Hey guys, I have a Cat D6C 76A that the tracks keep jumping off the lower rollers when going backwards. I tightened the tracks up to see if that was the problem but it was no different. None of the rollers are stuck. Is there something else I should be looking for?
Track frame alignment, sprocket bearing failure, track rails worn out, front idler alignment, any photos?
What photos would be helpful? It has near new bushings and sprockets. I watched as it was drove forwards and backwards and the sprocket didn't have any noticeable shift nore the idler. I had wondered if there was an alignment but no idea how to check it.
Can you back up slowly and have someone watch to see where the track is going sideways or wanting to come off? If you lift the front of the dozer can the idlers be rocked side to side? If both tracks want to come off indicates worn idler bushings and/or track frames out of alignment. You could try measuring across the tracks at the back and front of the machine as well as top and bottom. It may show if the tracks are toed in or out at the front. Also check the top carrier rollers are centered with the idlers and sprockets.
It's only jumping off the left side. I had dad move it back and it started to jump off at the rear roller right next to the sprocket. They spun good and didn't seem to have any side play. I didn't check the idler roller in the front for play by hand but it didn't wobble when changing directions. The undercarriage is pretty new. I'm feeling like they didn't get it put back together correctly and need to align it. Will the tracks measure the same to the body? Or is the body off center of the tracks? Thanks
If it's only jumping off one side start by posting photos of the track rollers, links, bushings, etc, etc, on that side. If there's something else someone want to see they'll ask for it. One question: Is the recoil spring & mechanism all in good order.? Spring not broken by any chance.?
The track frame alignment with the sprocket is pretty critical. With the track separated and laid out, you use a stringline along the top of the sprocket, carrier rollers and idler to set the alignment of all three items. The track frame position can be altered by inserting or removing shims from the track frame guide plate that is situated behind the big cast cover with 6 bolts in it, on the outer hub of the sprocket shaft. Toe-in and toe-out is also a critical measurement for track frames. You measure centre-to-centre between sprockets and idlers and compare the variation in measurements. It should not be any more than about 1-2" - 3/4" difference. Excessive toe-in or toe-out is caused by bent track frames, or wear in the outer hub bronze bearing, or wear/breakage in the bearing shells under the diagonal brace caps. Another factor is whether the diagonal brace is bent or not. A diagonal brace with a bend in it can make the entire track frame tilt in, or tilt out, at the top (not vertical). The diagonal brace looks unbreakable, but they're not as strong as they look, and they bend more easily than you might expect. In fact, when the D6C was released in 1963, the diagonal brace was so weak, and bent so often, that Cat had to produce a factory upgrade that involved welding plates top and bottom to the diagonal braces, to strengthen them. This was a free factory upgrade, and my first D6C, purchased in Dec 1966, had this upgrade applied to my tractor by the local Cat dealer, at no cost to me. So you will find a lot of early D6C's wearing plated diagonal braces. My second D6C, bought new in April 1968, had strengthened diagonal braces, and did not need the factory upgrade plating.
From your 1st post I thought both tracks were coming off. Check the roller closest to the sprocket is a single flange and it is centered with the sprocket and is square to the track frame. If it was installed with a bit of twist might cause your problem. Also look if there is a bracket or part of the track frame that may be bent or twisted and is pushing on the track chain. My machine has pieces welded on the track frames to act as guides for the track near the sprockets. I can see they have a bunch of wear but haven't had any issues since putting on new undercarriage. I'm wondering if your D6 could have guides that got deformed or twisted by a rock or something and pushing on the track chain. Also look for signs of rubbing on the sides of the track chains. If there is could be from the rollers or deformed guides. Pics. would help and could show uneven wear on the roller flanges or rails.
I the spring looks good and it takes grease without leaking off. Nothing looks to be damaged. I'll get some pics in the morning. Thanks
The track chain is definitely worn from jumping out. This looks to be a problem they had a while before I bought it. I'll get pictures of the guild. I think all the rollers on that side are double flange. I maybe about to get myself into a lot of work.
I thought the undercarriage was fairly new? Every roller a double flange is very odd and could be the problem. There isn't usually enough clearance from the sprocket teeth to fit a double flange roller next to the sprocket.
The pins don't have any visible wear, the sprockets look to have minimal wear, all the rollers are tight. I'm not sure exactly what all to look for or how to check the under carriage for a good number. I don't believe it was professionally replaced. I bought the thing for 8k not running ( it would start, just die after a few seconds.) I've never working on heavy equipment before this dozer but I'm a quick study so I'll probably call somethings the wrong thing. Sorry for any confusion.
Check this out. If you're right, this is the beginning of a problem.
Show some pics. of everything. It's really hard to diagnose what could be wrong without seeing what you're talking about.
