3.64 vs. 3.91 on your speedo face (pic of overlay)

[Conserv]

On 6/14/2014 at 10:31 AM, vinntagejoe said:

Love the discussion and the thorough insight but you guys are killing me; I've got a 3.91 LSD and use a compact TOM TOM gps unit to track my speed - I know it's lame but someday I'll reach back to this discussion and do the right thing - heh

Understood. I've got a spare speedometer head and I'm searching for someone who can make a concealed GPS unit drive the analog-style speedometer needle!

 

Regards,

 

Steve

 

[roadhog0]

Just send it in to someone like Hollywood speedo and have it cleaned and calibrated... It doesnt cost that much... I plan to do this with my 02 as soon as I get all my driveline sorted...

['76mintgrün'02]

I read a while back that the '76 cars typically get fewer mpg, which this error would help to explain.  I recently ran across this thread while researching which speedometer to get when swapping my 3.90 for a 3.64 diff.  

 

The triangular ink stamp on the back of my W1.393 is 119 over 10.75 (same as the production date for the car... Oct. '75).

 

If all W1.393 speedos are in fact the same as a W1.30 (3.64 companion), then I should not see a difference when I swap the differential... and therefore should not bother swapping speedometers at all?  

 

That would be fine by me.

[73touring]

OK, I bought a speedometer with a W=1.393 (correct for E21 3.91 LSD, according to records compiled by Curt Ingraham), and found out the W=1.393 just has an overlay over a different face. The face underneath appears to be the same as the one on my old W=1.297 (for a 3.64 diff, according to Curt).

So on the left is the 1.393 speedo with the overlay removed, revealing the face similar to a 1.297. On the right is the overlay in my hand.

Maybe this is is helpful, I don't know. But if you're running a 3.91 diff in your 3.64 car, you can get an idea where you're markings should be.

I love the street and sport kits in 76 + the Rad upgrade

I have a couple of new 1,393 speedos that I purchased from Wallouth & Nesch a while back. Both of them are dated 7/76 and don't have that overlay. What's the build date stamped on the back of the case of your speedo? Curt may have been on to something. Those speedos with the overlay might just be a rare piece of BMW history. ;-)

PS, Can anyone explain what the little white dots on the face of the speedo mean?

In the winter of '77 -- perhaps '78 -- a buddy, in his '77 Capri V-6 and I, in my '76 2002, entered the New York Thruway, at Rochester, at precisely the time a 911 blew past doing around 90 mph. Ever seen a dog race? Right! So we took off, passing the 911, who was then happy -- I suppose, given our willingness to serve as "bear bait" -- to run with us. I placed my pedal to the floor and didn't lift until Syracuse, 90 miles later. My speedometer read 110 mph on the (generally mild) uphills, nearly 120 mph on the downhills, and 115 mph on the relatively flat sections. And, no, I never bothered to look at my tachometer!

My conclusions: (1.) my '76 was one of those rare examples that was, by the accidents of manufacturing, perfectly balanced and just plain faster than the average production 2002; and (2.) I was a helluva great driver -- although it's unclear which driver skills were demonstrated by placing my foot to the floor and steering straight (I did turn on my brights and four-way flashers, despite the daylight, and that obviously averted the expected disaster).

And then someone invented GPS. And my dreams -- about my car and myself -- were crushed. My speedometer is nearly 10% optimistic. I was actually running between 100 and 109 mph, in line with factory expectations. Why have I subjected you to this long-winded tale of crushing defeat? Because it got me thinking about the great '76 49-state "Speedometer Fiasco"!

As we know, 49-state versions of the '76 U.S. cars came with a 3.90 differential (39:10 teeth, NOT 43:11 teeth as in an e21 3.91 differential). And every '76 49-state example for which I've seen, or heard, the speedometer back stamp had a head unit marked "1.393" (I've yet to see a 1.390 head unit). My car is typical. It was manufactured April 23, 1976. The instrument panel has 3 ink March '76 stamps, 1 ink February '76 stamp on the tachometer, and March '76 mechanically stamped into the back of the "1.393" speedometer.

