Speedometer gear ratio

I am have my speedometer repaired and tested and
this question came up:

I am switching from a 265/5 CR to a 265/6 overdrive.

Question: Is the speedometer gear ratio the same in both
transmisions or do I need to make some changes to
make the 265/6 overdrive read right?

How can I know without putting it in and seeing if it is correct?

Thanks,

Since the CR box has a 1:1 top gear, and so does a 4 speed, and I've never heard of anyone having an issue with speedo accuracy on a 4 speed to OD 5 speed swap -- I'd venture a guess you're OK.

Thanks, I agree, we will see.

I think you need to make changes to the speedo in order for it to accurately display your speed.

I did a swap from 4 sp to 5 speed dogleg. In this case no changes are necessary because both top gears are 1:1.

On the 5 sp overdrive gearbox however, 4th gear is 1:1 while 5th gear is .. well .. overdrive, i.e. your speedo won't display the correct speed.

I've never seen anything other than BMWs with cable driven speedometers have the different 'gearing' (for different differential gear ratios) in the speedometer.

As far as I have been able to determine, all the Getrag transmissions used the same speedometer cable drive part. For sure, they are the same for 2002, E3, E9, E12, and early (before 83) E24s, 4 speed or 5 speed.

The sppedo have to fit to the differential gear.

I have a speedo on stock, with the mark W=0,7125 on it.
To what differential gear does it belong?
A comparison list would be a nice idea....

Orangener said:

I have a speedo on stock, with the mark W=0,7125 on it.

Click to expand...

Interesting, I just checked my 'spare' speedo, it says W=0,758 :!:

OK all, here is the answer !

all BMW-tranny with machanical speedo drive, automatic or manuel have the same speedo drive.
ZF S4-3/18
ZF S5-3/18
Getrag 262
Getrag 265/5
Getrag 265/6
Autom. ZF 3HP20
Autom. ZF 3HP22
Autom. BW 65

10 : 4 = 2,5

The different is:
German Cars / (km/h)
diff = 3.25 / w-marc speedo = 0,69/0,68 old/new Version for CSi-CSL
diff = 3,45 / w-mark speedo = 0,7125 Version for 3.0 CS
diff = 3.64 / w-marc speedo = 0,785 Version for 2,5 CS

US/UK Cars / ( m/h)
diff = 3.25 / w-marc speedo = 1,078 Version for CSi-CSL
diff = 3,45 / w-mark speedo = 1,154 Version for 3.0 CS
diff = 3.64 / w-marc speedo = 1,207 Version for 2,5 CS

see also
http://www.e9coupe.com/forumviewtopic.php?t=2078&highlight=markings

gosch

I spoke with Carl today and he confirmed what gosch has stated.

The trans counts the rev's output to the speedo. The only
change needed is when the diff gears are changed.


Thanks,

Anyone know what the 3,07 final drive has as w= ??
It was predominantly used on the E24 with perhaps a larger diameter wheels/tyres, and a very different speedometer.
The values for the 3,25 3,45 and 3,64 don´t follow a logic curve with regards to the w= numbers.

pmansson said:

Anyone know what the 3,07 final drive has as w= ??
It was predominantly used on the E24 with perhaps a larger diameter wheels/tyres, and a very different speedometer.
The values for the 3,25 3,45 and 3,64 don´t follow a logic curve with regards to the w= numbers.

Click to expand...

The early version of e24 with mech.Speedodrive have the same wheel/tyres as e3/e9. And the 635CSi with 3,07 diff have a 0,638 w-marc. Of course Euro-Version km/h

Note...If you can build a Gearwheel with 3,45 teeth or so, the values would follow a logic curve.

@ DJSimca,
You right, the correct W for 3,64 diff is 0,758 not 0,785.
And the old/new Version for CSi-CSL is 0,67/0,68
It was a troubleturn of me.

Now, the Formula, to calculate yourself the w-marc´s:

km/h-Version
W = 0,67
Diff = 3,25
Speedodrive at Tranny is 10 : 4 = 2,5
Rolling circumference is 1,93 Meter
3,25 x 4 / 1,93 x 10 = 0,6735751 ~ 0,67

m/h-Version
Note: 1,93 Meter = 0,00193 km =~ 0,00119499 Mile
W = 1,078
Diff = 3,25
Speedodrive at Tranny is 10 : 4 = 2,5
Rolling circumference is 0,00119499 Mile
3,25 x 4 / 0,00119499 x 10 x 1000 = 1,0878752 ~ 1,078 :wink:

speedo info

WOW...

dave v. in nc said:

WOW...

Click to expand...

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