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Old 09-25-2013, 07:35 PM   #1
dilandau OP
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75 r75/6 transmission advice

Hi all:

I just made a deal on an r75/6 in pretty decent shape- except it has a blown transmission. I have no confirmed info on how bad the insides are, but from the riders description of grinding noises and power loss I expect its pretty bad.

What say you gurus of cyberspace? Do transmissions from other years/models mount up easily? are there specific years with better ones- should I rebuild this one or get a more robust one and build it up?

Frankly im tempted to just buy a used one on ebay, slap it on, and hope. this is because i have a 2 year old and a very busy work schedule.. so the avenue of least time is good.
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Old 09-25-2013, 08:13 PM   #2
Plaka
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Originally Posted by dilandau View Post
Hi all:

I just made a deal on an r75/6 in pretty decent shape- except it has a blown transmission. I have no confirmed info on how bad the insides are, but from the riders description of grinding noises and power loss I expect its pretty bad.

What say you gurus of cyberspace? Do transmissions from other years/models mount up easily? are there specific years with better ones- should I rebuild this one or get a more robust one and build it up?

Frankly im tempted to just buy a used one on ebay, slap it on, and hope. this is because i have a 2 year old and a very busy work schedule.. so the avenue of least time is good.
Looks like you have plenty of bikes to ride. You just bought somone elses problems. Figure they know somethjing. They sold the bike. Big hint there.

Buy one on ebay and you do it again. The sellers most often are breakers working with wrecks. They never heard the bike run. might see if the tranny will go through the gears on the bench. Says something but not a lot. if they won't give a 5 yr. warrenty, forget them.

Folks here know even less about that box. But they can tell you what they'd do if they were spending your money.

Call some of the well know rebuilders and find out what it would cost to get an estimate. Go from there. They also might have a line on a decent used box. Maybe a hopeless case they bought cheap and rebuilt in time to make some cash on.

I don't mean to be too harsh on you, but you bought a wreck knowing how little time you have to put into it. I'm guessing the price was irresistible. Ain't no free lunches. if you like to gamble or are just planning on flipping it, anything will work. if you want to travel on it ('cept you don't have time) you want a box a pro has gone through and evaluated, even if no repairs are needed.

Any tranny will work. There were some problem years but any of those boxes may or may not have been corrected. Have to open it up to know. The 4 spd. is more durable than the 5 sp. Means nothing looking at an unknown box. Any can be more or less worn or broken.
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Old 09-25-2013, 08:24 PM   #3
disston
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I will try to cover the pertinent data. You have a choice, to rebuild the currant trans or obtain a used trans. I'm a fan of getting another trans. But it may be more complicated. "loosing power" may be the clutch? This will have to be checked anyway while the trans is out or being swapped.

How long before you have the bike in your hands? Are you driven to rebuild this yourself or ship it out?

It is recommended that if you want a good rebuilt trans you have one of the few known transmission experts handle it.

So begin looking for a trans that is expected to be serviceable. A direct swap. There are a number of suitable years.

Any Airhead transmission built from the first /5 four speeds in 1970 through the 1980 model year will work.

I recommend you not go with a 4 speed, eventually these two transmissions will be used maybe to build one working trans. If you get a four speed now you don't have any parts later to fix a 5 speed. So stick with only 5 speeds.

The 5 speeds were introduced in the /6 bikes and the first year is 1974. Aside from the issues some 1974 transmissions have many of the parts are different in the 1974 model year. For the same reason you don't want a 4 speed trans you also don't want a 1974 5 speed. Don't sweat the issue of the 1974 trans having a kick starter. The kick starter has issues and you don't need it.

That leaves 6 model years for you to consider. 1975 though, and including, 1980. The Airheads of course continue through 1995 but these transmissions do not fit your bike. In 1981 the clutch was redesigned and the flywheel was eliminated. The transmission got some changes and one small change makes these two vintages not compatible. In 1981 the input shaft was shortened. The earlier transmissions, such as your bike, are called the long input shaft. The later transmissions, starting in 1981 are called short input shafts.

You need a long input shaft Airhead transmission.

There are almost always several for sale on Ebay. Don't buy a broken one just yet. The one with a broken cover is too expensive for needing a rear cover. Don't buy one with a kick starter, they are a waste of energy. A good one with no guarantee will go from $200 to $400 on Ebay. Wrecking yards may go for about the same unless they have a really nice one, then they want more.

At this point you just want to check out the market.
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Old 09-25-2013, 08:40 PM   #4
dilandau OP
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thanks for the replies.

1. It was cheap yes. so if i have to spend even 2k on the transmission id probably still be ok on resale.

2. I do not plan to sell.

3. I have heard they need rebuilds every 60k or so (on average) so I figured why not start fresh than deal with one that might go in 10k.

4. thanks for the rundown on transmission that will work. exactly what I was looking for- appreciate it. I have some time- so i'll be keeping an eye on ebay and making some calls.

5. I might have it tomorrow depending upon his schedule- otherwise next week. but i'm impatient and want to get a jump on the issue.

