OC-12 Capabilities w/ Passengers and a Plow

[IMPossible]

Hello everyone! I hope y'all have gotten more snow than we have here in Utah. We're itching to get some more.

We semi-recently ended up doing a trade on one of our old Imps ('64 1404) and got the Vancat that many may have seen listed on KSL or here on the forum.
It's a monster of a machine, reminds me of a monster truck with the tracks on. I believe the base is a 2100c. Its got a ford 391 V8 with a C6 automatic transmission and the OC-12 rear end. We're thinking of potentially doing an engine swap on it and wanted some of your experience and wisdom.

The goal of this machine is to make it into a reliable cabin transporter. Cabin is 6 ish miles on the snow with some decent inclines and lots of drifting snow. Right now it doesn't have a plow on the front and I'm wondering if throwing a plow on the front + having passengers will be too much for the OC-12.

First question: Can the OC-12 handle 12 people and a plow on the front? I don't think it will regularly be loaded with 12 people, but it does have the room for it.

Second question: What do you think about an engine swap for a little more power, reliability, and availability of parts? We were thinking maybe a 6bt or a Deutz air cooled engine. Maybe even a modified 4bt. If you have any other suggestions let me know.

I would love to get some of your thoughts on this. Thanks in advance.

 

[schmidt]

We have a 1969 Thiokol 1200B with the OC-12 and a 10-12 person cab, plus significant room for luggage. I am not sure of the gross weight, but the cab is fiberglass and I suspect its heavy. We have operated it for over 35 years, traveling 6 miles each round trip, a 1000' feet of elevation, with areas of a 28% grade, in the Cascade mountains of WA, with heavier than average snow (Cascade Cement). Putting approximately 100 hours a year on it. The machine has been well maintained. She's not fast with its 4 speed manual transmission and Ford 200ci. However, she has never failed us. Brake bands have been replaced twice in the OC-12 and she only had one driver. There have been no suspension failures and its original tracks were replaced back in the early 2000's with the newer offset 45" tracks. These were used tracks, and approximately 10 years ago we replaced the belts. In the off season the machine is stored outside, in a complete wrap. With all this said, the OC-12 maybe one of the most reliable rear ends you can find, as long as they have been well maintained, never any hard jerks on the sticks, especially under load and speeds are kept on the slower side, approximately 15mph. I would be concerned with "over powering" the OC-12. Keep in mind our setup... horsepower, torque etc. and it's longevity. A larger drivetrain will increase heat and friction and MAY be a cause of concern. Hope this helps.

 

[PJL]

That is a very cool machine. Custom made cab I presume.

 

[schmidt]

Our understanding on the cab is there were 25 made under the name Astro Cab. The original contract was issued by the Secret Service needing them for when Gerald Ford (then president) would stay at their condo in Snowmass. I did see a photo of another one in NY. The cab is nice, with the large windows and no diesel fumes riders are actually very comfortable.

 

[redsqwrl]

I think schmidt hit it right on the head. that post should be a sticky.
The only comments i ever heard about the more power issue was from don in nome. when he upped his power in a 6.2 L diesel he noticed the housing flexing in his OC-12 in a 2100 chassis.
Taking it is a term thrown around ( can it take it) I would say yes the diff will be able to take it. but why?
will you be bull dozing piles of dense snow?
Just cutting drifts?
Freighting heavy loads?
Lots of factors to consider.
My favorite power plant is the 170 in a spryte. the 6.2L diesel in a 2100. Both puts out gobbs of torque for their size and the 170 revs happily. I have been farting around with a 4BT turbo diesel and ZF-5 speed and I can't bring myself to install that combination into anything as it is really heavy.

 

[IMPossible]

Thanks so much for the replies! I guess I’m not as concerned about the passengers as I am about the plow. This cat has already carried a decent amount of people and gear and has done fine, but it has not had a plow. I’m wondering if the combination of the passengers and gear + the plow would be excessive. It wouldn’t be used to bull doze piles of snow, it would be for cutting drifts. The loads it would carry are passengers and gear, potentially a decent amount (max of 14 passengers + gear). I’ve heard many things from people with no experience in the snowcat area that plows are dangerous as they put a large load on the rear diff. This is coming from a truck application and I’m not sure how much it applies here, but I do assume that the weight of the plow and the amount of snow pushed does add some load to the diff.

As far as the engine goes, there is some worry about it. When we got it the oil pump was seized. They said that they had turned it off immediately after seeing the loss in oil pressure, but who knows. Not sure why the oil pump seized in the first place. Upon replacing it we saw that they had installed the shaft in upside down, so not sure if that contributed or not. Bottom line is that we probably are going to want to rebuild it soon for peace of mind and the thought was that if we were going to take the time and money to do that, we may as well switch to a strong, reliable power plant. Love the idea of a turbo-diesel with that low end torque for those steep hills.

As of right now, the ford 391 I’m guessing is around 700lb (please correct me if I’m wrong, I can’t find much info on it) where a 4bt is 750-800. So I’m not too worried about the weight (maybe I should be).
The OC-12 we have does have the drop down boxes, not sure if that affects anything.

