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Old 08-01-2003, 12:42 AM
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Join Date: May 2003
Location: NJ, Red Bank area
Posts: 57
What do I really need to repair/change?!

My 1991 300 SE has 110,000 miles. Depending on what MB specialist or dealer I ask I get different opinions on the yet to do's to bring it to its "nominal" shape. So I would like other opinions to try and reach the right conclusions. Here is the detail:

* My transmission rattles when backing up in the morning, and Reverse takes about 3 seconds to engage. Forward gear changes seem however fine. Some tell me that I should overhaul it sooner than later, others that I'll get ample warning signs before getting stranded. What's your experience?

* I had understood from reading this forum that the M103's timing chain was short enough that it's replacement wasn't really needed. I am however told that I should replace it in 10,000 miles or so, if only as a prevention: did I misunderstand what I read here?

* My power steering fluid was recently replaced, and ATF was used instead of proper power steering fluid, which I am told is fine on my car: true? Due to a slow leak, I had bought some proper power steering fluid (from FastLane, of course ): if the leak persists, will I be able to refill the ATF with the power steering fluid, i.e. are they compatible?

* My exhaust had a crack which was welded. I am told that the catalyst may no longer be doing its cleaning job properly, and that, if I want to stay OEM as I'd like, I'll need to change the whole system at a cost of $2,800, parts only. Is there really no way to change only the parts which are failing?

* I am also told:
+ by one specialist that my O2 sensor is working fine, and that the spark plug wires hardly ever need to be changed,
+ by another that my O2 sensor is original, made for 60k only and that I should change it, as well as my spark plug wires to fix my slight vibrations and surges at idle (which were not helped by changing the spark plug caps/connectors).

* Some hear "whistles" from my fan, air pump and idler bearings, some don't: is there a typical mileage at which these bearings should indeed be changed?

* Some tell me that my shocks and engine mounts are fine, some that I should change them: what are some reliable symptoms?
+ Could weak engine mounts explain the slight vibrations at idle (if not the --again slight-- surges, and even though L6's are supposed to be "ideally balanced")?
+ The rear of the car bounces more than once when pushed down by hand.

* What are the "rear control arm bushings"? Some say they are noisy, others that they are fine.
1991 W126 300SE (M103)
1995 W124 E320 Wagon (M104)
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Old 08-01-2003, 02:22 AM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 18,745
transmission - it'll be a while before your transmission strands you. Keep up with fluid and filter changes. Maybe the rattle is worn bushings in the shift rod. Wouldn't contribute to the delay in engaging reverse.

timing chain - it's more the absence of direction changes as in a V8 that allows the M103 chain a longer life. Replacement is more based on stretch than time. With a good oil change regimen you'll need a valve job before you need a new chain. If it's close to the stretch limit, have it changed. If the engine is apart for any reason, might as well get a new chain and as many guide rails as can be replaced based on how much the engine is coming apart.

power steering - MB says not to use ATF. If it's leaking, I doubt the right fluid will stop the leak. Fix the leak (probably just a tired retun hose) then flush and fill with the right fluid.

exhaust - try I believe they sell just the engine pipe set including the cat but you have to call and ask.

O2 sensor - a decent tech with a voltmeter can judge the health of your O2 sensor. A decent tech will have the proper tools and won't use just a voltmeter.

plug wires - these should be replaced periodically along with the distributor cap and rotor. Any good MB tech will know how to check these items.

various bearings - remove the serpentine belt and check all the pulleys. They should turn smoothly and quietly and have no axial play or radial play.

engine shocks - release one end and push and pull on them. There should be constant resistance throughout the travel.

suspension shocks - it's up to you to judge the quality of the ride. I don't buy that bounces more than once test. As long as the second bounce has less than 10% of the amplitude of the first bounce, you don't need shocks immediately.

engine mounts - maybe a tech can take measurements to see how compressed your mounts are without taking them off. Mounts are cheap. If you're going to take them off to measure them, put in new ones.

rear control arm bushings - something your car doesn't have. You have semi trailing arms with bushings and they're a PITA to replace. If your car makes noise when you get in or out, start with new rear subframe bushings and a differential mount. If they're original, new ones will make a world of difference.

You need to find a tech that understands your style and stop listening to everyone else.

95 S420
91 300SE
87 300SDL
83 300SD
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