Reverse Light Switch Woes
 

The 915 transmission in my India red 1982 911SC was rebuilt exactly one year ago. Prior to the rebuild the reverse lights worked fine, however after the rebuild the reverse lights will not go on.

Today I tried to troubleshoot the problem and narrowed it down to the switch. The switch itself was taken off and tested with a multimeter and checked out fine, however when the switch is installed on the transmission, slid into reverse, and checked with a multimeter, it does not work. It feels as though the pin that is supposed to actuate the switch may not be coming out far enough to actuate the switch, or possibly the switch is not as sensitive as it used to be and the pin can't actuate it.

Should I replace the switch or could there be another solution?

Thanks for the help,
Ryan

Is there a pin in the transmission? Perhaps it was left out?

Yes, there is a pin in the transmission, but my concern is that the pin might not be activating the switch because for some reason it isn't extending out far enough.

Ryan

Take the pin out and reinstall it in reverse position. In other words change the pin directions.

I tried to switch the direction of the pin, but that did not work either.

It seems the pin isn't coming close to even making contact with the switch. There's maybe an eighth of an inch or more of a gap between the end of the pin and where the pin should come in contact with the switch.

Not familiar with the 915 tranny, but I had the same problem on a 901. The pin on the switch had worn down and no contact was being made. Solution was a new switch and when it arrived, it was very clear that the old pin was severly worn.

Should the contact on the switch itself be recessed?

The plate that comes in contact with the pin looks to be a little warn, but not more than the gap that's present between the pin and the plate.

It just seems fishy that the lights mysteriously stop working after a transmission rebuild.

http://forums.pelicanparts.com/uploa...1217175730.jpg
http://forums.pelicanparts.com/uploa...1217175821.jpg

I've got the same problem with my 915. The pin is supposed to hit a roll pin in one of the gear selector shafts inside the transmission. If that shaft is twisted a little bit out of alignment, the two pins won't connect and the reverse light switch won't turn on the reverse light. I've decided to live without reverse light for a while...

/Peter

In my 914 with a 901 it did the same thing, I bought a new pin and fixed it. I think the pin was $5 from Pelican. I'm guessing the pin wears down with age? Or when your tranny was serviced the shims were changed and the old pin can't mate with whatever it is that activates it. So if you don't get continuity with the switch on the trans I'd say put in a new pin.

I also wouldn't rule out that the switch circuit isn't connected to the ground plane, I was chasing down rear turn signal problems for months. turned out to be a bad ground in the FRONT turn signal houseing. My starter circuit was completely dead when the engine was hot, turned out to be the 14 pin connection on the relay panel was dirty/corroded.

And make sure the wires go through a grommet in the tinware, and didn't get caught between the tin and the body.

PelicanParts
915-303-145-00-OEM
Activating Pin for Switch, 915 Tranny, 911 (1973-86)
Brand: Genuine Porsche
No Longer Available

That happened to me after a rebuild and reverse didn't operate.

I didn't know about the other nuances.


good thread

After some thought I decided the pin should be replaced with a longer one too see if that didn't solve the problem. The pin is almost exactly a 5/32 inch diameter so the hunt for an appropriate sized hardened steel rod was on. A trip to Home Depot yielded a solution. A 5/32 in. drill bit. Since I'm working on a Porsche, so only a German drill bit would do, and Bosch had just what I needed. It had the right length so that it could be cut into a nice substitute.

http://forums.pelicanparts.com/uploa...1217201815.jpg

The bit was cut and filed to an appropriate length, which turned out to be about 7mm longer than the stock pin.


http://forums.pelicanparts.com/uploa...1217201885.jpg

The pin was reinserted into the transmission, checked for proper length, and tested to make sure reverse was easily engaged.


http://forums.pelicanparts.com/uploa...1217202067.jpg

Works like a charm!

Thanks for all the help and advice!

wow

Great job...

can someone tell if G50 works the same way?

Love the ingenuity! Nothing like a backyard fix for a problem.

