Imp with leaf springs vs torsion axle

My leaf springs are probably original- look flat. Know I will be looking at a replacement of those as well as tires. Have several questions if anyone can chime in.
1) What do the leaf springs cost?
2) How difficult / costly is it to convert to torsion axle?
3) Does the ride improve with better springs/ axle?
4) Who is the best supplier for tires?
5) Do you stay with factory tire size or is there a reason to go bigger?
Thanks.

1. Leaf springs are not useally expensive(dont know about in alaska)
2. I cant think of any way for you to use a torqflex axel in your aplication.
3. A flat spring with fewer leafs will give the best ride but may lower you gvw.
4. Have you tried northern tool? they're online and have lots springs +tires.
5. It dosent look like you have room.

Thank you for your thoughts. I believe the torsion axles would be attached to the frame, would need twice as many as the current setup. I would cut off the existing axles. I am hoping someone post comments on how they have done this- it has been done by members of the forum. If you get more clearance via axles / springs / or tires i wonder if that would create problems elsewhere. I also wonder whether the front fixed idler could be replaced with a torsion axle to give a softer landing when you hit nose down- again- this may cause problems elsewhere. Feedback????

Working on a setup to adapt torsion axles to the existing frame members. The engineering is still in its infancy. I am still working on getting my engine to fit Here is a pictures of a mock up I did a while back. My goal would be to get some triangular plates laser cut that have 3 square holes in them. One for the origional frame and one on each side for the torsion axle to slide into. The working part of torsion axles is only in the first foot or so, giving the ability to cut them off where you need.

Maybe you could cut the axle shorter and have a tandem beam bolted to the hub of the torsion bar. Might even be able to build your own torsion axle right in the existing axle beam ???

I sure would like to gain some ground clearance on my Imp ....

Hadn't thought of your approach John- of actually attaching the torsion axle to the existing axle (One on either side). I still wonder if this is a much better ride than leaf spring. It Looks better. Are you replacing the fixed idler wheel axle with a torsion axle in the front? Here is a pic of an axle from northern tool . . . it looks like they have mounting flange on it already, unless that is a brake flange (??).

Pixie- as far as ground clearance I have wondered about putting a block between the axle and the leaf springs- the old fashioned lift kit approach. But I stll wonder if this will cause other problems (the idler and drive sprocket are fixed and not so easily moved moved down)

I bought replacement springs for my IMP from a business in Fairbanks last year for a $100 ea. They look good. Im sure he would love to sell you some. Jim @ tracer 907/456-7278

My Imp 1402 is probably the only one in the world that has been converted to torsion axles that I'm aware of so far. It was done somewhat out of neccessity. This cat had the axles changed from the original design by the previous owner. The whole chassis was lifted about 21/2" and the rearend was lowered to accomadate the change. With the geometry change, I was having some problems with the suspension. This is the reason I decided to make the change, plus possibly improve the ride.
There was a lot of calculating and measuring to get it right. I wanted to get the drive sproket off the ground about an inch and a half for a smooth ride. I considered dropping the front idler and adding another axle similar to the spryte. This could be done but I would go to the drop axle C-4 differential like the old spryte has to handle the additional track. I was told that the drop axle C-4 is stronger that the strait C-4 due to the gearing and heavier axles.
I welded the whole assembly together and then attached it to the chassis. Some overall length was added, so a slightly longer track was made to fit.
It has worked out wonderfully, but took some serious planning to make it work. The ride is far superior to leaf springs. I believe the larger wheels help a lot too. Just try rolling the two wheels over the grousers of a track and compare the wheel movement. The attack angle of the front end I think helps it get on top of deep snow. It tends to slightly pitch up when in deep powder, just the way I like it,

MM, I'm glad you posted some picks- I can't get enough of looking at your imp. Serious Imp envy. I also notice you moved your fuel tank(s)- that is something else I want to do. I believe you when you say there was some measuring- and head scratching. Perhaps teeoster and I will follow behind you on the axle change-out. To clarify though- the previous owner did a lift using leaf springs? If so, what problem did the lift create that forced a change to torsion? (hope I understand correctly)

Here's a good shot of the assembly just prior to installing it to the chassis.



