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Discussion Starter #1
Hi,

I was wondering if anyone has experience installing a re-manufactured Bosch
SR 459X starter motor on their W126.

Mine is a 1988, following the spec requirement, purchased the SR 459X instead of the older version SR 59X

With the help of a mechanic friend, we installed it on the weekend. It starts on the first two try, then the problem arise. It spins, but its not engaging to the flywheel. Numerous attempts were made when sporadically it starts. Essentially, the starter gear is not engaging properly.

We took it out, realize there are 10 tooth gears on the NEW starter but there were only 9 gears on the OLD starter. Also, the length of the starter is a little different. The NEW starter is thinner and smaller but all the mounting fits. Based on searching the internet, apparently, there might be a need for a centre plate/starter spacer replacement for the original spacer?

The question I have is whether it is the different gears 10 vs. 9 or perhaps the spacing/center plate issue or perhaps something else I am missing.

Really appreciate if someone had similar experience installing a SR 459X (thinner version starter) on their W126.

Thanks so much!
 

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Discussion Starter #3
Thank You for your advice, will take a look at the wiring to see if that is the cause.

However, the starter itself is still spinning every time I turn on the ignition, its just that the gears from the starter is not engaging the ring gear/flywheel.
 

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CH4S Admin , Outstanding Contributor
1985 500SEC, 1991 190E 2.6.
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Using a starter from a 380 sedan on the SEC, we experienced a similar problem.
It seems the models had different thickness gaskets / washers, and reusing the old starters washer let the bendix fully engage.

Please make sure to read the 'Welcome.....' announcement / tutorial on top of the 126 forum page, to be able to use all forum features, incl a free service manual.
 

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Discussion Starter #5
Thanks Tuetone for your recommendations! I checked out the service manual site, lots of great information, will definitely keep that as a future reference. So what did you do to fix your problem?

Talked to a few other people, most think it is either the 9 gear to 10 gear issue with the new starter or perhaps the ring gear/flywheel is probably worn out. Either way, plan to take it out again this weekend. In the mean time sitting in the driveway.. looking pretty..if I have to start it, need to crank it like a Model T...haha
 

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Common sense suggests the problem is more than likly the difference between the 9 & 10 tooth gears.. If you think about it logically, the 10 tooth gear will need to be bigger diameter to maintain the same size/pitch of tooth as the 9 tooth gear.
If the teeth are the same on both (ie put both gears together and they should fit into eachother perfectly), that's not the problem.

Next test will be to line the flanges/mounting points up and see if the length between the flange and the gear are the same..
Then test again by putting power to the starters to see how far the gear protrudes when activated.. This will tell you if you need a different spacer or not...
 

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Discussion Starter #7
Problem Solved

Thanks again for all the suggestions.

Anyway, after days of asking around, I was able to solve the problem.

Essentially, the new SR 459X replacement starter REQUIRES a shim or centering plate, part number 116 151 03 45 (which I had to order directly from Germany through a local MB dealer and waited 2 weeks for that little piece of metal)

You have to take out the original shim and replace it with this new shim along with the SR 459X to make it start properly.

The 9 gears vs 10 gears is not an issue at all (at least not for now). Actually, all new replacement motors from Bosch for the SEC are 10 gears. Unless you rebuild your original, you will get the 10 gears starter motor.

Hope it helps the next person who needed a starter installation on their SEC.
 

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Outstanding Contributor
1989 560SEC, 1989 560SEL, 1995 E420
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Thanks so much for closing the loop on this issue. Will be great future reference.
 

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CH4S Admin , Outstanding Contributor
1985 500SEC, 1991 190E 2.6.
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40,697 Posts
Thanks again for all the suggestions.

Anyway, after days of asking around, I was able to solve the problem.

Essentially, the new SR 459X replacement starter REQUIRES a shim or centering plate, part number 116 151 03 45 (which I had to order directly from Germany through a local MB dealer and waited 2 weeks for that little piece of metal)

You have to take out the original shim and replace it with this new shim along with the SR 459X to make it start properly.

The 9 gears vs 10 gears is not an issue at all (at least not for now). Actually, all new replacement motors from Bosch for the SEC are 10 gears. Unless you rebuild your original, you will get the 10 gears starter motor.

Hope it helps the next person who needed a starter installation on their SEC.
Glad you found the fix, but the different size spacers have been discussed in the forum archive.
 
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