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Hi all, we have an echo srm 3800 which we have had for a while now. Here lately, just after using it for 5-10 minutes, the gear box, not sure of the proper term for it, on the end of the shaft will get extremely hot. So hot, you can't use string or it will melt together and not feed out. After we found out it was doing this, we bought a new gear box and the same thing still happens. We bought a metal blade head for it since the string would not work but as I was using it today, and not for a long period of time, it got so hot, the whole head came off. The nut that holds it on was still attached, it just got so hot that it melted the plastic head around the nut.

I took the gear box off and can not find anything wrong with it, it has plenty of grease in it and in the shaft as well. It has a grease fitting on it and it gets greased periodically.

I hate to go out and buy a new one as I have a feeling it will have all kinds of emission crap on it and not run as good or last as long as this one. We do need a big one since we do cut some heavy stuff with it.

Remove gear head assy., disassemble completely, clean & inspect parts for replacement. There are bearings with different part numbers in unit. I think you will find bearings bad resulting in heat buildup.

I think I also read somewhere that if there is too much grease in the gearbox, it will overheat because grease traps heat better than air. :anyone:

Unforgiven said:

Hi all, we have an echo srm 3800 which we have had for a while now. Here lately, just after using it for 5-10 minutes, the gear box, not sure of the proper term for it, on the end of the shaft will get extremely hot. So hot, you can't use string or it will melt together and not feed out. After we found out it was doing this, we bought a new gear box and the same thing still happens. We bought a metal blade head for it since the string would not work but as I was using it today, and not for a long period of time, it got so hot, the whole head came off. The nut that holds it on was still attached, it just got so hot that it melted the plastic head around the nut.

I took the gear box off and can not find anything wrong with it, it has plenty of grease in it and in the shaft as well. It has a grease fitting on it and it gets greased periodically.

I hate to go out and buy a new one as I have a feeling it will have all kinds of emission crap on it and not run as good or last as long as this one. We do need a big one since we do cut some heavy stuff with it.

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Ok so let me get this straight. It gets so hot that it melts the string but not the string spool that would be the first part to get the heat and not the string. This does not seem possible. I have used all sorts of string that fused together just because is was crappy string(price does not make it good just expensive) I would suggest trying a different string first. One more thing OEM string does not make it good string either. Case in point I can go through a 100 ft of Husqvarna string in a day when the new string I use I will not go through that much in 2 months. Ok 2 things. The gear boxes get very hot. They have no cooling fins or real air flow. if you got a new one and installed it and it is still hot than that is probably the temp it is supposed to be.

BlazNT said:

Ok so let me get this straight. It gets so hot that it melts the string but not the string spool that would be the first part to get the heat and not the string. This does not seem possible. I have used all sorts of string that fused together just because is was crappy string(price does not make it good just expensive) I would suggest trying a different string first. One more thing OEM string does not make it good string either. Case in point I can go through a 100 ft of Husqvarna string in a day when the new string I use I will not go through that much in 2 months. Ok 2 things. The gear boxes get very hot. They have no cooling fins or real air flow. if you got a new one and installed it and it is still hot than that is probably the temp it is supposed to be.

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Gear boxes get hot, but they aren't supposed to start melting things. I am wondering if the OP put too much grease in the gearbox??

primerbulb120 said:

I think I also read somewhere that if there is too much grease in the gearbox, it will overheat because grease traps heat better than air. :anyone:

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Pure garbage OO grease has an R value substantially lower than air.
Overfilling leaves the grease no where to expand it when it gets hot so it blows the seals.
Bevel gears running is a pressurised housing suffer resistance from the pressure which generates more heat which generates more pressure.

bertsmobile1 said:

Pure garbage OO grease has an R value substantially lower than air.
Overfilling leaves the grease no where to expand it when it gets hot so it blows the seals.
Bevel gears running is a pressurised housing suffer resistance from the pressure which generates more heat which generates more pressure.

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Thank you for confirming that. I can't remember where I read it, but I think it's supposed to be filled with 30-40% grease. I put in grease until the head is quiet when turned (little to no gear noise.)

I am almost positive the string is not the issue as the same string gets used on a smaller echo with no issues and it does some heavy stuff as well.


As for putting to much grease in it, you talking about where the grease fitting is? How often are you supposed to grease that? Could there be too much grease in the shaft itself? As for the gearbox, I am trying to get that apart to check things out, just need the right pair of snap ring pliers to get the snap rings out. On the other end, it has what looks like a rubber seal. I assume that is supposed to come out but can't seem to get it to move without damaging it.

I think you're supposed to take off the grease fitting on the gearbox and blow the grease out with compressed air. I would not take the gearbox apart if I were you. As for how often to grease it, I would do it whenever it becomes unusually noisy.

primerbulb120 said:

Gear boxes get hot, but they aren't supposed to start melting things. I am wondering if the OP put too much grease in the gearbox??

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My point is that it can not be melting the string when it has the spool it has to travel through and the spool is not melting.

BlazNT said:

My point is that it can not be melting the string when it has the spool it has to travel through and the spool is not melting.

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It sounds like the bump knob is melting though.

We bought a metal blade head for it since the string would not work but as I was using it today, and not for a long period of time, it got so hot, the whole head came off. The nut that holds it on was still attached, it just got so hot that it melted the plastic head around the nut.

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primerbulb120 said:

It sounds like the bump knob is melting though.

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Lord how did I miss that? Irilly read that thread 3 times and it just did not register with me at all. I have got to do better with this.

Sorry to all for the bad answers!

get infra red temp gun reading and share?

I really don't get how the string would be melting but not the spool either. This same string has been used on a smaller echo and used to cut the same weeds and no issues at all so that is why I don't think the string is the issue.

What are you calling the bump knob? Is that the piece that you hit to feed the string out?

Ty for the replies so far.

OMG it's the line fusing together.
Most times from not letting enough line out

Unforgiven said:

I really don't get how the string would be melting but not the spool either. This same string has been used on a smaller echo and used to cut the same weeds and no issues at all so that is why I don't think the string is the issue.

What are you calling the bump knob? Is that the piece that you hit to feed the string out?

Ty for the replies so far.

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I had a homelite many moons ago. The strings also melted together when the bushing was going bad. The head being made of higher temp plastic- not quite the type an ashtray would be made of, but higher temp\harder than the string plastic is my guess.

According to the recycling code on the inside the heads they are High Density Polly Ethylene ( HDPE )
From there you get variations in the ratio of HDPE to fillers and they type of fillers used to bulk out the plastic.

So to melt the head it takes 250 f or higher
"can withstand somewhat higher temperatures (120 °C/ 248 °F for short periods, 110 °C /230 °F continuously)"
Like one of the last post said check you bearings.