1970 speed relay and 2 way valve

[jeffc280sl]

Hello all,

I have distributor advance and retard problems with my 280SL 4 speed.
The speed relay does not close at 2400rpms so the two way valve does not engage to supply atmospheric pressure to the distributor.  The two way valve appears to work properly.  I can pass compressed air through one pipe on the valve and out the other.  When I energize the valve I hear a click and I can no longer pass air through the unit.  All of the wiring appears to be correct. I have used an ohm meter to check wiring and connections to the two way valve, fuse block and relay box. Using a tachometer I can read rpms on pin 4 of the relay connector.  Both the low and hi temperature switches are open.   How can I be sure that the speed relay is the problem?  I can open it up and inspect the pcb but I'm not skilled at trouble shooting at the board/component level.  Any ideas out there?

Thank you for your comments.

Jeff

[n/a]

Jeff,

I am trying to identify a component in my 1968 280SL ignition system.  It may be be a speed relay.  The part number stamped on its base is 0332010001. Is this the same as yours?  I am attempting to analyzye the pcb circuit function.

Maxiemack

1968 280SL
One owner
Restored and engine rebuilt 1999.

[jeffc280sl]

I was unable to reference your part.  The speed relay is housed in a black plastic box # 000 545 08 32.  Another similar relay sits next to it with #000 542 93 19.

Jeff

[hands_aus]

Hey Jeff

There is a section in the Haynes manual that tells how to test the emission control devices and includes the speed relay.

Bob (Brisbane,Australia)
early 250 SL, RHD

[Tom]

Jeff,

The Big Blue Book has some detail on how to test the speed relay.

Note that testing the speed relay is done in part by testing the 17 degree switch.

I have an automatic and it may be different on a 4 speed, but I can actually observe (using a timing light on the crankshaft timing marks) that my timing advances suddenly at 2200 RPMs giving me a full advance range.  The spec says timing on a 70/71 is set at 30 degrees BTDC at 3000 rpm.  The only way to get this level of timing while being at 5 degrees BTDC at 1500 rpm (which I have also verified with a timing light) is to have the retard go away, which is done via the speed relay and 2 way valve.

I also note that the part number on my speed relay ends with 34 and I know from the emissions manual that the speed relays are different with an automatic and manual car.

Tom

[jeffc280sl]

Thanks to Tom and Bob for their help.

I have followed the BBB and the Haynes test procedures and I think I have a bad speed relay.  I was hoping someone had taken the relay apart to repair a component and in doing so they developed a speed relay test proceedure of some sort.   I suppose I will check all of the wiring and inputs again and if it still seems like the relay I will attempt to troubleshoot the device.

Thanks again,

Jeff