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Changing oil in final drive - 850T

S

Sporticus

Just got it firing!
Joined
Aug 25, 2013
Messages
23
Location
Western Massachusetts
I have a 1975 850T and my not-terribly-adequate Haynes manual only shows how to check the final drive oil level. I haven't crawled on my back to look at the underside of the final drive, but I can't feel a drain plug. Question, although it may be obvious: how do I completely drain the final drive? Thanks.
Scott
 
Remove fill plug. Then use a 17mm wrench to remove the drain plug. Once drained, install drain plug (with new sealing washer). Measure 250cc of 75W90 gear oil and pour it in. Do not believe the level plug. I lost a rear drive on my T when I filled to the level plug since it wasn't enough oil. Possible an air bubble or it just ran down the back side and out. Also some early 850Ts had the Eldorado style rear drive where a lower cover was secured by 6 Allen head screws. Apparently you have a later model, or the rear drive was changes somewhere along the way.
 
Thank you John. I have the Eldorado style drain with the allen heads, which confused me. Maybe my 850T is an early 1975 and missed the jump to the later drain?
 
On my 850T there is a ribbed plate held on by 6 allen screws - this needs to be removed to drain the oil. Oh yes, you will need to buy/make a new gasket.
 
Sporticus said:
Thank you John. I have the Eldorado style drain with the allen heads, which confused me. Maybe my 850T is an early 1975 and missed the jump to the later drain?
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Sorry, mis-read your post. I thought you said you could feel a drain plug. Also Carlo is correct, you will need a new gasket.
 
On the 850-T rear drive (and Eldorado) with the "deep sump", the correct oil capacity is 360 cc (340 cc of 80w90 gear oil and 20 cc of moly additive). As John Z. says, ignore the level plug - drain, measure and fill.
 
Charlie, Thanks for the correction. I had forgotten it has been so long since I serviced one. However, I'm not a fan of the moly additive and no longer recommend using it. No other manufacturer uses it in their bevel drives.
 
john zibell said:
Charlie, Thanks for the correction. I had forgotten it has been so long since I serviced one. However, I'm not a fan of the moly additive and no longer recommend using it. No other manufacturer uses it in their bevel drives.
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Guzzi themselves no longer specifies it's use in current models or any of the recent past. However, in my opinion, it is still beneficial in any older model that it was originally spec'ed for. Different materials, heat treating processes and tooth profile back then.
 
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Charlie, we are all entitled to our opinions. I stopped using it after viewing evidence of pitting on bearing surfaces. Haven't seen any since I stopped using moly, enen in old bikes that I work on.
 
john zibell said:
Charlie, we are all entitled to our opinions. I stopped using it after viewing evidence of pitting on bearing surfaces. Haven't seen any since I stopped using moly, enen in old bikes that I work on.
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107k miles on my '69 Ambassador's rear drive, gears look perfect, bearings show absolutely no pitting and very little wear. GL-4 gear oil with moly it's entire life. <shrug>
 
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