Ideas for rear suspension for off-road tractor.

Hey everyone.

I've had some ideas for potentially building a rear suspension setup for an off-road tractor. I was thinking to myself that it might be possible to mount the rear transaxle, say a MST-206 or similar to a set of control arms.

Depending on the application or perhaps after some trial and error, either just 2 lower control arms or a set of lower and upper control arms could be used. Then use either small leaf springs + shocks or a set of "coil over" type shocks w/ springs to attach to the control arms and tractor chassis.

If the above were possible I think it would allow for decent travel of the rear trans-axle and create a decent rear suspension.

I figure that the shift and brake linkages would need to be set up to allow for the travel of the "suspension", but this could be solved a number of different ways.

The only other thing I could think of is that the drive belt would need to be routed in a way to allow it to move and up and down with the suspension and not fall off the input pulley on the trans. I think some strategic placement of belt guards might be enough to solve this issue. I mean the blade platforms of these things move a good few inches and the belt stays on just fine usually.

Thoughts?

It is posible. Sorry cant give any secrets at the moment plan on doin this to my mower. One of the big issues with this is shift linkeg. What gonna happin when your running 25 an dit a rock and the flex of the axel throws it into 1st gear. To me the belt aint the problem its the linkeges. I plan on doing a post on it soon as i start

CornShuck4CE wrote:

It is posible. Sorry cant give any secrets at the moment plan on doin this to my mower. One of the big issues with this is shift linkeg. What gonna happin when your running 25 an dit a rock and the flex of the axel throws it into 1st gear. To me the belt aint the problem its the linkeges. I plan on doing a post on it soon as i start

Awesome dude. I look forward to seeing your posts about this! I had an idea for the linkage. I think that using something that is telescoping for part of the shift linkage should help. Like on some cars how the steering shaft telescopes. Or even a CV axle to a degree.

Good luck man!

Use a cable for the shifter. Probably something stiffer than your average throttle or brake cable.
I cant imagine it being too difficult...

Less there is something Im missing...?

Cables would work but cables to me are not as reliable as links. The key is the shift link would have to be the same lingth as the controle arm or link bars. Or from point of articulation to the point it mounts to the frame. 
Dang to many secrets.

I think it they are done properly, and maintained they ought to be fine. Though, I can understand something more solid and beefy being wanted.

I may rig up cables on the build Im planning... I think cables will give more opportunities of the where the gearshift can be ...

I was thinking 2 cables, one to pull the shifting arm on the transaxle forward, and the other to pull it back. But maybe a real stiff cable would work just fine.

I think the biggest issue with rear suspension and standard transaxle would be keeping the belt tensioned, and in place. But as was mentioned, some slick guards and tensioners should take care of that.

What about a mid engine setup on a mower? Trans could be suspended as stated, then the engine bolted onto a plate hooked to the a-arms as close to the trans as possible. Engine would move with the trans, but not as much because it would be right above the pivot point vs the trans being behind it. Would need to be a relatively light and smaller engine, single cyl. Also, major hacking of your mower would be required. Just an idea, not like I can draw up plans in five seconds or anything, you know...

Maybe a large swingarm starting at the front of the machine...

I'm lovin' all these great ideas folks.

I've also toyed with the idea of mounting the transaxle in the middle section of the mower frame. Cutting the axles mostly off and welding on sprockets...or using a smaller trans with side sprocket output shafts.

Then use a jack shaft and custom rear swing arm setup with a custom axle. This would also allow for the use of a nicer brake setup as well I'd imagine.

Thats probably the beast method. You would have more freedom with gearing it too. Thats also something I want to do sometime, use the stock pulley sizes, and use sprocket and chain for speed...

Mounting the trans on the frame and running chains would be good for a few reasons. "Unsprung weight" the weight that is below the springs wants to be a light as possible since it needs to follow the surface of the road / ground.

Imagine an engine and transmission bolted to the swingarm? It wouldn't handle too well bouncing all over and not absorbing the bumps. Also, you'd be taking more weight away from the sprung weight of the tractor. This is where you DO want weight to help keep the body of the tractor stable. It's all about Newton's three laws.

I think linkage and the power transfer would be easier to manage too. Chains running on horizontal shafts can get wet and muddy but won't slip. Belts would be a nightmare!

There's some interesting ideas floating around in here. Some good ones too- and a few that I have been entertaining, myself.

There's a guy on a couple of the related FB pages by the name of Bob Morris that suspended his rearend (peerless 930, IIRC) on leaf springs. Not a ton of travel, but some movement to be sure. Belt appears to stay on. With a larger amount of movement, I wonder about the reliable operation of the clutch, while flexed. Flexing will alter belt tension so some degree.

If I were to do it using this particular method, I'd likely turn to cable for the shifting duty. With a solid linkage, that handle would be all over the place! In the past, I had a car with a 5 speed manual that was cable-shift. The shift action was amongst the most crisp I have ever experienced! I'm gonna let WellThatsSurprising go ahead and guess what car I'm talking about!

Anyways, it's just a matter of cable selection and support. One COULD probably do a pull-pull (2 cables) but it wouldn't be as tidy in my opinion.

This would be for a linear shift transaxle. Something with an H-gate like a 2300 would be a whole other animal to try to engineer...