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81 240D, 82 300CD, 91 350SD, 93 300SD, 93 300D
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Discussion Starter · #1 ·
I guess I’m a collector… I have quite a few old diesel MBs. I just bought another w126 350sd, kind of fell into my lap unexpectedly. Thing is, while I’m very familiar with MB diesels, across the. W123/124/126/140 range, all the used cars I’ve bought have had some level of pedigree, owner involvement, records, owner engaged in delivering the car to me, etc. This new 1991 350sd I’m sflying blind. Paint and interior are really nice, but who knows what else. there are some receipts in with the owners manual but I haven’t reviewed them, and they’re old… the car has sat for a long while.

So, what are the main w126 issues and weakpoints that I should look into? I’d just like to scrutinize the car before I decide to put any money or effort into it. I know the engines and transmissions. I get it that the 603 3.5L can be a rod bender. I get the checks for the mechanical systems. What I’m really looking for is the common rust spots, common wiring and other system weaknesses, etc that I should look for. I have less experience with the w126 than other models, so any guidance would be great.

thanks!
 

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At this age, if it hasn’t bent a rod yet, it probably won’t. Get it up on a lift and look for under body rust, along the sub frame, along the jack lift points, under the rear window (stick your cell phone in the trunk pointed upward under the rear parcel shelf and look for rust by taking a video.)

Then just change all the fluids and filters, coolant, brake fluid, transmission fluid and filter, fuel filter, and drive it into the sunset!
 

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90 420SEL, 00 BMW X5, 00 Lexus RX300, 01 Chrysler Town and Country
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644 Posts

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1990 Mercedes-Benz 300SE (W126) In Astral Silver with Dark Blue Leather Interior
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265 Posts
Front brake support rod bushings, front lower ball joints, exhaust system front to back, you'll want to replace pretty much every piece of rubber on the thing but once you've done that, you'll have a wonderful car.
 

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81 240D, 82 300CD, 91 350SD, 93 300SD, 93 300D
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342 Posts
Discussion Starter · #6 ·
Thanks all. Yeah I’m prepared for rubber/suspension parts replacement, and generally know where to look for rust (thanks for the reminder about the rear windshield).

Are there any weak spots relative to wiring, fuses, relays, etc. that I should look for?
My other 1991 w126 is fully functional electronically, and is a very low mileage example so I haven’t had to mess a lot. Are there ground points that should get looked at?

thanks!
 

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1982 300SD
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10 Posts
Also new here so know very little but this thread seems like its useful:

 

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1989 300SE 247k+ miles
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4,360 Posts
For fuses, I'd just replace them all. For relays, some of the fuel pump relays are apparently becoming NLA. Though I think they're gassers. Check the instrument cluster. Some of those can not function because someone removed the cluster with the battery connected, and shorted something. Or, you could wind up like my car where neither the clock nor odometer work, but they're separate issues/repairs.

Also, some of the relays and such, the solder joints are cracking with age. And they can be rebuilt. The most common, I'd say, is for the cruise control module.
 

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85 500 SEC (Euro), 91 350 SDL
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Everyone I know who has bought an older Benz has had to do some (or all) of the calipers within a few months (usually weeks or right away).

Always buy a spare fuel pump relay. They do fail from age. Rebuilt ones are always on eBay for a lovely cheap price.
 

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81 240D, 82 300CD, 91 350SD, 93 300SD, 93 300D
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342 Posts
Discussion Starter · #10 ·
This isn’t my first old Benz. I have lots. It is my first sight unseen auction buy that literally was just dropped at my garage. It needs a tensioner shock. But I think I did good.

Automotive parking light Car Tire Wheel Vehicle

Wheel Automotive parking light Tire Automotive side marker light Car


first cold start:

 

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1990 Mercedes-Benz 300SE (W126) In Astral Silver with Dark Blue Leather Interior
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265 Posts
Fuel pump relay & the OVP (over voltage protection relay) would be the two most likely culprits with regards to the kind of troubles you mentioned.
 

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85 500 SEC (Euro), 91 350 SDL
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Like tusabes said, that car will go another 200k miles. Just watched the oil consumption with an SDL. Keep the oil at the correct levels and it will go go go and go go go some more.

These have the most insanely comfortable seats out there. The refreshed Gen II 126 seats are beyond amazing. As long as they are not worn out, obviously.
 
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