Imp Brake Adjustment

[cloudcap]

I'm preparing for my first foray into the bowels of my Imp and would like to ask a few questions of those who are older and wiser. The right brake band seems to have given up the ghost -- previously it was just weak, but now I get nothing from it. The master cylinder and actuator are working just fine, so I suspect that the band is either in need of serious adjustment or outright replacement. I've spent enough time with the manual to figure out what a "pillow block" is and that I need to remove two of them in order to lift the rear of the cat enough to expose the back plate of the transmission. But I'm still not clear on some of the other details. For example:

- Do I really need to uncouple the tracks? The manual says to do so in order to relieve tension on the axles, and while it makes sense, I'd really rather not mess with the tracks unless I have to.

- Once I've got everything exposed, how much do I tighten the bands? An earlier thread on Super Imps suggested that you should tighten the nut to 200 inch pounds and then back off a couple turns. Barring better advice, that's my plan.

- I've read the myriad threads on oil and am planning to use either Caterpillar TO-4 30 weight or Shell Donax TC-30. Seem reasonable?

- And as long as I'm in the neighborhood, is there anything else I should be working on?

As always, thanks for the advice.

Ron

 

[cloudcap]

Well that was fun!

I dug into the Imp this morning and was able to find the problem in just a couple hours, and it only took three trips to the parts store for tools. Working on a snowcat is more akin to a tractor than a car, so I've had to supersize my tools. Prior to today I had no use for a half-inch socket set, and I now own a full set, a bunch of extensions, and the longest breaker bar that I could find.

The problem with my wonky right brake was a broken bracket on the band. It must have been hanging by a tread for some time and then finally gave up. I'll order some new parts from our friends in Wallace and then see about pasting things back together. It is obviously too soon to declare victory, but I'm rather delighted that I was able to find the problem in just a few hours without causing any collateral damage to either me or the cat.

A couple photos are attached -- one of the broken band and another of the bent adjustment rod.

Also, I found that I was able to open things up by removing just the rear pillow block. The tension of the tracks did cant the differential down so that the backing plate was wedged against frame. Since I was working on the cat while it was on the trailer I was able to use the chains and binder to down-load the back of the cat and thereby balance the tension of the tracks. Voila! The backing plate was free and I was able to open it up and get to the brake bands. Probably hard to envision all this without a diagram, but it all worked out rather nicely.

Regards

Ron

 

[cabinboy]

Good find ,and it only took 2 hours !! what is the bent bolt for in the first picture for?

 

[cloudcap]

The bolt in the first picture is part of the linkage between the stick and the brake band. When you pull on the stick it pulls the bolt (and thus the lever) to the left (left in the picture, it is actually forward on the cat). The lever, in turn, twists a shaft in the side of the differential that applies the brakes. There's a nut on the end of the shaft (which I'd already removed) which keeps the bolt from just sliding through the lever.

The bolt is bent because the broken brake band allowed the linkage to be hyper-extended. Normally the end of the lever only moves 1/2" to 1", but because there was no resistance from the broken brake band it was able to move forward several inches. Far enough that it caused the end of the bolt to be bent by the lever.

Part of the repair will be finding a way to straighten out the bolt without munging the threads. I'll let you know how successful I was when I get that far.

Ron

 

[fogtender]

The bolt in the first picture is part of the linkage between the stick and the brake band. When you pull on the stick it pulls the bolt (and thus the lever) to the left (left in the picture, it is actually forward on the cat). The lever, in turn, twists a shaft in the side of the differential that applies the brakes. There's a nut on the end of the shaft (which I'd already removed) which keeps the bolt from just sliding through the lever.

The bolt is bent because the broken brake band allowed the linkage to be hyper-extended. Normally the end of the lever only moves 1/2" to 1", but because there was no resistance from the broken brake band it was able to move forward several inches. Far enough that it caused the end of the bolt to be bent by the lever.

Part of the repair will be finding a way to straighten out the bolt without munging the threads. I'll let you know how successful I was when I get that far.

Ron

You can use a piece of fine all thread to replace it. Just cut it to length, and thread it into the one end and run the nuts on the new piece.

When I was just going though and doing a visual before we started the season 100 mile runs we do to haul our freight, I pulled the unit apart to see if all was good, it was.... Brake Bands were still about 80 to 90% good.

Normally I would pull the system down with the tracks attached like you did, but I had removed them for installing all the new springs, seals and bearings on the boggies. I also installed (drove in with sledge hammer) the heavy wall pipes into the boggie axles to give them extra strength since that is where they break the most. Cut off the excess and ground flat, drilled a hole in both ends and ran a bolt though to keep the pipe from moving, but after about an two hour sledge fest, I don't thing that was much of a chance....

I just used a floor jack after removing the rear pillow bearing and shift linkage and it came down where I removed the rear cover.

 

[cloudcap]

Check out the new toys!!

The bracket on one of my old brake bands was broken, so I shipped both off to Spryte Improvement (http://wallace-id.com/foster.html) for a little TLC. A few days and a couple bucks later they were back on my doorstep with new brackets, new linings, and new paint. Pretty spiffy.



Similarly, the threaded rod on one of the linkages was badly bent and it didn't seem easily repairable. Fogtender made the obvious suggestion of just replacing the threaded rod and I felt a little slow for not having thought of that myself, but I found that the original rod was welded in place. Since I was already wasting Pat's time I asked if he could fab up a couple replacement parts and they showed up in the same box as the new brake bands. It seems almost magical to me that you can type a bit on your computer and have fun stuff show up on your porch.