Pelican Parts - Automotive Parts and Accessories - Porsche & BMW

Back-Up (Reverse) Light Switch on transmission, 911 (1965-89), 914 All


914-613-541-02-M260

Nice solution!
Never would have thought of that myself...

I seem to have the identical issue - just had my 915 rebuilt (4th time in 170k & 13 years) and no back up lights when it came back. Shop checked it and said it needed a new switch... but I decided to start investigating today. Switch & wiring is all OK, except the pin (which looks and measures pretty much exactly the same as yours in the pic) sits too far in to actuate the switch - in reverse, the pin seats a good part of a fingertip below the outer machined surface on the gearbox housing & is barely sticking out far enough to reach the back of the switch.

Tomorrow I'll have a buddy move the shifter so I can verify that I will get movement in a suitably lengthened pin (Bosch-derived, thank you!), and take measurements to nail it. Eyeballing, it does look like the pin is about 1/4-in too short, i.e., suspiciously similar to your final 7mm over-stock.

Does this 7mm correlate to some missing or modified or improved part... so far I haven't found a good drawing showing the pin and what actuates it, and I'm unable to visualize the roll-pin as described by RoninLB. At least the old Haynes shows the stepped-diameter pin in the correct orientation.

Can anyone who's rebuilt a 915 transmission explain this?

First, Lowes carry a Hilman rubber bung (3/4 x 9/16 x 1 long) in their hardware aisle for about a buck that fits well into the back up light switch hole to minimize fluid loss (i.e., avoid Swepco face). I got two, & 1/4" drilled halfway through into the smaller end of one (to provide clearance for a working pin), and thru drilled the other 5/32" to use to verify & measure pin movement without fluid loss - both worked great. I lost 3-4 oz total (caught in a plastic bowl) over half-a-dozen on/offs.

Also a magnetic pick up with a bendy aluminum shaft works a treat to extract the pin - but you can't avoid at least some oil dribbling out, especially if like me you repeatedly dropped the slippery parts while trying to install/remove them.

Continuing the saga of no back-up lights/too-short pin after 915 rebuild:

Using the same 5/32" Bosch drill bit shank as suggested by schmidter91, but first with the whole non-fluked portion in the drilled bung until a new length was determined. Then a bunch of measurements on the switch operation with a dial gauge, and testing for pin movement (there was!) & measured that, there's about a 10mm stroke from the reverse full out position if you push the pin all the way back in when in neutral. Of course the only important one re switch operation is the out/reverse-selected position. My original pin length was 52.28mm. It was WAY down in the hole with reverse selected - it looked like it would barely reach the switch body.

If anyone wants all the numbers & info I'll post a drawing, but the upshot was that, WITHOUT ANY WASHER, to put the pin tip in the middle of the switch ON stroke zone, a new pin needed to be 5.7mm longer than the original; my washer was 1.42mm, so added that on too, taking off an arbitrary 0.1mm to allow for any tip wear to move the pin end closer the middle of the ON range... so new pin length was 52.28 + 5.7 + 1.42 - 0.1 = 59.30mm, in effect exactly 7mm longer than the original, and suspiciously, the same new length as schmidter91 had also determined... strong implication that we are dealing with the same issue, thus it seems possible this will be something more folks will be encountering...

My shop was going to charge me for a new switch, but this wouldn't have helped at all. Just called my shop with this story and it rang a bell... revised internal parts suspected... something that's happened since 2003 or so at a guess, then, as this didn't happen with my last rebuild.

Figuring the original pin's stepped-down switch-end diameter was to allow for any off-center issues & prevent it from jamming, I compromised & just tapered (drill press, files & 400 grit) maybe 8mm switch end of the pin to make sure it could "find" the switch hole in case it was a little eccentric, and if it pulls out clear of the switch - the stroke length would allow for this even if there is little reason for it to do so, but it might get a bit magnetized, or the oil will stick it to whatever pushes the pin, who knows.

