Replace Starter on 420SEL - Mercedes-Benz Forum

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post #1 of 6 (permalink) Old 02-05-2012, 05:49 AM Thread Starter
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Replace Starter on 420SEL

About a month ago, my starter started not starting with every first turn of the key. Every 5 or 6 starts I would just get the "whiiiiirrrrrr" of the starter motor with no engagement. Usually, the second turn of the key fixed it. Nevertheless, I did not want to get stranded somewhere.

Advance Auto had this sale around new year's that was 20% off anything over $100 plus a $50 gift card for a future purchase over $100. I saw that they had a Denso unit in their selection. Personally, I have mostly heard good things about Denso so I decided to bite and take advantage of the offers. The starter was marked at $190 (free shipping to my door). After 20% off I was at just over $150. When I take my old core back I get another $35 back so that puts me out of pocket only $115.

When the starter came, I noticed two things:

1. The starter motor was much smaller than the unit in the car. I called a friend of mine who does more "mechanic'ing" than I do and he said Denso starters are typically smaller than Bosch and not to worry.

2. A prominent sticker on the box said "Remanufactured in Germany". I was expecting China to be honest. Since we all hold parts manufactured in the fatherland to a higher standard, let's hope it rings true here.

Anyway, this is not so much a DIY as it is a source of information. To be honest, the process of starter R&R is pretty straight forward. The FSM has all the basic steps. I'll just add in a few details. I had the same problems everyone on the web has. Getting the top bolt off can be a bitch. Luckily getting it on was no problem.

Tools used:

About three feet of extensions
20 breaker bar
19mm open end
Phillips Screwdriver
12mm ratcheting box end
10mm Hex Socket
10mm Long Ball Hex Socket
Air ratchet (optional)
Torque wrench (if you want to follow the FSM to the letter)

Step 1: Disconnect battery

Step 2: Jack front end up and turn wheels all the way to the left. Please use all traditional safety precautions (stands, chocks, etc) when working under your car.

Step 3: Get under the car and undo the power cable (12mm) and the solenoid wire (phillips)

Step 4: I started with the bottom starter bolt. I used 1 12" extension, a universal, and my 10mm hex head socket on an air ratchet. Came off pretty easy. The rear of the bolt is captured by a 19mm nut and washer. You may need to hold back on this. This bolt also captures the ground wire. Remove and push to side. At this point, I was 15 minutes in and was only 1 bolt from having the starter off.

Step 5: The top starter bolt is a doozy. Luckily, this bolt is captured by threads on the starter and not an unreachable nut. Problem is it is very hard to reach on top of the starter. In theory, if you dropped the exhaust, this would be 10x easier. If I ever have to do this again, I may just do that. The challenge is the bolt is high up in the cavity and there is no room to turn your ratchet. I could not actually even get my air ratchet in there to simply push a button. What you have to do is link a bunch of extensions and a universal together so you can get 2.5-3 feet back and angle the extension downward so you can actually turn your ratchet. Once you figure this out, it's cake. Unless, like me, your top bolt is frozen. Out comes the breaker bar. Trying to loosen this bolt on mine put two of my universals to rest (thank god for Craftsman tool replacement). After breaking the two universals, I decided the try a different approach. I decided to try getting a long neck 10mm ball hex socket on the fastener along with my three feet of extentions and my breaker. I knew I was playing with fire here but at this point, if this did not work, it was going to have to go to the shop anyway. Well, those starter bolts must be made of some pretty high grade steel (plus kudos to Craftsman's ball-end hex socket) because literally pulling with all my might, on my side, out from under the car (I hate being under the car when I am really pulling on something) I finally broke the connection. It was a lound bang and all my tools snapped apart so I did not know until I got up in there if I broke the socket, the bolt, or had success. Success it was. Once the freeze was snapped, the bolt pretty much turned by hand.

Step 6: Remove the starter from the bell housing. Lots of stories on the internet said people had problems with this and they talk about removing the steering link. I had no problems and the starter that was in there, presumably original, was huge. The key is in step 2, turn the wheels all the way to the left. There is a 1/2" thick spacer bracket and a metal gasket between the starter and the bell housing. They should come out with the starter but make sure they did not stick to the bell housing and get left behind. See pics of spacer and gasket below.

