Old Mustang 1200 drive issues

[BrianBryan]

70's era Owatonna Mustang 1200 Loader. Engine is good but will not go forward or reverse on either side. The secondary sheave spins and responds to the throttle so I believe the belt is fine but the shaft does not spin. Anybody have any suggestions as to what could be wrong. I don't even know how the shaft is supposed to engage an spin. Thanks for any help.

 

[BrianBryan]

When engine is off, I can spin the shaft with my hand and it spins freely from the sheaves. Seems to me the shaft should be connected to the sheaves with a pin. But i can't see it. Does this make sense?

 

[BrianBryan]

I think the pin has been sheared off since I can see a bit of a bump where the pin should be.

 

[Sapientoni]

Does it have a hydraulic feed to the sheave on the gearbox? The sheave on my gearbox also has issues. working loose. I have pinned it. Should be a tight fit on the shaft but mine is very loose and wants to flop around some. A keyway is supposed to do the driving and a setscrew securing it in place. but again, at some point before I got my {1972} in 1985 it was allowed to spin and create a loose situation. Replacing the shaft in the gearbox would and maybe boring out and truing up the sheave would eliminate the flopping. It causes the rotary hydraulic coupling to leak and fail.

 

[BrianBryan]

Yes, there is a hydraulic feed. But the problem is on the shaft for the secondary sheaves. I need to remove the shaft and put in a new pin.

 

[T-rustyfix]

It looks like there may be a bigger problem. The picture seems to show a crack around the cast sheave pulley.

 

[BrianBryan]

It looks like there may be a bigger problem. The picture seems to show a crack around the cast sheave pulley.View attachment 9812

Yes, that's gonna have to come out. A welding/machine shop may be able to fix that. Do you know if I need to open up the side cover to get at that shaft? I've already remove the union for the split shaft.

 

[Sapientoni]

When engine is off, I can spin the shaft with my hand and it spins freely from the sheaves. Seems to me the shaft should be connected to the sheaves with a pin. But i can't see it. Does this make sense?

Does the drive shaft from the engine spin? My 1700 had the drive coupling (a Ford clutch disc minus the linings) fail shortly after I got it. The center disc and springs disintegrated. A trip to the clutch rebuilder, acquiring a disc without the linings, drilling holes in the appropriate place to bolt to the flywheel, and I was back in business. This failure resulted in no hydraulics as I was replacing the drive belt and wanted to lift the arms to get clearance into the engine/trans area.

 

[BrianBryan]

Does the drive shaft from the engine spin? My 1700 had the drive coupling (a Ford clutch disc minus the linings) fail shortly after I got it. The center disc and springs disintegrated. A trip to the clutch rebuilder, acquiring a disc without the linings, drilling holes in the appropriate place to bolt to the flywheel, and I was back in business. This failure resulted in no hydraulics as I was replacing the drive belt and wanted to lift the arms to get clearance into the engine/trans area.

Yes, the drive shaft from the engine spins, and the primary sheaves seem to work fine. Its just the secondary shaft that doesn't spin. From the picture it looks like the pin holding the the sheave to the shaft has been sheard off.

 

[Sapientoni]

I don't know if you can get a replacement sheave assembly. My 1700 has the input from the engine, a Cessna hydraulic pump on the right side (flange with female input of the pump shaft), and an output shaft with the sheave on it. Leaking hydraulic union allows the speed adjustment to drift back to low as the spring loaded sheave reverses the hydro sheave due to the leakage. I had no guidance for the adjustment of the spring loaded sheave when I replaced the belt and shortly after the new belt broke. I asked the factory about the adjustment, got no response but they replaced the belt under warranty without comment. I had not asked about that. I have since found an industrial belt that's cheaper and has maybe one dimension a little different but it works great. It's a learning experience for mechanically inclined. My industrial experience helped a little.

 

[Sapientoni]

Yes, that's gonna have to come out. A welding/machine shop may be able to fix that. Do you know if I need to open up the side cover to get at that shaft? I've already remove the union for the split shaft.

