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Bosch horn repair

lauffer6996
Posts: 81
Joined: Fri Oct 27, 2006 3:00 am

Bosch horn repair

Post by lauffer6996 »

Who repairs Bosch horns? Mine is from a low mileage bike and looks close to new but wont toot. It is getting juice and I have fiddled with the adjuster screw a bit, but cannot get any sound at all out of it.
Thanks,
Scott

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schrader7032
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The Fall 2010 (Volume 37 No

Post by schrader7032 »

The Fall 2010 (Volume 37 No 3) issue of the Vintage BMW Bulletin has a nice article on overhauling a Bosch horn. It was written by our own Darryl Richman. Worth getting a copy and checking it out.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

lauffer6996
Posts: 81
Joined: Fri Oct 27, 2006 3:00 am

Bummer, those appear all sold

Post by lauffer6996 »

Bummer, those appear all sold out in the "store".......
S

lauffer6996
Posts: 81
Joined: Fri Oct 27, 2006 3:00 am

Icarus, thanks I will take a

Post by lauffer6996 »

Icarus, thanks I will take a crack at it.
thanks,
Scott

312Icarus
Posts: 458
Joined: Fri Jul 15, 2016 1:53 am

Assuming it is a OEM Klaxon

Post by 312Icarus »

Assuming it is a OEM Klaxon horn, or similar, they are very easy to fix. Unscrew the screws that hold the two halves of the case together. Carefully separate the two halves. There is a simple coil and reed vibrator. Carefully clean the points of the reed vibrator with a point file or sand paper. Then carefully put the two halves together, centering the bar over the contacts properly. Then adjust the bar with the adjustment screw, which just adjusts the tension on the reed vibrator.

Be careful if you take the vibrator apart, as there is a very exact order of re assembly keeping the proper bolts/post isolated from ground. The horn wiring terminals work in series. In other words, send voltage this through, from one terminal to the other, and then to ground. It doesn't matter which is connected to positive and which to ground. Wiring it improperly will make the horn sound when you turn on the lights, as the horn button simply completes the circuit by providing the ground.

Hope this helps,

Icarus


312Icarus
Posts: 458
Joined: Fri Jul 15, 2016 1:53 am

Your welcome. Avoid taking

Post by 312Icarus »

Your welcome. Avoid taking the coil studs out, as I said it is a pain to put together. The current simply energizes the coil, creating an electro magnet, the reed switch opens and closes causing the bar to vibrate, resonating in the case. Adjusting the tension on the spring regulates the vibration frequency. If the coil has continuity with a Ohm meter, there is no reason to take it apart, and, as I said, you run the risk of not getting it back together in the proper sequence. (It took me a few times to realize what I had done wrong, putting the coil at risk due to short.)

Icarus

lauffer6996
Posts: 81
Joined: Fri Oct 27, 2006 3:00 am

repaired - thanks

Post by lauffer6996 »

Wow it is loud, especially in the office!

I found a post with some pictures that also helped, see below.
The points were corroded, a bit of abrasive took care of it, I also loosened and tightened all the contact screws inside.
I had to take it apart about 5 times until I discovered I had to tighten the adjustment screw significantly tighter than I originally felt comfortable doing, the spring was really compressed pretty hard. It works well now.
Thanks for the help.
Scott

http://bmwvmca.org/joomla/index.php?opt ... iew&id=456


312Icarus
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Glad to see you got it!

Post by 312Icarus »

Your welcome.

Glad to see you got it working. These things are drop dead simple, and as long as the coil isn't burned up there is no reason you can't fix them!

Icarus

PS Edit. Looking at your picture, I assume it is a Bosch horn. It looks very different than the Klaxon on my /2. The coil on the Klaxon is much smaller. The basic design is the same however.

Icarus

Daves79x
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Just Passing Along

Post by Daves79x »

I just finished repairing 2 horns, a Bosch and a Klaxon. Neither would work when I started. I had no continuity between the terminals on either, and I discovered that you have to have continuity there or the horn will never work. I had sanded the points on both, but could still not get continuity through the points at rest. So I took both points mounts apart and dressed the points on the bench with a file. Back together and had continuity on the Bosch, so assembled it and it worked, minor adjustment for tone is all it needs. I installed new paper gaskets I got from Europe and they are not exactly the same thickness, but you can account for that by the adjusting screw. On the Klaxon, I had continuity when the base was assembled, but none when I assembled the entire horn. Seeing how the adjuster works and the fact that I had it completely out, I realized that the prong that activates the points was pressing them open when I screwed the whole assembly together, losing continuity. So I held my meter at the terminals and slowly backed off the adjusting screw until I just had continuity. It about blew my ear off when touched to a battery. So just wanted to pass on and reiterate that you MUST have continuity at the terminals for the horn to work and you need to first look at the adjustment and then the points to see why you don't. Neither of these horns had been used in years, but both now work like new.

Dave
Dave

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Twocams
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Ill look at my Klaxon again.

Post by Twocams »

Ill look at my Klaxon again. It has never worked. Just got tired of messing with it one day. Maybe those are other places to look.

twocams
Twocams
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