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Replacing Speed Transmitter (Sensor)

I am in the process of replacing the Speed Sensor on my 1983 944, and I need some advice on removing and replacing the sensor. I have removed the 5mm Allen screw holding the Speed Sensor, but the sensor is not yet loose and doesn't appear that it will come off by simple hand twisting, although I have not exerted extraordinary force on it. I do not want to risk upsetting the mounting, since I want to be able to merely just screw in the new replacement sensor. The sensor has never been replaced, and it is probably well sealed after 20 years and 130,000 miles of intense heat. What is the proper procedure for breaking the seal to remove the device. And, can I expect to just screw in the new sensor without going thru the rather complex procedure of verifying that the clearance is indeed correct at 0.8 mm. Afterall, it worked well until the sensor failed (open circuit).
Old 09-01-2004, 03:25 PM
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A lubricating spray would be nice............some gunk builds up for sure.

You are right to becarefull with the bracket. It can and will break. But usually it will hold up well unless you really start prying at it. Spray the edges with a lubricating spray....let it soak in....twist a little ...etc.

Take your time and it will come out.

The only times I have seen real problems if the sensor has actually been hit (debris) from the inside. Bends the sensor just enough to keep it nicely wedged in.

If you have not disturbed the locking bolt the sensor should go back in at the clearance of the old one. So bolt up and plug in. Be very carefull with the plugs coming from the harness they can easily disintegrate in your hands! Plastic harness plugs on these cars are brutal. I had to rebuild one of my entire harnesses because of corrosion at the sensor plugs.

Good luck.
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Old 09-01-2004, 04:01 PM
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Thanks. I will try WD40 and allow it to set overnite.
Old 09-01-2004, 04:18 PM
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Hi Tooter -

I hope all the above advice works, because let me give you an indication of what you'll have to do if the sensors are fully stuck, like mine were.

My problem was that I could not get my sensors to pull out of the bracket, and actually broke off the top of the front sensor trying. I also couldn't get the bracket unbolted. Further, my large hands, when I would wedge one down in there, were unable to even hold the allen wrench properly to the bracket bolts, much less unbolt anything.

I ended up doing the following:
1) Removed Exhaust System
2) Removed the Transmission, Torque Tube, and then found that I couldn't remove the bellhousing until I got the sensors removed
3) Removed the Intake Manifold (Did an engineer on cocaine design the vacuume hose system? Or was it Meth? I have never seen a more confusing bunch of hoses. You can be sure that I wil replace everyone of them for re-assembly, because I never want to go back in there again)
4) Removed the Oil Filler Tube
5) FINALLY got the bracket bolts to loosen (had to use a 6mm allen wrench, and ground it to fit. I also had to shorten the legs of the allen wrench to where the short leg was only about 1/2 inch long).
6) Had to CAREFULLY pry on the bellhousing and sensor bracket to get them off (the bracket was kind of corroded to the mounting post.
7) Then, after I got the bracket off, lubricants would not help get the sensors out. Sure, it made some improvement, but I could not get them to pull all the way out. Finally I noticed that one of the sensors had dents in the cylinder, and the other one was mushroomed on the bottom. Since I was replacing both of them, I used channel lock pliers to "reshape" the cylinder, until I was finally able to extract them from the bracket. Corrosion between the sensor and the bracket made for a pretty good "weld".

Part of the reason I had such troubles (I've been working on this problem for almost a year, but that's because I only get to play with my toys about 4 hours per month), was that whoever last assembled the car prior to my purchase, literally mangled every nut and bolt. The allen bolts holding the bracket to the block were so rounded out, I'm surprised that I was even able to get them out, sort of taking out the motor.

Sorry for the rambling post, but I was just able to remove the bracket and senors at 10:00 PM last night, so I'm still fired up about it.

By the way - thanks to Todwick, Socal, et. al., for having given me advice on how to deal with these sensors.

