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OC-4 transmission disabled and wonder why

SOS RANCH

Member
I am new to this forum and a recently acquired a 1400 (1404?) IMP and was told by an online parts company that it was 1976 (via serial#) with an OC-4 rear end. It needed a new water pump (current one is leaking, I have a new one to install) and thus the cowling around the engine needed to be removed to gain access to the alternator so it can be removed to install the new pump. The cat runs great, starts immediately, engine sounds good, bought it from a friend that I trust, and etc, etc. The online guy asked me, where is the second shifter? As I sent him a pic. (new poster so I cannot post pics yet..).

When I removed the cowling and the part behind the normal transmission shifter, I noticed the small square box with the pivot pins in place and below that the shift rod that extends to the OC-4 transmission. The last two people that owned this had no idea that it had the 4 speed rear end and were bummed that it went slow. So the shift rod that extends to the rear works, is not frozen, but is a bit rusted (just light surface rust) but it rotates easily. The shift post coming out of the transmission moves easily so this is intact to this point. (I have Spryte folks in Idaho looking for shifting parts to rebuild the ability to shift at the front next to the front transmission as was usual). By the way, the cowling that this shifter came out of is covered with diamond plate so the hole was not seen but is there as the diamond plate is glued to the original cowling. One reason no one recently knew it had the 4 speed rear end.

I am hesitant to try to shift the rear transmission for the reason stated below in question 1) a).

So, the questions are: 1) Why would this be disabled? Several reasons come to mind: a) there is something wrong in the rear transmission and it will only work in the low gear (but there is no noise in this tranny, no grinding, no issues that are noticeable in any way), and b) This cat was used as a search and rescue operation in Truckee and perhaps they did not want anyone driving it faster than slow.

2) If something was wrong internally and the gears are intimate with each other, would not there be some noticeable symptom when driving?

3) My plan is to a) contact the folks that had it in Truckee and ask, and b) to remove the cover plate on the transmission and visually inspect the gearing (mirrors and all to see as I don't want to remove the unit unless necessary to repair if needed... and HOPING it is intact and just needs to be reconnected with front shifting levers and knob !!)

I eagerly await anyone's thoughts and comments.
 
I am new to this forum and a recently acquired a 1400 (1404?) IMP and was told by an online parts company that it was 1976 (via serial#) with an OC-4 rear end. It needed a new water pump (current one is leaking, I have a new one to install) and thus the cowling around the engine needed to be removed to gain access to the alternator so it can be removed to install the new pump. The cat runs great, starts immediately, engine sounds good, bought it from a friend that I trust, and etc, etc. The online guy asked me, where is the second shifter? As I sent him a pic. (new poster so I cannot post pics yet..).

When I removed the cowling and the part behind the normal transmission shifter, I noticed the small square box with the pivot pins in place and below that the shift rod that extends to the OC-4 transmission. The last two people that owned this had no idea that it had the 4 speed rear end and were bummed that it went slow. So the shift rod that extends to the rear works, is not frozen, but is a bit rusted (just light surface rust) but it rotates easily. The shift post coming out of the transmission moves easily so this is intact to this point. (I have Spryte folks in Idaho looking for shifting parts to rebuild the ability to shift at the front next to the front transmission as was usual). By the way, the cowling that this shifter came out of is covered with diamond plate so the hole was not seen but is there as the diamond plate is glued to the original cowling. One reason no one recently knew it had the 4 speed rear end.

I am hesitant to try to shift the rear transmission for the reason stated below in question 1) a).

So, the questions are: 1) Why would this be disabled? Several reasons come to mind: a) there is something wrong in the rear transmission and it will only work in the low gear (but there is no noise in this tranny, no grinding, no issues that are noticeable in any way), and b) This cat was used as a search and rescue operation in Truckee and perhaps they did not want anyone driving it faster than slow.

2) If something was wrong internally and the gears are intimate with each other, would not there be some noticeable symptom when driving?

3) My plan is to a) contact the folks that had it in Truckee and ask, and b) to remove the cover plate on the transmission and visually inspect the gearing (mirrors and all to see as I don't want to remove the unit unless necessary to repair if needed... and HOPING it is intact and just needs to be reconnected with front shifting levers and knob !!)

I eagerly await anyone's thoughts and comments.
Pictures, pictures, pictures please! Sounds interesting. I know there are multiple shift forks in the rear end. Maybe someone disassembled and reassembled incorrectly and couldn’t get it to shift so they removed a fork? I do t know? I’ve had my forks apart but I haven’t studied the idlers and gear movement much at all. You could jack up the whole cat so the tracks float and manually select gears and rotate driveshaft by hand with front in neutral. If everything moves accordingly and appropriately and the tracks rotate, you should be ok. This would provide some clarity. Keep us posted!
 
I would be delighted to post photos as soon as I am able. One must post 10 times before adding any attachments and I will abide by the rules! I have read all 20 pages of this forum on Snowcats (as posts related to Imps) and have found it all very helpful. I was never planning to purchase a snowcat but then ran into this one for sale by the road heading to my home.

