E34 diff speedo sensor technical questions

[bradley]

Hey folks

Have a question about the 2-pin speedo sensor at the rear of a E34 5-series diff. I should warn you first that I don't have a BMW, I have a trike with a E34 diff and rear axle :D

I'm trying to fit a digital speedo to my trike and would like to use the diff's sensor. Does anyone know what voltage the sensor needs? 12V? 5V? I'm assuming one of the pins is speedo signal and the other is power - does it matter which pin I connect to which?

Also, any idea how many signal pulses there are for a single wheel rotation?

Its probably blasphemy what I've done but if anyone's interested there's pictures of the trike at http://homepages.nildram.co.uk/~tangram/trike/

Another related question - I know the diff is off a E34 and its an Open diff, not a LSD but I've no idea what model its from or of the ratio (my check but I think the metal tag is missing from diff). Which E34 5 Series modesl came with Open diffs and what ratios were they?

Thanks in advance for any help

[632 Regal]

That is one Kickass 3 wheeler dude!!!

You need Javier, he is our electrical genius. He will find you probably later today.

[shogun]

differential ratios are here
http://www.vinesauto.com/techinfo.htm
see on the left. But these are the U.S. specifications, maybe in Europe they were diffferent. At least on my 750 it is the case.

As for the sensor, please ask on this board
http://www.the7seriesregister.co.uk/forums/index.php?
It is mainly for the E32, but there are many parts identical to the E32.
But you can also check the wiring diagrams here
http://www.e38.org/e34/

[Javier]

a magnetic operated switch. The Brown wire is connected to ground in the cluster, and the Brown/Red wire go to the sensing input trough a biasing diode and a pull up resistor, so when the wheels turn, you get a pulsating signal (see picture). I have no idea what the "pulses per turn" ratio is, but you can simply test it. Just connect a 10 Kohm resistor from Vbatt to the Brown/Red wire, connect Brown wire to battery ground, and measure voltage to ground at Brown/Red wire. Slowly turn the wheels, and verify the number of pulses per turn, then you should know your ratio. If pulses are too many, you may need to switch meter to Frequency metering and determine the speed/frequency ratio (I doubt you'll need to do so).

If you have a speed instrument that requires a pulsating ground signal, just connect to its input the Brown/Red wire and connect the Brown wire to ground. If the instrument input does not have its own pull up resistor, just add it trimming the value according to the instrument behavior. Input resistance of the instruments should be around ten times the pull up resistor, but you would not like to use very low value resistor to limit sensor current to the minimum.

If you have any doubt calculating the proper instrument setting, just let me know the instrument programming parameters, your pulses per turn ratio, and your wheel diameter.

Regarding Diff ratio, sorry, I cant help, but shouldn't be that hard to find out what you have.

Javier

[SRR2]

You might want to confirm what's actually in there. I'd suggest hooking an ohmmeter across the sender. See if there's a nominal resistance, say somewhere over 100 ohms. Slowly rotate a wheel and see if the resistance materially changes. If you see open/close kind of behavior, then the 'switch' model of operation is right. If the resistance doesn't vary significantly with slow (like 1/min) then the sender might actually be a magnet with a few hundred turns of wire around it that generates a low level sine wave as the gear teeth pass its pole. You could switch the meter to AC volts and then spin the wheels at driving speed to see if it's generating a voltage.

As far as the scale factor goes, you best bet might be to get the interface working and then calibrate by using a GPS receiver.

LS differentials were an option on some E34s. Which ones, I don't know, except that my '89 535 had the optional $200USD LSD. I think they're uncommon.

[632 Regal]

9 pulses per revolution, just checked a rear end in the barn.

[winfred]

the easy way to check the ratio is turn the axles one revolution and see how many turns the pinion makes, slightly more then 4 would be a 4.10 and slightly less would be a 3.91 and so forth, posi was way more common on the e32 7 series which uses the same diff but with sometimes a different input flange

[winfred]

per revolution of the driveshaft or axle


9 pulses per revolution, just checked a rear end in the barn.

[Bill R.]

the ring gear which has 9 tabs sticking out of it



per revolution of the driveshaft or axle

[Javier]

seting for the instrument should be about 0.50737 mph/Hz. Is't it?

Javier

[Anthony (M5 in Calgary)]

the ring gear which has 9 tabs sticking out of it

From dismantling a speed sender from an E30, it is a reed relay on one side of a slot, and a fixed magnet on the other. The spider (choppper) fits between the magnet and relay and hence the relay provides a square wave on the output.

Same spider for all ratios, right? That way the speed output is a function of tire rotation, not drive shaft speed.

[Bill R.]

http://www.bimmernut.com/%7Ebillr/images2/Speedo.jpg
From dismantling a speed sender from an E30, it is a reed relay on one side of a slot, and a fixed magnet on the other. The spider (choppper) fits between the magnet and relay and hence the relay provides a square wave on the output.

