D7F Powershift problem

[chuck767]

On my D7F, after initial start up for the day, I have to wait about 5 minutes before I can pull the lever into forward or reverse. This wait seems to be getting worse, (longer) as time goes on. The length of the wait seem to be dependent on the angle the dozer is setting.

Anyone have any idea what is causing this?

The tranny oil level is right at the full mark.

Thanks,
Chuck

 

[DRMCO D600]

Hi Chuck,

Low transmission oil pressure comes to mind.
I stand to be corrected

Best of luck

 

[Nige]

I'd say that somewhere in the transmission oil lines on the suction side of the pump you have a seal/gasket/o-ring that is leaking, allowing the pump to suck air until such time as the oil warms up a bit and the pump actually starts sucking oil instead of air.

 

[Bluox]

Chuck,
Clean out the magnetic screen.Then check pump pressure.
Good luck
Bob

 

[chuck767]

I'd say that somewhere in the transmission oil lines on the suction side of the pump you have a seal/gasket/o-ring that is leaking, allowing the pump to suck air until such time as the oil warms up a bit and the pump actually starts sucking oil instead of air.

Nige, Thanks, I will check for suction leaks.

Anyone have a schematic/photo/diagram of the "transmission oil lines on the suction side of the pump"?

Thanks,
Chuck

 

[wilko]

If there's a pickup screen, you have classic symptoms of sludge/spooge buildup.

 

[Z2898]

First 2 checks I would make are: 1-Transmission oil pump pressure (should be around 400 psi) pressure tap is right on the top of the pump. 2- Linkage adjustment ( possible adjustment incorrect.)

You mentioned it has been getting worse over time. How much time? Hours-days-years?

When it finally starts to move after initial engagement does it work good all day? No trans slipping?

Have you had any transmission related failures recently? Pump-valves etc?

 

[chuck767]

First 2 checks I would make are: 1-Transmission oil pump pressure (should be around 400 psi) pressure tap is right on the top of the pump. 2- Linkage adjustment ( possible adjustment incorrect.)

You mentioned it has been getting worse over time. How much time? Hours-days-years?



When it finally starts to move after initial engagement does it work good all day? No trans slipping?

Have you had any transmission related failures recently? Pump-valves etc?

I won't use the machine much, so every couple months I fire it up and It seems to be getting worse.

Once I start using it, it works fine, no slippage at all. It needs to sit at least over night to have the problem again.

No tranny problems at all and I have had the machine for 12 years.

 

[chuck767]

If there's a pickup screen, you have classic symptoms of sludge/spooge buildup.

Anyone know if there is an intake screen and how to get to it?

 

[Check Break]

Anyone know if there is an intake screen and how to get to it?

If you had a screen that was blocked, your problem wouldn't clear up the way you describe. Go with Nige's comment and start looking for air. Sounds like your trans pump is loosing prime.

 

[wilko]

If the screen was completely or mostly blocked with metal or seal material it wouldn't clear up, but if it has a thin layer of "gelled" oil and water it would start to flow after it warmed up. I've seen it happen. I also have a machine that sucked air like Nige says. On that one a few extra gallons of hytran is the accepted go around for the problem.

 

[Bluox]

If you have had the tractor for 12 years and have not cleaned the trasmission screen you shoud hire someone to service your tractor.The screen is below the transmission pump 4 3\8 nuts on cover.10 bucks says its full.
Good luck
Bob

 

[chuck767]

If the screen was completely or mostly blocked with metal or seal material it wouldn't clear up, but if it has a thin layer of "gelled" oil and water it would start to flow after it warmed up. I've seen it happen. I also have a machine that sucked air like Nige says. On that one a few extra gallons of hytran is the accepted go around for the problem.

I tried two extra gallons of oil and the problem cleared up. I need to find the suction leak, but there is no hurry now that things seem to be working fine.

I also need to take Bluox's advice and service intake screen.

Thanks all for all the response on my problem.

Chuck

 

[wilko]

......... but there is no hurry now that things seem to be working fine.



Chuck

I think I wouldn't wait too long. Where I did it, it's an accepted "fix", no down side, won't hurt the machine, everybody does it. That may not be true with the D7F, and you sure don't want to find out the hard way.

 

[DPete]

We had an 8H suction leak on the bottom plate o-ring on the mag filter the one you never remove. Just an example of what can happen

 

[68M]

Late D7F's, with the small transmission (like a D6c) have an "o" ring on the suction line at the bottom of the transmission housing, where it bolts onto the backend. They can suck air here if the "o" ring is not good. Have seen mechanic's leave this out causing the same problem you have. Only way to check this is pull the trans out. D7F's can also break up their brake linning's and the pieces get sucked into the suction line. If it has the later trans there is a suction passage in the back housing, under the bevel gear, leading to where this "o" ring is. The passage is an odd shape and it is hard to see if there is anything in it. I have see brake linning jammed in here causing a suction problem. Transmission screen is near the trans pump on the back right hand side of the motor and should be checked first, also check the "o"rings on the top and bottom of this screen, and also all the "o" rings on the suction hose from the back housing to this screen. Could also be a worn pump but does sound like a suction leak. D7F's also have a tendency to lose their transmission pressure when working on steeper slopes, Caterpillar's recomendation to fix this is to run your transmission overfull by 2 gallons. Good luck 68M