MTD tractor

jimengeleSeptember 10, 2013

I have the option to have a tractor for free if I can fix it. There are a bunch of problems with it that I think I have correctly identified and come up with solutions. Some of those I would like to run by the forum to see what others think starting with the biggest problem, the transmission.

I was test driving this "free" tractor, and It ran fine. I drove around a bit and then I was having trouble going into neutral and then forward. When I finally did move forward, I heard a crunching sound and the transmission case busted open. I have since taken it apart after watching youtube videos and looking up the parts diagram online. The part that broke, is a bolt that holds the 'spider' gears of the differential together. The bolt is broken right where the threads are and I can't find a nut or the broken off part anywhere(I have the bolt with aluminum washer). This actually seems like an easy fix to me. I think I can just put a bolt in there with washers on either end, locktite the nut on it, make sure it's short enough that it won't hit the casing. I'm wondering two things: Can it really be that simple, and: what caused the bolt to break in the first place? There shouldn't be any torque on these gears, they float freely transferring power from one side to the other as needed right?
Unfortunately, the parts diagrams online don't show the differential parts, they only list the differential as a whole, $190. The broken casing I am JB welding back together and maybe some fiberglass reinforcing over the outside (the upper half is undamaged, only the bottom case is broken).

MTD 13ag675g033
transmission: 618-0163A

I will post pictures if needed.

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Chewing gum would be as effective as JB Weld and/or/including any kind of superficial resin overlayment.
Yes, there is torque transmitted through the spider gears any time the tractor is moving under power.
The spider gears carry half the load when traveling straight ahead, as does each of the side gears.
The spider gears along with the side gears allow the 2 axle shafts to move at differential speeds (hence the name "differential") during cornering to keep the tires from having to slip or scuff against the tractive surface.
The fact that a standard (non locking) differential will permit a wheel on one side or the other to spin freely when traction is reduced is a CONSEQUENCE of the design, not a "feature".
But rest assured the spider gears are heavily loaded when traveling in a straight line where the traction is good.
In fact, I would bet the bolt broke because the tractor has been subjected to more than a few "jack rabbit" launches in its past.
The broken bolt may thread into a mating threaded hole instead of having a separate nut, so look closely at all the parts to see if a stub of bolt shows.

    Bookmark   September 11, 2013 at 12:24AM
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With the bolt out of the gears, I can look into the differential and see both 'spider' gears. The axles turn freely if a little sloppy without the bolt in place. The broken bolt easily slips back into place through both 'spider' gears and the broken edge of the bolt is flush with the outside of the gear (there is part of one thread still visible on the bolt). This assembly has maybe 1/2" clearance around it from the aluminum case.

So, from what mownie tells me, it makes sense then that as there is power being driven through these 'spider' gears, and because they are beveled, I would assume that the bolt is there to hold them together, opposing the force that drives them apart. I can see that all those jack rabbit starts could weaken the bolt and shear it right off eventually. I don't want to fix the symptom, I'm looking to fix the problem here and I think this was the problem.
So, can I just take a hardware store bolt, 1/2" diameter, stick it in there with a couple washers, grind it down so it clears the case and I'm good to go? Or would a stainless steel bolt be stronger?
fwiw, I stopped at a service center today and they didn't have any parts available from MTD for this or any better suggestions than a hardware store bolt.

    Bookmark   September 11, 2013 at 5:18PM
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A grade 8 bolt is the only grade of bolt to use if going with SAE (fractional sizes) bolt/nut.
If going with metric bolt/nut, use only grade 10.9.
Stainless Steel does not mean superior strength, only corrosion resistance.

    Bookmark   September 12, 2013 at 12:17AM
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Thanks, that's good advice.

    Bookmark   September 12, 2013 at 1:50PM
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I picked up a grade 8 bolt that was too long. I sawed it off to the right length and it fits right in. I'm still working on reinforcing the broken aluminum casing. I ordered some Shell grease type 0 from mcmaster carr $6 for 14oz. This weekend I'll try to get it together.

    Bookmark   September 16, 2013 at 5:35PM
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Here's a photo of my blown out transmission that occurred while I was test driving it.

    Bookmark   September 23, 2013 at 1:43PM
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I JB welded the large parts back together. Then I JB welded strips of aluminum sheet over top. Then I reinforced inside and out with fiberglass sheet and resin.

    Bookmark   September 23, 2013 at 1:51PM
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The bolt that holds the differential gears together snapped at the threads. I used a hardware store grade 8 1/2" bolt 4 1/2" long. I have access to a lathe at work so I machined the head and nut down to the same thickness as the head of the bolt that came out of the machine. I never found the nut that came off or the washer that must have been there. I had one existing washer that I replicated for the other side, I made it out of brass because that was what I had available. This washer and the other one are pressed into the steel housing for the differential until they contact the free-floating gears. I locktited the nut on.

    Bookmark   September 23, 2013 at 1:57PM
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This shows the Shell gladus type 0.5 grease in a bowl. I was concerned I didn't have enough and that it was still too thick so I mixed it with 2 or 3 ounces of gear oil 95w140 with a hex wrench in a drill. No Peerless Bentonite! I'm still not entirely convinced that Peerless made these transmissions.
I packed about 16 or 17 ounces of grease into the box and bolted it up.

