Speedo Question

[marcmax]

Now that I have my 82 LS prety much the way I want it, its time to start on the 84 LS that was going to be a rolling parts caddy but now is going to get rebuilt. The speedo is a 120mph model andt looks like it had water in it. There is a slight rust line up to the trip odometer opening. It does not work. Palo Alto Speedometer wants min of $350 to rebuild it, if it is even salvageable. So I have been looking for a used replacement. Now the question. I found another 120mph speedo from a '79 R65 but it is a W:1768 and the one from the '84 LS is a W:1318. Also the 80mph speedo on my '82 LS is a W:1318 Checking the parts on Real OEM I can only find one rear drive listed for the R65 so I can't figure out what the difference is. I am sure the readings will be off if I use this speedo but does anyone know which way it will be off, readiing lower than actual or higher?

[marcmax]

My memory is getting as bad as my old bikes. The different speedo's are W:1276 and W:1318

[nhmaf]

Check the top of the rear (cardan) drive on your bike, near where it bolts onto the swingarm - it should have a numeric ratio stamped into the top of it, like "31/9" or "32/9" - these represent the ring/pinion gear tooth ratios and determine what "magical number" you need on the bottom of your speedomoeter face to most accurately represent the bike's speed (though all these BMW speedos tend to read high, sometimes as much as 5% - 7%).

31/9 = 3.44 final drive ratio = speedo # W1276 120 MPH (I think this # is right? or maybe it is for 85 MPH speedo)
32/9 = 3.56 final drive ratio = speedo # W1318 85 MPH speedo

I don'tthink I  have any record/info on a W1768 speedo on an R65.

[Bob_Roller]

I just checked both of my R65's .

The '81 with a 3.56 final drive, has a W=1318, and it's an 85 mph speedometer .

The '84 LS with a 3.56 final drive, has a W=1318, and it's a 120 mph speedometer .

I thought I read somewhere, that the numerical value on the speedometer, was the number of revolutions the drive cable would have to rotate to indicate a measured distance .

[nhmaf]

I do also believe that the 1318 number is the  RPM/MPH ratio for the speedometer gearing, but I wasn't sure if they changed the "w" or another thing to indicate the difference between the 85 MPH full scale calibration and the 120 or 140 MPH full scale calibration, as they had both at one time or another.

Marcmax - are you certain that the numbers on your speedo are 1768 ?  Perhaps it is in Km/h not M/h ?   If it said "1186" it would be for a 3.2 final drive ratio which was available on the R80/7 or R100/7 between 1978-80?

[marcmax]

The W:1768 was me being brain dead before the morning coffee kicked in. I should have said W:1276.

Both of my R65's have a 32/9 rear drive and both of them have a W:1318 speedo (one is an 80mph and the other is a 120mph. The 120mph speedo is dead and needs to be replaced (rebuild isn't cost effective).

In searching the RealOem parts lists there are two rear drives for 1979 R65's listed, a 31/9 and a 32/9. I am making the assumption that the speedo with W:1276 is for the 31/9 rear drive as all the other listings for R65, both standard and LS, show a rear drive of 32/9 and a speedo of W:1318

I guess what I need to know is how far off and what direction will it be if I use a speedo meant for a 31/9 rear drive with a 32/9 rear drive.

[Bob_Roller]

I got an answer from Boxerworks, the W=1318, is the number of turns the drive cable makes to indicate one mile at 60 mph .

I kinda sorta had it somewhat right .

[marcmax]

Bob, you're a braver man than I am. I browse the Boxerworks forums but won't ask a question. I have seen too many of the discussions get way too personal.

So I am guessing that since a 1318 speedo cable is turning faster than a 1276 speedo cable and BMW designed their speedo's to read faster than the actual speed, using the slower moving speedo with the faster moving cable I would just exaggerate the difference between actual speed and displayed speed.

I guess if I get stopped I can't say I didn't know I was speeding.  

[Bob_Roller]

You just have to know how to ask the question .

It was suggested to visit Snowbum's BMW tech site, here's what I found .

http://bmwmotorcycletech.info/ringgears.htm

Don't know if this will help you, or confuse even more . 

[Mike V]

Palo Alto Speedometer wants min of $350 to rebuild it, if it is even salvageable. So I have been looking for a used replacement.

Marcmax,
Not to divert from the current direction this thread is moving but; I wanted to mention "if" you decide to further investigate repairing your original speedo give Forign Speedo a call here in San Diego.  I've had them do numerous repairs on my speedo's and I've found them to be quite good and very affordable. You may consider giving them a call to see if they can resurect your original instrument and give you some kind of estimate. These are "old school" guys with lots of foreign instrument experience and very affordable.

Foreign Speedo
2246 1/2 University Ave
San Diego, CA 92104
(619) 298-5278

[marcmax]

Thanks Mike. I tried another shop, Fort Lauderdale Speedometer, who specializes in VDO instruments. They wanted $125 just to open it and see if it was repairable. Between that and Palo Alto I had pretty much given up on repairing it.

I would prefer keeping the original parts if I can. The fact that you have had good experiences with Foreign Speedo and are willing to recommend them is encouraging. I will give them a call.

[nhmaf]

Actually, using a 1276 speedo (31/9 final drive ratio) in place of a 1318(32/9 final drive ratio) MAY actually yield a more accurate measurement of true speed, as most of these airhead BMW speedometers measured between 2% and 6% "higher", and the difference in ratios is almost 4%.

BUT, the 85 MPH speedometers are also generally considered the MOST accurate speedometers of all the BMW airhead speedometers, so that may negate any potential improvement from the above example, by substituring a less accurate speedo intended for use with 4% taller final drive.

Getting a speedo repaired can be cost effective in many cases - at least it can often (as with Palo Alto) be done AND retain the odometer value, so that you don't have any questions to answer later with registering or selling the bike (yes, the odometer is correct, sir).

[Bob_Roller]

I contacted this speedometer repair shop about a year ago to see what they would charge for a typical non-working odometer .

http://www.InstrumentClusters.com

Companies name is Southern Electronics, located in Richmond, Virginia .

You could contact them, and see what kind of quote they might give you .

I got a quote of $195 to repair an non-functioning odometer, cleaning,  recalibration of the speedometer and return shipping in the US .

If yours is in as bad of shape as you described, replacement of the speedometer, may be more cost efficient .

[Yikes]

Keep looking, Marc.  They sometimes do pop up on ebay for reasonable prices.  Besides Southern Electronics, Re-Psycle in Ohio will refurb your speedo for (I think) about $190 plus parts which usually totals $220 more or less.

[marcmax]

Mike V recommended a place in San Diego that he has used and was happy with their results. I called and was quoted a price of $80 to open it, clean and adjust. If it needs repair (Yes the odometer doesn't work) it will be $20 more. The problem is the little button over the trip odometer is gone and that is how this problem got started. He said they are no longer available but he may be able to find one. If not I told him to just remove the trip odometer reset button and replace the speedo lens with a solid one and I will just have a non-useable trip odometer. That is $18 to replace the lens. I thought the prices were very reasonable and I am shipping it out. I'll keep you posted. Here is a pic of the state it is in now.