Basically, now it is reverse of the above. Putting mine back was much easier since the frozen bolt was my nemesis getting it out. Plus, since my new starter was so small, and much lighter, that helped as well. I cleaned up the spacer and gasket with steel wool since mine were a little rusty. I put anti sieze on the bolts in case this needs to be done again.

Step 7: Re-install starter. I just hoisted it up there and got the bottom bolt started to hold it. Used my extension and universal set up to start the top bolt.

Step 8: Reconnected wires at this point. My unit came with new hardware but I re-used my old as it was just fine.

Step 9. Torque the bolts. This was a little tricky just because of lack of room. The torque spec is 55nm. I hate torque'ing things when using exptensions and universals because I am afraid not all the torque is transferring to the fastener, but I had no choice. Again bottom bolt torqued fine, but top was a bit more challenging.

Whole job took just under 2 hours not including two trips to Ace.

New starter works great. Seems to spin the engine faster. Also, and I know this is trivial, I like the sound of the new starter. It's a higher pitched sound that almost chirps starting the engine. Sound like a more modern car. My old one was that lower pitched sound and old car makes!

Pic of old and new starter. New one quite a bit smaller:

Pic of space and gasket:

1986 Black on Grey 420 SEL (560 Interior Swap)
1986 Smoke on Burgundy 300 SDL - SOLD

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post #2 of 6 (permalink) Old 02-05-2012, 07:11 AM
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Great write up Chris, another job well done on the 420.

1989 560SEL
702 Smoke silver
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post #3 of 6 (permalink) Old 02-05-2012, 08:38 AM
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Nice write up for sure. Mine just started "whirrring" and I have zero desire to tackle it. Maybe this can help motivate me.
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post #4 of 6 (permalink) Old 02-05-2012, 10:11 AM Thread Starter
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This whole process should apply directly to a 560SEL. In fact, in the FSM, it categorizes the procedure for M116/M117. If you have dual down pipes and smaller cats (or none at all) if might give you some more working room. My 420 just has the single downpipe and the "oversized football" cat sitting there right behind the starter bolts.

1986 Black on Grey 420 SEL (560 Interior Swap)
1986 Smoke on Burgundy 300 SDL - SOLD

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post #5 of 6 (permalink) Old 02-25-2012, 04:14 PM
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My starter in Rose was doing the same thing, but only when cold on a first start of the day. I read this post and was able to replace my starter.
A heads up: Carquest uses WRE as a supplier of re-manufactured starters. When Mine arrived(3 hours after I ordered it) it was in a Carquest box with WRE on the label, but what did i find inside? A Bosch Re-manufactured starter with their warranty of one year and one year of Roadside assistance on top of WRE's lifetime warranty. As I buy a lot of parts there (mostly World Pac MB parts) I get a discount. I paid $97.00 plus the core charge, which I got back when I took the core back.

Rose is a Euro with Tri-y's and down pipes, so this wasn't a big deal, but if you don't have small hands to get in there to reach the Allen bolts it will still be a bear. Took a cheater bar to break loose both starter bolts. I have it lucky as I have an oil change pit and was able to stand up to do this job. I removed the bottom brace for more access. It is best to do that left turn before you pull the starter...ask me how I know.

The Bosch re-man. starter was very small diameter as well, but works great. Things must be a lot better 26 years newer.....and smaller.
BTW Air tools are really good things to have too.
Thanks for a fine write up Foolio2! (this needs to be in the sticky up top. HINT! HINT!

"I know you think you understand what you thought you heard me say, but what you thought you heard me say is not necessarily what I meant!"

Last edited by Chadahar; 02-25-2012 at 04:18 PM.
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post #6 of 6 (permalink) Old 08-08-2013, 09:25 PM
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Once again this forum saves my bacon. Wheels turned left made my life way easier. I ended up using a 3 foot extension and U-joint on the top bolt. I know it seems a bit extreme, and it was a pain to thread up through the side of the trans, but having the least amount of angle on the U-joint lessens the chance of failure. Even with an overnight soak with penetrating oil those suckers were very hard to break loose!

Shamelessly stolen, yet wholly appropriate: Your car is not a Camry. You have to keep feeding her with Dollars. When it is running well it is so sweet. The Camry is more a kitchen appliance and just as enjoyable.
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