What makes e30 speedometers fail?

[mach schnell]

Why do e30 speedometers fail?

Mine has stopped working. Sometimes it will flicker, and maybe work for a few minutes, if I drive through a puddle or in wet weather.

How do I fix this? How much?

[Rocco335i]

the gears inside bav has replacements for like $40

[nando]

I think he means speedometer, not Odometer.

The speedometer usually fails because of a bad sensor in the diff, or loose/broken wires at the diff plug, and sometimes a loose ground on the back of the cluster. There are no gears in the E30 speedometer, these things weren't built in the '60s ;)

[mach schnell]

I think he means speedometer, not Odometer.

The speedometer usually fails because of a bad sensor in the diff, or loose/broken wires at the diff plug, and sometimes a loose ground on the back of the cluster. There are no gears in the E30 speedometer, these things weren't built in the '60s ;)

Yes definitely the speedometer.

I replaced the diff sensor already but that's not it.

Where is the ground on the back of the cluster, that you're talking about? How do I fix it? Is it plugged in, or is it soldered on, or what?

[Knockenwelle]

Are you having problems with more than the speedo? Cluster grounds will usually affect more than one instrument. Check the harness for the diff sensor.

[mach schnell]

Are you having problems with more than the speedo? Cluster grounds will usually affect more than one instrument. Check the harness for the diff sensor.

Right now it seems like only the speedometer is not working properly. The others appear to be fine.

How do I check the cluster grounds? Where are they?

[gmiller5m]

I had the same problem where everything worked fine except the speedo. It would only appear to work when i drove over a rumble strip. The problem was that the PO replaced the two screws holding the cluster face to housing with screws that were a little too long. When these longer screws were turned all the way in they dug into the SI borad on the very edge and cut the printed curcuit board. So i guess the high frequency rumble caused the screws to jiggle around enough to complete the curcuit.

[Adrian_Visser]

check out these links :

http://www.unofficialbmw.com/speedo/speedo_d.html

http://www.unofficialbmw.com/speedo/speedo.htm

First isolate where the problem is. i think pretty much the only way your going to know for sure if your getting a signal from the sender is by using the frequency (hz) function of a DMM that has such a function. when i tested mine with just the volt measurement of a cheapo DMM all i got was a fluctuating reading which didnt tell me much. the last paragraph of the first link says : "20mph it read 40 Hz, at 60 mph it read 120 Hz".

If the problem is in the speedo read on...

Do your SI lights work still? When the batteries for the service interval timer wear out they leak their electrolyte. The electrolyte is very corrosive and fucks up the circuit board which happens to be where all the signals to your gauges etc go. I think it's like $140 for an SI board. But first you can try reflowing the circuit for the speedo on the circuit boards in the cluster if your lucky it might just be a break in the circuit.The first link has a pic which shows you what circuit to flow.

[wakeboardr42393]

What are the SI lights? Where are they located?

[Gregs///M]

SI lights means Service Interval, which is located in the center of the cluster. It has 7 or 9 LED's that indicate service interval/oil/ and inspection indication.

Now the SI board barely interfaces with the speedometer but I don't believe an SI board failure would cause the speedo to not work. The speedometer has an vehicle speed output that feeds the engine vehicle signal input, which is used for OBC calculations.

The speedo itself has three main input functions. 12 volt power, ground, and vehicle speed signal. Power comes from fuse 12, so if you have speedo problems, I would check/change that fuse first. Think...20+ year old fuses are no good, just replace the cheap little bastard. Old fuses can develop micro cracks and cause intermittent connection based on temp, etc.

Grounding is done via the brown wire in the white connector. You can try cleaning this but it rarely causes a problem as its grounded with several other clusters grounds. When these grounds go bad, most of your cluster will fail, not just the speedo. However, individual wire failure is possible but rare.

Finally, signal. It comes from the brown/red wire in the white connector. It is the wire that is fed from the vehicle sensor in the rear differential. It is imperative that connector be clean, corrosion, and oxidation free. Clean it real well and make sure it is secure. The sender itself is pretty robust unless it is in poor mechanical condition.