Oz Dozer,you are right about those track braces not being as tough as they look. I had one break on an early D8H 68a 7 roller frame.Wasn’t a big job to weld it though. All my later D8H’s has the thicker wishbones/diagonal braces and have no trouble. The big bushes at the back need looking at.They will be pretty worn in the op’s D6
Ok now that I know what I'm looking for the sprocket doesn't line up with roller at all. It's withing 1/4 inch on the inside and close to an inch on the outside.
I didn't mean to send the same picture 2 times but I also measured to the body from the idler and it seems to be about 1/2in out. Which is close to what my sprocket offset is off. Also my back roller is a single and the rest are doubles. The otherside appears to alternate like the book says to do
At least you have a single flange in front of the sprocket. That eliminates a double flange issue. You have an alignment issue that others have raised.
It's not looking good. The nut just fell off when I took the cover off. I feel like I'm about to learn a lot.
That roller is completely wollered out. Now to figure out how many more have suffered the same fate.
Yeah that's the sprocket
There's an entire thread on final drive repair you can read through if you haven't already, entitled "My D6D". Is there a handful of metal in the other side as well.
Well I am no expert and there is no other way to put this, but I think that is completely buggered. You can even see the bearing that supports the outboard end of the bullgear/sprocket hub.
Repairing older style dozer final drives D6D Had a friend that ran those older cats he told me if your doing the final drives go with cat easy stuff to get at use after market he would do his finals every 3 thousand hrs. he always replaced the bearings gears he would sometimes just switch sides. HeavyEquipmentForums
That's not only a steep learning curve you're staring at, it's going to hurt your wallet, big-time. Not only the outer hub major repair, but the final drive needs to come apart, and the dead axle will have to be pulled as well, to rebuild that destroyed thread - and it's entirely possible the taper on the dead axle has been damaged, too.
Even looking at the sprocket in relation to the roller in front of it, something looks off. The sprocket teeth should center with the roller. It looks like the roller or the sprocket is offset. Could be camera angle though. I feel sorry for you and hope it doesn't cost too much to fix.
I have a service manual and parts book for my machine but neither tells me any thing about tolerances. The service manual gives how to replace or tear down but not how to tell when a part is out of tolerance. Is there a book I can get that does?
Sounds as though you are missing the section entitled "Specifications" for both the powertrain & undercarriage (if they are separate). Unfortunately the system does not contain information on the 76A prefix machine.
Yeah I can find it for the engine but the rest doesn't seem to be there. It seems as though the 76A was a rare serial number.
I have a D6C with the serial# 76A5579 I'm told it was manufactured in1968. When you do decide to look for parts for yours, if you go CAT you'll need to be sure and tell the parts slingers to look up your serial number/parts in the Legacy Book, otherwise you'll not be getting numbers/parts for your machine. I bought some manuals for my machine from a reprinter that handles the older CAT books. when I get to the manuals I'll get you a website. I lied, there is no identification on the books I have and I can't find the name of the company that printed/sold them to me. I thought I purchased them using Paypal but no record of that transaction. It just says 'Licensed under Caterpillar Tractor Co.' I'll try and find the site on the internet....I think that's how I got the information before.
Specification is listed as part of section 16B-40 in the service manual which is 28 pages. If it's just the one page of Specifications you need I can post that.
Here's some manuals on Ebay to, look like originals. CAT Caterpillar D6c Service Shop Repair Manual Tractor 10k 99j for sale online | eBay Find many great new & used options and get the best deals for CAT Caterpillar D6c Service Shop Repair Manual Tractor 10k 99j at the best online prices at eBay! Free shipping for many products! www.ebay.com
The 76A D6C is not rare, it was a very popular tractor, and Cat built over 6000 of them in Peoria. The problem with the Cat service manuals is that they comprise a number of separate books - Specifications, Assembly and Disassembly, and sections for each major component area. But sellers pull out sections of the manuals, and try to sell them separately for big $$'s. Look for a complete service manual that hasn't been raped of the good sections.
That one seems to cover a plethora of Serial Number prefixes but unfortunately not 76A.
And the $64k question to ask any online seller is - “Is it complete.?” In other words is every separate document that is listed on the Contents page (1st page inside the hard cover) actually in the binder.? Often a reputable seller will put in the description of an item that section “X” is missing.
I didn't notice that Nige, I gave the link because of all the books in the listing thinking there may be one in the complete listing if the OP looked through them all. But good catch on the one in the primary listing.
With 6000 machines built, it would seem there would be a set of manuals floating around somewhere a person was done with and would like to unload. Seems odd that the 76A model is the one that's the rarest.
Interchangeable models with the 76A are 73A (Australian-built), 83A (U.K built) and 96A (Japanese built). All these tractors are virtually identical, just built in different countries. There are small differences, such as the Japanese tractors originally used Nippon-Denso or Mitsubishi electrics, whereas the U.S. built ones used Delco-Remy electrics. But the service manuals are interchangeable between all these models of D6C. In fact, when I bought my new 73A D6C in 1966, it came with a 76A (PS) - 74A (DD) service manual. I still have it.