280sl basic electric question

I am trying to get the two way valve working my 1969 280SL. That's the valve that turns the vac retard on and off at 2500 RPM. It has not worked since I bought the car.

The valve operates when tested directly off the 12V battery, but not when installed in circuit. The circuit puts out 12V according to my multimeter, and the ground is good.

What am I missing here?? Is something "wrong" with the 12V being supplied by the speed relay?

Steve.

[ctaylor738]

The exact same effing thing happened to me with my AC blower - it was the fuse seated incorrectly.

Check the fuse to be sure it is properly seated, the wiring for soundness, and all connections must be tight and clean. You may be getting voltage but not enough amps.

[gmask]

Originally posted by ctaylor738
The exact same effing thing happened to me with my AC blower - it was the fuse seated incorrectly.

Check the fuse to be sure it is properly seated, the wiring for soundness, and all connections must be tight and clean. You may be getting voltage but not enough amps.

Hmm guess that could be a simliar explaination as to why my electric fan does not come on when connected to the circuit even though everything tests OK??

[Arthur Dalton]

Your system is early emissions incorporated into the last of the 113 chassis.
This basically means decel fuel shut off and controlled retarding of the timing via temp switch/speed relay/trans sw/ and idle switch.
The speed relay has 2 speed circuits, one for decel and one for vac valve.
There is a sequence of test for proper operation and these are covered in the Haynes Manual # 346. Should be able to get at any decent parts store for $15-20.
If not , I can scan the procedures for you , but it will take some time...
The basics are the vac transfer valve is looking for voltage
above 2400 rpm, [ advancing dist] no voltage below.[retard].
The earlier 113 simply used vac at idle/closed throttle fed to the vac retard servo on dist. So as throttle opened, less vac resulted in more advance [ actually, less retard]. from there, the advance was only mechanical .]

[toms]

Arthur,

I have the early emissions on my 71 280sl and when it does not work, the retard stays engaged through all RPM ranges. Is there a way to convert the system to eliminate retard above a certain RPM or otherwise defeat the retard with a selection of different springs in the distributor (i.e. centrifugal weights)?

Thanks,

Tom Sargeant

Hi Tom,

Good question - I'm interested in acheiving the same thing. Eliminating vac retard entirely, and modifying the mechanical advance probably won't provide optimum performance.

I have temporarily adjusted my timing to compensate for the vac retard problem at 3000RPM. Performance at higher RPM has improved, but of course now the idle is too advanced.

Ideally, I would like to use early 113 timing, but I don't know how best to acheive that. Perhaps the throttle switch on the venturi can be rewired to shut off the vac advance when the throttle opens?

Steve

Thanks Arthur,

I have the Haynes manual and the shop CD. Mine is probably wired wrong, but it is hard to troubleshoot because they changed the pinouts with every year, model and transmission, and mine doesn't match any of the schematics. I get 12V at idle and 0V at 2500 RPM.

Do you know what is involved in converting to an earlier W113 timing curve?

Steve
1969 280SL
Vancouver, BC

[Arthur Dalton]

Yeah, the US versions had some changes..
The earlier system requires the vac line to go to the tap right behind the throttle plate at the front of the intake and go directly to the vac retard.
I would then get the servo from a 230/250 dist that has no emmisions. According to the advance curve charts I have , that should do it.
The one you have calls for ATDC, but they run best at TDC /2 BTDC
at idle with the retard and 30/32 at full advance.
You can get the 2 BTDC with vac by shortening the rod on the vac servo. But always set the 30 advance w/o vac first and then do the idle with full closed throttle plate [ at the full stop].
The idle rpm is then set with the air bleed screw at the end of the air hose in FRONT of the throttle plate. That is how they get air for idle with the throttle plate fully closed.
If it is an auto . 750-/800 rpm is good, but sticks like to run up in the 850/900 range.
The older system will give you instant off idle advance and it is quite noticable.....

[ctaylor738]

Guys -

I may be the only one old enough to remember this.

In the glory days of hot rodding - like 1963-73 or so - you could not pick up a magazine that did not discuss "putting a curve" in a distributor. The state of the art was basically to have 8-10 degrees "static" advance and the then increase to 32-34 at 3000 rpm where the advance was "all in". On street cars there was a vacuum advance to give early advance under load.

These articles always included a picture of a distributor machine, operated by a guy in a white coat, which spun the distributor and measured the advance while various combination of diaphragms, weights and springs were tried until the desired "curve" was obtained. As I recall, this depended on the cam timing, weight/cubes ratio, trans type, and so on as well as what the car was going to be used for.

The retard aspect did not enter the picture until emissions became a concern.

So what you need to do is get rid of the retard function altogether, leaving the electronics convincingly hooked up. Send your distributor to someone like Randy Durrance (www.durranceeng.com) and tell him what you are after - tractability in traffic, mid-range pep, high-end power, etc - and let him give you a curve.

[toms]

Chuck,

I am in contact with Randy to do just what you describe. Hopefully he can help.

Best,

Tom Sargeant