# Bombi differential oils



## lupinelandscaping

Greetings,

I have recently purchased a 76 (I think) Bombi and have spent the past few weeks restoring it. It was actually in pretty good shape to start, so it was a good base for my first cat. I have been reading all the posts here for a few months and wanted to thank everyone for such a great forum.

Anyway, a couple of issues that I have run into are about electrical and the differential. There have been so many splices in the electrical, I am at the point of looking into a new wiring harness. Does anyone know if they exist and how much?

As for the differential, I have called around and read a bit. I have come up with many different oils to use...is that why they call it a differential? I have heard to use Shell Donax TD, TO-2, TO-4, any 80w-90 synthetic, any ATF....and a few more. I run this machine in SW Colorado at anywhere between 7500-10,500'. I was at a loss a few weeks ago and went ahead and ran a 75w-90 synthetic. After running for a while, I can hardly keep my hand on the outside of the diff housing. It also smells like burnt oil. What happened? This stuff wasn't cheap either. Any advice is much appreciated. 

Thanks,
Steve


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## Radar4xfour

Steve,

As a fellow Bombi owner I’ll take a stab at answering your questions. First off I’m just about finished with the rebuilding of my Bombi differential, take a look at the post http://www.forumsforums.com/3_9/showthread.php?t=23114 for a few pictures and comments. I initially started by wanting to change just the brake bands but ended up finding a tooth missing from the ring and pinion gear, hence the rebuild. What started the whole ordeal was poor steering of the unit. I can tell you that 80W-90 is the wrong lube to use. It’s great for the ring and pinion gears but stinks for the brake band material. The gear lube saturates the brake lining material turning it to mush creating poor steering characteristics. Have you ever had a full floating truck rear end with a bad axle seal? The gear lube contaminates the brake linings and creates braking issues. Replacing the seal and lining cures the problem. Currently, at the suggestion of forum member Boggie, the Bombi differential is filled with Caterpillar TO-4 trans-hydraulic fluid. The fluid is designed to operate in gear cases with steering brake applications. John Deere and other have similar products. I will know more in the next 2 weeks when I’m completed with the reinstallation of the cab and a few other items and am able to take out for a test. I’ll be sure to let you know how it turned out. Prior to the rebuild it took 2 hands on the steering levers and lot’s of muscle to turn the machine. I’m expecting a huge difference when I have it up and running again.

Do you know if your machine has a differential oil cooler? Lift the operator’s seat and down in the hull there will be a small hydraulic oil pump driven off the drive shaft. In turn the hydraulic fluid is filtered and runs thru an oil cooler mounted at the rear of the machine on the radiator. My task this weekend will be flushing the cooling system.

Electrical wiring on these machines is straight forward. Your biggest issue will be correcting the 30+ years of others adding to the wiring. Sometimes it’s best to remove the added on circuits and start over.

Do you have the operator’s manual, engine parts manual and the machine parts manual?

Hope this sheds a little light onto your issues.

Radar


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## snowbird

Welcome to the yellow world (at least that's my Bombardier machine color)!  I've gone to Fleet Farm and bought the trans-hydraulic fluid listed for John Deere.  I'm suspecting that might be less expensive than "brand name" supplies, and I'm assuming old Uncle Sam has someone protecting us poor ignorant consumers as to product compatability. (Does that imply I'm in the market for the purchase of a big bridge in San Francisco?)


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## mtncrawler

If you think the differential is running too hot it might be your operating habits. With these steering differentials don't ride the levers, be firm and point the machine briskly. What part of SW Colorado?


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## lupinelandscaping

Thanks for the replies everyone.  I will be draining the 80w-90 in the morning.  Now that you mention it Radar, my steering SUCKS!  I had much better control with whatever was in it previously.  I only changed it because it had been sitting for a while.  I'd love to see some pics of your diff rebuild.  I suspect I will be doing this after the season.  Unfortunately, I don't have a diff cooler.  This is just the straight ol Bombi with no options.  It came with the canvas doors and a poorly fabricated wood top.  It does have an original roll bar and the Bombi ROPS.  I have since fabricated a new top.  I will get some pics up soon.

I suspect that it is getting to hot because I have to use some good force to turn.  It it much easier to turn when the cat is cold, then gets increasingly worse the more she runs.  

Yeah, the worst part of the electrical is the splicing.  It drives me up a wall.  I used to be an electronics tech and that certainly helps for this aspect.  I guess I was just looking for a cleaner, easier way out.

Mtncrawler, I'm just east of Durango in Bayfield.  My shop is in Durango on a private ranch.  I got real lucky with that!!  1200 acres or so to romp around on and trails conecting 4 neighboring ranches.  That, totals a little over 2000 acres of playland!!  

My goal is to set the Bombi up nice and sell it.  I really think I'd like to try out an Imp, Super Imp or Spryte.  I have a line on a old Thiokol Packmaster 1200B  (i think thats right) with a Ford diesel if anyone is interested let me know.  

Thanks again for all your help.

Steve


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## lupinelandscaping

Just a thought...when I drain the 80w-90 out is there something I should try to "flush" through there to clean off the brakes?  Hopefully they're not shot or that rebuild may come sooner than anticipated.


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## Radar4xfour

At this point your brake bands are saturated with the gear lube.  I would remove as much lube from the differential as possible (maybe vacuum the last little dribbbles out the drain plug?) and refill it with trans-hydraulic fluid.  Then run the machine to get the lube good and warm (lots of turning to help heat the brake bands and hopefully "cook" out some of the gear lube from them), drain it while it's hot and refill again with the trans-hydraulic fluid.  It's not a great solution but may bring the steering back into acceptable levels until you can dig into the differential case.

