Jerry Feather

When I got the 90 GT home and started driving it I found that the tire pressure warning was on showing one of the tires was "loss." I checked it and found that it was just over 40 pounds, so I let some more air out bringing it down further to about 36. Then I checked the others and found that they were in the mid 40s. So I let them all down to 36.

Then the RDK shows all four tires "loss." I have been driving around canceling the warning when it comes on but still being irritated about the little red icon on the instrument cluster.

Then the week before last I had a flat tire on the back, so I replaced the tire and wheel with one from a set of D 90s I had bought on eBay some time ago that still had tires with air in them. I thought that would work well until I could either replace the tires on the car or get the flat fixed.

Then the next day the other rear tire was flat. I did the same with it with another from the spare set I have. Then I pumped the two flats up again and found that one has a slow leak, but the other is holding its pressure.

Nevertheless I have had the two flats dismounted so that I can refinish the wheels and put new tires on them. In the course of that I learned that I need to remove the RDK sensors. Some research here and a look at the WSM gave me a lot of insight into the whole system.

So I took a little break from the Intake Tube project to make me some RDK Sensor Tools. The WSM suggests having a helper to do the sensor removal, so I got C. C. to help. That is short for my Charlie Clamp. That worked really well. The only purpose of the C clamp is to hold the tools lightly in place while I torque on them to loosen the nut. I found that all you really need to do is break the sensor nut loose and then it will come off pretty much by hand.

I have removed all four 3.0 BAR sensors from the two rear wheels so I can strip the wheels and then I think I'll powder coat them. Then I am going to replace the sensors with the 2.5 BAR sensors out of the front two wheels from my spare set. I hope to do the same with the front wheels off the GT, but will continue with the 2.5 BAR sensors that I hope are in them. I haven't removed them yet to see, and I have some doubt since they have 36 pounds of air and are still showing "loss." I am half afraid that this GT may have had 3.0 BAR sensors all around.

When I finish with the wheels for the GT Then I think I will have the sensor holes in the left-over D90 wheels welded up and put new tires on them and use them on the 85 in place of the man holes. At the price of even good used sensors I can't see any value in trying to preserve these wheels for RDK use, especially given the limited application of the system and the fact that everyone is likely going to 17 18 and 19 inch wheels these days.

Here are some pictures of the RDK tools I made and put to good use.

Alan

Jerry weld it up, balance & use an aftermarket TPMS so you can set your own pressure warning levels and temperature thresholds, and get absolute readout of instantaneous pressure and temp for each tire as you drive. RDK was ahead of its time (as we can see now) however its a fundamentally limited system (fixed pressures) warning only and the temp compensation is poor. There is much better possible today - with easy mount in-the-valve-stem sensors (like most modern systems).

Look at Orange TPMS.

Alan

RKD in OKC

Beg to differ. When I had a 90 GT and set the tire pressures according to the owner's manual PDK worked great! 36 front and 44 rear were good pressures for the 16 inch rims and any of the various brands of tires I ran. It only falsed when my mechanic tried to set the pressure with the hammer. I liked not having to worry about what the pressures were unless they were low. And temps didn't seem to make any difference...again when set according to the owner's manual.

Saved me from coming out to a flat tire twice due to nails. Still had enough pressure to drop by and get the tires patched.

If my GTS had RDK I would be trying to fit the sensors in 18 inch wheels and run the 2.5 bar front and rear.

Alan

I think you are crazy... I've tried several other systems and in retrospect the best I can say about RDK is that it 'kind of works' - if you want to live with Porsche's high fixed pressure settings (on what are by now typically very different tires...), on stock porsche wheels, and as long as you don't live anywhere really hot...

Too many compromises... very good fully programmable systems now exist that just totally blow it away.

In its day it was the best there was, does it still work today - Yes, but times have changed.

Alan

RKD in OKC

Have been accused of being crazy many times before.

36 psi seems fine to me as that is the tire pressure recommended on most new cars with those very different tires. In fact, my 2007 BMW X3 with sport package, wider wheels and tires and speed limiter raised from 120 to 150mph, recommended 36psi unless exceeding 100mph then recommended 44psi to keep tires from over heating.

When my PDK did give the tire pressure warning the pressure was 30psi from 36psi. and found a nail both times. Just crazy.

ROG100

I have to agree with RKD my sensor system on my GTS worked perfectly as long as you read the WSM first. Then I moved to 18" wheels and lost the capability.

Alan

RKD - If you had RDK on your GTS the sensors would be 3 bar front & rear - so 43.5 psi all round

I think its too high to be optimal for almost all modern tires - it certainly is in Phoenix - with temperature the pressures go up even more and you get uneven central tread wear - so just unacceptably high here.

I never said it doesn't work (within its narrow parameter window) - I said you can do much better.

Alan

SeanR

I can't bypass this system fast enough for people around here. One customer has an aftermarket setup that works very well installed on his and I think it was only $350.00 for the set up, digi display and a warning tone.

RKD in OKC

My Owner's Manual recommends 36psi front and 44psi rear. I would assume the PDK would be the same as the recommended pressures.

Kiwi928S4

Hi Jerry

I like the tool that you made to remover the RDK sensors - how much for one of those sets?
Cheers

ken

Jerry Feather

Thanks Ken. Unfortunateley I think that set of tools is a one-off. I have more time than money so sometimes it is better for me to make something than to buy it. For the amount of time it takes, however, to do it for someone else will likely be more expensive than buying a set from the factory or from someone who has a factory set they will sell.

Vilhuer

Instead of welding its possible to use plugs to close the holes. TechArt made some 18" OZ Mito-3 wheels with RDK sensor holes. They also made or found some ready made plugs. We have few of them around. Copies could be made but it might be somewhat expensive solution.

Nicole

Hi Jerry: It looks like you have the 16" factory wheels on the GT - those require 44 PSI in the rear - not 36 like 17" rear wheels. My previous 91GT was not happy with anything less.

IIRC, the pressure would be the same in the front, regardless of whether you have 16 or 17" wheels.

Schocki

My GTS (MY 92) still uses the original factory wheels and sensors. Front and rear axle use 2.5 bars or 36 PSI.
The system works just fine and is very exact and reliable. I run (like the factory recommends) 2.7 bars on the tires to eliminate false alarms due to temperature changes.
If you "only" run on 2.5 bar and you don´t give the tires enough time to warm up on the Autobahn, the warning will be triggered at about 130 MPH...

The red light in the digi dash is always an annoying "show stopper" at speeds beyond 120. But keeps a good amount of adrenaline going to keep you awake.

DKWalser

I would like the factory system to work for me. It doesn't. I'm running 18" wheels on my S4. One of my first questions on Rennlist was whether it was possible to adapt the factory system to my 18" wheels.

Ideally, the factory receiver would read the signals from the modern senders in each wheel, allowing the warning light on the dash to work AND allowing me to mount a modern display in the cassette tray that shows pressure and temperature for each tire. Unfortunately, the factory unit is incompatible with modern senders. While it might be possible to wire something up that would flash the warning light when pressures are too low or too high, that would prevent the factory system's use in case a future owner wants to run the original wheels.

So, I understand the desire to keep the factory system. A light on the dash is more likely to be seen than is something mounted in the cassette tray. However, the factory system -- even when its working as designed -- is inflexible (you cannot change the set point for when the light comes on), cannot be used with new wheels, and does not display ANY information unless tire pressure is too low. My GMC and my Toyota both have factory systems. The Toyota only has a warning light. The GMC has a warning light AND the ability to see the pressures in each tire. I much prefer the GMC's system. I'd like my 928 to have something similar.