something new 1986 560SL
 

Hi -- the noise continues.

Question: Is there an SRS sensor in the differential (there is some sensor there -- I have seen it)? If so, could this be a cause of the fluttering noise in the car -- specifically, the SRS light in the car has been lit since I bought it -- if the SRS system is tied to the differential could a problem with the differential cause the SRS system light to come on; and working the other way, if it is a faulty sensor in the differential could it cause the differential to behave badly because the car thinks that a crash (or other) condition is existing?

Wouldn't the SRS system be tightening the seat-belts if that was the cause? If my SRS light were on constantly, I'd want it fixed immediately. As for the fluttering, does it happen when the car is warmed up, every time you go fom an acceleration or only when the car is cold?

In a 1986 560sl the seat belts do not have srs sensors -- and the srs does not tighten the seat belts - that is another system. I would want it fixed too, but not at the cost that every mechanic (dealer and indy) project -- it is only a "supplemental" system, and the main safety comes from the seat belts and the car crumple zones. By the way, there is no way to tell exactly what is wrong with the system (no OBD) -- therefore it would be a hit and miss part replacement exercises -- very costly!

Flutter happens everytime I accelerate from a stop and pass between 1500 and 2000 rpm (when the gear shifts) after that no fluttering until I stop and then accelerate past that rpm zone. hot or cold

So it is only on the first 2-3 shift? Does it do it if you do a 1st gear start? I assume your car normally starts in 2nd gear...

best,

Dave
87 560sl

I tried accelerating past 1500-2000 rpm in each of the different (forward gear) positions on the shifter -- and I got the flutter each time.

To do a 1st gear takeoff you have to slide the shifter to the right when in "L", er, or is it "2" in our car - then move it back to D (or whatever) and the car will take off in 1st.

Did you do this?

All other shifter positions are 2nd gear takeoffs.

best,

Dave
87 560sl

yes -- did that

I think I know the problem....there is a bird living in the under-carriage of your SL and it likes to go very fast. From a stop, it flaps its wings (hence the fluttering sound) to assist with acceleration, and then stops flapping when you get up to speed.

no, thats not it -- remember, there is a "cat" under there too.
groan :p

In all seriousness, I'd be concerned too...these little sounds/issues have, in my case, been indicators of something more serious so I hope you solve it. I thought your dyno idea sounded very sensible.

How about ABS? Does it at all sound like the ABS system engaging...? (I doubt it)

What about a relay - does it sound at all like a relay actuating? They are all over the place...

Just brainstorming here...

best,

Dave
87 560sl

thanks Richard.

Back to my new question -- does anyone know about the sensor in the distributor -- is that an srs sensor?

I don't think its ABS --

It really seems to be associated with acceleration -- which gives you: something loose --looked at; drive shaft -- replaced and recently re-balanced; transmission -- noise comes from rear, though; differential -- likely (but why only at those specific rpm's); fuel pump -- but again, only at certain rom's; bird or playing card in spokes?

by the way, its a noise and a vibration

thanks for the brainstorming!

any ideas on the srs sensor?

SRS to me means Supplemental Restraint System - the airbag.

The sensor in the diff is probably for ABS...If I was at home I'd look it up...

You say "on acceleration" but I am hearing "acceleration after a stop." The process is "remove foot from brake, step on accel pedal, <noise/vib>".

Where are the vibes noticeable - floor, steering wheel, seat, etc?

best,

Dave
87 560sl

I guess I feel the vibes in the seat.

The SRS idea came from a mechanic that I took the car to this weekend -- they are still looking at this (I have not heard from them today). There is a sensor in the differential -- they thought it was hooked up to the srs system. I think they looked it up.

I think that you are correct - acceleration from stop -- it was my thought that such a situation puts the car back into a default start position (i.e. back to 2nd gear) -- but as I noted, starting in 1st (if I did it correctly) does not seem to change things.