We’re not attempting to make a hotrod or get a massive amount of power in there. We’re more concerned with just getting something that is a little more common so parts and info aren’t impossible to find, and that is reliable, bulletproof if possible and can easily handle the load of the passengers and a snowplow.

 

[redsqwrl]

I say go for it.

With common sense applied I believe a 6BT will nicely move that around. the RPM is close enough and the weight is in the right spot.

Thiokol used a 384 diesel

so a 360 diesel should be just fine

I put 2100 chassis's under a custom cab, I moved the motor back 18 inches and cut the tunnel off. I figure the weight of the plow will put me where I want to be, I don't have giant inclines to circumvent so there is that.

 

[IMPossible]

What would you mate with the 6BT for the transmission?

 

[redsqwrl]

I would stay away from the Dodge transmissions in your case.

I mated a ZF-5 to a 4 BT for a forward engine tucker project ( low first and OD) all syncro'd

I am currently debating a 727 3 spd for a 6BT snow project. ( otherwise the much heavier Allison 540,542,545) the 727 is very small and light. I am known to pull 10'x28' grooming drags full of snow on occasion so that is causing my indecision.

You will need to pay attention to the governor and shift settings in the trans you select.

 

[TheSkipper]

After tending to 5 of these at at CA ski resort, one of which was a trooper with a full roll cage, it seems that an underpowered I6 with just the right amount of torque would be ideal. Even with the added weight the trooper could handle anything we threw at it. The other four machines had relatively heavy blades that were used to plow lift terminals after heavy snows so that the big machines could get in and make everything look nice. Never once saw or heard of someone getting stuck and never heard anyone complain about an under powered cat.
We can put all the power we want into these machines but when it comes to having to replace housing on the OC 12 it would probably be cheaper and easier to replace an engine. I’ve mulled over this one quite a bit and settled on a Jeep 4.0 L (depowered if possible?) and automatic transmission. It’s cheap(!), its small- so it fits, its light, it has the power (about 80 more horsepower than the 4.9 ford iir), a brand new engine is available, there are parts galore and they are easy to work on, and and and and and......
Basically, pick your component that you want to be the weak link and engineer to that point-
engine(maybe), tranny(maybe), OC12(probably not), drop boxes(again, no), sprockets(maybe not), track belts/grousers(how? no operator has been willing or able to reproduce destroying track for me yet), and finally -overlooked but realistic- traction.
Take your pick!

 

[Snowy Rivers]

The OC-12 Box is damned tough.

Big thing with these is to be sure that the bearings are all in good order and that the oil stays water free.

Snow water is the softest water on the planet and can find it's way into things.

Rusted bearings WILL FAIL....

The 2100 chassis used hydraulic pressure from the main system to activate the bands at 400 psi (Nominal) so the bands are either ON OR OFF.

Hand lever controls like was common on the spryte can lead to band wear due to far more slippage and operators "Ridding the bands" ON OR OFF is the key to band longevity.

AS far as power goes....The old Ford 391 is a boat anchor....but it will produce the needed torque.

An automatic tranny is far easier on the drive line parts (OC-12 and such)

The torque converter takes up all the harsh application of power and keeps things in one piece.

The Ring and pinion in the OC-12 are good sized and the gears in the drop boxes are huge.......

Axles are herky as well.....

Some early axles had a snap ring holding the axle bearing on.....The axles saw some breakage at the snap ring groove...
All newer axle bearings were held on by a press fit collar.

If you break an OC-12 YOU ARE in waaaaaay too far......

A small block chevy 350 or 400 makes a very nice simple power pack and will fit the 2100 tub easily.

Trannies like a TH350 or TH400 are a sweet choice....Simple and rugged...

The bands are a "consumable" item and the big groomers with the 57" or wider tracks would use up the bands much faster than a Spryte....

The later Hydrostatic cats like the 3700 or 4200 were a sweet ride...Just very spendy to work on the HST system.....
The small diesels offer a good choice as far as a repower goes.

As mentioned.....Make the "Fuse" a cheap easy fix.....

The innards of the OC12 are tough...but like any mechanic gear box....things do wear.

Make sure the bronze bushings in the equalizer are in good shape and also the inner pinion teeth are not worn badly.....

Standard inspection of the ring and pinion for chipped or broken teeth should be done.

The thrust washers "AS delivered" are cheezy as are the washers behind the heads of the inner pinions.

These issues are easily dealt with.

Oil choices are a bit critical...DO NOT use 85/140 gear oil.

There are many good "Tractor fluids" in a 30wt that work sweet and are designed for use with friction bands.

IF your OC-12 has been worked on ......it likely uses the main box oil to also flow into the drop boxes and the axle bearings too....

The previously mentioned "Thrust washers" have a habit of chewing up and the pieces get ground to bits by the R&P and the resulting trash goes through the bearings and raises hell....

My OC-12 had a couple bearings that had actually fractured due to the junk...

Good luck....