Someone, before I purchased this machine, chopped off all the wheel axles and then welded new axles below the positions of the original axles to get a 2.5 " lift. They also added length to the axles to make the tracks set further apart. A spacer was machined and added to the rear drive axle to match it to the wheel stance. But to make it all work, they had to also lower the C-4 rearend to match the lift. To do this, it was dropped so that the drive shaft would just barely clear the bottom of the chassis. The rear of the C-4 differential was tilted about 20 degrees down at the rear to gain even more drop. The simpler answer would have been to install a C-4 with drop axles from an old spryte. Since I now had a wider wheel stance, similar to a wide tracked Imp, I could make a wide track symmetrical track like my DMC 1200's.
I decided to run larger wheels matched to the size of the drive sprokets for a smoother ride over the grousers.
When I switched it over to torsion axles, all that was necessary was add the assembly to the bottom of the chassis. You can order torsion axles at any with load and swing angle. I had TJ Trailers in Ogden order exactly what I needed. They had the spec sheets showing the amount of normal and max travel that also had to calculated.
I had to totally rebuild the front idler assembly and make it adjustable for simpler track removal. I also installed a larger front idler wheel for better rolling performance.

I have worked for four winters now on this machine to get it where it is now.
Since it was butchered up a bit prior to me purchasing it, a lot of this came out of necessity to correct problems from the changes prior to me owning it.
I owe Dan, my friend at Wilkenson Construction for life. They helped with their shop and great welding job. I think Dan hates to see me coming, because he knows I have another idea to try on this machine. I have done a lot of the changes myself, but he has helped with the heavy stuff and serious welding.
Sometime, I need to get some shots of his four cat's that he has redone with larger cabs. One even has a refrigerator and microwave.

Hmmmm. A lot to take in and consider. I did find a spring shop locally that can make replacement springs in a couple days. . . 8 spring, $600 plus. For $600 I could get the new torsion axels. Tempting. I do wonder if I should mess with changing tire size. This draws on the part of the brain where geometry, physics, math reside. On another note- what is the story with the rocking chair? Is that where the supervisor sits?

nutsster said:

I believe the larger wheels help a lot too. Just try rolling the two wheels over the grousers of a track and compare the wheel movement. The attack angle of the front end I think helps it get on top of deep snow. It tends to slightly pitch up when in deep powder, just the way I like it,


View attachment 10067

View attachment 10068

Click to expand...

I have also read (I think) that you want to be nose heavy. I wonder how much of the performance has do do with weight/balance -vs- track geometry.

Nutsster- If you were doing it again, what would you do different with regard to the idler? I am contemplating whether it is really necessary.

Group- Any comments on what would happen if you removed the front idler and just repositioned the full-size tires so that the forward-most tire was on a torsion axle and acting in place of the idler?
Specifically- would it improve ride and/or performance?
Specifically- would a moveable front tire cause the track to be stretched or over-strained in some way?

First, that seems awful expensive for leaf springs. I had individual springs made for $20-$25.00 in SLC. All you really need to do is replace the really bad springs. You could stay with the wheel axle spring, unless it's really messed up. I would probably run four springs in the front if your not doing that. Also, with a full cab you will need that many for the rear too.

I have went back a forth on installing the front idler again. Like I said, that attack angle was to help get the front up on top of the snow. The Imp is so close to the ground and has such small wheels, that I can see that it was necessary to do it that way.

If you don't run the idler and install another torsion axle you will have a few more issues to deal with.

You will gain more surface for traction and floatation.

You will need to make a new and longer track.

The added length will make the cat turn much harder on hard pack snow and put more stress on the differential.

At this point, I'm glad that I did it this way. If I had the C-4 with drop axles, I would drop the idler and add another torsion axle.

