Reverse Light Switch Woes

[schmidter91]

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

[Dixie]

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

[schmidter91]

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

[RoninLB]

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

[schmidter91]

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.

[ossiblue]

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.

[schmidter91]

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.

[Peter Bull]

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

[JP Noonan]

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.

[RoninLB]

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

[RoninLB]

Originally Posted by schmidter91

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

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

I didn't know about the other nuances.


good thread

[schmidter91]

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.



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




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




Works like a charm!

Thanks for all the help and advice!

[RoninLB]

wow

[BMAN]

Great job...

[rnln]

can someone tell if G50 works the same way?

[mycastle]

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

[RoninLB]

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

[Ole Petter]

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

[BarryJB]

Originally Posted by schmidter91

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

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?

[BarryJB]

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.