Bonster

I have been seeing this "VDO" on my gauges for years. Up until today, I've either been too lazy to look it up or I just plain forgot. So I look it up. Turns out it's just a brand name of gauge. But I also found that many of the "earlier Porsches" had problems with the accuracy of the gauges.

My first question is easy -- these are the OEM gauges, right? I figured they were, but thought I'd ask as I am not the original owner of the car.

My other question would be about the accuracy. Do I have anything to worry about with the gauges in my '95? Or is this an issue even in the newer generations?

Silly questions, probably, but you don't know what you don't know. Thanks . . .

Matt Lane

Yup, VDO has been the original supplier to Porsche (and Eurpoean cars) for donkey's years, as far back as I know.

Up to the end of our car series, they are not digital gauges and as such they can all be calibrated/serviced.

They are in fact well made and reliable, so if you do in fact confirm a gauge is off by x%, most of us just mentally correct for the variance to actual.

Calibration and repairs or restoration are easily done by either Palo Alto or NH Speedo in CA. Not sure who is the favoured of the 2...

Best,

Matt

nile13

Well, VDO and European electronics "provess" in general... don't start me on that.

993s are fairly lucky in that we only have two well known and common problems with gauges. One is, of course, the genius use of lube that actually eats through the odometer gears turning them to Jello. The other, that wouldn't affect your '95, is the OBC display that goes dim.

I've have had previous and current experience with VDO in BMWs and VWs and I often have nightmares that my shrink files into the "cold soldering" folder. I think he'll asked me to buy him a larger file cabinet soon. But take heart. They could be Lucas.

Bonster

Thanks Matt, both for the advice of a shop and of the history. The speedo gauge, at least, seems to match within 1-2 MPH of my GPS unit, so I suppose it is doing right. I'm kind of used to cars not having perfect speedos as I used to race. The RPM gauge I cannot check, but it feels right in the seat of my pants from past experience. I was just wondering if I need to be checking on these little gems.

Thanks as well to Mike, for more history and the great Lucas joke. How can you tell when the lube is breaking the odo apart? I have just over 90k on my baby (that I flog whenever I can, lol).

I truly appreciate you guys turning my curiosity into a learning experience. As far as I know, my gauges are okay. I just thought I'd get a little education in case it happens one day.

nile13

As Matt said, I think the 993 gauges are more reliable in general than most VDO stuff and I would not worry about them if they work. The odometer gears are easy to tell - the odometer simply stops working.

One of mine died at 140K, the other at 80K. The one ounce of prevention seems to be not to zero the trip meter while car is moving (or better yet not at all). If the odo stops, the replacement gears at $25 each (there are two gears but usually only one dies). Replacing by yourself is not difficult if a bit tedious.

IXLR8

Ahhh, Lucas, the Prince of Darkness, makers of light switches with "Off" - "Flicker" - "Dim" for positions.

The other European maker of gauges is Motometer. I had the speedometer on my BMW motorcycle replaced under warranty because the needle started doing a bounce routine.

As for crap electrical components, there is Valeo who in their infinite wisdom decided to glue their starter magnets to the starter motor housing. All very nice till one detaches, sticking itself to the armature for a locked rotor scenario.

IXLR8

Also note that speedo accuracy and odometer accuracy may not be the same.

Gunter

That myth just doesn't die. Especially over at Pelican.

Resetting the odometer while the car is moving has absolutely no effect on the mechanism and doesn't break the gears.

Hartmut Behrens at NHS can confirm this and taking one apart shows that it is designed for reset when in motion.
It is my understanding that the infamous little plastic gear is supposed to fail when something goes wrong inside the mechanism to prevent further damage.

I think VDO is good stuff. My 80 SC turned 250k Miles before the little gear failed and all other gauges still work just fine. My old Volvo has 300k on it and all VDO gauges are still working.

nile13

I have taken two apart and one is sitting on my desk right now. I have a pretty decent understanding how it is made inside. It is, of course, "designed" to reset while in motion. Every single odometer known to man is. That does not mean that resetting while in motion is not the last straw in breaking the gear.

If you ever take a speedo apart and actually see how reset is done, the "tenth of a mile" little wheel is turned during reset and it is still connected to the motor-driven gear at this point. Take a wild guess what happens when plastic gear turned to mush gets any appreciable mechanical resistance. Right, it strips gears. You are welcome let us know if you have personally seen or can point to a gear failure mechanism other than what has been described numerous times here - gear turning into gel and stripping teeth without "something going wrong inside the mechanism".

Is this the only gear failure on a 993? Of course not. At the very least the cab roof latch gears fail consistently. BTW, the great "redesigned" gears also fail. So do side transmission gears, although less often. All of this amounts to poor engineering. No if ands or buts about it. of course a bad engineer can always come up with reasoning for his prowess (trust me, I used to be an engineer and there's a reason I'm not one any more - I wasn't very good at it). Parroting the propaganda that breaking that gear is a fail-safe mechanism is beyond comprehension. Especially to those of us who have seen the failed gears and actually understand that their failure is due to initial bad design. Look, my E30 cabs used to bend roof raising longitudinal rods into bloody pretzels. Because engineers were not smart enough to put a damn fuse to blow and stop the motor from bending the damn forged 1/2" rod. Can you imagine the amount of current that takes?

I have had personally re-soldered at least 6 VDO Gauges after they start doing the St. Vitus's dance on my BMWs and was too lazy to re-solder some more before selling/dumping the cars. The cold soldering is a European epidemic as far as I'm concerned. Do a search for Convertible Control module on 993 board.

Don't let me tell you how I really feel about European electrical devices I'm just happy that there's a great minimum of them in my 993 compared to modern cars.

IXLR8

You mean like on them DME relays.

nile13

Didn't even want to mention DME relay as it's a mechanical part after all. But, yeah, damn it!

IXLR8

The mechanical part works, its getting it to work when the coil doesn't energize due to a cold solder joint.

But I did come across a high resistance contact on a RLers old DME...as high as 200 milli-ohms; cleaned it and measured 2 milli ohms (thats damn low - usually a bit higher) with a 4-wire meter.

Q8drill

I'm having a problem with my RPM guage OBD light, It's dim where i cant read it at night time, I removed the guage and removed the back cover and changed the bulb, Still my OBD light is dim, So i pulled the guage again to change the transistor but i found out that my gauge is SMD (Surface Mounted Components), here when i stopped, i dont have much of information to repair it. Any input will be appreciated.

Cheers

Ed Hughes

I'm superstitious enough about the odo reset, that I don't feel like I HAVE to do it while moving. Part of my gas fill ritual, right after Replace-The-Cap, Get-In-Car, is Reset ODO.

IXLR8

The OEM clock on my Honda stopped working. All SMDs. I took a low power soldering iron to all SMDs. Bad solder joint, even on an Asian car. Works now.