 

[Sapientoni]

The 4 bolt flange bearing also looks toasted. There's another bearing supporting the extended shaft. Probably it extends thru the gearbox to the pump out put (if like my 1700). The gearbox probably needs rebuilding or replacing. There's lot of pressure on that short shaft when the belt is properly tightened. If the spring loaded is too loose, it will have a lot of slip at the lowest speed. Too tight and it will break something when you tension it to high speed. While you've fought that heavy gearbox out, do it all correctly and then cruise it. For certain have that sheave tightly fitting to the shaft. A dognosed setscrew will help secure it better as the setscrew should be locating it pushed all the way to the bearing collar on the gearbox output.

 

[jimsdog]

I don't know if you can get a replacement sheave assembly. My 1700 has the input from the engine, a Cessna hydraulic pump on the right side (flange with female input of the pump shaft), and an output shaft with the sheave on it. Leaking hydraulic union allows the speed adjustment to drift back to low as the spring loaded sheave reverses the hydro sheave due to the leakage. I had no guidance for the adjustment of the spring loaded sheave when I replaced the belt and shortly after the new belt broke. I asked the factory about the adjustment, got no response but they replaced the belt under warranty without comment. I had not asked about that. I have since found an industrial belt that's cheaper and has maybe one dimension a little different but it works great. It's a learning experience for mechanically inclined. My industrial experience helped a little.

What is the number for the belt? Jim

 

[Sapientoni]

I'm 250 miles from that machine right now. I don't remember exactly but I think it was a 2" X 50" something X 3/8 " thickness. I thing the original was a 1/2" thickness but I didn't find that in the catalog. Almost ever part in every machine is off the shelf from somewhere. It's a "cogged V-belt for a variable drive". You have to measure the outer circumference. McMaster-Carr only show 1.187" wide. I'm sure It's closer to 2" . I don't have time right now to search more. I'll comment again later.

 

[jonesallu]

The Parts Manuals for the 1200 and 1700 show different belts. The part number for the 1200 is 020-26433 and matches another thread on this site.

Al Jones

 

[T-rustyfix]

I rebuilt this part back in ‘21 here is a post with the details.

Thread 'Rebuilding the driven variable sheave'

Oct 22, 2025

In October of 2021, the driven sheave on my ‘73 1200 sheared off its drive lock pin. I replaced it several times, and those also broke. The sheave was wobbling on the shaft and the play around the pin from the cast iron was slamming the pin ends until they broke off. It was clear that it needed attention. I was in the middle of a foundation dig, but she went up on blocks anyway and I took her sheave out. For two weeks, I used my friend’s abandoned shop and junkyard to put together a plan and engineer an improvement for this component. He had an old 14” metal lathe and a smaller 6”...

• T-rustyfix
• Replies: 5
• Forum: Mustang Skidsteer Forum

• 

 

[BrianBryan]

As happed to T-rustyfix, the fixed sheave on my 70's era 1200 sheared off the drive lock pin and damaged the fixed sheave in the process. The sheaves were wobby on the shaft and the 3 side bolts had worn away the holes on the moveable sheave. I didn't know how to repair it and a welding repair was not possible because the sheaves are cast iron. T-rustyfix shared his experience and pictures and I used that information for my own repair. I found a local machine shop, Alfa Machine and Tool Co. in Whitby, Canada, and had them build a similar DonutDrive. The shop also built new cast iron bushings to fix the wobbly sheaves and new cast iron bushings for the side bolts as well. Then I used a 6" long 3/8" diameter Grade 8 bolt as the drive pin. Hoping to install it tomorrow along with a new belt.

 

[jonesallu]

As happed to T-rustyfix,... Hoping to install it tomorrow along with a new belt.

Brian,

Looking good! I hope it gets you back in operation. Thanks @T-rustyfix for posting your fix to help others out.

Al Jones

 

[T-rustyfix]

Glad to hear the post was helpful.

 

[BrianBryan]

Tried today to get the sheaves installed today but was stymied. First snowstorm of the season did not help. I wanted to first change the belt but I am unsure how to get the hose off the drive motor sheave assembly. The rotor union at the sheave seems fragile so you can't really pull hard with a wrench. Any suggestions?