Thermo time switch testing

[wwheeler]

I have three thermo time switches - one brand new, one used but was working and one from '59 that I have no idea of its condition. According to the tech manual: With the switch off the engine and below 35 C (95*F), the G terminal should read 20 ohms and W should read 0 ohms.

The new one G- 25 ohms and W 0 ohms. That is good because it is new and right on the specs.
The "good" used one - G was 50 ohms and W was about 25 ohms.
The unknown used one - G was 50 to 60 ohms and W was NO continuity.

So for the good used one, is it common for the points to gain resistance over time (25 ohms when it should have been 0)? Is it still usable? I also assume the heater "G" gains more resistance over time and not surprised about that. Both used switches noted the same ohm reading.

But the unknown sounds like the points are fried. I tried every which way to get continuity, but could not. These are expensive, so I want to make sure this correct.

Thanks for the help!

[wwheeler]

I put the bad one in the freezer for a couple of hours. I measured the W side and amazingly it read 0 Ohms. But after a short time it went back to no continuity. I guess it is done. I was told that the Classic Center will rebuild these with exchange. So there is an option if yours is gone like mine.

[Pawel66]

Classic Center rebuilding/exchanging the TTS - this is new to me and a very interesting topic! I have just asked the MB dealer to figure out if it works like that and how much is it....

I have recently replaced mine with the Bosch substitute. Of course I kept the broken one hoping it would be of use one day.

[Benz Dr.]

That is interesting. I was told recently that they're no longer available and yet MB can somehow rebuild them? Does that not seem odd to anyone else? Then I'm told by Bud's that they can get new ones, so I'm not sure what to believe.

Very easy test to see if a TTS is working. Use a jumper wire from the W terminal on the TTS and fix it ground. If everything works after that the switch is likely faulty.

[wwheeler]

I talked with the Classic Center and that is what they told me. And I am sending mine off Monday. Could take 6 to 8 weeks and I think that depends on if they have it on the shelf or not and they have to have a core for exchange. If I remember correctly, they also rebuild the throttle switches for auto transmissions using cores. Same deal with the rear axle Hydromats for the W111 and W108 cars. So not unusual that they have a rebuild program for some hard to find parts. Contact the Classic Center yourself and hopefully they will tell you the same thing.

The one from Bud's is similar but not an exact original. At least that is what is on their website. You have to alter the connections at the switch.

[Benz Dr.]

I'm aware of the larger switch that has the plug on connector as I've used one already.

[wwheeler]

http://www.authenticclassics.com/Mercedes-Thermo-Time-Switch-fits-230SL-250SL-p/auth-004360.htm

But more than what the "rebuilt" part costs.

[Pawel66]

I will get back and report what they said in Europe. A couple of months ago, when I was looking for replacement, they just said "NLA. Use aftermarket part or fix it yourself", which is their code formula that we do not like to hear.

[Benz Dr.]

It just seems kind of odd that they can rebuild them but not make new ones.

[Pawel66]

Ok, I cannot say what they said in MB Classic Europe for now. I am sorry to say this, but Europe has a long way to go as far as customer service orientation is concerned.

Tom from the US Classic Center answered within a couple of hours: rebuilding is $680 and it takes six weeks. I "forgot" to mention to Tom that this part, A0015459224, can cost even $1000 on e-bay.

I will push back on Europe for an answer.

[Shvegel]

As far as a replacement there are numerous Bosch Thermo Time switches from the CIS era (1975-1982 ish) Volkswagons, Mercedes.  Saabs etc  that have nearly the same specs.  I started to research thread pitch etc at one point but lost interest.  The CIS era ones will not have the same terminals but should be available for a song used on eBay.

http://www.bosch-classic.com/media/bosch_classic/teile_1/nachfertigungen/motor_2/thermozeitschalter_1/Mini-Katalog__Thermozeitschalter_F026T0310x.pdf

[Pawel66]

Yes, there are replacements, I did one myself recently from Bosch (the thread is there).

I guess this is the quest to find a way to use the original parts without necessity to buy them for $1000.

I am still pushing MB Classic Europe. I am sure the gentleman there already hates me. But I cannot get a straight answer if the same service as in the USA is available in Eurpe or not.

[Shvegel]

Beyond getting it open again and resealed there isn't much there.  A coil of wire and a bi-metal spring with contacts at the end.  Pretty simple to rebuild.  If the W terminal is open then the contacts are corroded(most likely) or the bi-metal needs adjustment.  If the G terminal is open there is a broken wire on the coil.

If someone wants to send me an absolutely dead one I will stick it in my lathe when I get home in October and see if I can figure a way in and out again.

[mbzse]

Beyond getting it open again and resealed there isn't much there.  A coil of wire and a bi-metal spring with contacts at the end.  Pretty simple to rebuild.../...

Here is a picture of a TTS opened, showing its innards...  Seems it can be de-soldered.

[Shvegel]

Thanks for the great pictures.

Unfortunately, that way in is no good.  If you look closely you will see they broke the connection to the terminals.  You could probably slice the peening away from the white porcelain but you would have to epoxy it back.

The ideal would be to make a new upper section of the housing so you could just cut it open and put it back together with the new housing.

[wwheeler]

Anybody unsoldered the bottom part, cleaned the points and re-solder successfully?

[Shvegel]

Ohhh.  Now there is an interesting idea.  It was soldered with the innards in place so it should work to un-solder and re-solder it.  as a precaution I would not have my body in the path of either end in case water has gotten into the switch.

[wwheeler]

Yes, according to the tech manual picture, the points are easy to access once the bottom is off. I would assume the internal guts were assembled, the upper brass piece crimped on and then the bottom soldered. BTW, the newer TTS has a solid brass body and do not have the separate lower soldered piece. 

To prevent pressure build up during de-soldering, you could drill a tiny hole in the lower copper piece, then solder the hole back up.