And I recall reading at least two Roundel notes (below) in September and October '76 about the problems with speedometers in 49-state '76 cars. I asked my dealer at the time and the service advisor told me the problem only affected early '76 cars. April '76 is not "early '76" so I erroneously assumed my car had no issues. The fix for the problem, which I thought I didn't have, was not a new head unit, not new gears, but simply a face overlay. I'm still looking to buy one of those overlays!

Since my speedometer is marked as a 1.393 -- theoretically correct for a 3.90 -- but still has the error, it would appear that the specific problem was NOT that they installed entirely wrong speedometer heads but, quite simply, they put the 3.64 speedometer gears in many (all?) 1.393 speedometers. (Perhaps the new Walloth & Nesch units are correctly geared!) And it was easier to throw a faceplate overlay at the problem than to open up speedometers and replace the gears. I gather the odometers are off as much as the speedometers.

Yes, I know I can have my speedometer re-calibrated, but I really want an overlay to document the '76 49-state Speedometer Fiasco, and BMW's weak attempt at correcting this now-obvious defect. But even an overlay can't help recover the self-confidence I lost when some darned guy/gal invented GPS. Until that time, I was Fangio, I was Moss, I was triumphant!

Steve

[pkchopp]

Then you throw one of these into the mix!

[M3M3]

Just send it in to someone like Hollywood speedo and have it cleaned and calibrated... It doesnt cost that much... I plan to do this with my 02 as soon as I get all my driveline sorted...

+1

[Conserv]

Quote

I read a while back that the '76 cars typically get fewer mpg, which this error would help to explain. I recently ran across this thread while researching which speedometer to get when swapping my 3.90 for a 3.64 diff.

The triangular ink stamp on the back of my W1.393 is 119 over 10.75 (same as the production date for the car... Oct. '75).

If all W1.393 speedos are in fact the same as a W1.30 (3.64 companion), then I should not see a difference when I swap the differential... and therefore should not bother swapping speedometers at all?

That would be fine by me.

I'd bet dollars to donuts that your October '75 speedometer is precisely that: the same as a W1.30! I assume that your speedo's face shows 63 mph at 12:00 O'Clock, and not 59 mph as the overlay does. I do wonder, however, whether the new Walloth & Nesch units correct the error: I'll bet they do!

 

(The ink-stamp number over the month and year date, "119" for your speedo, is simply the inspector's number.)

 

Thanks and regards,

 

Steve

[Conserv]

On 6/14/2014 at 12:52 PM, pkchopp said:

Then you throw one of these into the mix!

With the "right" (speedometer) gears, my '76 could max out that speedo as well!

 

U.K. turbo?

 

Regards,

 

Steve

 

[Conserv]

On 6/14/2014 at 11:50 AM, roadhog0 said:

Just send it in to someone like Hollywood speedo and have it cleaned and calibrated... It doesnt cost that much... I plan to do this with my 02 as soon as I get all my driveline sorted...

Yes, as I said above, "...I know I can have my speedometer re-calibrated." I've had speedometers re-calibrated previously and I've saved up sufficiently to re-calibrate this one!

 

But I was trained as an historian and I'm trying to capture the "Oops" represented by both BMW's original error and its weak-at-best efforts to correct that error! If I have Hollywood simply calibrate it, the history is lost. ?

 

Regards,

 

Steve

 

[calw]

One more comment- Those Digital Displays that you see along the road are not accurate.  I always use a GPS on road trips to guide my speed, 'specially if I'm in a rental car.  Experience shows that those signs generally give you about 3 MPH leeway in moderate speed zones ( 30 - 45 MPH).  But I've also seen some that were accurate according to GPS, and just a very few that seem to have been there to strongly influence passing drivers' behavior- indicating 5 MPH or more above actual speed.  I have not passed one at normal highway speeds, no experience how they're calibrated.  My assumtion at that they're radar based. Being stationary and normally on straight sections of road, I see no reason that they can't be very accurate.  Perhaps there is some programmability available to the local authorities....

 

GPS speedometers are extremely accurate, including while going around turns, as long as your rate of change in speed or direction isn't way ahead of the GPS's calculation rate. 

['76mintgrün'02]

I'd bet dollars to donuts your October '75 speedometer is precisely that: the same as a W1.30! I assume that your speedo's face shows 63 mph at 12:00 O'Clock, and not 59 mph as the overlay does.

We have a winner!

 

I guess I will be looking for a good home for the W1.30 I just bought.