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Imp Rear End

Lost Dad

New member
Here you go. I have been reading this forum for a month or so & I am impressed with the technical knowledge available here. Our snowmobile club in Maine has 2 Imps with C4 rear ends in them. We have successfully used them for grooming for the last few years. But, this year our luck ran out. We blew up both rear ends. I read the following in an old post:

"You know I have no issues with the OC-4 in my unit, but if it ever goes I think I would replace with a cut to size Ford 9 inch axle. They are super common and there is a limitless supply of gear ratios. A standard issue unit is rated for more than 600 hp! Putting an automatic trans and something like a 5.13 ratio would be sweet. Putting some tough disc brakes on the unit should do the trick for steering."

I am looking for info on installing a Ford rear end in both of our machines. Further, we are considering upgrading the motor size & utilizing an automatic transmission in the drive line. We are blessed with having mechanics, fabricators and machinists as part of this project, talent is not the issue, knowledge is. I am particularly interested in ideas such as ring & pinion combos to replicate original speed/power specs. All of our machines are set up for Ram Steer so the steering part of the formula is not very demanding; ram steer is just the ticket for these machines. Once this discussion gets going, some other members of our club may join in as my technical knowledge will quickly run out. All ideas & suggestions are welcome. Thanks
 

Snowcat Operations

Active member
SUPER Site Supporter
The problem with the ford or any standard rear diff will be the ability to turn. I believe SNOWCAT PAT built his own snowcat with a standard rear diff and found they dont work very well at all. Most steering rear diff snowcats have two things going for them. First they have wet bathed steering bands. This really helps keep them cool and last along time. A standard or heavy duty rear disc brake on a standard truck diff would need brake pads replaced once a month depending on the terrain ect. The other advantage a snowcat diff has is they have some type of gear reduction on the side the brake is being applied to. This reduces the speed of the track which by itself starts to turn the cat. I just dont think a standard truck rear diff is the way to go. It would be MUCH easier to just install an OC12. It would last forever compared to the OC4 and you could run 10' wide tracks on each side and still never break the thing! If it were me this is what I would do (if you have to keep the two imps) drop in a Ford 250 Inline 6. Get the one with the bellhousing for a C-6 automatic transmission. Install a Ford C-6 automatic transmission. Not the C-4 but a C-6! Much much stronger! Now you have the best combination there is out there! In gas engines that is. You could even go with a Cummins bt4 and a manual trans. This would get you some really good fuel economy compared to ANY gas engine. BUT you would need to go with wider tracks for sure. Send us some pics of your broke imps!
 

mtncrawler

Bronze Member
GOLD Site Supporter
When you say you 'blew up ' your OC-4's what does that mean exactly? What parts broke to where you don't just fix them? As far as the Ford 9" I have a really hard time believeing it is anywhere near as strong as an OC-4 even if it was possible to scab one in.
 

Lost Dad

New member
As usual, money is a difficult issue for our club. Our thoughts were to utilize salvaged parts so the cost was minimized. This gets into the repair/replace conversation that has confounded the engineering world for years.
If we were to consider buying 2 OC12's what is a cost estimate and who has them (I assume that they would be salvaged) Also, I imagine that shipping costs would become significant.

Is there any value to the machines with broken rear ends in them?

We are considering updating our grooming fleet and our thoughts are that a broken machine has little value, but if we were to build it bigger & stronger it would have some decent value. I then start to wonder if we should leave the machine close to original specs or are we hurting ourselves by bastardizing our machines.

We do not have either machine apart yet but at least one of them has a broken housing. We suspect that one machine could be repaired with a new ring & pinion and the second machine will need a complete replacement.
 
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mike2

New member
I,m one of the operators of the imp's with the broken rear end's,one of them has a crack in the housing,we think this is why we keep loosing the ring and pinion,the oather one got some water in the rear end which seemed to take out a bearing on the pinion shaft which took out all the teeth on the inside of the ring
 

Snowcat Operations

Active member
SUPER Site Supporter
Unfortunately no. The oc4 is an expensive item to have fixed or replaced. I have one OC12 here. I know where a few more are at. I'll get some prices for you. Its at least an option.
 
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