The early spyte used the C-4 rearend. I believe they geared it differently and installed drop boxes to take some of the stress off the planetaries.
It also had a stronger axle than the one for the Imp. It was somewhat successful, but not even close to an OC12.

Okay, by four springs I think you mean a stack of 4 individual springs in the "leaf spring", right? I have that now- not a spring guru but I was thinking fewer gave a softer ride (?). I know flat give a better ride than eliptical. OR, install air-ride seats. Funny, soft powder makes the ride sooooo much nicer.

I took a photo of the plates I had laser cut. The torsion axles slip right into the two square holes, one going in each direction. I had two of these made just for fit up, I will probably have to adjust the exact shape once I get the machine put together a little more and see how the weight gets distributed. I guess you could say everything is adjustable until it all gets welded together.

Hey John, that is pretty much what I had envisioned you meant. Looks like you are designing in some lift too. (?) ps, engine is in town- haven't picked it up yet.

Here is a screen shot of a design generated in AutoCad to convert a 1404WT Thiokol Imp to torsion suspension.

This design uses torsion half-axles bolted to mounting plates that are welded to a sub-frame boxed in with the existing square tubes. In addition another square tube is added in the rear for support.

The sub-frame is made from smaller square tube so that it can be welded at an angle to the existing tubes. The torsion half-axles come with a camber built into the mount so as weight deflects the torsion axle they do not end up "splayed out". Testing with the maximum weight on the torsion half axle showed about 1/8" deflection.

The torsion half-axles chosen have removable trailing arms with an internal spline that mates to an external spline on the torsion mount. This allows for adjustment of the angle of the trailing arm.

The bogie wheel locations have been chosen so that there is no possibility of contact between bogies, front idlers, or rear drive sprockets, regardless of trailing arm position. (If someone decided to mount one as a leading arm, then all bets are off.)

The cost for the steel, torsion half-axles, hubs, tires and galvanized wheels was less than the cost of the springs, u-bolts, spring plates, spindles, axle bolts and replacement tires and wheels.

These suspension modifications are just beginning, so it remains to be seen how the end result turns out.

The labor cost to design and install the sub-frame, well you're not suposed to figure that in are you?

Alaska Spring in Anchortown can make any leaf setup you would want. In fact, if you know what you want in spring tension, they will custom make a set as well. I would set the spring pack up so that it has more flex for a smoother ride in the normal setting but stiffer with a load. They can do that with different spring rates.
Comfy!

Did you ever get your springs. I had Alaska Spring make me up 8 of them. Had a few cracked ones, so just replacing all of them. May have a few used ones left over, would trade for other parts....

GSSDO6,Since by lowering the suspension, which efectively raised the drive sprockets off the ground, the surface area of track on the ground has been reduced. Have you considered lengthening the frame & track and adding another bogie? The length of the contact area of track to ground would still be similar to the original design so the load upon the OC-4 diff shouldn't be a whole lot more, should it? Otherwise I think the "rocking chair" ride would counteract the improved torsion bar suspension. Very sharp job with the autoCad images. I hope you will treat us to more of these.

Nice research and CAD work. Would you disclose the maker of the torsion axles? I like that they are adjustable.
I am very surprised that the torsion setup could be less $ than leaf springs, since trailer springs are about $20 each.
-Pat

Give these guys a shout for springs.
http://www.alcanspring.com/

Yes, leaf springs are cheap, and easy to get made a lot of places around the country in any configuration you can imagine. The expensive part of a suspension rework for me was the hollow tube spindles (1405011) and shoulder nuts (1405012). A previous owner had put in some grade 2 axle bolts and did not preload the spindles or lubricate properly, so they needed to be replaced.

