A number of questions related to 560 SL

Greetings,

I just purchased a 1987 560SL with 105,000 miles on it. I just had a great deal of work done to the front end including the replacement of all four shocks, new tire rods, center track rod, steering stabilizer, upper control arms, lowe ball joint, and idler arm bushing. You really don't want to know how much all of this work cost!

A couple of days ago, the antilock light came on. prior to light coming on, when I tried to apply the break, I could hear some locking noise and, there seemed to exist some slack between the time I pressed on the brake and when the car actually stopped. After I parked the car for a few hour, once I turned the engine on, the antilock light never came back on again. The mechanic is recommending replacement of factory updated front ABS sensors. He says that the sensors are known to cause pulsation in brake pedal. Could you confirm this statement

I have some problems with the ignition switch. To enable A/C to come on, I have to jiggle the switch. Could you tell me what are the ramifications of this if the switch is not changed? How difficult would it be for me (not too mechanically oriented) to replace the switch and lock cylinder?

When I press on the gas to speed up, I hear this extra, buzzing noise that goes away when I take my foot of the gas. It comes back when I accelerate. Is this normal? I sure love to find another way to eliminate it beside the turning of the volume on my car's radio? Could this noise have anything to do with the alternator?

The last question, could I replace my factory wheels with other wheels with different offsets? Some people tell me that this is not a good idea because it throws off all of the alignment settings and will hurt the car. I really like to upsize my wheel size as well to 16" or 17" wheels.

I appreciate your feedback and the time you are taking to address these questions.

Best regards,
Abe

[G-Benz]

I can't help you on the mechanical and electrical aspects of your model, since I am not familiar with it, but I will put in my 2 cents worth on the wheel/tire issue.

Going to a larger diameter wheel/lower profile tire combination will not affect alignment if you purchase a set with the same or close to the same offset as the factory. You will experience a more firm ride due to the lower profile of the tires, and those tires typically wear faster than the factory setup.

Going to wider tires may affect handling. I had a Conquest that took 205s in the front and 225 in the rear by factory specs. I wanted a more aggressive stance, so I replaced them with 225s in the front and 245s in the rear. The result was a nagging "shimmy" at low speeds that all the balancing and alignment in the world could not solve. Plus the tires wore out extremely fast. So I went back to the factory width, and the problem went away.

Larger diameter rims also mean added weight, and that needs to be considered if you are already having braking difficulties. Going to a 16" or 17" won't affect much, but I wouldn't do the now-popular 20" combo that I see around here. I did see a set of prototype 22" rims on an Expedition at a car trade show, but it had DUAL calipers on each wheel! At least the manufacturer rep had the foresight to keep that in mind.

BTW, do you work for FedEx...just a guess being that you are from Memphis...

If the buzzing noise sounds like it is from the right rear of the
560SL, it is most likely one of the two electric fuel pumps. When
the fuel pumps get to their service life they will make this noise.
The way to diagnose this is to have the car motor running with
the transmission in park, get a narrow stick about 24 to 36 inches
( I mean 75 centimeters) long, look under the rear of the right
rear tire to locate the two electric fuel pumps and the fuel
filter canister (all colocated to the right side of the fuel tank.
Place one end of the stick on either of the electric fuel pumps
and place the other end of the stick flat against your ear. The noise will be loudest on the failing fuel pump and you will know which pump needs replacement.
When one of the pumps is failing it will be noiser when the fuel
flow is needed to be greater such as when you press the
accelerator.

The other cause of the noise when you accelerate can come from
loose bolts on one of the rubber flex disks located on the
driveshaft either immediately behind the transimission (most likely
if the transmission has been removed and replaced) or in front
of the differential. If the bolts and washers were installed incorrectly (the washer must be under the nuts with the washer
on the rubber flex disk and not the bolt heads, the bolt heads should be against the metal flange ) they will loosen up and cause the noise when the drivetrain is under load. No washers should be between the bolt head surface and the metal flange.
Washers should go between the rubber flex disk surface and the nuts on the end of the bolts..... Needless to say all six of the
bolts need to be (uniformly) really tight on both flexdisks so use a torque wrench....

Having to jiggle the ignition switch to get the A/C to turn on is a
problem I have lived with on my 560SL. Replacing the ignition switch assembly behind the lock cylinder is the fix but disassembly
is something I have not attempted yet.

The ABS light coming on while driving or turning a corner is
symtomatic of the ABS sensors on the front wheels needing replacement. I had the same problem and lived with it a while
since turning off the motor and restarting would reset the system.
I replaced both ABS sensors on the front wheels three years
ago and the problem has not reoccurred. When the brake
pedal starts to go slightly disfunctional (i.e. pushing the pedal
may result in reduced braking since the pedal goes too far....)
or the ABS system kicks in and pulses/releases the brakes is
a real good sign that you must replace the ABS sensors (and
possibly the ABS servo valve immediately. I recommend that
you replace the ABS sensor first (like right now) and if the problem disappears you will not need to replace tha ABS servo valve.