# Craftsman 247.88790 (9 HP, 320cc) keeps throwing rubber friction ring (root cause fix)



## XJ4fun (Feb 22, 2021)

FYI. If you have a blower with a 'friction drive' system, where the rubber friction ring/disc keeps popping off (under load) the metal friction disc assembly, the root cause may be the metal disc assembly itself.

My 247.88790 kept popping the rubber friction ring/disc. I initially replaced 'solely' the friction ring, making sure the metal friction disc wheel that holds the rubber disc was properly torgued, etc. Still kept popping off. Reassembled the rubber ring several times with no fix in sight.

Ultimately, I replaced virtually all the main internal drive components (noted below), with no fix in sight (rubber disc kept popping off under load). Finally I concluded there was only one option left, which was a problem with the metal friction disc housing that holds the rubber friction disc.

History of repairs

First - Replaced 'solely' the rubber friction ring/disc - 935-04054 (ring that was actually popping off). This didn't fix it.
Second - Replaced the actual metal friction plate (656-04025A), as it had worn ring depressions in it from years of use for each gear selection That didn't fix it.
Third - Replaced the drive clutch control cable (746-04229) as the old cable was badly stretched. Adjusted new cable, which didn't fix the problem.

Root cause - The outer metal lips of the metal friction disc wheel assembly (2 halfs bolted together that holds the rubber friction disc ring), had stretched from years of pressure applied to it under drive conditions. The inside diameter of the bolted metal assembly (at the lip) measured 42mm. I compressed the metal ring lips down to 38mm using a vise. The new rubber ring outside diameter measured 51mm. Reassembling the rubber ring into the smaller (38mm) assembly has held for several snow removal cycles.

The easiest fix for this (looking back) would have been to replace the entire friction disc assembly as a unit (684-04159)..


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## Big Ed (Feb 10, 2013)

But then how would you learn?


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## JLawrence08648 (Jan 15, 2017)

On some units, specifically Murray built, you cannot buy the rubber ring, you buy the metal ring with the rubber on it.

But it's good to know especially if the rubber is very worn it probably puts more pressure on the metal. Thanks for the tip.


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## XJ4fun (Feb 22, 2021)

Big Ed said:


> But then how would you learn?


Excellent point . I did learn a ton on how friction drives work and the 'hidden' things that can cause them to fail .


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## XJ4fun (Feb 22, 2021)

JLawrence08648 said:


> On some units, specifically Murray built, you cannot buy the rubber ring, you buy the metal ring with the rubber on it.
> 
> But it's good to know especially if the rubber is very worn it probably puts more pressure on the metal. Thanks for the tip.


I initially noticed that most parts web sites suggested replacing the entire friction disc assembly (684-04159). In hindsight, that would have been a simple one time fix . I just didn't see the point in replacing the entire assembly when (it appeared) that only the rubber ring was worn. 

Even though I've now fixed my original friction disc metal frame, I did buy a full replacement assembly (684-04159) as a backup.I figure the metal frame may fail at some point due to metal fatigue.


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