Meanwhile, it's sooooo nice to have my halogen back-ups working again.

Thanks for blazing the trail here, schmidter91 - still be nice to know what internal part is the culprit though.

http://forums.pelicanparts.com/uploa...1269290139.jpg

Hello reverse light switch experts.
My 89 3.2 G50 - the reverse lights are not coming on.
I have the engine/trans out and pulled the switch off to check using an ohm meter.
In the activated position - I assume this is when the rod presses in on the swtich the resistance is ~130ohms. I was expecting this to be close to zero. Has any one checked this? I looked in Bentley and it only shows the switch is a contact, no resister function is indicated. Thanks,
-Henry

Henry looks like bad switch, bit I'd short wires on connector to make sure your lights work first, and also double check your meter reads 0 with probes shorted-(just in case!)- if lights op ok with shorting wires and 100 plus ohms is what you've gotthen yo definitely have a bad switch same part thru 89 at least 915 & G50 for sure as you surmise should be 0 or thereabouts! Good luck!

I have a 993 and tried to extract the pin. Its not just simply sliding out. Can anyone tell me if the 993 tranny (G50 I believe) pin is different? Or is it that Im not trying hard enough? Should I take some needlenose pliers to the pin to extract?

Im on my 3rd reverse switch and it intermittently works. I was blaming the switch, Im thinking that its the pin since the switch is working when I bench test it. THe tranny has 130k miles.

After installing my new reverse switch on the G50 the reverse lights are staying on all the time. I ended up disconnecting for now. Either the switch is hung up or the shaft is hung up I guess. I'll dig in to this more on the weekend. Which way does the shaft go in? I assume it gets lubed from the transmission side. The other thing I was thinking, if the oil fill is too high maybe the oil gets in the switch and shorts it somehow.

Sounds like a worn pin &/or too many washers...

First though, you might want to short the reverse switch pigtail connector to make sure your reverse lights actually of themselves are not intermittent, - i.e., that the wiring/grounds are good and not the cause of this.

While I don't know how similar the pin set-up is with a 993, (if your tranny is a G50 as you suggest it would be the same) it may use the same switch/pin concept.

If the set-up is similar, it sounds like you may need to remove one or more washers from the switch, which is the best solution as then you don't need to remove the pin in the first place.

If there already are no washers on the switch, you'd need to replace the pin with a new (unworn, so longer) one, to increase the amount the pin protrudes in the activated position. In this case you do have to remove your existing pin...

Re pin removal: Removal facilitated if you have reverse selected so there is more pin to grab. One old pin I pulled out once had a little circlip on it but this was outside (to the front) of the narrow bore in the transmission so it wasn't there to prevent the pin from being removed. While a magnetic retrieval tool worked for me, suitable needle-noses would offer more pull for sure. I can't imagine you'd hurt anything... only way I could imagine this would not work is if your existing pin had got mushroomed or otherwise distorted inside tranny case, but I'd guess you'd be able to feel a definite stop, bind or jam. Also try rotating and jiggling it in case there just a ridge worn in the pin which is hanging it up but not so burred up as to make it impossible to remove. If it jams I'd still definitely try to pull it out or even flex it a bit - but that'd be up to you of course - but removing tranny would be a real chore!

If you are using a new pin (if availble), add/remove washers as needed. If making your own new pin, I'd make the new pin long enough to require one, preferably two washers, to give you some wear adjustment later.

This assumes your switch isn't intermittent in bench tests, as you indicate. I did a load of dial gauge & caliper measurements with my switch/pin and transmission case to arrive at the exact same solution as schmidter91 but this was a likely a 915-specific issue; it sounds like you may just have a slightly worn pin, and thus too many washers.

New pins are apparently unobtainable for thru '89 cars, maybe not for the 993 (:-( if it uses a G50...) but a suitable diameter long Bosch drill bit as per schmidter91's suggestion is a great solution, especially as even the likes of Home Depot & Lowes carry them...