6. I can do most the heavy lifting mechanics myself- but might send the unit out for a rebuild depending upon how hard it is- and how much it is for someone else to do it.
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Old 09-25-2013, 09:50 PM   #5
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It only takes 45 minutes to get the trans out (when you've done it a few times before) so it's will worth running the 'new' one to see if it's gonna work out.

Transmissions don't necessarily go out at 60K, some last twice that or longer.

I'd recommend watching for a late 70s transmission. I think LamontSanford has one for sale right now. He's an airhead owner and you can trust his evaluations. He'll say right up front whether it's good or not, or that he doesn't know.
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Old 09-25-2013, 11:48 PM   #6
dilandau OP
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on CL is a local 74 r90/6 transmission- but you are thinking that is a pass right? if i could get it for like ~100 is it worth it or just forget it and get a later model.
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Old 09-27-2013, 11:04 AM   #7
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Originally Posted by dilandau View Post
thanks for the replies.

1. It was cheap yes. so if i have to spend even 2k on the transmission id probably still be ok on resale.

2. I do not plan to sell.

3. I have heard they need rebuilds every 60k or so (on average) so I figured why not start fresh than deal with one that might go in 10k.

4. thanks for the rundown on transmission that will work. exactly what I was looking for- appreciate it. I have some time- so i'll be keeping an eye on ebay and making some calls.

5. I might have it tomorrow depending upon his schedule- otherwise next week. but i'm impatient and want to get a jump on the issue.

6. I can do most the heavy lifting mechanics myself- but might send the unit out for a rebuild depending upon how hard it is- and how much it is for someone else to do it.
Where did you get 60k from?

I get 110-120k on a 4 speed then you turn the shift forks around and throw in fresh bearings just because and do it again.

I have heard 5 speeds are not quite so durable. I have about 100k on one now with no issues. But I also have a backup in a crate so I'm not down while it's being worked on.
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Old 09-27-2013, 02:09 PM   #8
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?????

Who said anything about having a noob work on a transmission?

How the heck do you turn shifting forks around to wear on the other side?

Are we all talking about BMW motorcycles here?

Am I missing something?
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Old 09-27-2013, 08:41 PM   #9
Plaka
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?????

Who said anything about having a noob work on a transmission?

How the heck do you turn shifting forks around to wear on the other side?

Are we all talking about BMW motorcycles here?

Am I missing something?
You did.

Beats me, ask Matt, he did my last transmission. He's forgotten more about them than I'll ever know. I may also be mistaken and he was talking dogs or something. Tranny was popping out of 1st or second @about 110k miles. I'll ask him when I see him next. I have a crap 5 speed and rear drive that need attention. That garbage from Mike is really something. I'm tempted to crack the box just to have a peek, but I know how little mechanics like you bringing them them pre-monkeyed with stuff in boxes.

Yes.

Yes.

Any idea if the pushrod tubes through the heads are the same OD as the pushrods in the jugs?
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Old 09-26-2013, 01:00 AM   #10
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1974 is the first year of the 5 speed transmission. It was extensively redesigned for the second year, 1975. Many of the internal parts, gears and shifting forks, from a 1974 do not fit any of the other years.



1974 is called the one off transmission year.

PASS

Is my advice. There are people that want that transmission. They are trying to fix another 1974 transmission and used parts are their only hope.

http://www.ebay.com/itm/BMW-Motorcyc...5a3a9f&vxp=mtr
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Old 09-26-2013, 05:02 AM   #11
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Originally Posted by disston View Post
1974 is the first year of the 5 speed transmission. It was extensively redesigned for the second year, 1975. Many of the internal parts, gears and shifting forks, from a 1974 do not fit any of the other years.



1974 is called the one off transmission year.

PASS

Is my advice. There are people that want that transmission. They are trying to fix another 1974 transmission and used parts are their only hope.

http://www.ebay.com/itm/BMW-Motorcyc...5a3a9f&vxp=mtr
My June 75 transmission also has the NLA 74/75 shifting forks. I'm not sure when BMW made the change but likely that 1976 model years, ie built from September 75 will have the later parts.
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Old 09-26-2013, 06:24 AM   #12
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I would wait until the bike is home then determine for yourself what the problem is. Too often I've seen people start buying things they think the bike needs before thay actually get the bike, only to have most of those things spend years on the shelf.
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Old 09-26-2013, 10:33 AM   #13
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You may be amazed at what a fluid change will do. Give it a shot, it is only a few dollars and you may be sitting pretty.
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Old 09-26-2013, 11:55 AM   #14
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Originally Posted by Pokie View Post
I would wait until the bike is home then determine for yourself what the problem is. Too often I've seen people start buying things they think the bike needs before thay actually get the bike, only to have most of those things spend years on the shelf.
I agree here. I don't know tons about airheads but am learning every day.
I bought my bike with a host of 'big issues' that got me a good price, but not as good as yours it seems.
Took less than an hour to take a barely running bike with all sorts of strange issues into a solid machine.

Could be anything at this point that is causing your issues.
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Old 09-26-2013, 02:02 PM   #15
dilandau OP
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have the bike in hand now- actually I have the transmission in hand now as well.

Does not turn well, makes grinding noise. opened up- and i do not see where its binding yet, but yes, its fubared somehow.

pics later.
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