I put it back on the machine and took it for a spin. The transmission worked perfectly and everything held together fine, I ran around the neighborhood testing it out for at least a half hour, no leaks or anything. I don't know how long it will hold up, we'll see.

I put a new electrical connector on the anti afterfire solenoid and the machine no longer stalls out so it appears that there was a bad connection there. I suspect that the shop who 'fixed' this machine was searching for a bad safety switch or other electrical problem and opted to remove all safety switches and wiring instead!

    Bookmark   September 23, 2013 at 2:07PM
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"No Peerless Bentonite! I'm still not entirely convinced that Peerless made these transmissions."

I'm not aware of any other brand that used Bentonite grease.

Maybe someone else is???

    Bookmark   September 23, 2013 at 2:52PM
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Good photos to go with everything.
Hey......the missing nut and washer.........are probably out in the grass somewhere when the trans case blew open. The damaged case looks like something got between the differential carrier assembly and the case and whammo!
You turned out to be a capable person.
When you opened your thread, well.....I groaned a little :^)
But it's all good now.

    Bookmark   September 24, 2013 at 12:41AM
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I searched the yard with my friend and we combed through it. I hadn't driven the tractor very far, just a big circle. I can't believe I can't find it, oh well.

I'm sure that when the threaded part with the nut busted off it jammed in between the differential housing and the aluminum case and busted it open, I could see the marks in the case. Also, the first photo shows that there wasn't really much grease in there, there wasn't any on the ground where all the aluminum bits were. when I packed it back together, there was way more grease that I put in then I took out.

Thanks for the compliment. I might add that this will be the first tractor I have owned and worked on too!

    Bookmark   September 24, 2013 at 1:16PM
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Ok, bill_kapaun, I will certainly defer to your expertise on the matter of whether this is a peerless transmission. I went on the peerless website and downloaded their pdf manuals on all their transmissions. None of them were exactly like mine but some were very close. I think it's a safe bet.

    Bookmark   September 24, 2013 at 1:23PM
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I too groaned a little when I read your thread title. You have mastered the next level of your training -- soon you will be an MTD-JEDI.

These Peerless transaxles can fail in some really entertaining ways. I must say I've never seen a housing fragment like yours did, and cudos to you on the great job with JB Weld. You can often score a used housing on Ebay, should the need arise.

My own transaxle was eating itself, slowly. The long side axle shaft had eaten thru its bearing, and was in the process of sawing through the housing. I always wondered how the back wheels were taking on a certain positive camber (like an old VW Dune Buggy). And then one day the tranny locked up solid, and I had to drag the mower in from the pasture.

Found out the reverse gear had siezed on the intermediate shaft (pic of mine attached below). You can actually get internal parts for these trannys from the internet. They can be rebuilt. I see from your picture you're doing the right thing with lots of grease. This, plus keep the loads light and the speeds low on these trannys, will help them live.

    Bookmark   April 7, 2014 at 1:54AM
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I made it through the end of last season with no leaks and working fine. I'm about to pull it out of storage and get it ready for another season. Hopefully it will hold up! I'm thinking about a pull behind trailer/leaf vacuum project this summer.

    Bookmark   April 7, 2014 at 8:58AM
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Fingers crossed here :^)

    Bookmark   April 7, 2014 at 9:50AM
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We all wish you the very best of luck on this! I don't know of anyone else who has grenaded the tranny housing, and then made such a skillful repair on it.

Caution should be used when considering pulling any kind of trailer implement with this class of mower. Yes, they can pull fert spreaders, aerators, and light trailers, but keep in mind these transaxles are operating close to their limits just pushing along the mower and our (sometimes) big butts.

For those who haven't yet had the pleasure of tearing into their Peerless transaxles, below is a diagram which shows the top end parts not shown in the previous pictures.

The Input Shaft is driven by the big pulley on top of the outside It drives a Pinion Gear, which is in constant mesh with both the Forward and Reverse gears. The Fwd and Rev gears are free-spinning on the Intermediate Shaft, so they constantly spin in opposite directions from each other.

Between them is the little Shifter Shuttle, which is splined onto the Intermediate Shaft. When the F-N-R shift lever is in Neutral, the Shuttle sits right between the FWD/REV gears, and not meshed with either one.

When you shift into FWD or REV, the Shuttle is pushed into mesh with the FWD or REV gear via those triangle dog teeth. The Shuttle splines then drive the Intermediate Shaft, which drives the Differential unit, and away you go.

What's important to note here, is that when you're moving along in normal forward motion, that Reverse Gear is actually spinning against the Intermediate Shaft at 2x normal speed -- it's being driven in reverse at normal speed by the pinion gear, and the Intermediate Shaft is turning under it at normal speed foward.

What this means is, if your tranny gets low on lube grease, this Reverse Gear bushing is probably gonna be the first part to die (due to the 2x speed). So, keep the lube good, keep the speeds and loads low, and the tranny will live.

    Bookmark   April 7, 2014 at 12:34PM
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