Reference sensor removal

[Dark Skies]

Hello there. New member crying out for help.

Does anyone have any ideas as to how I can easily remove the speed sensor from it's seating on my 944? It proving to be a right song & dance.

About five months back I replaced the flexidisc (sits on the back of the flywheel) in my automatic trannsmission Lux. I had to remove the reference / speed sensors to facilitate the job and simply undid the adjustable bracket and took it and the speed sensor to my bench. It was well seized in and had to be drifted out with a rubber mallet. I bought a second hand sensor to replace it as it got a little out of shape. It was easy enough to replace, gap (with a .8mm thick rubber o ring stuck to the bottom - I left it to be swept of by the flywheel) and tighten the bracket with all the other pipes and cables already removed .

The car was running well for a few months and then refused to start. A swift test with a multimeter revealed the s/h sensor had packed up (open circuit on two of the three connector pins) and was the likely cause.

I have a new sensor but can't seem to shift the old one. I can lift it clear as far as the rubber o ring between the very top of the metal body and the plastic of the sensor but no further. Try as I might I can't get the bloody thing to pull out. I've tried getting grips to it but just can't get the leverage (very tight on space).

Twisting it and pulling doesn't seem to get me anywhere.

Brute force doesn't work either. I even tried using a 6mm screw placed in the mounting hole of the sensor with a nut either side and turning it to act against the mounting bracket in the hope of pullng it free as on might split a ball joint. The plastic body broke.

How can it be so tight??? Surely the o ring can't be holding it in???

I thought I might try using one of those corroded bolt easing fluids to break down the rubber o ring. It seems like a long shot but I'm fresh out of ideas. I'm trying to avoid removing the whole bracket because then I'd need to pull a lot of other stuff off to gain sufficient access to refit the fixing bolt.

Has anyone out there got any tips?

[Scott R]

Use a little PB Blaster and let it soak for a few hours. Then twist it some more. Twisting has removed even the most stuck sensors for me.

[Dark Skies]

Thanks. What is PB Blaster by the way - I'm in England so I'm not sure if it's marketed here. I'm sure there's an equivalent though.

[Chris_924s]

Good Luck- I thought I was the only one with an auto around here- i too replaced my flex disk in August, without a car for 2 weeks, and $2200 lighter, but fine ever since. How did you determine it was the sensor? and welcome to the board, btw.

[Dark Skies]

I couldn't afford to have a dealer do the disc. I had to do it myself but it proved remarkbly easy all things considered. The autobox had to be removed but thereafter pulling the bellhousing and torque tube back gave me just enough room to access the flywheel. Job cost something like £350 all in.

Re the sensors. They're both identical and test the same. There are three pins in the conector block, touching the multimeter probes to two of them should give about 900 to 1000 ohms resistance. The other pin is a ground and you simply test that by sticking the sensor on the engine block and touching your multimeter against the pin to check for continuity. If you're getting nothing then they've gone tits up. Bloody expensive too - even pattern ones go for about £90 Unfortunately they're both vital as they chat to the DME about TDC and spark pulses and lots of other stuff that I only tentatively grasp. Chances are that if you have no spark from the coil then the reference sensor is playing up.

I sound like I know more than I do. I found out that lot AFTER I'd replaced the rotor, the distributor, the spark plugs, the (EXPENSIVE BEYOND BELIEF) plug leads, the coil and earth lead.

[robm-951]

Originally posted by Dark Skies
Thanks. What is PB Blaster by the way - I'm in England so I'm not sure if it's marketed here. I'm sure there's an equivalent though.

PB Blaster is just a penetrating lubricant that works very well. Spray the sensor/mount with whater you can find over there, then as Scott R suggested, let it soak a while then start twisting.

Rob

[AFJuvat]

Having them stick is a frequent problem. Failure usually occurs in the plug itself rather than the sensor.

PB Blaster, as stated before, is a very strong penetrating oil that comes in a spray can (think WD-40)

Wurth makes an similar product that will probably be available in your area.

Hint: When reinstalling the new sensors, spread a little anti-sieze compound or vaseline in the bracket. Just take care to ensure that the tip of the sensor remains spotlessly clean.

Best of luck

AFJuvat

[Dark Skies]

Eh! This is driving me nuts. Arthur had an easier time drawing Excalibur out of the Stone than I'm having pulling this sensor.

I've spent an entire day spraying a very aggressive penetrating fluid onto the sensor, giving it an hour, pulling and twisting and repeating the whole process. No success whatsover. It will easily twist and turn its way up to the o ring and no further. At one point I even tried to pull it up by hooking a pry bar under the exposed body and using it like a slide hammer. Made absolutely no difference.

It's obvious to me that I'm having to use wayyyyy more force than a Porsche technician woud expect to use. I suspect that the support bracket hole hasn't been machined out to spec. It REALLY shouldn't be so tight that I have to remove the whole bracket in order to hammer it oput with a mallet again.

A whole day fiddling around with a serviceable item just isn't on - I could have unbolted the bracket and refitted it in an hour or so. I've decided to pull it tomorrow and then have the whole bracket machined out so that the o rings on the sensor barely touches the metal.

I'll gap it using a depth gauge - gluing washers / fitting / removing / refitting is just too much like buggering about.

Thanks to all who took the trouble to post ideas though.