You might find my post #20 above helpful.

Good luck!

Try adding washers, and the skinny end of the pin is supposed to be to the front, i.e., goes into the switch. The Haynes Manual is the only place where I found a picture confirming this... Bentley shows a non-stepped pin.

The neck presumable helps with off-center entry into the switch orifice - when not in reverse there is enough clearance that the pin could be positioned clear of the switch.

Thanks Barry
 

Wow - thanks for the information. I do know for a fact that I have a washer in place and didnt realize that you can/should tailor the washers to compensate for wearing pins. I will short out the pigtail just to make sure that the circuit is working. Believe me - I know how not to do it - after trying to short the leads just to accidently touch the tranny case and blowing the fuse!

Anyway, I will play with removing some washers, and see if it resolves the problem. I will also take out the pin and measure it. I will post the results just to compare the length to what you guys are calculating is original length.

I was always scared to remove the pin because I was concerned that I would screw up something inside the G50 case and end up with no back-up lights unless I split the case. It sounds like removing the pin is no big deal.

Your point on mushrooming is important for me to look at - maybe the end if its not rounded or slightly not centered could be preventing proper pin insertion into the switch and cause for intermittent operation.

This is a great place - I really appreciate the feedback and help.

TJ

This forum has bailed me out so many times for over 13 years now, Pelican folks are a wonderful resource for sure. It's rare others haven't already gone through some weird issue & posted nifty solutions - it's that all are so willing to spend the time to document & share that makes it special.

IMO worst part is having oil come out (whether just on floor, down arms or in face) - increased flow after removing pin. Hence overly obsessively detailed (the alternative word for that phrase would not go well together with the next word) bung suggestions in my post #20.

You can also just start the switch back in to limit loss, or, if like me you just had to play with the switch/pin out of the car and didn't have a spare/old switch, cut more taper onto a wine cork, but getting that just right was, ahem, challenging, so having the exact bung size ready to slam in there ASAP on pulling the pin might prevent you from frightening sensitive neighbors & passing pedestrians with outbursts of colorful language. You only need the plain unmodified bung if the pin is out.

Besides if you end up having to make a new "Bosch" pin, the bungs are only a few aisles over...

Update for me. My old switch wore out and was not close to zero ohms when in reverse. I put in a new switch and the BU lights stayed on all the time. Yesterday I figured it out. The design does not move the rod much but the switch depth location needs to be just right. I added the washer from the old switch to "shim" out the switch and it seems to work correctly now using an ohm meter. I need to hook up the wires today.

So I took the pin out of my 95 G50 tranny and was surprised to see a difference with the pin versus what you guys have. Take a look at the pin compared to the 5/32" bosch drill bit.

I measured my pin at 44.98mm long: 5.95mm dia for 37.3mm and 3.66mm dia for 7.83mm.

Not even close to the 5/32" bit so I just reinstalled the old pin. It didnt look mushroomed or anything.

I took out the only washer to get the switch to seat deeper in the case and closer to the pin. Lights are working once again, but Im not holding my breath b/c this is the 3rd or 4th time that Ive disassembled, got the switch working just to discover that it stops working weeks later.http://forums.pelicanparts.com/uploa...1278352204.jpg

BTW - I was saddened to see the BOSCH bit was made in China. Back to Lowes!

Wow they sure changed the pin size, what a fat little puppy. True for 964 & 993 I guess. I think my Bosch bit was made in Germany, so I don't expect any transplant rejection, LOL.

Just FYI if it's the same switch, it takes a minimum activation stroke of ≈1mm and can handle a maximum stroke of ≈4.3mm before it bottoms out. The reverse pin in my 915 shows ≈10mm stroke on engaging reverse.

Assuming a similar scenario exists with variations using a switch and pin, it appears that the number of washers is important to prevent the pin from either inadequately exceeding the (1mm) minimum stroke to ensure reliable activation after a little bit or wear or settling, but not to exceed the maximum (4.3mm) and bottom out, probably damaging/destroying the switch once you've forced the lever back far enough to get it in gear!

