1976 240D won't even crank

[Hdavis19]

Good morning gentlemen.

I've recently completed a top end engine overhaul on a 1976 Merc 240D (manual trans). I'm very good with mechanics, but I just can't do electrical!

So I go ahead and try to start it, and I get no cranking action. I don't even hear the starter trying to move. No click, nothing. So as of yet it cannot be a mechanical binding issue. My glow plugs are hooked up, and my glow plug indicator is shining bright. Battery is band new, I even took it to Oreilly for a test and it passed. Starter also passed a start test at Oreilly. Jump starting it hasn't been attempted, since I figured it would be irrelevant with a mint battery.

Other electrical things work like the headlights, the warning buzzer comes on, wipers etc... All fuses check out.

I've also installed a brand new starter switch located in the dash behind the ignition lock cylinder.

I've done some reading up on a few other threads and a lot of you guys say that it could be the starter relay (when this problem presents itself in an '82). Is this still a good place to investigate even with a '76? What else should I look into?

Thanks in advance.

-Harrison

[Phillytwotank]

neutral safety switch?

[Hdavis19]

Would it have one, if it's a manual?

[socalbenz]

Check the grounds first. There should be a large ground strap attached directly to the starter.

I don't recall if the w115 manuals needed to have the clutch enganged to start or not. That would be the equivalant of the nuetral safety switch. It is kind of hard to believe that switch would fail while you where doing the top end, but anything is possible.

On the 76 240D's the starter solenoid is mounted on top of the starter. You might try lightly tapping the solenoid to see if you can wake it up. If that does not work check for voltage at the solenoid when you engage the starter. It is a pretty simple system, turn the key to on and all of the assesories etc. get power. Turn to start or pull the gorilla knob all the way out and the solenoid should get power telling it to provide the starter with all the juice it needs to turn the motor. If the solenoid is getting power in from the gorilla knob/key, but not out to the starter the solenoid is bad. If the solenoid is not getting power the problem is with the key, gorilla knob, nuetral safety switch or wiring somewhere before the solenoid.

You can bypass the key/gorilla knob and provide power from the battery directly to the small post on the solenoid and see if the solenoid clicks or the starter might even turn. This can be dangerous. Especially if the car is in gear. That method is not advised, but is easy if you are working alone. Best method would be to hook up a test light you can see from inside the car while you try to start it to see if power is getting to the small post on the solenoid.

[socalbenz]

One other thought, Make sure you are giving the gorilla knob a good solid tug. The cable from the gorilla knob can stretch or otherwise get out of adjustment and not engage the starter. On my old 75 240D I had to (pay some else to) replace the gorilla knob cable because it became too difficult to pull the gorilla knob far enough to start the car. Much easier with a new properly adjusted cable. I never realized it was a problem until I lent the car to someone who was not strong enough to start the car.

[Hdavis19]

So yesterday I went and arced the two large posts of the starter, to force it to turn over that way. The starter spooled up and spun nice and strong but never connected to the flywheel (which would obviously mean that the solenoid didn't engage.) Took the starter down to Oreilly again for a test and it passed with flying colors; the solenoid engaged on their machine.

I also took a look at the ground wire connectrd directly to the starter and it wasn't that bad. I sanded down all the connection points but it didn't help any.

Originally Posted by socalbenz

One other thought, Make sure you are giving the gorilla knob a good solid tug. The cable from the gorilla knob can stretch or otherwise get out of adjustment and not engage the starter. On my old 75 240D I had to (pay some else to) replace the gorilla knob cable because it became too difficult to pull the gorilla knob far enough to start the car. Much easier with a new properly adjusted cable. I never realized it was a problem until I lent the car to someone who was not strong enough to start the car.

When I pull the gorilla knob out, the "salt shaker" coil indicator lights up real bright. I may have forgotten to pull it out on numerous occasions while trying to start it.

I used a multimeter to test continuity to the starter, while a friend attempted to start it. My meter read 0.00 on all tests, but I KNOW we forgot to pull the gorilla knob during these tests so I suppose that makes it a moot point.

[socalbenz]

The solenoid itself does not cause the starter to engage the flywheel. All the solenoid does is allow the low amp ignition circuit to turn the bendix starter on. There should be two large posts on the solenoid and one small post. Arching accross the two large post ( I think this is what you said you did) effectively bypasses the solenoid, but does not test its functionality. There is a third small post that if you apply 12 volts to will tell the solenoid to connect the two large posts in essentially the same manner a properly working ignition circuit would.

Once the starter gets power through the large leads it should spin up and engage the flywheel exactly like it does on the bench. It is the bendix in the starter that actually makes it extend and engage the flywheel, not the the solenoid. I suspect in your test you did not have enough current flowing over the "arc" you created between the two large posts of the solenoid to spin the starter fast enough for the bendix to work properly and engage the flywheel.

You said you pulled the gorilla knob and the salt shaker glowed bright. Once the salt shaker is bright are you giving the gorilla knob an additional tug? It is that last tug once the shaker is glowing that actually completes the starting circuit and applies 12 volts to the small post on the solenoid. Perhaps that is obvious but based on what you wrote I could not tell if you continued to pull the knob the last bit to complete the starting circuit. I don't mean to offend but I am not sure how long you have had this car and the operation of the gorilla knob is somewhat unique.