Now, I've got some cleaning to do, new bolts and hoses to order, and repeat the process in reverse.
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Old 09-02-2004, 08:15 AM
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Well, I have not been able to remove the Speed Sensor yet. In fact, I have been unable to "move" the sensor at all. The lubricants that I have tried (WD40 and Liquid Wrench) have not helped at all. As I stated in my initial post, I easily removed the 5 mm Allen mounting screw using a 3/8 socket. I can get my hand into the opening and I have exerted all the physical force I can muster in this awkard position in an attempt to rotate or pull loose the sensor -- all without any movement whatsoever. I have not resorted to a ball peen hammer since I don't want to damage either the mounting position or the bracket. I have considered fabricating a long pry bar in an attempt to pry the sensor loose. I am the original owner of the vehicle; therefore, I know I don't have any problem other than a severely stuck sensor. With all due respect, I am sure that I would not go to the trouble that you did to replace your sensors. If anyone else has any ideas or knows of a "proven penetrating solvent" for this application, or an alternative approach to remove the sensor, I would appreciate your input.
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Old 09-02-2004, 10:51 AM
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Well if you can get your hands in there with some visegrips you might be able to twist it a bit............

The dilemna is ....... If you end up breaking the mount ........You will be doing what Proff had to do.
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Old 09-02-2004, 11:01 AM
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I have an idea that I would like feedback on. Irrespective of how I attempt to twist the sensor out of the bracket, it appears that I need to get some penetrating oil down into the bracket in order to break the seal. Based on a photo from Clarks-Garage.com (http://www.clarks-garage.com/shop-manual/ign-02.htm), the upper half of the sensor (7/8 inches), which is a polypropylene material, is in contact with the bracket around the entire circumference of the sensor. Therefore, I'm really not surprised that the sensor is difficult to remove on a 20-year old 944. I am proposing to drll a small hole in the sensor near the edge where it extends into the bracket. This would hopefully enable the penetrating solution to work its way down into the bracket. Currently, the top is obviously fully sealed and the solution is not getting into the bracket. Obviously, I would have to be very careful not to damage the bracket. Any comments or alternatives would be appreciated.
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Old 09-02-2004, 02:28 PM
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The most recent clutch job that I did required that I break both the sensors and the bracket. Both of the sensors were stuck tightly into the bracket with corrosion and the allen bolts which attach the bracket to the block were also seized.

After breaking the heads of the sensors off (by twisting), I had to chisel the bracket into several pieces in order to remove the bell housing.

Trust me, I only did this after futzing around with this for over two hours, but it was the only way that they were coming out...

YMMV

gb
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Old 09-03-2004, 03:56 AM
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I was unable to remove the Speed Sensor from the mounting bracket. I have successfully removed the two allen bolts (Pivot Bolt and Locking Bolt) holding the mounting bracket to the engine. However, I am having difficulty removing the bracket. I need to know how to negotiate the removal of the bracket. There is a Key (round insert) in the Locking Bolt that appears to be preventing me from lifting up on the bracket. There is very little space to move the bracket forward to separate it from the Key. I would appreciate info on how to proceed to remove the bracket.
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Old 09-07-2004, 10:11 AM
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The reason that you cannot remove the bracket is that the sensor is extending down into the bel housing. So, it's kind of like the key piece in a chinese jigsaw puzzle. You have to remove the sensor in order to remove the bracket.

Perhaps you can understand why a lot of sensors and brackets end up being broken (out of frustration).

If you cannot remove the sensor, you may be able to remove the bell housing and then the bracket, but that's a lot of extra work!

gb
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Old 09-07-2004, 10:21 AM
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You are correct. It is a classic "Catch 22" -- I haven't been able to remove the Speed Sensor, but the mounting bracket cannot be removed without removing the Speed Sensor. The culprit is the roller pin (denoted Key in the Workshop Manual). Therefore, I must remove the sensor. End of story.
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Old 09-07-2004, 06:49 PM
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Catch 22 - boy, that's a phrase I haven't heard in a long time (and I was a teen-ager when the movie came out) - But it fits this situation perfectly.

Forgive me for not responding sooner, but I've just spent two weeks in Memphis, TN on work (and listening to the blues players on Beale Street at night).

Just thought I'd check in on Tooter's progress - hope you were able to get them out by now.

Back to the subject matter - there is an o-ring on the sensor at the junction of the plastic portion and the metal portion. This may be what is sticking. Prior to my breaking off one of the sensors, I used a REALLY LONG (like 12") needle nose pliers that I got at Sears to twist the sensor and pull on it. Then I modified a long screwdriver to make a pry bar and was able to get the sensor to come up about 1/4" (6 mm). It would not come up any higher, even though I was able to push it back down and pull it up again. It was at this point that I snapped off the "hammer head" of the sensor.

