

You seem to be missing the pressures for the speed and directional clutches.
What about pressures when it is playing up?

Need the answers to those questions.

Torque Out 37 PSI

Is that with the transmission stalled against the brakes in 3rd speed forward.?

Still need an answer to the question of what type/grade of oil you are using in the transmission.

 

[Fin020]

Not so. T&A is not clear on this. 140psi converter inlet is MAX pressure with cold oil. You'd usually expect something around 100-110psi.

Need the answers to those questions.

Is that with the transmission stalled against the brakes in 3rd speed forward.?

Still need an answer to the question of what type/grade of oil you are using in the transmission.

Hi Nige,

What type/grade transmission oil is correct to run in this instance?

 

[Nige]

Hi Nige,

What type/grade transmission oil is correct to run in this instance?

I would go for an SAE30 oil meeting Caterpillar TO-4 specification.
You don't necessarily have to go for a Cat-branded oil. Any major oil company brand will work just fine.

 

[Dazcoy]

Hi all,

So we have done an oil change on the transmission to SAE30 as we weren't 100% sure on the oil grade that was used previous to us working on the machine and we also changed the filters. We have run it up to the problem temperature and found that at 3/4 transmission temp that the speed and direction clutch loses all pressure when trying to select a gear. This is around the 4hr of stick raking work so nothing super heavy. We also did some time working it with the rippers in forward only without any long tracking in reverse and had the same result. I only had enough gauges to be able to see the pump pressure, torque converter inlet and the speed and direction clutch pressures at the same time so we could see that the pump and inlet pressures never changed but the speed and direction would drop to no pressure when a gear was selected in either forward or reverse once the higher temp was received. The speed and direction clutches where up around 350 psi at working temp and dropped to 300 when the issue starts to occur.

The converter outlet pressure that was previously mentioned was with it stalled in 3rd. It didnt seem to change at all.

 

[Nige]

When you changed the oil did you remove and inspect the magnetic screen in the transmission pump suction line.?

If P1 & P2 are dropping to zero, or close to, it when you make a shift then the indications are of worn/leaking clutch piston seals.

Going back to the OP you mentioned an overhaul of the engine and the torque converter but it's not clear if the transmission was also removed and overhauled. Has the tranny ever been out in your ownership of the tractor.?

 

[Dazcoy]

Yes we cleaned the magnet but only a little bit of shaving paste was evident. No the transmission hasn't been removed or touched as I am aware

 

[Nige]

Certainly if the problem only appears when the transmission gets up to operating temperature it sounds like hardened-up seals somewhere. Maybe take a good look at the transmission control valve and the seals that live between it and the transmission case. If that turns out to be a dry hole then I suspect the transmission is coming out.

 

[Wiggo]

We have had this machine for 4 years, the problem has always been the same, we have worked it for 3-4 hours per day until it starts to play up, park it over night and it operates normal for the same time the next day. We have checked the magnetic screen many times expecting to see signs of the problem. The filter has never had anything to talk about in it. I have no history on the transmission. I didn't want to pull the transmission if it's oil bypassing in something outside the transmission. It's like something opens up and bypasses at the same temp or operation duration with out fail and it not getting any worse over the past 4 years.

 

[Wiggo]

Back 3 years I asked a bloke that had run a few of the same machines about the problem. He said to drop the oil and run a heavier grade oil, and if it's something leaking it will improve. We changed it to a 50 grade, I think. It made no difference at all.

 

[Nige]

Back 3 years I asked a bloke that had run a few of the same machines about the problem. He said to drop the oil and run a heavier grade oil, and if it's something leaking it will improve.

Sorry to tell you but that's BS.

I'd still suggest to go for the control valve first (less invasive/less work) and if that doesn't fix it, well..........