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Author Topic: "Drop Box" Q. Pinion Gear & third member  (Read 2003 times)
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Posts: 31

« on: May 23, 2010, 12:32:23 PM »

So, what is the Pinion Gear and where does that fit into the drop box drive train?  Someone mentioned the "third member" as a componant relative to this setup. What's the "third member".  
Also, I'm wondering if the oil from the drop box is in common with the oil in the differential?  If so, and I have ground the gears to distruction in the drop box, what's the likelyhod of having created a problem with the differential and axel?

Really appreciate all the help you guys have been. Monday will be a pivital day talking with the repair shop whether they will work on it in the emediate timeframe or not.  It's costing us a bundle having to rent a van and stay in motel.  Hopefully they will take that into account and help us get back "Playin On The Road Again".

Thanks again,  Tim.


'66 MCI5 6v92 w/HT-740
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« Reply #1 on: May 23, 2010, 01:16:25 PM »

I'll try explain a little, the drop box has only 2 gears 1 the input at the where the drive shafts connects 2 a idler gear in the middle of the box.
The differential some call a third member or pumpkin instead of a yoke the drop box systems have a gear on the pinion shaft inside the drop box, that gear is separate from the 3rd member or drop box and cost around a 1000 bucks new. 
The idler meshes with pinion drive gear to work and the oil to both are common.
One thing if you need a 3rd member one from a Eagle will not only the drop box is the same Eagles have larger axles than the MCI 5 confused ?

good luck wishing you the best

Life is short drink the good wine first
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1980 MCI MC-5C

« Reply #2 on: May 23, 2010, 02:28:28 PM »

I'm not a thousand percent on this, but my manual strongly implies that the drop box and the differential/rear axle share the same lube.  so if you lost the drop-box to differential joint, you lost the fluid in both.  the wheel bearings are lubed by the same fluid, I do believe.  Until you take it apart, you really can't tell what's broken.  It could be anything in there.  It might even be the differential gears, not the drop box or the ring and pinion at all.  I've blown up differentials on things and it sounds just like what you describe - kind of skipping and sounds like missing teeth.


1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Tatamagouche, Nova Scotia
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