Other possibilities are solder joint failure on either the speedometer circuit board or the cluster main board. Also cracked electrical traces on the cluster main board, which can occur from tightening the cluster screws too much. Also intense vibration over many years. These problems can be fixed by re-flowing new solder onto these circuit board or performing electrical trace repair.

Good luck

[Northern]

loose/broken wires at the diff plug

2/3 cars have had this issue so far. Seems pretty common.

[roberto967]

my speedometer too is beginning to fault, often by hitting it hardly once or twice with my hand, it restarts, so I think it is a sort of faulty contact. In fact, also the "econometer" gauge is faulting. All others gauges go fine. This simply means that the suggested re-doing of the solders of the speedometer gauge cannot be the true solution, and it possibly it works for other reasons (e.g. moving the faulty contact).

Looking at the diagram the input signal from the speed sender is input to the computer (feeded across fuse 12) and from computer goes to feed the econometer gauge too. So or it is the computer (and its fuse 12) or the input signal to it. I already demounted twice the instruments and most contacts seem fine. Also checked tha batteries seem ok.

My next step will be fuse 12 (it also powers a radio connector), and test C2 connector 12 and 8 where the speed signal arrives..

[cgk_iii]

just send it to e30_dad on instagram hell fix it right up for ya

[Gregs///M]

my speedometer too is beginning to fault, often by hitting it hardly once or twice with my hand, it restarts, so I think it is a sort of faulty contact. In fact, also the "econometer" gauge is faulting. All others gauges go fine. This simply means that the suggested re-doing of the solders of the speedometer gauge cannot be the true solution, and it possibly it works for other reasons (e.g. moving the faulty contact).

Looking at the diagram the input signal from the speed sender is input to the computer (feeded across fuse 12) and from computer goes to feed the econometer gauge too. So or it is the computer (and its fuse 12) or the input signal to it. I already demounted twice the instruments and most contacts seem fine. Also checked tha batteries seem ok.

My next step will be fuse 12 (it also powers a radio connector), and test C2 connector 12 and 8 where the speed signal arrives..

Vehicle speed signal interfaces directly to the speedometer first through the brown/red wire. Tapping your cluster and causing intermittent operation
Is sure sign there are cracked solder joints on the speedometer and/or main cluster board.

just send it to e30_dad on instagram hell fix it right up for ya

I've talked to Diego (e30_dad) and i don't believe he performs electrical repair. He can swap out the parts until it works and reset the mileage and dress up the cluster. But you would have to pay those parts and labor.

I can perform repairs to the component level and test the speedo or whole cluster on my test bench. It would only cost labor, not parts.


Sent from my Nexus 7 using Tapatalk 4

[roberto967]

thank you for your reply. You are right, I checked the wrong schematic!

In fact the sensor signal is fed directly to the speedometer, that is a single chip IC meter with very few components.
The pcb and solders seem not so bad ( I renewed all them but they were fine and also pcb was fine, no cracks and all routes ok under a lens).
However the sensor signal passes through two connectors that I "reworked" because I think they can easily fault.
One is on the pcb, when remounting the meter to the cluster care must be taken to push well down the contacts, not just inserting the meter.
The second is the connector that comes to the cluster, ( C2, in my e30 front looking at the cluster is on the left side). the sensor signal owns two pins, 8-gnd and 12-signal; I run the risk to try to rework them with a very small screwdriver.. may be it was unneeded, however I did.
That said my speedo is ok now, I'm satisfied, the problem were fault contacts. Will not do any other action.

However i noticed that the speedometer seems to start measuring low velocities (e.g under 25km/h) slower, never noticed it before, cannot be sure, but this made me mumbling.. On the IC a big capacitor slows the movements, but I checked its value was ok.
Must say that the meter is very simple, very few compoments, the only IC is a UAF2115 that can be found for less than 10$, but is not probable that it is truly "broken"..
One possibility is that, due to contacts, the input signal can become weak and the meter faults; in fact the sensor must short the signal wire to the ground to send each pulse, due to the schematic, shorting to ground about 3 ma, IC generated. It is therefore possible that if the IC or the sensor are beginning to have some loss, the meter becomes very sensible to leaks in the connectors. Probably putting a 20k resistor shorting the sensor wires on the meter could help by presinking some current.
Hope this helps.