Engineering challenge

ernestedward · 06-24-2004, 08:02 AM

OK all you amateur (and professional engineers out there - I have a challenge for you:

My ealy 944 was upgraded with 928 S4 brakes by the PO. Therefore all the suspension and everything is somewhat custom, and definitely not stock. The problem is this: The speedometer is an early with a manual sender, only there's no where to stick the end of the cable anymore. If I wanted to get it working, I'd have to replace not just the spindle, but the hub and A-arms and more (on BOTH sides) and I probably would lose my good brakes. So I have a few options that I can think of.

-Live without and and try to make some markings on my tach so I'll at least know where 70 and 35 are (in top gear). You can see why this is not preferable.

-New transmission (I have an early on the car) with the hole for the electronic sender, then a new gauge. Would I need to replace the whole gauge cluster? This also seems like a bit of overkill.

-Aftermarket speedo. This is my favorite option but I know nothing about them. I don't know if you can just bolt one in somewhere. Anyone have an idea on this?

My neighbor pointed out (correctly) that all I need is something to spin the end of the speedo cable once for every tire rotation. Do you think it might be possible to jury-rig something like this?

barlowdo · 06-24-2004, 08:33 AM

Buy a GPS with Speed info displayed.

sasquatch · 06-24-2004, 08:37 AM

Have the spindle bored out by a machinist with the same diameter bore as the early spindle.

SoCal Driver · SoCal Driver's Garage

First (and I know this is not your fault) the PO was a DS for upgrading an 83 chassis with later parts.

Now for a possible "cure". Check out the rotors/hubs and see if these have the "teeth" and the mounting points for the anti lock brake sensors. If they do then it's possible to use the output from the sensor and an aftermarket electronic speedo that can be tuned to these pulses.

It's also possible to use a sensor off of the trans to read the back side of the CV bolts as they stick through the mounting flange. Would have to be a magnet and coil pulse generator like the speed and reference sensors.

The left front wheel would be easier.

ernestedward · 06-24-2004, 09:20 AM

barlowdo - Good idea. I thought of this a few minutes after I posted. It's probably literally the easiest thing to do, but I'd really like to have an actual speedo..plus I'd have to get into wiring and mounting to where I could actually see it, and due to the lag time in calculating it, it's really only useful at sustained highway speeds. Thanks though.

sasquatch - Do you (or anyone else) know for sure that this is possible? Sounds too good to be true...

SoCal - In his defense, it was a track car so it didn't really matter if all the "niceties" worked as long as it went fast and slowed down. It is proving to be a bit of a challenge to get those niceties working again though..

For your first suggestion: Can you be a little more specific as to the type of sensor I'd need? Electronical or manual? How (generally) would I go about mounting it to the ABS mount points? Are you talking about using an ABS sensor? Can you point me to any sites or stores with aftermarket speedos that might work?

This is all very exciting, as my mechanic made it seem hopeless cause of the upgraded suspension..please keep the ideas coming!

SoCal Driver · SoCal Driver's Garage

An ABS sensor is basically a pulse generator -- wire wound magnet. You would have to search here or the internet for after market electronic speedometers.

A race car. What class did the S2 engine put him in?

ernestedward · 06-24-2004, 12:06 PM

Excellent. I'll bring this up with my mechanic today.

Racing - I honestly don't know, other than the fact that he did race (only twice with the S2 though, then he let it sit). Is there something special about S2's racing I should know?

SoCal Driver · SoCal Driver's Garage

You have checked the chain tensioner pad and the timing belt....

ernestedward · 06-24-2004, 02:19 PM

Haha yup..it's all been replaced. On an engine this new I'd never take the chance..plus it had been sitting for about 4 years...

On the original topic, I think I've found a solution. Racelogic (www.racelogic.co.uk I think) makes a gps unit with an electronic pulse sender for the speedo. Now all I have to find is a speedo that 1) fits and 2) will work with the sender. Anyone know what size an early speedo is?

SoCal Driver · SoCal Driver's Garage

Go out and measure the hole. The body is a tad smaller for a slip fit.

ernestedward · 06-24-2004, 04:13 PM

Will do as soon as I get my car back from the shop, just wondering if anyone knew offhand. No big deal.

SoCal Driver · SoCal Driver's Garage

Can OD is a tad smaller than 3 15/16".

Can depth is 2 3/4".

OD on the bezel is 4 5/16"

This does not include the cone shaped lens as I can't find it.

ernestedward · 06-24-2004, 04:59 PM

No idea. I know the work was done by a local porsche customization/racing shop called Reliable Performance Modifications. Someone asked for pictures of the brakes a while back, so as soon I get it back (hopefully tomorrow, it's been three weeks :-() I'll take some pictures and post a new thread. Maybe someone on the board can tell me some new things about my car...

ernestedward · 06-24-2004, 05:01 PM

Thanks a lot SoCal. Exactly what I need. Now I just hope I can find an electronic speedo that fits for less than $arm.

1.2gees · 1.2gees's Garage

Would love to see pictures.

I'd bet that the car's not running 928 suspension other than the brakes, and perhaps a couple of other parts. I'd LOVE to be proven wrong here though.
Ahmet