I told my wife about it and she said "Don't do another Impulse Buy !!!" So, I didn't. I waited 2 days..... (baddaBoomm...)

We live on a 100 acre ranch next to forest service so we can use this a bunch in the winters and have lots of fun... as long as it is reliable so I am working to make it so as much as I can.

I still think taking the side cover off of the rear transmission and inspecting it is appropriate. But there are no metal parts and pieces in the transmission fluid I am told but will investigate this myself. I don't even know yet if parts are still available regarding the shifting mechanism up front. Nancy from Spryte Improvement is looking for me (she has been so nice and helpful!!).

I'm an old mountain man, lived in log cabins for some years (without running water or electricity) in both Aspen and Sun Valley and am used to snow, cold, and etc. I was a certified back country guide and cross country ski instructor so I know how to survive should something break down.. but I DON"T want to exercise those skills.. if you get my drift (pun intended).

This cat's cabin was modified so it has bench seats in back that seats 6 (6 seat belts). Heck, I could put a small wood stove in it and turn it into a camper!! I will go through everything as it as a little over 3K hrs on it. The body is in great shape, all lights work, heater works, wipers work, and the carb was recently rebuilt.

It may need a clutch and Nancy says the parts are available but a couple of holes need to be drilled and tapped as what is available is not exactly correct... but then, we are just talking about the pressure plate itself so I don't know. I was first told that this was a T90 transmission but then found that it is rather a T96? The T90 is what is in my 1951 M38 and my M38A1 jeeps.

The prev. owner said he would pump the steering handle once to steer ( which I did not have to do when I drove it) but that is likely that the lines need to be bled.

Maybe I will post more 7 more times so I can attach some photos!
 
I forgot to mention that I have zero experience with snowcats, never even have ridden in one until this came up on my radar....

(4 more posts to go !! ;o)
 
Dont open the trans yet.

The shifter sticks out the top.

It shifts easy. Should have 5 positions.

You are likely correct. Disabled to avoid breaking. Or broken and in its only functioning range.


Lots of imps have oc3 diffs shoved in them. Lots of smart people have done smart things to keep them going.

Welcome to the fun a 2 day wait is admirable. You are entitled to a back rub
 
Well, I'm a patient guy... why I did not just wait 1 day. Got less than a back rub... got a good scratched back though and a smile.. after a few days ;o) She will have a blast in this thing.

I will drain the fluid to change it clean anyway so why not pull the side plate to inspect is what I am thinking. ?? Thus, I don't want to try to shift and then won't go.

My math was wrong.. This is post #4 so SIX more before pics.. Dang
 
If I can talk to the owners in Truckee, I may be able to answer the question... if they know. If not, then it makes sense to open the side to view the internals, eh? I don't know any other solution to figure it out without making it inoperable. If it is messed up, I will want to fix it of course but maybe not right now as it has been driven successfully for distances for years in the lower gear.

OK.. Now I'm need only 5 more posts to lift off.. Or the moderator could join the conversation and say "Go ahead.. We know you are legit and you are a funny guy..." LOL
 
Nancy found one and so I put the Habeus Grabbus on it ! Now all I will have to do is see if the transmission is OK.

OK, 4 more posts....
 
The shift forks are easy to put in..... when its in front of you.

When the tracks are on and you miss for the third time... know im in wisconsin pulling for you. I believe in you. I was able to save a bad oc4 once upon a time. The po had it locked up. Shift fork was out of place and it had an extra neutral
 
Go up and look at the envelope. That 1 is a message from me. Maybe u can sneak a photo there
 
I forgot to mention that I have zero experience with snowcats, never even have ridden in one until this came up on my radar....

(4 more posts to go !! ;o)

LOL, that was me 13 years ago. It's just money and time from this point forward!
 
Thank you Zspryte. Nice and clean.. I talked to Zimmer (?) that does OC work in Pennsylvania this morning and he says parts are available. He also said that, if I can gain access (I believe I can and view the interior with mirrors and lights) to the side plate on the OC-4 transmission, it was a decent idea to view inside to see if there are any obvious issues.

3 posts to go before pics !!
 
What the heck.. I thought I would try a photo..
 

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Looks like it worked so here are some more. You can see what I found and traced to the rear transmission. I can gain access to the bolts for the cover on the right (passenger) side of the OC-4 and slip the cover off to view.
 

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In the IMG_`1361 photo, it looks like the shift rod is forward and to the left? That would be 3rd gear? Someone with experience might be able to tell...
 
You are in the first range if you pull it straight back you will be in the third range
 
1 r 2 across the front
3 _ 4 are to the back.

The odd placed screw in the cover is the alignment screw. pay attention to it When you pull your cover.
 
Aaaahhh Yes. I do recall the shift pattern on the OC, duh on me. I saw it, it is in the photo, and so there you are. Thanks ! The reason I got confused is in the attached pic that I got off a YouTube video on someone working on their IMP.. but it must have had a different rear end.

Redsqwrl, (and by the way, squirrels are my favorite comedians in the forest!!) What does the alignment screw do (yeah, I know it aligns something ;o). But specifically, what does it interact with on the interior of the transmission? Any advice on this would be helpful and thanks in advance..
 