Once the car starts you let go of the gorilla knob and it returns to the run possition Similar to a traditional key. To turn the car off you push the gorilla knob in and turn off the key.

[Hdavis19]

Originally Posted by socalbenz

The solenoid itself does not cause the starter to engage the flywheel. All the solenoid does is allow the low amp ignition circuit to turn the bendix starter on. There should be two large posts on the solenoid and one small post. Arching accross the two large post ( I think this is what you said you did) effectively bypasses the solenoid, but does not test its functionality. There is a third small post that if you apply 12 volts to will tell the solenoid to connect the two large posts in essentially the same manner a properly working ignition circuit would.

Once the starter gets power through the large leads it should spin up and engage the flywheel exactly like it does on the bench. It is the bendix in the starter that actually makes it extend and engage the flywheel, not the the solenoid. I suspect in your test you did not have enough current flowing over the "arc" you created between the two large posts of the solenoid to spin the starter fast enough for the bendix to work properly and engage the flywheel.

You said you pulled the gorilla knob and the salt shaker glowed bright. Once the salt shaker is bright are you giving the gorilla knob an additional tug? It is that last tug once the shaker is glowing that actually completes the starting circuit and applies 12 volts to the small post on the solenoid. Perhaps that is obvious but based on what you wrote I could not tell if you continued to pull the knob the last bit to complete the starting circuit. I don't mean to offend but I am not sure how long you have had this car and the operation of the gorilla knob is somewhat unique.

Once the car starts you let go of the gorilla knob and it returns to the run possition Similar to a traditional key. To turn the car off you push the gorilla knob in and turn off the key.

No offence taken. I've never actually driven the car, in fact when I got it, it had a cracked head so that's what I've been occupied with since I first got it.

I'll try and properly use the gorilla knob next time and see how that goes. Will report results.

[Pooka]

Since you did the top end....

Was there a grounding strap connected to the head and to the firewall or frame?

If this strap is not connected, or is not making good contact, this could be your problem.

A quick way to check is to first look and see if it is connected, then with a volt meter check to see if you have power flowing from the head to the firewall.

These block and head grounding straps can break down internally and drive you nuts when you are trying to figure out why a gasoline car is cutting out. In both gas and Diesel they can cause the starter problems you are dealing with.

This is a simple thing, but it cost nothing to try and very little to repair since all you need is a new grounding strap like you can get almost anywhere.

[Mark DiSilvestro]

Originally Posted by Hdavis19

No offence taken. I've never actually driven the car, in fact when I got it, it had a cracked head so that's what I've been occupied with since I first got it.

I'll try and properly use the gorilla knob next time and see how that goes. Will report results.

First off, on these starters, in addition to passing battery current to the starter-motor, the starter-solenoid DOES engage the starter-gear with the flywheel. That is why jumping only the two large terminals on the solenoid simply spun the starter itself, without engaging the flywheel.

Before the head work, did you ever START the engine? Or even just get it to crank?
Once you pull the gorrilla-knob out to get the glow indicator to light, it has to be pulled out further, agaist a very strong spring, to power the starter solenoid.

If you have been using the gorrilla-knob correctly, a 12-volt jump to the small starter-solenoid terminal should at least get it cranking.

Happy Motoring, Mark

[Hdavis19]

Originally Posted by Pooka

Since you did the top end....

Was there a grounding strap connected to the head and to the firewall or frame?

If this strap is not connected, or is not making good contact, this could be your problem.

A quick way to check is to first look and see if it is connected, then with a volt meter check to see if you have power flowing from the head to the firewall.

These block and head grounding straps can break down internally and drive you nuts when you are trying to figure out why a gasoline car is cutting out. In both gas and Diesel they can cause the starter problems you are dealing with.

This is a simple thing, but it cost nothing to try and very little to repair since all you need is a new grounding strap like you can get almost anywhere.

I haven't seen a head grounding strap, however it has a strap grounding the glow plug circut (on the head obviously) to the engine block. Like I said in a previous post, I've checked the grounding strap that connects the engine block to the frame rail, which is located on the passenger side below the exhaust manifold.

Originally Posted by Mark DiSilvestro

First off, on these starters, in addition to passing battery current to the starter-motor, the starter-solenoid DOES engage the starter-gear with the flywheel. That is why jumping only the two large terminals on the solenoid simply spun the starter itself, without engaging the flywheel.

Before the head work, did you ever START the engine? Or even just get it to crank?
Once you pull the gorrilla-knob out to get the glow indicator to light, it has to be pulled out further, agaist a very strong spring, to power the starter solenoid.

If you have been using the gorrilla-knob correctly, a 12-volt jump to the small starter-solenoid terminal should at least get it cranking.

Happy Motoring, Mark

I did make the mistake of diving into the project without trying to crank it over. Slightly unrelated side note: I have been able to hand crank the engine with a wrench once the head was taken off.

I haven't had a chance to get back to the project since my last post, but like I said I will try and use the gorilla knob properly and report the results.

Thank you all so much for the help!

[Kpmurphy]

Originally Posted by Hdavis19

Good morning gentlemen.


I've also installed a brand new starter switch located in the dash behind the ignition lock cylinder.


Thanks in advance.

-Harrison

I have a started button that just engages the starter, I have it located under my dash.
You may try this.