Continuing transmission issues on 1977 Yard Man 8/26 - Snowblower Forum : Snow Blower Forums
 
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Old 02-10-2018, 11:51 AM Thread Starter
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Question Continuing transmission issues on 1977 Yard Man 8/26

Hello. I've noticed a couple issues with my 1977 Yard Man model 31850-8 snowblower's transmission. Hoping to get some help here. The observations:

#1: Reverse sometimes doesn't work. In either R1 or R2, it sometimes doesn't engage the wheels at all. I can push or pull the blower without any resistance. I tried running the selector across all forward and reverse ranges, no luck for reverse.

#2: When going down a mild slope with auger running, I had been hearing an occasional sharp "chunk" sound. I attributed this to a possible stone thrown from my neighbor's stone driveway, but then noticed this still occurred when no snow was being thrown or when auger wasn't engaged.

#3: When in any forward gear, I notice a random momentary drop in forward momentum. So every 6-8 feet, there is a very brief slowdown, and then return to normal speed. The engine is perfectly smooth during this.

A couple summers ago I replaced the drive belt and the friction wheel. This winter, I tightened the tension on the transmission shifting linkage (puts more pressure between friction wheel and disk).

I've attached a parts list PDF, one full low res and another detail in higher res. Last time I had the transmission open, I noticed slack in at least 1 of the chains, #64 was definitely loose. I know these sometimes stretch over time, so I'm curious if the shafts can be adjusted or if it is just better to replace the chains and shaft bushings. Maybe a chain is binding or skipping a tooth? Or maybe a gear tooth is missing?

No clue about the reverse. Toward the end of my stint outdoors this morning, reverse was working again.
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Old 03-02-2018, 07:43 PM Thread Starter
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Well, the machine died today, meaning the transmission wouldn't work in forward or reverse. I was able to trace the issue down to a very slack chain that had worn down a sprocket. This is part #72 in the PDF I originally attached, and had tons of slop.

I ordered the new sprocket and the bronze bushings, and this should tighten things up.

Just wish it didn't happen at the bottom of the driveway. I had to drag it 300 feet back, part uphill, in about 8 inch increments. Numbing the pain now with "liquid pain reliever."
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Old 03-02-2018, 08:44 PM
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Garage
I'm glad you got back to us especially with the pic. The worn gear is that little one? I'm surprised it lasted this long, that is very worn.

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Old 03-02-2018, 08:54 PM Thread Starter
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Yeah, I think what ended up happening is that one of the bronze bushings failed (one is seized in the other end), it loosened, and then every rotation had the chain skip a tooth. This had been going on gradually for at least 5 years, likely skipping more every year.
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Old 03-02-2018, 09:14 PM
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I hope you're replacing the chain too as it would also be worn and won't match the sprocket tooth pitch properly and lead to advanced sprocket wear again.
Also check the bearings (#34) for play on the shaft that the friction disc is mounted on. That friction disc should rotate smoothly without any sideways or up & down movement in it.
The rubber tire that the friction disc drives may be glazed and that may cause intermittent drive issues, especially in reverse. If water or snow finds its way onto the friction disc, or oil or grease, it will cause lack of friction to drive machine. Clean the friction disc and the rubber tire and if glazed, use a somewhat fine sandpaper to clean the glazing on the rubber tire.

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Old 03-03-2018, 02:47 PM
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First off, I'm not doing that well on the schematic, but I think I've figured out the gear that failed.
I have seen similar damage before where a gear is able to shift side-to-side when running. It caused the chain to chew up the sprocket, much like your example but not as bad. If that sprocket is capable of moving horizontally, maybe see if you can shim it to take up some of that slack, having the chain aligned between the 2 sprockets.

Good to hear you've fixed it. Thanks for getting back with both the problem and the fix.
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Old 03-04-2018, 03:28 PM Thread Starter
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I think I can explain better.

If you look at part #72, you'll see flange bearings #55 on both ends. You'll also see a sprocket hub tubing #59.

When I disassembled it, there were no flange bearings, just 2 thin brass washers, which I presume were the flanges. What happened to the rest of the bearings is anyone's guess. I suspect it was repaired improperly in the past because the bolt and locking nut were reversed.

In any case, I am really looking forward to eliminating the slop and getting a strong transmission back.
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Old 03-04-2018, 08:38 PM
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If those 2 bushings were gone, that would explain a lot. I'd also check the other 2 sprockets along with the bolt for excessive wear.
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Old 03-08-2018, 10:59 PM Thread Starter
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I just got the sprocket assembly from the parts guy. Came with bushings pressed in. HUGE difference in the small sprocket!

I've been watching a lot of Donyboy73 videos, and am going to apply his guidance to my snowblower this weekend. It's kind of a mess in the transmission area, so I'm curious what you use to clean the old grease off the parts. I was going to use carb cleaner and old rags to strip everything. Apply light amounts of lithium grease on the hex shaft, chains, and sprockets. Don also uses chain lube on most of the other moving parts and bushings.
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Old 03-10-2018, 06:33 PM Thread Starter
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I'm documenting this journey in case someone else has a similar issue. Nothing worse than finding a thread with no happy ending, right?

First off, the inside was filthy: blackened hard grease was coating just about everything, so I wiped down as much as I could with a rag soaked in straight gas and a followup wiping with carb cleaner and a rag.

While I had it apart, I removed another sprocket, which had a bronze tube inside to hold it more tightly against the shoulder bolt that went through it. All inner surfaces got a treatment of white lithium grease. The new sprocket I ordered likewise got a lithium grease treatment prior to installation.

Prior to application of lithium grease, I thoroughly cleaned all parts with straight gas and then carb cleaner. All the chains I serviced likewise had the same cleaning. The half-shafts have a long pin running through to toggle between dual wheel and differential wheel, and this was cleaned and lubed with lithium grease. The hex shaft that has the rubber wheel "gear" slider on it was cleaned and a thin film of lithium grease was applied...I thought shifting was good before, but now it is like butter!

All the chains got a spraying with chain oil, which I am starting to become a big fan of. The friction plate and rubber wheel were cleaned with a clean rag and carb cleaner.

It is pretty much unstoppable now! I ran it through all the gears and applied as must resistance I could muster and there was no bogging or slippage.

Lessons I learned:
1. Don't skimp on annual inspection of the critical parts. While this post is about the transmission, this would include the auger gearbox and belts as well. I learned that a slack chain is a signal that something is wrong, and I made the mistake of ignoring it because I didn't think it was an issue. This is also a good time to check the friction plate, rubber wheel for cracks, hex shaft for corrosion and build-up, tires for cracks, etc.

2. Take the time to clean and apply grease. This means potentially removing the half shafts, cleaning off old grease, and applying new white lithium grease. I got a tube at Home Depot for I think $4. It has consistent viscosity in all temperatures (some grease gets gummy) and when applied to clean surfaces it also suppresses corrosion.

3. Lube your chains and bushings with chain oil. I used a product called Blaster Chain and Cable Lubricant which was applied liberally on the chains and the drive shaft bushings. I really like this lubricant because it sticks well and is very slick.

4. When replacing nuts and bolts to exterior surfaces, take a moment to use an anti-seize compound to make future servicing easier. The classic places are the skid shoes, but also consider the belly pan bolts and wheel bolts/studs/nuts.

So I hope this helps someone if they find this post in a search. I'm actually very happy to breathe new life in to this 40 year old snow blower, and I pretty confident it has another 40 years ahead of it.
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