Finally, I went on a quest to find the mythical Shell Donax TC-30. None of the local parts suppliers had a clue as to what I was talking about, so I finally resorted to calling Shell Corporate (800.990.9811). They were able to refer me to a local supplier (http://www.overlakeoil.com) who was willing to get me a 5 gallon pail via UPS or Will Call. I suspect they'd be willing to ship anywhere, so if you need a source you may want to give them a call.



This weekend I'll try putting it all together and see if it actually works.

To be continued....

Ron

 

[fogtender]

Congrats on the new parts (they paint them to make you think the bill is worth every penny of it).

Enjoy the ride!

 

[cloudcap]

OK, the job's finished. Overall it went well, although as with most jobs if I knew at the beginning what I'd learned by the end then it would have taken less than half the time.

Threading the bands through the back of the case was a bit of a challenge. Eventually I tied a piece of parachute cord to the lead end so that I could pull the cord from below while I was pushing the band through the top. That seemed to help it slide into place with less time and effort.

The hardest part was getting the brake strut to slide underneath the brake shaft. Pat warned me that it was a "tight clearance", but I think that's a code word for "it won't fit". I finally hauled out my Dremel tool and ground off about an 1/8th inch from the lower lip of the strut and that did the trick. I don't have a photo of the strut post-grinding, but the one below shows where I did the deed.



The next trick was getting the bands tight enough. Pat suggested using an aluminum bracket as a fulcrum to lift the loose end of the band while installing the pin (as shown in the photo he provided below). I tried that, but was only able to get an inch or so of lift -- not enough to take the band from sloppy loose to good and tight. My alternate approach was to use a block of wood about a foot back from the differential as the fulcrum and a 6' steel bar as the lever. Same principle, but on a slightly larger scale. That gave me more than enough lift to close the gap (about 3") and enough force to literally lift the back end of the cat off the ground.



Everything is back together and I can now turn left and right with equal travel on the sticks. Previously the throw on the left stick was fairly short while the right (the side with the broken band) was long. Right now the travel on both sticks is longer than I'd like, but I should be able to take care of that by tightening up the external linkages. I’m hoping this will get me through next season, and the following Spring I'll go in an tighten up the bands again once they've had a chance to settle in.

Regards

Ron

 

[fogtender]

Everything is back together and I can now turn left and right with equal travel on the sticks. Previously the throw on the left stick was fairly short while the right (the side with the broken band) was long. Right now the travel on both sticks is longer than I'd like, but I should be able to take care of that by tightening up the external linkages. I’m hoping this will get me through next season, and the following Spring I'll go in an tighten up the bands again once they've had a chance to settle in.

Regards

Ron

Congrats, you will enjoy the machine! Hope it is all good rides!

 

[rodre]

Going to revive this thread as it looks like I make be digging into the C-4 sooner rather than later. I had a couple of questions:

1. Where did you get the gasket for the rear access plate on the C-4, did you have to make it?

2. Did you just order new brake bands from Spryte improvement? I would like to have an extra set on hand so I don't have to take them out and wait for them to be relined.

3. Was the Donax TC-30 the final word for the C-4 diff oil? I read alot about various oils for the C-4 while I was waiting on my Imp and I recall having no sulphur in the oil was important due to some bronze internals but now I have forgotten which I decided on lol

Thanks.

 

[rodre]

I have the tracks off my 1404 and it's perched on jack stands and I am at the point where I am going to drop the C4 to get the cover plate off and have a look at the brake bands. I am a little confused with the Imp manual as it says to losen the bolts on the "bearing cover" of the forward pillow block but then to remove the bolts for the rear pillow block and raise the chassis, is this the two bolts holding each pillow blocks to the chassis in both front and rear pillow block or is the "bearing cover" something else? If I just loosen the 2 front pillow block bolts does this give it enough play for the cover plate to pass the chassis? I am guessing I need to disconnect the brake leavers from the slave cylinders as well and the also detach the shifter as well, is there anything else that should be disconnected to avoid breakage? Any help here would be appreciated. Thanks.

 

[rodre]

Wow was that ever easy but a little messed up at the same time. I disconnected the shifter, loosened the 2 bolts holding the forward pillow block, removed the 2 bolts holding the rear pillow block jacked up the diff onto jack stands, jacked up the cab but after about an inch off the rear pillow block it started lifting the diff with it. This left me scratching my head for about 4 hours of inventing new swear words as I was convinced the u joint wasn't letting it drop down enough. Then a few shots of WD40 where the chassis touches the cover plate and prying down on the pillow block while jacking up the chassis I got this:

 

[Snowcat Pat]

Check to see how much gap between the end of the claw and loop end. In other words the end gap, when the brakes are fully actuated.

New they are about 5/8 inch.

If they are touching, reline the bands or risk breaking the claw end.

New linings are 1/4 inch thick, the claw end wears down faster, especially if the claw is bent. Which they usually are.

The roll (spring) pins are sticking out, thats good. Makes it much easier to remove the strut for relining.

You may (probably will) need to do the internal adjustment. There is a well written procedure from mtntopper on this website somewhere.

-Pat

 

[rodre]

Hi Pat,

I am getting Chris at olivercrawlers.com to reline the bands for me. He mentioned he cuts the linings a little longer on the one end to offset the premature wear and the rivets coming through. He also said he will send me the instructions and photos for adjusting the bands from the Oliver Crawler shop manual, I will post the pics and instructions here when I get them.