Is there a sign that your starter is on the way out?
 

Over the past two weeks my starter engages a split second later than usual about once every 10 or 15 starts. The battery seems to have plenty of juice and the car always starts on the first bump when there isn't this delay. Is there anything I can check so I don't end up in a no start situation before heading off to work? Thanks

it'll just keep getting worse. doubt it will just up and die on you. i have experience with three diesel starters going bad. it'll start giving you just a click maybe once every twenty starts. then every ten, then every five. then it'll do it every time, but it'll eventually turn. then it'll eventually turn if you bang on the housing with a hammer. then it'll be completely dead.

you may have some other problem. ground strap corroded or loose? corrosion at the battery? corroded or loose negative cable?

Thanks for the reply. I checked the ground cable and terminal, and everything is tight and clean. I have an extra starter in the garage, but don't want to install it just to find out that there is an issue with the ignition switch.

when my starter went out its turning power diminished gradually, but i never saw a late reaction. perhaps the solenoid is at fault and not the motor.

I was thinking of replacing the solenoid on my starter with the one currently on my spare. Is there enough room in a W126 to replace the solenoid with the starter still on the engine?

You might could, but I would not want to try it.;)

Sometimes just loosening the solenoid mounting bolts half a turn cures one that is slow to operate, yes its still has a fault but this helps.
I have had a starter that had rusted up internally and would turn slow.

Slow Starter Engaugement
 

This is the classic BOSCH solenoid failure .

When it stops fully, you can often make it start by using an unbent paper clip in the terminal box on the inner fender but the smart money is to take the starter off (yes, I know, I do it on hot engines, no complaining) and take it apart, clean and lubricate it , add new brushes (maybe, eyeball them) and install a brandy new BOSCH or (again, -maybe-) Echlin brand solenoid and forget about it for another twenty years .

I have had short lived success with any other brands so beware .

No need to put out big $ for a rebuilt starter unless it doesn't crank with authority, then it's still a maybe, take it to bits and look at it .

VWNate is right, of course. You CAN redo a starter yourself. When I started wrenching we did all of ours in-house at the Buick dealer. If we redid one and it didn't work it meant it had a bad armature (rare) and we'd get a replacement (we didn't have a growler to check them nor a lathe to turn the brush area). These were the days when there weren't parts stores on every street corner and there were few rebuilders in the business and none in our area.

All that said, we have a good rebuild shop here in Wilmington and they stand behind their work so I have them do my stuff these days. They did the starter and the alternator (both Bosch) on Mutt and everything works groovily. I've decided that I only have so many hours in my day and I need to decide where to spend them. If they do my electrical bits I can do other stuff, like build a race truck.

Dan

Well ;

I've been wrenching since the 1960's so I approach the job perhaps a little differently .

I also got sick and tired of others doing shoddy works so I now tend to try and push the DIY'er to at least trying do fix it them selves....

YOU will usually do a better repair job because YOU CARE .

The BOSCH starter solenoid thing is well known to any older German vehicle Mechanic .

It's a simple thing to add a little cube relay in the circuit between the battery and starter solenoid, this is called adding a " hard start solenoid " and will often allow a few more years out of a dying starter .

It works gangbusters on anything 6 volts .

Before pulling the starter as the suspect, you want to make sure it is not an electrical issue in the circuit between the ignition switch/neutral safety switch/ starter solenoid. If the key switch does not give you a normal start but jumping the terminal block does, then the circuit mentioned above is suspect.

A slow solenoid will quickly kill the electrical contacts, as the contacts will only survive if smacked together quickly.

In many cases it is a simple matter of opening it and cleaning all of the old thick grease that is making it move slowly when it's cold.

That usually works very well on the older typ of Delco Remy solenoids but not so much on the BOSCH ones, I am not sure why this is so .

If you take a solenoid apart, be sure to POLISH the internal contacts ~ never, EVER use sandpaper etc. on electrical contacts .

A Bosch starter solenoid like the ones on 617.xxx engines cannot be taken apart to "polish" the contacts. The solenoid is crimped together and not easily taken apart without ruining it.

Last night and this morning I realized that there is only a delay when the engine is warm. I jumped the wires at the terminal in the engine bay and got a click, but no crank. I have a spare starter that worked well on my old engine. I think I'll just swap that one in. Do I need to remove the steering damper or anything else to make room for the starter to drop down? Do I need the long swivel socket extension that is needed for the W123 chassis?

Can't help with the SD specific questions. Symptoms you just described could be the starter, but it could also be wiring and loose connection issues. Did you check the heavy gauge wires on the terminal block and also the connections on the starter motor? On my 85, I peeled back the heat shrink on the crimps of those heavy gauge wires, wire brushed the corrosion away then soldered the crimps to restore good connections, have not had starting problems since.

The heavy gauge wires on the terminal block looked clean when I went to jump them. I'll check the connection at the starter.

To see if they are clean or not, you have to remove the wires on the terminal block, cut away the heat shrink that is covering the crimp before you can see if there is corrosion under the heat shrink.

I replaced the starter this afternoon with the spare I had from my old 617 engine. The good news is that the car starts on the first bump, no hesitation. The bad news is that it appears as if the starter gear is disengaging slowly because there is a buzzing sound coming from the engine bay right after start up. It barely lasts a second and isn't very loud, but it's obviously not good. I didn't have this issue when the starter was on the other motor, so I'm hoping that things will loosen up after 5 or 10 more starts. Otherwise, I'll get the starter that I pulled off of the car today rebuilt locally.

You didn't bench test the starter before installing it? Just power it up with a battery and listen is all that's needed if you have a trained ear (like a starter rebuild shop tech with 30 years experience). If you do not have a trained ear, use a photo tach.

On the starter you pulled out, bench test and shoot a video and post it. Take it apart to inspect, replace the 2 bushings (they're cheap), clean and lube, replace brushes if worn. That's all that's needed in a rebuild if the parts (armature, solenoid, centrifugal clutch) are good, which they usually are.

Routine Starter Service
 

That was my thought too ~

At the very least, have the bad starter rebuilt and save the working one in there now for a spare....

Never, EVER accept any BOSCH brand starter in exchange that doesn't have a brandy new solenoid ! you can always tell by looking at the solenoid closely .