This may explain why the thing works at first then quits - either extreme could create that... adding washers to your set up would safely probe which condition without busting the new switch or requiring the use of calipers, rags and bad language.

Just did the post 12 and 20 fix to my last year's rebuilt 915. Lights are working fine.

2 rubber stoppers $2.08 / 5/32" x 6" Bosch hammer drill $3.97

Don't know the "why" regarding why a switch won't work, but you can view what goes on inside the trans nose cover here...

How-To: Porsche 915 Transmission Repair Tutorial Part 8 - Porsche Wiki

...and also consider the tip to not immerse the switch in a cleaning solution. If you need an accurate measurement for the switch pin let me know (I've never encountered a worn one).

Thanks Peter.

Seems that folks with recently rebuilt 915s are having reverse lights that don't work because the pin needs to be lengthened 7mm for a mysterious, but apparently, consistent reason.

That is a cool article. Well done.

There is a guy with your name that hosts some of the Wiki forums, too (FYI)

Just wanted to update the thread that my latest switch is still working in the G50 tranny after 6 months! I ended up removing the stock metal washer that comes with the switch so that it would sit deeper into the tranny. With the washer I wasnt getting the lights to come on consistently. I quickly learned that removing the washer allowed tranny fluid leakage. I ended up adding a "fiber" type washer (its like a fabric/plastic material) that compresses more than the metal one and seals the tranny fluid in. It has held up to the heat, seals the leak and most importantly allows the reverse lights to work 100% of the time!

I think I've solved the "short pin" mystery!!!
 

For those of us with 915 transaxles, that have after much measuring & fiddling - or were lucky enough to find this thread - determined that mysteriously, after a tranny rebuild, we needed to fabricate a new reverse-light-switch actuating pin that was ≈7mm longer than a new Porsche one (≈52.28mm), by cutting 59.30mm from the smooth end of a Bosch Blue Granite 5/32-in drill bit as described in this thread...

I think the picture below explains this - the tranny rebuilder either omitted the rolled pin shown in the photo, or perhaps it can be inserted too far (I can't imagine it would readily bend).

Legal: I found this picture on:
How-To: Porsche 915 Transmission Repair Tutorial Part 8 - Porsche Wiki
The site on which this page was found is copyrighted under "Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0)" which in good faith I believe allows this type of posting of their content with the accreditation just given. Gee what a world, that it takes that much to say something's OK ;-)

So with the longer pin we are using, it appears it is actuated by direct contact with the selector fork. Can any rebuilders confirm this? No one piped up about this during the thread - maybe it's one of those embarrassing little secrets no-one talks about...

Now I can sleep... I foresee a friendly little chat with my shop next time car's in for service ;-).
http://forums.pelicanparts.com/uploa...1313992027.jpg

Nice!!!

just my two cents,
the pin was missing completely from my gearbox, so i made one up out of a drillbit, 59.3mm long as barry had done.
turns out it was too long, so i did some measuring, and came up with a length of 52 mm (2 1/16") that it needed to be, so cut it, filed it, put it in and works great! i then checked back on here and realised that 52mm (give or take) was the measurement of the original pin. So i guess i wasn't missing whatever part you guys were missing that required you to lengthen your pin.
just putting this out there in case anyone else is missing the pin altogether, that it could be either of the 2 lengths that you need to make your new pin!
also, only jacking up the front of the car, mean a bit less gear oil will dribble out when you remove the switch.

Uro switch
 

The URO switch got intermittent then went bad after about 6 mos after being installed, I replaced it with another URO so well see .....Seems like
Question, no oil came out of the trans when I swaped it out, I heard that oil pours out, is it because my car is an 87 G50 , and that it pours out on 915s?????
Thanks,

Connect the two wires together, if the lights work then you know its the switch, replace it, they are cheap....really looks like the after market ones are not very durable but you might get lucky.