Just got done rebuilding the differential on a JD 310C after it failed (cross shafts broke and damaged the housing and some gears). I was getting ready to put the axles back on and noticed some damage on the side of one of the brake plates. Pulled the plate and found the dowel pins were sheered and pieces were loose behind the plate getting ground up. The holes are pretty badly wallered out on both the axle housing and plate side. I checked the other axle, and the pins had also snapped, but the damage hasn't gone as far. Does anyone have any experience with this and what the cause might be? I believe the brakes were still working at the time the machine went down due to the differential, but I'm trying to figure out if there is a connection - I'm guessing not, since it affects both axles. These are the older design brakes for these machines, with the return springs and no automatic adjuster. Any suggestions on how to repair it? Sleeve the holes, or drill new ones? If we put new holes in, they would probably need to be outside the ring gear circumference. We're looking at through-drilling a pilot hole from the inner (braking) surface of the brake plate into the axle housing to get alignment, then reaming out to right size and depth for the pin from the outer back) side. Seems like this would be a common problem, those pins are going to be under some pretty serious sheer load while extended when the brake is activated, but I haven't been able to find any discussions about it. Thanks for any help you guys might have, HEF has been awesome for tips working on this machine, so this is the first time I've needed to post a question of my own! Not a lot of experience working on this big stuff. - Steve
I have never seen those dowels get damaged. FWIW ,Deere has been using dowel pins to locate brake pistons for 50 + years. I believe the dowel is part # T21428 . Dowel specs are 3/8 in diameter and 1 3/4 in long. Did you remove the 3 sheared dowels from the axle housing before taking the picture ?
What does the brake disk and the planetary assembly look like
Thanks for the spec, I had the p/n but wasn't sure about the length. Yes, I fished them out with a magnet. They were broken about 1/8" below the edge of the hole, roughly the same as the other pins securing the ring gear. Here's a close-up of one of the pins still in the hole on other (left-side) axle, along with the piece that broke off. On that side, they were still trapped in the holes and hadn't gotten rolled around the axle yet, but they still wore out the holes on the plate. On an aside question, is it normal to find a paste of fine filings in these transaxles (some visible in the this pic of the plate)? I assumed it was material from the parking brake band, but it could be ground-up differential parts - just seemed like way too much for that, literally a couple cups of it.
Thanks for the reply. I think both discs and planetary sets look good, along with the bearings. Measured 0.030" - 0.040" on the disc grooves, no sign of scoring or damage to the planetary gears and the bearing runs and looks smooth. There is some scoring on the surfaces the inner brake plate O-ring runs on, but that's about it.
A couple of cups of filing paste is not normal. May be a poor clean up from a previous failure ? Any signs of someone being in to the transaxle before ? . Also the braking surfaces of the piston and the transaxle housing ?
Not that I could tell, seemed to be be all original parts and the retaining tab on the parking brake cap screw didn't look like it had been re-set before. Other than the obvious damage to the differential (shattered cross-shafts that got ground up a bit), everything looked pretty good - even the diff gears were pretty clean. The ring and pinion barely showed any wear, just a small chip in a ring tooth at a non-contact point where a diff shaft hit it as it came out. It's a relatively low hour machine, despite the age. The parking brake band was pretty worn (I know it had been operated while engaged more than a couple times), and I replaced it, so that's why I thought the sludge was from that. Edit: All the sludge was on the differential side as well, and some that had gotten out into the axles through the ports I assume. The transmission side was clean on the bottom. Looks very smooth, no sign of scoring or anything like that. I can get a pic in the morning if it would help.
I suspect some operator abuse was involved here. I question what would happen at road speed if the diff lock was engaged and the operator nailed just one brake pedal. That may exceed the shear load of the piston dowels.
It's hard to tell how long they've been broken, but we've had it about 25 years and I'm sure nothing that extreme happened since then. It only gets used by two owners on a 10-acre parcel on dirt roads in first or second, and only use the diff lock if it it gets stuck somewhere. The most load the brakes see is holding the machine while positioning on a hill or going down it, hardly what should cause that kind of damage. It's previous life was working for the power company, so who knows what might have happened there. We don't even put 100 hours a year on it, so I guess it's possible they've been like that for ages, but I would have thought allowing the pistons to rotate under pressure would have chewed up the O-rings and caused the brakes to fail by now, and they're in pretty good shape and we weren't having any trouble with brakes holding. We'll try to figure out a solution and I'll try to post updates. Thanks for the input!