As you've noted, the "roller pin" is about 1/4" long and the bracket needs to move that amount toward the driver to come off - but the sensor is in the hole in the bellhousing, and can't move that 1/4". This is probably why most brackets get broken. It may be possible to simply loosen the transmission (supported on a stand), unbolt the bell housing, and shift everything back that elusive 1/4" to get the bracket off, but I didn't go that route.

Also, it is so dad-gum tight, that doing it my way is a major PITA. Breaking the bracket and getting another one would be much more time/money efficient.
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Old 09-20-2004, 05:08 AM
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Speed Sensor Removal

Thanks Prof for your reply. I have been unable to remove the sensor. I finally got it to rotate plus and minus 90 degrees with extreme force using 12 inch pliers, but no vertical movement. I'm resigned to breaking the bracket, which I can replace for about $30. Most other alternatives, such as breaking/cutting the head off the sensor and trying to fish out the remnants, involve more risk of debris falling into the bellhousing.
Old 09-20-2004, 05:55 AM
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If you remove the 4 bellhousing to engine bolts, can you separate the bellhousing far enough to give the necessary clearance to remove the bracket intact?

I had the same problem getting the sensor out on my clutch job. I took the bracket off with the bellhousing. FYI, it took a hammer and a punch to remove the sensor, no amount of paitence or PB Blaster (I tried lots of both) was going to allow me to pull the sensor from the bracket.

Best of luck, hopefully you don't need to break the bracket, but if you do, so be it. I used anti-sieze after cleaning my bracket for future sensor removals.

P.S. If the sensor hasn't moved in 20 years, that means your clutch is original. If a clutch job is in the near future, I'd pull the sensor with the bellhousing, it is easier to clearance without the bellhousing.
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Old 09-20-2004, 05:14 PM
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When I did my clutch, I forgot to install the bracket when I put the bellshousing back. Installing the sensor bracket with the bellhousing already installed is a PITA. I had to shave half of the hollow dowell sleeve for the pivot bolt in the bracket so I can slide it into place.
Taz said
Quote:
If you remove the 4 bellhousing to engine bolts, can you separate the bellhousing far enough to give the necessary clearance to remove the bracket intact?
I don't think you can move the bellhousing far enough without undoing the transmission support and moving the TT back.
Good luck.
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Old 09-20-2004, 05:51 PM
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That whole design really kind of got to me. It seems completely unnecessary. If you don't move the bracket, you can replace the sensor without clearancing. Why make the bracket adjustable in the first place? Simply bolt it solidly from the top. Or simply make the top of the sensor such that it covers the hole, making the o-ring and tight wall tolerances (and eventual seizing) unnecessary.
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Old 09-20-2004, 06:26 PM
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Better yet - mount the sensors to read the crank pulley and where a person can reach them.

I've seen units for race cars that mount in the front, but they only control ignition and not fuel injectors.

Has anybody ever heard of or seen a dual side-draft Webber carb kit for a 944?
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Old 09-22-2004, 10:26 AM
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Re: Speed Sensor Removal

Quote:
Originally posted by tooter884
Thanks Prof for your reply. I have been unable to remove the sensor. I finally got it to rotate plus and minus 90 degrees with extreme force using 12 inch pliers, but no vertical movement. I'm resigned to breaking the bracket, which I can replace for about $30. Most other alternatives, such as breaking/cutting the head off the sensor and trying to fish out the remnants, involve more risk of debris falling into the bellhousing.

Those sensors are a lot of fun, aren't they? Loosening all the bolts on the bell housing without removing them ought to give you enough clearance to take out the bracket and sensors as one - although it's still a piece of work.

Somewhere on this board there is a sensor adjusting tool I designed that you ought to use. Sticking the washer on the end of the sensor as per Haynes often doesn't gap the starter ring - sensor clearance properly. Getting it wrong means you'll be having this all to do again soon should the two clash.

Oh, hi y'all did you miss me?
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Old 09-22-2004, 03:48 PM
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I've seen lots of cars with the sensors on the front. I don't know why Porshce couldn't do the same?... Or at least put them under a cover on the bottom, or somewhere access is a little better!
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Old 09-22-2004, 04:53 PM
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Hi Dark Skies - long time.
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Old 09-23-2004, 07:05 AM
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