Gearbox lube for string trimmer

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I've got a few year old Ryobi straight shaft string trimmer and there is a bolt which apparently allows service access to the gearbox. The manual doesn't mention anything about gearbox maintenance, but if it's maintenance-free, why not make it sealed?

Unless I hear otherwise, I'll probably just leave it alone, although I have thought about spraying out the gearbox with something like carb cleaner, letting it dry out, and then relubing it. Would this be wise, and if so, what type of grease/gear oil would you recommend?

Thanks,
Matt
 
if its got any seals they are probably shot. just squirt some grease in there and button it up. thats what i did for mine and my hedge trimmer too. it quiets the gearbox down a bunch.
 
On mine there a small machine screw up on the collar of the gearbox. This screw is not a grease port, it holds the gearbox to the shaft drive and prevents rotation of the gearbox in relation to the hollow shaft. The screw works in conjuntion with the clamp bolt futher up the gearbox/shaft.

I end up taking the whole thing apart to re-grease the gears and just use #2 synthetic grease. I can't find a specific lube recomendation from Ryobi but this is what lube is recommended for my hedge trimmer gear box. Some Toro mower self propel gears use #00 grease which is "semi-fluid".

It really bothers me that these small gear boxes get so hot. All of mine do it but it just doesn't seem right. I have yet to have one fail on me but I'd rather see them with good seals and bathed in gear lube instead of having to hope the grease doesn't just sling off the gear teeth after running for 10 sec.

I may be using the wrong spec grease but since these boxes are not really sealed some lube is better than no lube. Good luck with it.
 
Dead thread revival:
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I've had warranty work done on the gearbox of my Troy-Bilt once already and now the new one is making noise already.

Shame too because the powerhead seems to be pretty good.

The gearbox does get hot. Right away, out of the repair shop before I even bump fed it or put it under load....and it whines. The repair shop didn't repair it, They just put a new one on.

The stupid thing is that I have this sealed gearbox on my cheap Poulan brush cutter attachment and it doesn't get that hot at all. Nor does it whine.

So, #2 syn grease sounds like a winner. What concerns me is if I have to set the pinion depth on it or anything else tricky. I haven't taken it apart yet. I'm probably overthinking it.
 
On a string trimmer, where is the gearbox? I thought they were direct drive, with a small centrifugal clutch for ones that stop at idle.

Also, I've wondered about trying to grease/oil the gearbox on the lawnmower for the drive, but then I shake my head and tell myself I'm being too OCD
grin.gif
 
Originally Posted By: Nick R
On a string trimmer, where is the gearbox? I thought they were direct drive, with a small centrifugal clutch for ones that stop at idle.


Down at the end of the shaft on a straight-shaft trimmer. There's a gear box with beveled gears. On a curved-shaft trimmer, there is no gear box because the flexible cable inside the shaft changes the direction of power from "angled" to "vertical".

Originally Posted By: Nick R
Also, I've wondered about trying to grease/oil the gearbox on the lawnmower for the drive, but then I shake my head and tell myself I'm being too OCD
grin.gif



It's not unreasonable to want to service the transmission on the mower. I need to do that on my Lawn-Boy 10330 this season.
 
Gear boxes should be less than 50% lube. Grease does not transfer heat well, but air does. If you fill a gearbox all the way up with lube it will get hotter than [censored], and hot very quickly. After a gear box has lost some of its grease it will actually run cooler.
If your gear box on your trimmer has a service port then you can change out 98% of the lube without taking it apart.
Get the gearbox warmed up by running for a few min, and remove the service screw. Point the hole on the gearbox away from you and blow compressed air across the service port until all the grease has sprayed out. Try to blow it on a towel to prevent a mess. Those gearboxes use a high sulfur grease like this stihl part number. #0781-120-1117. Estimate the volume of the air space in your gearbox, and fill to aprox 40% by volume. Enjoy. If it has no service port remove the bump feed head. Then remove the output bearing from the gearbox housing. You will need a pair of internal snapring pliers most likely, and a heat gun. A butane torch is too hot. remove the snapring, and heat the gearbox to aprox 240f. The bearing should fall out when tapped on the ground. Remove the factory grease with compressed air, and fill to 40%. Put the bearing in the freezer for 10 min, and reheat the gear box housing. The bearing will fall in to place. As the bearing warms up, and the housing cools off(about 10 sec) the bearing will be cold welded in place. There is a lip that keeps the bearing from going to far in so seat it all the way in.
 
