1972 350SL trigger points

[A350SL]

After a 300 plus mile road rally with the SL. Going up a steep incline the engine started missing like it lost 2 or 4 cylinders for about 100 yards, then settled down and has not had a similiar miss since then. Last sunday is when this occurred.

The car has 130k, is over maintained, new plugs, distributor cap, rotor, in last 2k miles, has an allison ignition system. It had a slight shake at idle in gear when stopped in traffic during the rally run.

Trigger points were replaced about 20 years ago.

Any feed back will be appreciated.

Jim Houk
Seattle Section

[Tom Hanson]

It could be a problem in the "pointless" unit you put in. If it were pure stock, I could be of better help. Just for asking, did your tachometer quit or jump around during this occurance ?

[A350SL]

I do not recall if the tack stopped or not, but was working when we were stopped at a traffic light after the incident.

The breakerless system has been on the car since the early 80's and has been flawless.

thank you for the reply.

Jim Houk
Seattle Section

[A350SL]

The tack was bouncing - was going up a hill and was trying to keep it running -- then it just settled down and was normal.

Jim Houk in Silverdale, Wa

[ja17]

Hello Jim,

Usually the first sign of trigger point problems is a brief cold idle miss which may come and go or be inconsistant. After a period of time, oil vapor from the cngine may cause oil to collect on these trigger points. During a cold start this oil is thick and gummy and will cause the trigger points to miss fire. This will usually cease as the engine warms up and the oil on the points thins out. During a regular tune up I usually remove the distributor and slide the trigger points out and flush them with electrical contact cleaner. Ether (starting fluid) will also flush the oil from the points. In severe cases the plastic covers over the trigger points can be removed and left off to facilitate cleaning of the trigger points. I suspect Mercedes-Benz suggests replacing them $$. The cheap fix has always worked for me. This information applies only to the electronic fuel injection system cars, since the later cars did not have trigger points.

A bit of water in the fuel of my 74 450-SLC caused a similar (on the road) miss for me one time. (too much time sitting in storage). It went away on its own. Hope your problem turns out to be as simple.

Joe Alexander
Blacklick, Ohio
1955 190-SL (first car at 16)
1965 300-SE (108 one of 2700 made)
1969 300-SEL 6.3
1970 250-C (modified SCCA Pro Rally retired)
1974 450-SLC euro (4spd stick)
1984 280 TD (wife)
2002 SLK 32 AMG

[Tom Hanson]

If the tach was bouncing around somewhat drastically, it might be the ignition switching unit going bad. These usually just quit, but can be intermittent.

[A350SL]

Thank you all for the reply's. The MB service manual does not provide a lot of detail on the removal and cleaning of the trigger points. I will give them a good cleaning and inspect for any pitting of the points.

The SL is not a daily driver, it spent most of the summer at the upholstery shop for a new top and R&R the seats. (repair torn panel, redye the tex and new horse hair pads. and in the garage last winter.

A dumb question, will the distributor need to be removed to remove and clean the trigger points?

To day is work on the SL day, again thank you for the reply's.

Jim Houk
Silverdale, Wa

[ja17]

Hello Jim,
Unfortunately the distributor does need to be removed. Just no room to do it otherwise. You will need a 5mm allen. The wires just unplug. Be sure to note the position of the distributor itself and the rotor. You probably should re-time the engine afterwards.
It does sound like it could be the ignition as mentioned. Trigger points do not usually just cut out when driving down the road. However it is a good to do a cleaning just for the sake of preventative maintenance.

Joe Alexander
Blacklick, Ohio