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Pre Unit Transmission Oil change #530025
02/24/14 7:55 am
02/24/14 7:55 am
Joined: Sep 2013
Posts: 745
Westminster, Colorado
stubbicatt R.I.P. Offline OP
In Remembrance
stubbicatt R.I.P.  Offline OP
In Remembrance
Joined: Sep 2013
Posts: 745
Westminster, Colorado
Well fellas, was finally a nice day here Saturday, so changed the oil from the transmission/gearbox. Took a long while to drain from there. Then, rather than take off my greasy garage clothes, go inside, get the manual, verify capacities, and then add oil, I decided to take the "level plug" from the back of the transmission, and add oil slowly. With every dollop I added, some came out that infernal plug.

At first I thought maybe I hadn't drained enough from the transmission. But no, I look and see the overfill plug orifice is right in line with the stream of oil being added to that top bung, and some oil is obviously being diverted out that hole, thus giving a false suggestion of being full.

Before riding again I'll add maybe pint with the plug installed, and then remove the overfill plug to see if it drains out a bit more oil.

Used a 20w50 dino oil, as it seemed appropriate. Read somewhere that the bronze bushes in the gearbox do not like dedicated 90 weight transmission oil.

Also changed out the primary chain case lubricant, which was ATF. It hadn't appeared to leak any from there, and I feel better changing that out say every 500 miles or so.

Snugged down the nuts on the sump plate to hopefully staunch what seems to be a slow leak from that spot. Wiped down the frame an underside bits with towels to remove accumulated grime and oil, and felt quite satisfied.

I still think that this Thunderbird has to be one of the best, if not the best, quality motorcycles I have ever owned. It is just put together right.

Last edited by stubbicatt; 02/24/14 8:01 am.

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Re: Pre Unit Transmission Oil change [Re: stubbicatt R.I.P.] #530026
02/24/14 8:03 am
02/24/14 8:03 am
Joined: Oct 2012
Posts: 3,732
Running from demons in WNY
Hillbilly bike Online content
BritBike Forum member
Hillbilly bike  Online Content
BritBike Forum member
Joined: Oct 2012
Posts: 3,732
Running from demons in WNY
Originally Posted By: stubbicatt


Used a 20w50 dino oil, as it seemed appropriate. Read somewhere that the bronze bushes in the gearbox do not like dedicated 90 weight transmission oil.


Vintage gar guys say the same thing...I use Brad Penn "Classic" gear oil in my vintage cars and bikes. It's a GL4 oil and reasonably priced at about 6-8 bucks a quart.
I have also used Redline MT 90 ,it's also recommended for trannys with yellow metal parts inside.
But.....I know many who run modern GL5 gear oil in old vehicles and have no problems...


I ride junk
Re: Pre Unit Transmission Oil change [Re: stubbicatt R.I.P.] #530035
02/24/14 8:41 am
02/24/14 8:41 am
Joined: Dec 2004
Posts: 9,375
Scotland
kommando Online content
BritBike Forum member
kommando  Online Content
BritBike Forum member
Joined: Dec 2004
Posts: 9,375
Scotland
Quote:
Read somewhere that the bronze bushes in the gearbox do not like dedicated 90 weight transmission oil.


This is an old problem that modern oils have been modified to eliminate, even then the non modified oil has to get to 100C to have an effect on bronze which a pre unit box will never hit.

I have been using EP90 in my Commando box with Bronze bushes for 25 years with no issues.

Re: Pre Unit Transmission Oil change [Re: stubbicatt R.I.P.] #530036
02/24/14 8:49 am
02/24/14 8:49 am
Joined: Aug 2001
Posts: 7,456
scotland
triton thrasher Online content
BritBike Forum member
triton thrasher  Online Content
BritBike Forum member
Joined: Aug 2001
Posts: 7,456
scotland
I find it easier to engage first gear at a standstill, with gear oil in the gearbox, rather than engine oil.

Yes, there's a story that GL5 oil is worse for yellow metals than GL4. There are conflicting reports from people who have used both or either.

The recommended level is slightly higher than you really need.


Amateur Loctite enthusiast.
Re: Pre Unit Transmission Oil change [Re: stubbicatt R.I.P.] #530052
02/24/14 11:16 am
02/24/14 11:16 am
Joined: Jan 2014
Posts: 1,956
South cone
R
reverb Offline
BritBike Forum member
reverb  Offline
BritBike Forum member
R
Joined: Jan 2014
Posts: 1,956
South cone
...mine is a pre unit 500 and I have been using 90 since I have it, about 20 years ago; without any problems with the bushes; and I ride it almost everyday and strongly.
In fact, the other Sunday, I went to another town, so I rode about 150kms mostly at 95-100Kms/h and happened that the oil content was too low and the 4th bush gripped a bit, so no Neutral; I bought 90 oil and filled up (no oil, seems that lost the content in the road cause no trace in the floor of my house) then to get back to my house I just pushed it on a slope street (in the town but directly to the road)with the clutch engaged to start the engine.

Then I tear it all apart slightly touched the 4th bush in the lathe and checked all other bushed and gears, all looked right; rebuilt all again and in 1 day I had primary, clutch and box all again working.

Re: Pre Unit Transmission Oil change [Re: stubbicatt R.I.P.] #530098
02/24/14 2:55 pm
02/24/14 2:55 pm
Joined: Jun 2007
Posts: 5,910
Maui Hawaii
HawaiianTiger Offline
BritBike Forum member
HawaiianTiger  Offline
BritBike Forum member
Joined: Jun 2007
Posts: 5,910
Maui Hawaii
I have never used engine oil in any pre-unit tranny feeling that the books that recommended it were in error. However, a lot of you have seen what damage is done to the mainshaft and the output sleeve gear bushing from a tight chain. EP90 is too viscous in my opinion to adequately lubricate this area. I used multi viscosity synthetic gear oil. It pours like engine oil and protects like gear oil. I think it's not a bad idea to park your bike on its sidestand from time to time.....get some oil up into that poor bushing.

ATF has worked for me in primaries for 40 years now.

One service issue that every pre unit owner must be aware of is the problem with the gearbox mountings. They can loosen after a while allowing the gearbox to move around. This does loads of damage. Broken gearbox mounts, tight chains, thrown chains, chains coming into contact with inner chaincase. In an effort to reduce this damage, the factory installed two gearbox adjusters in late '61. This helps a lot. For bikes with some power and ridden hard, I replace the upper gearbox through bolt with a grade eight bolt and tighten it with all my strength.
Bill

Last edited by HawaiianTiger; 02/24/14 3:10 pm.

Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.

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