Radar


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## lupinelandscaping

Thanks Radar.  That's exactly what I did.  It seems like I have a bit more steering, especially once things get hot.  I'll cruise around for a couple of days and change the oil again this weekend.  I let you know what happens.

Steve


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## lupinelandscaping

Steering still really hard.  Haven't changed oil the second time yet...wondering if pads are shot????


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## snowbird

If by steering hard, you mean you really have to pull hard on a lever to get your machine to turn, you might have low level of brake fluid in your master cylinder, leak in your brake line, need to adjust the brake band (right in front of the differential if the Bombi is similar to my SkiDozer).  I'm suspecting that my own steering difficulty might be that the brake linings are really worn thin.  I think replacements are about $300, so I've been trying to live with tired arms and shoulders.  Maybe you'll have to bite the bullet.


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## lupinelandscaping

Snowbird,

Yeah, that's exactly what I mean by hard to turn.  I didn't know there even was a master cylinder or brake lines on the Bombi.  I thought it all just ran off the differential or "in" the differential????


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## Radar4xfour

There is no master cylinder in a Bombi.  The steering levers are connected to a simple linkage system that act directly on the brake bands.  Skidozers on the other hand do have a master cylinder that in turn provides fluid to 2 slave cylinders which act on the left and right steering bands.

Hope that helps,

Radar


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## lupinelandscaping

Today I just couldn't take it anymore...I dug into the dif. Not really all that bad getting to it, but taking it all the way out I can see a good amount of shop time. I was able to move the cab forward and pull the gas tank to access the top of the diff and finally inspect the pads. While digging in I found that the left pad was riding off center of the drum and wore the pad a little funky. Both bands were grabbing where they are connected together and not much wear or no wear on the other part (toward operator). Both drums are scored a little but nothing too deep. Also, I found that that the drum have a little (maybe 1/8") of play side to side and little to no play up and down. Is this normal? Is this OK? I included some pics this time. Now comes the questions of: Where can I find new pads or someone to replace them? What should I do about the drum movement? I am desperately hoping to not remove the entire dif.

#1 points to the worn out (front of dif) side of the bands.
#2 points to the uneven wear on the outside of the L band.
Thanks,
Steve


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## Bushwacker

I  have a 78 Bombi and got the diff cooler pump working- It was recommended that I use Type F trans fluid


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## lupinelandscaping

I don't have a cooler pump.  Was that stock?  can you take some pics of the line set up?  Thanks


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## Radar4xfour

Steve,

I don’t know when the coolers became available on the Bombi. If yours did not come with one from the factory it will somewhat difficult to install one. Take a look at the attached picture for reference. The yellow arrow points to the suction tube on the differential case. Do you recall seeing this when you had your machine apart to do the steering bands? If it was there the machine had a cooler on it at one point. The return line back into the differential case is visible from the cabin without having to disassemble anything. Look for a line or may in your case a pipe plug close to the pinion yolk / driveshaft flange. This is where the return oil comes back into the differential case. The return oil provides lubrication for the pinion bearings. One other thing to look for is a bulge at the bottom of the differential case about the size of a hockey puck. This is the sump for the suction line. I have attached a page from the Bombi manual that shows the hydraulic layout of the cooler. The circle with the triangle in it (item #7) is the hydraulic pump that runs off the drive shaft.

I had my machine out for the first time this winter after the ring and pinion surgery. With the correct oil, new brake bands, new ring and pinion it is a very different machine! Steering is 100% better! Not much force is needed on the steering levers to change direction. I think Boggie is the man that deserves some of the credit, that’s who I got the brake lining material from. So far it's good stuff and recommended!

Hope this all helps,

Radar


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## Alpine Man

I also put 80-90 in my diff and now expierence turning difficulty. Did the flush and oil replacement work that was recommended earlier in the post. Or did you have to do a brake lining replacement?

Don


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## Bushwacker

I just drained and replaced the fluid, I haven't touched the diff or bands


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## Alpine Man

Bushwacker said:


> I just drained and replaced the fluid, I haven't touched the diff or bands


 
 Did you have 80 90 in there before and were you having steering problems with 80 90? Did the problem go away after just changing the lube to transmission fluid?

Don


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## Bushwacker

The reason I changed the oil was due to a leaking seal on the sprocket hub. After i repaired the hub i asked through this site what was the recommended type of diff oil. Also I got the info about the diff oil cooler and pump operation. I put a new belt on the pump and installed a new spin on filter that's used for the diff oil. The steering seems to have inproved with the type F fluid that was recommended to me. I have not experienced any temperature problems while using this fluid. I might add that i have not used the Bombi much this past year so I may drain and flush the diff again this spring.


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## Bushwacker

When i drained the diff i did'nt know what was in the diff but it appeared to be a thicker oil such as 80-90 gear oil


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## Farmer Joe

Radar4xfour said:


> At this point your brake bands are saturated with the gear lube.  I would remove as much lube from the differential as possible (maybe vacuum the last little dribbbles out the drain plug?) and refill it with trans-hydraulic fluid.  Then run the machine to get the lube good and warm (lots of turning to help heat the brake bands and hopefully "cook" out some of the gear lube from them), drain it while it's hot and refill again with the trans-hydraulic fluid.  It's not a great solution but may bring the steering back into acceptable levels until you can dig into the differential case.
> 
> Radar


I have been told to use type F automatic trans fluid have you ever heard that ?


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## 300 H and H

Farmer Joe said:


> I have been told to use type F automatic trans fluid have you ever heard that ?


Farmer Joe, Do you realize these posts your asking questions in are from 2009?


Post #2 in this thread has the correct answer. Do not muddy the waters with hear say please...


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