The torsion half-axles I purchased from Southwest Wheel are Flexiride FR-1400B made by UCF America with 5 lug on 4.5" bolt circle and 2-3/4" pilot hubs.

http://www.etrailerpart.com/halftorsionaxles.htm

The FR-1400B is the smallest half axle in the series with the splined trailing arm. The smaller sizes have fixed trailing arms. The FR-1400B is rated at 1400 pounds per pair, so heavier than needed and will no doubt be a stiffer ride than desired. However I have yet to ride in a two-track snow cat that did not have a stiffer than desired ride on those hard packed bumpy roads.

I even went so far as to reverse engineer the spindles and shoulder nuts and get a few quotes from local machine shops. But the overall cost of properly reworking the suspension with the part sources I found was higher for the stock spring arrangement than for the torsion half-axles. By the way, the drawing of the spindles and nuts was for quoting purposes only, not sufficient to make the parts properly.

Hi mtncrawler you bring up a good point I had no idea about when I designed the suspension modifications. The drawing shows the trailing arms mounted to give more ground clearance, but could just as easily be rotated to the stock location.

I was never happy with the lack of track tension adjustability on the Imp. But it did not seem to be that much of a problem, perhaps because I did not encounter situations where it might have been.

Also, when I developed that design I was struggling with an "easy" way to make the front idler adjustable. Now that I have a Super Imp, I find the track adjustment very useful. The bulldozers we had when I was growing up also used a grease gun to tension the tracks.

What I do with my Super Imp is tighten the tracks just enough so that I do not jump a tooth on the drive sprocket when I am going down hill and make a turn. I find that when the track pops over a tooth it is really hard on the sprocket.

My plans for the Imp have also changed. When I designed the torsion suspension I was planning to modify the two person cab to a full cab and wanted extra weight carrying capacity. Now that I have a full cab Super Imp, I want to keep the Imp as light as possible for better deep powder performance and to be able to get up that last steep pitch at several radio sites I visit in the winter.

Also, now that I know more about the Imp differential compared to that in my Super Imp, it is another good reason to keep the Imp light and not over tax the differential. For this winter I think I will keep the cab completely off the Imp, add a roll bar, maybe a soft top, and hope for some real deep snow to test out the performance.

I appreciate all the comments, they are very helpful to consider the pros and cons of several options.

If you like the AutoCad images, have a look at an off-road trailer I am designing in SketchUp, a free program from Google. Having the ability to draw easily in 3D and rotate the items and zoom in really helps to think through how pieces fit together.

I will be doing all of my mechanical design in SketchUp now, so anything I develop I will gladly share.

I used those half axles on a couple of quad trailers I built, they're pretty nice.

RedRocker, thanks for the lead on springs.

If I decide to go that route I will certainly call them.

RedRocker, I see you used bearing buddies.

I have stainless ones I bought for the Imp suspension, but then I need to make a keeper so they don't get knocked off.

You guys got me think about the suspension on my IMP again. I have not had the chance to work on it lately, but have put some thought into the design I came up with. I attached a few more pictures to better illustrate what I am trying to to do. I value the engineering savvy of you guys and appreciate any comments or suggestions.

I an effort to get the maximum results per $ I am trying to use these surplus axles I came across a few months back. this guy is literally selling these 1400# axle assemblies to me for $50 a piece, and he has allot of them. Enough to share with my IMP'ing friends if this works out Before final welding I intend on using a fixture to make sure all the hubs are in line with the rear end and square to the rest of the machine.

So the prototype mounting plates I had made at my shop are just that prototypes and can be changes in anyway to accommodate attack angles, ride heights, camber, ect.

I guess I have a few concerns I would like to ask the experts opinions on, and please feel free to toss any possible suggestions out there.

The fist is track and guide clearance; I have 24" drop center grousers, will they clear, if not will small well placed "skid" plates solve the problem?

The second is proper suspension for weight; Will the 700# each torsion units be enough, or can they be rotated to individually tune the specific location they have on the machine?

The third is original frame strength; is the new setup going to exert more twisting force one the frame member it is mounting to than the stock units did? if so is it too much for the design of the IMP frame?

The forth is mounting plate thickness; Is 1/4" material strong enough or should I go to 3/8"?