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Contributor
Location: San Rafael, CA | I'm wondering what is the best way of determining how worn the ring and pinon is without disassembly? Not having ridden in an FMC before purchasing #1027, I don't have a reference point for the noise coming out of the unit. There are 3 distinct noises... a whirring when on the gas especially going uphill, a 'wha...wha...wha' when cresting the hill as pressure is released from the gearing and a more significant whirring sound when going downhill and the load is resisting the gearing.
I have replaced the differential oil with 140wt hypoid oil as recommended and there were no metal shavings in the oil, didn't smell burnt but, had a bit of metallic sheen. I have checked all the u-joint components which were upgraded by Len without any issues noted. The differential main input shaft shows minor spline wear by noting the yoke moves ever so slightly though the nut is tight.
With the transmission in neutral and the parking brake off, I can move the main input shaft back and forth taking up 'the lash' more than seems appropriate. Any ideas???
Anyone familiar with having these differentials rebuilt? Any source for new ring and pinon sets or good condition low mileage units?
Lastly, I'll be attending the Oregon rally and would be open to picking up a unit if mine is at the end of its service life.
Thank you for your comments in advance.
Robert Craig
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Extreme Veteran
 
Location: Ignacio Colorado | Better explain the yoke moves and nut is tight. Does the yoke move sideways? Front to back? I get the twists to take up gear back lash but the other isn’t right.
Bill |
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Contributor
Location: San Rafael, CA | Got it... when looking closely at the nut securing the main input shaft yoke turning it back and forth taking up the slack, I noticed an almost imperceptible movement of the yoke where it meets the nut.
There is very little play forward and aft when pulling or pushing on the yoke or driveshaft.
Hmmm... |
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Extreme Veteran
Location: Ignacio Colorado | No play front to rear is acceptable with a pinion shaft or yoke. Hmmm. Need to figure it out before putting more miles on it. That yoke tightens a little past hell if I remember right. Need to check the service manual specs.
Bill |
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Extreme Veteran
Location: Ignacio Colorado | Just looked and the yoke nut spec is 500 to 600 foot pounds then install cotter pin. Hell plus a couple!
http://www.fmcmotorcoach.com/files/Manual/18_diff.pdf
Bill
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Elite Veteran
Location: Oceanside, CA | I had to borrow a 5ft long 3/4" drive snapon torque wrench to torque that nut...hard to believe it would have loosened but if you're in there then definitely double check it. You do get a lot of rotation of the yoke, those are huge gears so the combination of the ring/pinion lash and the differential spider gear lash/load is more than you get on a light duty vehicle. Can't say I ever noticed any particular noise like you mention...maybe it was something it always did and I just accepted it as normal...I know I towed nearly 8000lbs back and forth to Moab (7000ft climbs/decents) 3 times without issue so I'd have to guess that this is a new issue. Good luck chasing it down! |
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Contributor
Location: San Rafael, CA | Hi Len,
Thank you for your comments and it's most likely my unfamiliarity with the beast as my father had a similar comment in both his '55 Flexible and '65 MCI buses had a particular drive train noise due to the gears being cut differently than passenger vehicles.
Also, with the platform bed and storage covering the area completely it was impossible to hear it but, with the transmission cover exposed and no carpet down yet it is easy to identify the sound.
I want to be a good steward of this unique FMC and simply don't want something to be ignored leading to anything catastrophic.
Any suggestions of another FMC owner in the San Francisco area that might be open to taking a test drive to compare it with their coach?
Thanks again, RC
Edited by TravalonSF 2020-07-29 1:20 AM
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Elite Veteran
Location: Oceanside, CA | Yeah, I hadn't thought about that, but, with you removing all that, there probably is a lot more engine/trans/diff noise than before, I remember taking it for test drives before I built the bed structure when it was just plywood floor back there and the bare aluminum cover and saying to myself..."I hope I don't have to live with all that racket!"...some sound proofing might be the only needed fix! LOL!
Honestly, large rockwell axles are fairly loud, the military 6tons we haul on the craft drive by me when I'm riding my bike back and forth to work and you can distinctly pick them out..
Maybe drive it another couple hundred miles and take a small sample of diff fluid, if it remains clean I wouldn't worry too much, that doesn't mean there isn't any wear but, some wear would be expected. If it's making actual chips/shavings of any kind then that would be a different discussion...another troubleshooting tip would be to clean off a couple spots on the diff and install some stick on temp tabs that will record the max temp, that would give you an idea if it's running hotter than you want. A diff temp gauge was something I considered but just never got there.
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Extreme Veteran
Location: Ignacio Colorado | I thought pinion yoke movement has been found. That is what needs to be investigated. That would match your noise.
Bill |
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Elite Veteran
Location: Oceanside, CA | Yes, I agree (and recommended double check of torque on the yoke nut above).
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Contributor
Location: San Rafael, CA | Sounds good and I'll report back on the oil sampling and heat readings.
How did you hold the yoke for tightening the bolt? I can't image it is good for the unit to twist against the internals.
Thanks for the advice!
RC |
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Elite Veteran
Location: Oceanside, CA | It was a SOB, I took a piece of 1/4" thick flatbar steel (long enough to get to the driveway at an angle and then welded a small landing pad on that) and bored a hole in it large enough for the yoke socket and also drilled the 4 ubolt holes in it and used standard hardware to bolt it up, this did a good job of holding the pinion still.
If (after you recheck torque) still believe you have movement of the pinion (moving toward the front or back of the coach) it may just be that the pinion bearings are worn, you can pull that entire pinion input group and just have a shop replace the bearings (keeping the pinion depth shims the same) and reset the preload, they can do all that on the bench pretty easily...since you aren't changing gears you wouldn't have to do a full gear "set up"
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Elite Veteran
Location: Medford, OR | I would probably make an appointment with a shop that has a good quality (snap on, matco etc.) 3/4" air impact gun and have them buzz that nut tight. No need to worry about hurting anything inside the pumpkin, that steel is hard. A 1" gun would be better, but your not going to get something that big in there. |
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Elite Veteran
Location: Oceanside, CA | I think even that would be a tight fit...that prop shaft is only maybe 8" long. |
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Contributor
Location: San Rafael, CA | Thanks guys and I'll try to record a video of the microscopic movement of the yoke. It might be me simply being overly cautious!
Stay tuned on this issue...
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Elite Veteran
Location: Medford, OR | Alright....Time to pull the tranny back out. lol
3/4" rat$hit and socket, long piece of pipe, block the tires, have someone stand on the brakes if you think you need that. Crank on. If you had 4' of length, and say you weigh 200 pounds, that's a lot of torque. |
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Contributor
Location: San Rafael, CA | You mean something like... http://www.fmcowners.com/mbbs22/photos/show-album.asp?albumid=214&p...
I'll report back in a few days!
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Elite Veteran
Location: Medford, OR | Yep!!! lol
One thing to take into consideration before removing that driveshaft.... I would drive the rig up onto blocks to get it higher off the ground, you will need room for breaker bar function. Don't ask me how I know this.
http://www.fmcowners.com/mbbs22/photos/show-album.asp?albumid=200&p...
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Differential whining... how much is too much???
