changing really old gearbox oil

[dejswa]

I recently purchased an old bush hog rotary 10' cutter - 3 gearboxes.

The gear oil looks really nasty, so I would like to do a 'flush' if possible or practical.

So far, I have suctioned the oil out using a suction pump can from Northern Tool. Works OK, but the oil is really thick - took about an hour for each gearbox to empty.

Now what I am thinking about doing is to add some 30 weight oil to each gear box, then run the cutter for about a minute, then suction again and maybe repeat until I get the gunk out.

Then finally add the gear oil.

This is similar to what you can do with a really dirty crankcase.

Does this make sense or am I making things way too complex?

DJ

 

[mattman]

Sounds good to me. I might fill mine with diesel and run it for a just a minute to really clean the insides up. Is there a drain for the gearboxes??

 

[rdln]

yeah, I was gonna say diesel also, it will carry more stuff away. Arent there any drain plugs?

 

[stuartshomepc]

I recently purchased an old bush hog rotary 10' cutter - 3 gearboxes.

The gear oil looks really nasty, so I would like to do a 'flush' if possible or practical.

So far, I have suctioned the oil out using a suction pump can from Northern Tool. Works OK, but the oil is really thick - took about an hour for each gearbox to empty.

Now what I am thinking about doing is to add some 30 weight oil to each gear box, then run the cutter for about a minute, then suction again and maybe repeat until I get the gunk out.

Then finally add the gear oil.

This is similar to what you can do with a really dirty crankcase.

Does this make sense or am I making things way too complex?

DJ

If I were to go the motor oil route I would heat the bulk oil up first. Get an old metal pot from the kitchen and set it on the BBQ grill for a while. When it starts to have wisps of vapor coming off of it it's ready. You don't want it boiling as they may hurt the seals. Add the hot oil to the gearbox and run it for a minute or two. The hot oil would thin out the old gunky gear oil and let you siphon it out. In the end whatever residue left in there would be a lubricant. Not true with a flush with Diesel fuel. I used to flush engines with kerosene but I was always leery of having solvents in the engine. The hot oil does wonders.

 

[dejswa]

Thanks, good ideas from everyone here.

Yes, diesel or hot oil makes more sense. I was thinking 'motor oil' since I did not want the residual fluid to thin the gear oil too much.

There is no drain on these gear boxes, just a filler hole and a hole about mid way down that I am told is the "fill to" level. If I am wrong, let me know.

Don't know why there is no drain plug on the side near the bottom. Would make life easier. But would still leave a bit unless you tilted the machine.

On a search of this thread, I read about using the FEL to tilt the mower to help empty the box, but wouldn't really do much unless you got it to 90 degree tilt. Not sure I want to do that with this big and OLD mower, something might give or being new to this, I might get squashed!

Will let you know how it goes!

DJ

 

[phyxer]

Are you sure the stuff in there is gear oil and not grease? I've heard of folks filling the gear boxes with grease when they start to leak to keep from having to repair/rebuild the gear boxes. Just a thought

Troy

 

[DieselPower]

phyxer brings up a good point. Someone may have installed a NGLI #0 or #00 grease to try to stop leaking seals. These greases are semi-fluid and the #00 could easily be mistaken for really thick gear oil.

 

[dejswa]

Grease in the gearbox?

The seller of this mower said that if he had decided to keep it he was going to put 'synthetic grease' in the gearboxes. I wasn't sure what he meant - like squirt a grease gun into the filler hole?

Would take a lot of grease tubes, I guess. Maybe that would work if you really topped it off and did not have it sticking to everything except the gears.

 

[Diamondpilot]

Scrape underneath the deck where the shafts come out and look for a drain plug. If I could not find a drain plug I would go the kero or diesel route. What little is left will evaporate after a few days of use.

Chris

 

[DieselPower]

Grease in the gearbox?

The seller of this mower said that if he had decided to keep it he was going to put 'synthetic grease' in the gearboxes. I wasn't sure what he meant - like squirt a grease gun into the filler hole?

Would take a lot of grease tubes, I guess. Maybe that would work if you really topped it off and did not have it sticking to everything except the gears.

Yep, grease in a gearbox. Some gearbox's actually spec either a NGLI #0 or #00 grease as the preferred lubricant. It's actually pretty common in rotary gang mowers and some bat wing mower gearbox's. These type of greases normally have a solid film lubricant and have much higher anti-oxidant additive packages. Here's a example of what I'm talking about. Millennium 2200.