Same spider for all ratios, right? That way the speed output is a function of tire rotation, not drive shaft speed.

[bradley]

9 pulses per revolution, just checked a rear end in the barn.

Cool. So how'd you check it exactly?

[bradley]

I'd suggest hooking an ohmmeter across the sender. See if there's a nominal resistance, say somewhere over 100 ohms. Slowly rotate a wheel and see if the resistance materially changes. If you see open/close kind of behavior, then the 'switch' model of operation is right. If the resistance doesn't vary significantly with slow (like 1/min) then the sender might actually be a magnet with a few hundred turns of wire around it that generates a low level sine wave as the gear teeth pass its pole. You could switch the meter to AC volts and then spin the wheels at driving speed to see if it's generating a voltage.


I was down with the trike builder yesterday (its getting overhaul at moment) and we tried putting a ohmmeter on the sensor. I suspect the sensor works off the half-shaft nearest the sensor as we tried moving the propshaft and the other half-shaft. Unfortunately due to some work he's doing we couldn't try the half-shaft nearest the sensor.

Its also possible the sensor might need replaced anyway as the diff was powdercoated recently.



As far as the scale factor goes, you best bet might be to get the interface working and then calibrate by using a GPS receiver.


Yeah, I'll be using GPS for calibrate, just need to work out if this will work in principle first.



LS differentials were an option on some E34s. Which ones, I don't know, except that my '89 535 had the optional $200USD LSD. I think they're uncommon.

I think the open diff is off a 525. The problem is the metal tag with the ratio marking is missing from when the diff was overhauled and modified for the trike (its mounted upside downas the bike engine shaft rotation is opposite).

[Javier]

its mounted upside downas the bike engine shaft rotation is opposite

Is it lubricating properly?

Javier

[bradley]

its mounted upside downas the bike engine shaft rotation is opposite

Is it lubricating properly?

Javier

Oh its fine - the trike builder been using BMW diffs like this for years - he blocks up the existing breather and drills another one of the other face. If think the filler hole then becomes the drain and vice versa.

This trike has been on the road fine for over 2 years. Nice and torquey :D

[632 Regal]

looked at it...I have one disassembled laying on the floor...lol.


Cool. So how'd you check it exactly?

[Javier]

then the helical gears should be attacking the edges in the undesirable way!!! Guess it is not designed for that job. Wonder how long would it last, or may be, how deep my taboos are.

Javier

[SRR2]

But it's only pushing around 20% of the normal vehicle weight. Still, it does seem a little dodgy with the thrust load on the helical in the wrong direction most of the time.

[bradley]

But it's only pushing around 20% of the normal vehicle weight. Still, it does seem a little dodgy with the thrust load on the helical in the wrong direction most of the time.

I'm not really mechanically mind so I don't know the real details. Its a common enough procedure in the trike world to use car diffs mounted upside down for shaft bike engines.

As for weight, the trike comes in at 470kg, not sure what the weight of a 5-series is.

[bradley]

looked at it...I have one disassembled laying on the floor...lol.

Cool. So just to confirm - it works off the RHS half-shaft rotation, not the prop-shft, right?

[632 Regal]

It works per revolution of the ring gear not driveshaft speed.

Cool. So just to confirm - it works off the RHS half-shaft rotation, not the prop-shft, right?

[Bill R.]

big block chevy 914 conversions. Alot of people want to use the 915 transaxles since its much stronger than the standard 914 one, a 915 will tolerate 800hp from a big block. On the 914 you flipped the 915 transaxle over since the 915 is for a rear engine and the 914 was a mid engine.. If you didn't flip it over you ended up with 5 gears in reverse and one forward gear. On some of the racing ones you ended up having to put a pressure fed pump to oil the gears. I've seen many mid engine vw sand rails done the same way and they didn't use a pressure pump. Doesn't seem to affect the life at all on them... the other alternative was to swap the ring gear from side to side and on some of the we had to machine the case out for clearance when flopping the ring gear.





But it's only pushing around 20% of the normal vehicle weight. Still, it does seem a little dodgy with the thrust load on the helical in the wrong direction most of the time.

[bradley]

Anyone know if any of the BMW Service Manuals or books like Bentley/Haynes cover testing procedures for the diff speedo sensor?

[632 Regal]

I think the Bently does, not sure its at home now.

Anyone know if any of the BMW Service Manuals or books like Bentley/Haynes cover testing procedures for the diff speedo sensor?

[bradley]

I think the Bently does, not sure its at home now.

Hi

I got a copy of the Haynes book on the E34 and it has nothing at all about the diff speedo sensor - the single reference to it is a picture showing where it is to unplug it when removing the diff. The book doesn't even go into any procedures about inside the diff itself (says its too advanced and best left to a proper mechanic).

Did you get a chance to check Bentley?

[Javier]

Javier