Mercedes W126 gas - advice?: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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July 15, 2011 1:59 p.m. SlickDizzy SuperDork

I have the opportunity to trade my Fiat for an '85 500SEL. Mind you, this would not be for me, but a gift to my father as he has a bad back and has wanted something more comfortable than his old Dodge truck for a long time.

I know the diesels are bulletproof, but what about the gassers? What should I know/look at/service/etc? If I do this, I'd like to give him a vehicle that is basically ready to go. He drives all of 2000 miles a year, so once I do the maintenance it should be fine for YEARS down the road.
July 15, 2011 3:20 p.m. chandlerGTi Reader

Do it. They are bulletproof for that. I lurved mine.
July 15, 2011 4:34 p.m. Travis_K SuperDork

I agree, do it. I don't know a huge amount about the gas ones, but I have heard that replacing the timing chain and related parts is a good idea, other than that it should be pretty good. Probably needs a front suspension rebuild, it takes $1k in special tools to do it all yourself, so just buying a $200 spring compressor and having a shop swap the lower ball joints and control arm bushings would likely be the best choice.
July 15, 2011 6:12 p.m. benzbaron Dork

One issue with the M117 is they like to crack exhaust manifolds, but that shouldn't be more than a junkyard away. The vacuum can be problematic and vacuum leaks will make a mercedes run like a sick dog.

I'm not sure how much "tooling" is required for a suspension rebuild but aside from a CIS pressure tester and spring compressor I don't have any special tools. If you can use imagination and floor jacks you can get some of the other bushings out without special tooling. I'm not entirely familiar with the w126 suspension but it probably is similar to my r107. Some issues are that to get at the rear control arm(trailing arm) bushings you have to drop the diff and axles to get at the bushings. Engine oil leaks will eat the motor mounts/front subframe mounts.

If it has the automatic climate control system hopefully it works because they use an AC servo which is both failure prone and expensive to replace. Their is a digital replacement though which costs about the same as the original. I think the AC servo controls all the heating controls but I'm not sure about the Gen 2 w126 cars.

Good luck!
July 15, 2011 6:33 p.m. Travis_K SuperDork

The main expensive tool is the lower ball joint press, it costs about $450-600.
July 18, 2011 12:33 a.m. PNW_E46 None

Do it.

The 500SEL has the M117 which is the good engine of the two 80's Benz SOHC V8s. The M116 (3.8 and 4.2 liter) had lots of timing chain issues, especially in the earlier 3.8 liter iteration. The M117 doesn't have those issues. Just don't overheat it and make sure the cooling system's in good shape.

Window regulators can get a little iffy but overall the electronics are far more solid than in newer German sedans.

Automatic transmissions are super solid. I know of a 380SE that went 230k miles before the timing chain tensioner failed and valves hit pistons. The transmission was still working fine up until the time of failure.

Mercedes sure doesn't build their cars like they used to (which is why the W126 went for $40-50k in 1985 dollars).
July 18, 2011 1:21 a.m. benzbaron Dork

If the window regulator doesn't work check the switches, mercedes uses a piece of metal to toggle between positions, if the window quits working pull the switch and take it apart. Most of the parts on older mercedes are servicible so you just pull the switch apart by prying on the tabs, then you pull the thing apart and clean out the old grease, surface the contacts, and regrease. My stupid light switch came out of alignment and wouldn't work in Frisco on a rainy night. Just pulling it apart and cleaning fixed the issue. Then just reassemble the switch and if it doesn't work go for the window motor contact and grounds. Mercedes of this era are built to be serviced so do so.
July 18, 2011 6:25 a.m. KATYB HalfDork

you can get hf ball jointpress and make it work. or autzone rents them also.... not familiar with the design on the merc but it will prob be able to work.