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Is it in 1st or R? If its "R", maybe the carrier got installed 180 degrees off like BoyToy's did (thread Tranny woes on 1404 Imp) and disabling the OC-4 shifting is how they addressed it. If it really is in 1st gear, I pity the previous owners.
 
I have found out more thanks to Nancy at Spryte Improvement. The panel that I was thinking of removing to look inside is what the shift forks are on so It is not simply, pull the plate off and look. For one, there is not enough clearance to the frame of the cat to allow removal and inspection and also, it would be difficult to impossible to make sure the forks are aligned properly when putting the plate back on.. or at least that is how it appears. Anyone the reads this that has done this, let me know please!

It is in first gear in the rear transmission, as redsqwrl noted in the shift pattern. So, you pity the previous owners but not me, Z ?? LOL. If it is in first gear and shiftable.. then yes, too bad for them and great for me. I'm still trying to get the name of the Truckee search and rescue that had it. My local contacts have not gotten back to me on this.. so maybe I will just call around Truckee to find out contact info and do the search on my own (likely the thing to do).

I will look up the thread you mentioned and see what I can learn.. Thanks for the input!!
 
In the end, if I can't find out anything by contacting previous owners beyond the last two, I will install the shifting mechanism being sent to me by S. Improvement and try to shift it. If it works, what a wonderful thing that would be. If it shifting it creates a problem, then it will get repaired even if I have to trailer it to Utah... and then go again to pick it up... or find someone closer that understands these transmission/rear ends. I've too many projects already to spend the time attempting this myself.

At any rate, I will post anything new I discover and thank all for the help and if anyone has more to add, please do so!
 
SHIFT IT MANUALLY FROM THE BACK!

the suspense is killing me. Z spryte is 100% onto something that is very common amongst OC4 operators...... for the love of god, move that shifter at the rear...... in 2 minutes you will know the data necessary for the us cheer leaders to cheer for you.

and yes that screw aligns your shift forks. don't take that cover off until you feel you need to, as opposed to want to. imps are hands down the most versatile cats ever created 90% of the problems are created by the operator.
 
Whoa... !!! OK... I'll do that, sheesh, LOL. Love the passion Mr. Squirrel... I'll give her a go and let you know. Within all my posts above are the reasons I was hesitant to try....

I have thought about this for days and always came back to this: No bad sounds out of the rear transmission. No metal filings in the fluids. Why would someone want to use this vehicle for backcountry search and rescue knowing that there was something wrong with the rear transmission? Doesn't make sense. The optimist method is the shift the darn thing and see what happens. I've been very tempted and I have felt like the kid that wants in the cookie jar but thinks he may get in trouble as his hand hovers over the lid. Go on, Kid... JUMP !! haha.

I can't drive it right now since I need to change the water pump, which I have and was only waiting for some warmer weather out of the rain but I can see if it will shift.

I'll check on it in the morning.... Thanks for the enthusiasm and the slap... ;o)
 
Another thought here, if you haven’t already, drain the lube from the rear end and use your camera to see what side the ring gear is on. You may have a case of the backwards ring gear. Seriously though, in my previous post, I lined out jacking up the machine or removing tracks and manually shifting per Red Squirrel, and hand rotating drive shaft to see what you have going on. If you have a borescope or have a gastroenterologist for a friend, stick a camera through the drain. I think there are some fairly easy steps you can take to diagnose your issue.
 
I don't know why I did not think of that, Idaho IMP. My dad was a General Surgeon and I have his scope (I've offered, over the years, free colonoscopy's to my friends but (pun intended) no one took me up on it....) Actually, I have a perioscope for endoscopic periodontics that has a 8x10 computer screen and a strong light at the end of the camera fiber that would work perfectly (with a protective disposable sheath so tractor fluids don't contaminate the sensitive camera fiber). Duh (which happens to me now and then...). Thank you for nudging me out of the weeds on this one!!

I will do that before anything else (sorry, redsqwrl.. have to wait a tad.. ;o)

But the colon endoscope reminds me of this fine story: BB King, who's music is revered by many including me, had a birthday. His wife wanted to get him something and she thought and thought about it and then she knew what to do for him! She had a "B" tattooed on each of her rear end (see? there is the connection to this thread) cheeks. When he came home, she bent over to show him and he said "Who's Bob??"

Can I get in trouble on this forum for telling a joke? Hope not.... if so, I swear I will not do it again....
 
Man, I about spewed my coffee with that dialog, I haven’t laughed like that in a while so thank you!
back to the ordeal at hand: I’ll attach a shot I found of my innards of the front half through the side cover. I removed my cover only to reseal. I did not fiddle with the forks at all. Once reassembled, I was paranoid with proper fork positioning So I manually spun the gears with the driveshaft. It seemed fine. Anyway, have a look at your carrier and which side the ring gear is on.
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Your good tell all the joke you care to. In regards to the diff, I would be shocked if it needed to be in one gear (except the reverse option) or something bad would happen. The pinion is the output the input is just a cluster. We need to start a pool. If the ring gear inspection is chossen just pull the back cover, then u can check the brake bands as well
 
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