Last edited:
Originally Posted By: 660mag

If your gear box on your trimmer has a service port then you can change out 98% of the lube without taking it apart.
Get the gearbox warmed up by running for a few min, and remove the service screw. ...


I removed what I thought was a service screw. Couldn't get anything out. Put a few drops of gear oil in there just to see what happens.
It leaks out.
lol.gif

opened it up. there was a little smear of grease on the inside case. Not really an appreaciable amount.
Wiped off the grease and applied new grease. Quiet and running a lot cooler now.
 
Originally Posted By: 660mag
Gear boxes should be less than 50% lube. Grease does not transfer heat well, but air does. If you fill a gearbox all the way up with lube it will get hotter than [censored], and hot very quickly. After a gear box has lost some of its grease it will actually run cooler.
If your gear box on your trimmer has a service port then you can change out 98% of the lube without taking it apart.
Get the gearbox warmed up by running for a few min, and remove the service screw. Point the hole on the gearbox away from you and blow compressed air across the service port until all the grease has sprayed out. Try to blow it on a towel to prevent a mess. Those gearboxes use a high sulfur grease like this stihl part number. #0781-120-1117. Estimate the volume of the air space in your gearbox, and fill to aprox 40% by volume. Enjoy. If it has no service port remove the bump feed head. Then remove the output bearing from the gearbox housing. You will need a pair of internal snapring pliers most likely, and a heat gun. A butane torch is too hot. remove the snapring, and heat the gearbox to aprox 240f. The bearing should fall out when tapped on the ground. Remove the factory grease with compressed air, and fill to 40%. Put the bearing in the freezer for 10 min, and reheat the gear box housing. The bearing will fall in to place. As the bearing warms up, and the housing cools off(about 10 sec) the bearing will be cold welded in place. There is a lip that keeps the bearing from going to far in so seat it all the way in.



Hmm, interesting info here.

My Echo SRM-210 has a "grease port" on the head. It says that it takes lithium grease. That's what I found it full of and that's what I replaced it with when I tore into it one time. It would be nice if they used a fluid bath like differentials instead of grease that you need to balance this air space against actually getting grease in the right places.

Maybe I should crack into it again this spring just for "fun". On the other hand if it isn't broke....
 
You could always add a little gear oil to the grease...make it a little more fluid.

I popped the plug out of a newly acquired Husqvarne, and it looked like a bentonite grease? I was thinking of flushing it...and using a regular grease.
 
i have a polan PL25 trimmer that when i got it the gearhead had stripped out due to lack of grease. Fortunately was able to buy a new gearhead for $30 from partstree. the new one came with minimal grease. i ended up cleaning the new grease out prior to using it and using lucas red n tacky, been great for past 3+ years.
I know on mine the input wire shaft spins at 2-cycle engine speed which is 4000+ rpm under throttle, so with gearspeed in the head fairly fast so you want a light grease that will give up oil easily, which redntacky does well. I had tried lucas polyurea grease and found it was too hard a grease. Probably any lithium complex wheel bearing grease would work well, I'm sure the original oem grease is bargain basement lithium and they put less than enough in.

i find it hard to believe any manuf. would use bentonite grease. first it's more expensive and not needed. bentonite grease is kind of a paradox, the bentonite thickener is high temp but the oil in the grease usually can't make it to the high temp the thickener does, so whats the point. lithium complex is more than good for this type of application. when you're worried about water washout then use an aluminum complex grease which can be hard to find locally, or a marine calicum sulfonate grease like pennzoil or lubrimatic which you can usually get at walmart.
 
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