Rear Axle Problem

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PaulLima
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Rear Axle Problem

#1 Post by PaulLima » Mon May 08, 2017 12:13 am

I recently installed a newly rebuilt 741 transaxle in my '60 Roadster. After about 200 miles, on left turns, it sounded like the RR tire was rubbing on the fender. I looked at the tire, there were no marks on it, so I jacked up the car and found that I could easily shake the wheel. I removed the axle nut (the cotter key was in place and in tact) and found that the axle nut wasn't even finger tight; it took about 1/8 turn to be finger tight. When I put it together I am certain that I applied over 400 lb-ft torque to that nut before installing the cotter key. I re-torqued to over 400 lb-ft and re-installed the cotter key, and it seems to be ok now. I cannot figure out how it could become loose, and very loose at that. Any theories or suggestions would be appreciated. Thanks!

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Bill Sargent
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Re: Rear Axle Problem

#2 Post by Bill Sargent » Mon May 08, 2017 3:08 am

Paul,

I had the same issue on a newly rebuilt 741 in my 59A on my way back from Santa Fe to Seattle in 2013 after the holiday. About 1700 miles after installation the axel nut came loose. I too had used 400+ foot pounds and we theorize that the splines in the drum were worn, which caused the nut to come loose. We reinstalled the drum with over 400 ft lbs and made it back to Seattle. Upon removal back in Seattle the splines in the drum were worn and I had a new splined insert installed (Martin Wills in Colorado Springs). No problem since. Did you check the splines in the drum before it was reinstalled?
Regards,

Bill Sargent
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Vic Skirmants
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Re: Rear Axle Problem

#3 Post by Vic Skirmants » Mon May 08, 2017 7:34 am

Did you use the correct shim under the small O-ring? The hardened one, not the soft VW type?

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PaulLima
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Re: Rear Axle Problem

#4 Post by PaulLima » Mon May 08, 2017 9:17 am

The splines are a nice tight fit with no discernible play. The washer, however, is unknown, and is now chief suspect. Thank you both!

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Re: Rear Axle Problem

#5 Post by Felix Macaluso » Mon May 08, 2017 11:22 am

I had the same problem driving home to SoCal from a PCA parade in Boston. Noted a skroacking noise from the rear at certain times and did an inspection in Dayton, OH. Found a rear axle nut loose to the touch. Only the cotter pin kept the wheel on. Why the Porsche engineers thought they needed that with 400+ ft-lbs is beyond me but it saved the car. Fortunately I had the correct socket and found a breaker bar. Jumped on it and drove home without a problem. I replaced the thrust washer and tightened to spec. I drove the car for many years without incident but never got a definitive answer as to what happened.

Felix
 

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Jacques Lefriant
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Re: Rear Axle Problem

#6 Post by Jacques Lefriant » Mon May 08, 2017 11:28 am

lesson: retorque the nut after running a while.
 

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PaulLima
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Re: Rear Axle Problem

#7 Post by PaulLima » Tue May 09, 2017 5:31 pm

I think Vic nailed it. I just got a new Rear Axle Seal Kit from Stoddard and I HOPE that washer is correctly hardened.
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washer 356.34.402.JPG

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Re: Rear Axle Problem

#8 Post by Jon Bunin » Tue May 09, 2017 6:03 pm

Paul, that minor deformation on the inner edge is common, even with hardened washers.
Can you flex or bend the washer easily with your fingers, or is it very stiff?

Based on that one photo, I don't believe that washer was the reason your axle nut was coming loose.
Jon Bunin

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Re: Rear Axle Problem

#9 Post by Jon Bunin » Tue May 09, 2017 11:06 pm

For comparison, here are the remains of a bad washer and o-ring.
The outer portion was extruded, separated, and folded itself around the bearing race.

This would cause the rear axle nut to loosen.
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DSCN0975.JPG
DSCN0976.JPG
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Phil Planck
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Re: Rear Axle Problem

#10 Post by Phil Planck » Wed May 10, 2017 8:23 am

Great photo and explanation Jon.

Thanks - Phil
Phil Planck

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PaulLima
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Re: Rear Axle Problem

#11 Post by PaulLima » Wed May 10, 2017 9:38 am

The washer was not bendable; very stiff. I now understand that it was normal and probably not the cause of my mystery. But I've re-assembled the axle with new seals and washer and lots of hope that whatever it is is now behind me...

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PaulLima
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Re: Rear Axle Problem

#12 Post by PaulLima » Tue May 30, 2017 6:33 pm

Final update. As mentioned above, the washer/oil slinger is correct (the hardened one). Also as mentioned above, the problem is with loose splines. Martin Willis at The Machine Shop in Colorado Springs (nfo@mwthemachineshop.com) was able to tighten my drums up to where they fit like the factory wanted (they cannot be put or or taken off the axle without using proper tools!) Many thanks to responders, and especially to Martin, who is a very nice, very knowledgable Porsche friend and asset.

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PaulLima
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Re: Rear Axle Problem

#13 Post by PaulLima » Sat Jun 10, 2017 11:21 am

Well, that wasn't the end of the story. The tight splines definitely are a very good thing and certainly helped, but didn't completely solve the "coming loose" problem. After 100 miles I checked both rear axle nuts and one was loose again. After talking to Martin Willis, he suggested that the spline insert was slightly too short (depth) and that the axle nut was actually clamping on the axle splines and not the drum. He suggested an appropriate washer, which I did install. After another 100 miles, both axle nuts remain at ~400 lb-ft torque. Thanks Martin!

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Re: Rear Axle Problem

#14 Post by Jacques Lefriant » Sat Jun 10, 2017 12:06 pm

Hi Paul
were you using an "A" nut with the wrong washer or the proper "B" nut??
j
 

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PaulLima
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Re: Rear Axle Problem

#15 Post by PaulLima » Sat Jun 10, 2017 6:36 pm

I think it is the correct one; they look like this
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Rear Axle Nut.png

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