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Old 08-07-2010, 08:08 AM   #1
elmontanero OP
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Opinions on that Airhead higher 5th gear?

This has changed into the too well known: getting an airhead transmission rebuilt fiasco... With questions about that higher 5th, shift kit info... and we'll see what all else.
Quick conclusion.. if you're in So Cal. There a guy that can do your Airhead Trasmission! Bike is happy, so is this owner!

Pawl spring broke on the '81 g/s and the transmission is going in for a rebuild while it's out (50k miles)... So should I do the swap for a higher fifth? Sources for the preferred one?

I do some highway miles and few off pavement miles...
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Old 08-07-2010, 08:18 AM   #2
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By all accounts its a good thing. Drops you at least 500rpms up top.
Anton Largiader usually has a supply ready to install, on hand.

I'm going to do it next time my geabohx needs opening.
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Old 08-07-2010, 08:46 AM   #3
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Quote:
Originally Posted by Stagehand
By all accounts its a good thing. Drops you at least 500rpms up top.
Anton Largiader usually has a supply ready to install, on hand.

I'm going to do it next time my geabohx needs opening.
How much?

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Old 08-07-2010, 08:54 AM   #4
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Beats me. Gear itself is probably not all that expensive, but obviously you might not open a perfectly good transmission to add it. Thats the money part, just getting in and out I should think.
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Old 08-07-2010, 08:58 AM   #5
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Old 08-07-2010, 09:02 AM   #6
Lornce
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I can do that for free. How much for the gears?

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Old 08-07-2010, 09:30 AM   #7
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Quote:
Originally Posted by Lornce
I can do that for free. How much for the gears?

145 Euros including VAT, so a little less for all of us outside of Europe.

http://www.bmwboxersupplies.com/prod...e09494dc973d65
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Old 08-07-2010, 09:32 AM   #8
AntonLargiader
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$200 each for the 6% tall 5ths. I have several 17.5 gears and a 15 gear for early bikes (1977 through February 1982).

Short 1sts (5~6% lower) for $150 but installation is a bit harder. I personally like this mod more than the tall 5th but it comes down to riding style.

$5 shipping.
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Old 08-07-2010, 09:33 AM   #9
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I understand Ted Porter sells them as a set. Which, if you know anything about gears, makes more sense to me.

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Old 08-07-2010, 09:43 AM   #10
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I do, but by all means....
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Old 08-07-2010, 05:51 PM   #11
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Quote:
Originally Posted by Lornce
I understand Ted Porter sells them as a set. Which, if you know anything about gears, makes more sense to me.

Does this mean that you would get 4 gears in total? Would the purpose be to have similar gear mesh surfaces?
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Old 08-08-2010, 06:01 AM   #12
AntonLargiader
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Don't hold your breath awaiting details on that.

Back to the main topic, it's an easy swap while the gearbox is open (the O.P. would need the 15 version if the gearbox is original) and probably pretty useful on a G/S or ST due to the short FD. They're available from several sources and whoever is doing your gearbox repair probably has one or has a source.

There are several manufacturers. I have the Kayser gears, which is what Beemershop seems to have at the moment also. They are made in a lovely old workshop outside Stuttgart by Wolfgang Kayser...

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... who is a really interesting guy who has done a lot of really interesting things with gears, such as [allegedly] putting Yamaha internals into a BMW gearbox for a well-known racing effort, adding reverse to just about any gearbox out there, making 4-speeds into 5-speeds, 5-speeds into 6-speeds, sport gearsets for bikes built before I was, all sorts of stuff. I've installed several of his tall 5ths on R1100 transmissions. The gears are cut and then hardened, which is different than the gears made for HPN which are finished after the hardening. I can't say either is better; I haven't heard of any durability problems.

On higher-mileage bikes it's more likely that the output shaft is worn where 5th gear spins on it. The shaft and the gear both wear; sometimes the use of a new gear is enough to reduce the slop to an acceptable level, but for a bike that's going to have a lot of miles put on it, I like to plate/grind the shaft to match the new gear. That way the gear stays true to the plane of rotation of the meshing gear on the intermediate and future wear is minimized.
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Old 08-08-2010, 08:43 AM   #13
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Quote:
Originally Posted by AntonLargiader

Short 1sts (5~6% lower) for $150 but installation is a bit harder. I personally like this mod more than the tall 5th but it comes down to riding style.

$5 shipping.
Anton, What makes it a harder install?

I agree the lower first makes more sense than the higher high. For instance, I have a 2.91 final drive in a 90S, my fourth gear is the same as fifth with the standard 3.00 FD, shifting up to fifth drops the revs about 3%. 70 mph is about 3700 rpm in fifth, so I still have 3500 rpm to play with.

What I do notice is how much clutch slipping I have to do to get rolling. Two up and luggage, you can smell the bike a quarter mile down wind with all the clutch aroma.

Problem is my bike has a late run '74 box according to the numbers that Snobum posted. So I don't want to do any internal messing around with it. But what would you do on a 50K miles box?
No issues or noises now, but thinking ahead...
Just bearings and springs and seals, if the the gears are good? Or just don't bother....
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Old 08-08-2010, 08:47 AM   #14
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I've done both the lower first and higher fifth gear on mine. Worth the money if you already have to tear it apart.
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Old 08-08-2010, 09:11 AM   #15
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I've got a 37/11 rear end monolever r80G/S with the higher 5th gear. I used to run 5000 rpm at 70, now it's 4650 at the same speed. I think it was $200 for the gear when I got it last year.
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