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My mower deck won't disengage

Disengagement of my mower deck blades, slow or total lack thereof, that's my problem.  You're all done mowing or you want to take a shortcut through the garden and not throw clippings all over the place.  You disengage the clutch on your mower deck, or so you think, and boom the clippings keep flying!  What the heck?  I wear hearing protection when I mow so the problem is worse, you may not realize the mower deck has not disengaged.

My Sears 42" mower deck.

Yep, that's the problem on my Sears deck.  The mower won't disengage and it's slowly been getting worse.  In the past I have worked on the tensioning idler release spring.  I found the coils of this spring drag across the edge of the tensioning idler support pivot bracket (Idler Arm).  So I found a piece of PVC tubing to partially support this spring so it is less likely for the spring coils to drag on the edge of the bracket.  This fix cured my problem of the deck not disengaging for more than a year, BUT, it's back!

Deck not disengaging problem is back!

This time I thought I'd get more serious because this non release problem has gotten more serious.  This is a substantial safety hazard!  My wife uses the tractor for various reasons and may occasionally engage the mower deck and cut some grass.  I'm pretty sure she would not realize that the mower deck has not disengaged when she was through with it.  To compound the safety issue, this failure mode lets you start the tractor engine with the mower deck blades still engaged!  The safety switch is on the lever behind the dashboard of the tractor and this switch will indicate the deck clutch is disengaged!

Disengaging failure related to blade brakes

Most of these mower decks have two blade brakes.  The blade brakes are mounted on pivots and are disengaged by small rollers on their mounting brackets.  These blade brake rollers both glide on surfaces on the idler tensioning pivot bracket (Idler Arm).  After looking very carefully in the Sears manual exploded drawings of the mower deck for model number 917.275820, part or Key number 55 "Arm Idler" I could see that the blade brake roller had worn a substantial notch into the roller surface of the "Idler Arm".  So much so that when manually trying to release the "Idler Arm" tension a definitive binding occurred at this notch.  The notch should simply not be there!

Sears exploded drawing of my mower deck:

Exploded Drawing

Disclaimer:

Please remember you must take responsibility for this repair.  Certainly a mower deck is a dangerous piece of equipment.  On this web page I have documented what I have done to repair this particular disengagement problem on this particular mower deck.  You must be the judge if your mower deck remains safe after this repair, or should you replace the deck?

I could replace the deck's Idler Arm

Yes I could, but I could also tell that the blade brakes still had plenty of clearance even with this excess wear on the Idler Arm, so why not fix it!  You can see in the picture their are two notches worn in the Idler Arm.  Those notches prevent the deck from easily disengaging.

So I used my belt sander and magicut file to remove enough material to make the notch disappear and restore a nice flat roller surface.

Replace the deck Idler Spring? (Maybe not)

Please note that on the Internet I've seen numerous "posts" recommending replacing the Idler Arm spring (Key No 148).  This "spring" quick fix may work temporarily but it's likely your deck is not as safe as it should be!

After filing a definitive improvement

After I eliminated the first wear notch the mechanism disengaged much more easily.  However, I could still fell it hanging up some.  So I examined the surface on the Idler Arm that disengages the second blade brake and sure enough there was another notch worn on what apparently should be a flat surface.  Again the blade brake still had plenty of clearance even with the wear, which meant I could safely grind out this wear point on the mower deck too.

It's very difficult to see, but the "U" shaped notch in the Idler Arm also has a notch worn into it.  Again even with this wear the blade brake had plenty of clearance.   So, I ground out this notch as well.  This repair was done exclusively with my magicut file.

What's a magicut file?

Years ago I ordered a downhill snow ski tune-up kit.  This kit came with all the tools needed to maintain a ski.  One of the tools was a "magicut" file.  This file makes all the difference when it comes to removing metal from your mower deck parts or anywhere.  I started seriously skiing in 1978 ( a long time ago! ), which means this file is now about 32 years old, and as far as I can tell it works like it was new!  I even used to use it to sharpen my mower blades.  But recently I've been experimenting with my belt sander for this task.

What a difference in the disengagement!

With the parts reinstalled there is a very substantial improvement in the disengagement of the mower deck blade clutch.  The mechanism now moves very smoothly.  I could have replaced the release spring, but with the Idler Arm restored the spring really did have enough force.  I could tell starting out that simply replacing this spring (Key No. 148) would probably not permanently fix the problem.

Why the wear on the mower deck idler arm?

I can see, with the mower operating, the Idler pulley and arm are constantly oscillating.  This could be do to belt tracking, blade balance (I balance my blades, even brand new ones, they need it), or just engine piston pulses, etc.  I believe this oscillation is normal.  But it means the little blade brake rollers are constantly rolling a small distance back and forth on the Idler Arm.  If the rollers were to stick, for sure, there would be a lot of wear.  They tend not to lubricate mower deck moving parts simply because there is so much dust that can turn into "sand paper".  These little rollers probably have an internal flat spot raising their friction and thus over time there is wear on the Idler Arm.

This fix should last several years

I think this fix will last quite a while, and better still, there seemed to be enough material on the Idler Arm to allow this repair to be done several times before blade brake interference becomes an issue.

Another story: I've already replaced both blade spindles on this deck!

The original Sears spindles are pretty light duty and the castings simply break!  The replacement spindles I bought were much heavier duty and cost less too.

Well I hope this helps with your mower deck.  This has been a disengaging experience!

Bob