drive train noise

[richard230sl]

Hello everybody,

I am new to this forum and I want to say that I am very happy with this site. The information has been very usefull to me in the last few months and I have been able to fix the fuel injection pump and some other issues on my car thanks to you all.
I own a Mercedes 230sl with manual transmission which is in need of a lot of work so I will be searching a lot on this forum in the future.

I am currently occupied by a drive train noise and I hope that you guys can help me to find the cause of this problem(s)
The problem(s) (I think there is two of them) can be described as follows:

Problem 1
-When the car is in neutral and the clutch pedal pushed to the floor there is no noise
-When the clutch is up a whining (bearing?) noise is evident. It is not very loud but clearly there


Problem 2
-When driving the car a really irritating rear axle whine does occur. Again this isn't a VERY loud noise, but on long trips it is becoming irritating.
This noise is clearly coming from behind the seats from the area of the rear axle (the noise of problem 1 comes from the front end of the transmission tunnel) and is linearly related to wheel speed (proportional to travelling speed and not depending on gears).
-The pitch of this noise seems to be higher than the wheel frequency
-This noise is always there as long as the wheels are turning. Braking, rolling in neutral with the clutch up or down or steering actions do not seem to alter it

Some extra information:
I took out and checked the differential mounting rubber in the trunk and there is no metal to metal contact, the rubber is clearly not new, but seems to be in order.
I drained and have filled the manual gearbox with fresh ATF to the correct level (previous owners might have filled it with normal gearbox oil)
I have drained and filled the rear axle with the correct type of oil.
After renewal of the fluids no effect was detected

Can you please help me to find a good diagnosis for this problem?
Can this problem be caused by one problem or is it more likely that I have two separate problems.

Any help will be highly appreciated.
Thank you very much!

Richard
Student Mechanical Engineering
The Netherlands

[awolff280sl]

Hello Richard,
While I cannot speak to the transmission noise, your rear noise may be "differential whine".
Your would want to check your pinion pre-load with the axles level and no resistance (ie no brake rubbing) on the wheels.
In the case of an aleady well-used rear axle, this should be somewhat, but not alot, less than the factory spec of 20-24 in/lbs (if I remember correctly).
In my case, when I replaced my rear axle with a 3.27 I set my diff pre-load initially at 12 in/lbs. I had a whine with this pre-load between 40-60 mph.
I then utilized the procedure decribed at this website:

http://www.bernardembden.com/xjs/diff/index.htm

I then ended up with a pre-load of 16 in/bls and this cured the whine.

[Peter van Es]

Richard,

welcome! Why didn't you register earlier?

1. How's your flex disc (hardy schijf)?

2. Have you inspected your brakes really carefully (brake lines, brake shoes, lining, etc)

Peter

[richard230sl]

Thank you for your reactions,

I have checked the brakes earlier on this car, checked the discs and pads and hydrolics and replaced the fluids. Everything seemed all right. (no parts rubbing etc)
The only thing I didn't do is take the rear drums off. All the brakes seem to function just fine, there is no binding of the rear wheels and adjusting the rear brakes further back didn have any effect on the whine.

I will check the flex disc asap (can this be done visualy or do I have to take things apart?)
Does the pre load also effect whining noises that are evident at all wheel speeds? I might want to check the pre load issue asap.

Any thoughts on the noise in front? (could this be a bearing failure in the manual transmission box?)

Thanks again

Richard

[jeffc280sl]

Hi Richard,

The noise coming from the front of your drive train may be the throw out bearing.  Basically the clutch pedal causes hydraulics to move a two pronged fork back and forth in the bell housing.  The fork is connected to a throw out bearing.  The throw out bearing sits a top a pressure plate.  As you push on the clutch pedal the fork and throw out bearing pull a spinning pressure plate away from the engine flywheel.  As the clutch pedal returns to the up position the pressure plate is returned to the flywheel.  In this position with the engine running and the transmission in neutral the flywheel and pressure plate are spinning at engine rpm levels.  On half of the throw out bearing connected to the pressure plate is also spinning.  The other half of this bearing is stationary and connected to the fork.  This maybe the source of your noise.  In order to replace the throw out bearing the drive shaft and transmission need to be removed.  The bearing costs about $80 usd I believe.

The noise could also be comming from inside the transmission.  In neutral with the clutch pedal out some transmission gears are spinning.  As you press the clutch pedal in the pressure plate disconnects from the engine flywheel and the transmission stops spinning.  Have you checked fluid levels in the transmission?  Does you speedometer indicator bounce around when driving the car?

[jeffc280sl]

Here is a pic of the clutch mechanism in your car.

[richard230sl]

Hello Jeff, peter and awolff

Thanks for your replies. I didn't know that the throw out bearing was able to produce noise with the clutch pedal up.

- I have checked the flex disk (hardy schijf) and it there are no cracks or other obvious signs of damage to it looking from underneath the car
-All the fluids have been replaced and are on the correct level.
-The speedometer has a tiny bounce of approximately 1mm with a frequency of approximately 2 times a second (is this a clue for a certain problem?)


Thanks to your information I am currently making the following diagnosis which I would like to share with you to see if there is any mistakes in my reasoning

Diagnosis for noise 1: (gearbox noise)
I think that there is a worn out bearing inside the transmission box. When engine is idling and in neutral the noise is evident, when the clutch pedal is pushed to the floor it takes 3 or 4 seconds for the noise to die out. (this would not be the case if the throw out bearing was the problem, am I right with that?). (Apart from the noise, the gearbox is functioning great)

Diagnosis for noise 1: Differential whine that might be cured by the link posted in the message of awolff.

Hoping that you can help me out with drawing the right conclusions.
Thank you!

Richard

[Naj ✝︎]

Hello, Richard,

On the 230, there is an adjustment for free play of the throw out bearing on the slave cylinder push rod.
Later cars with with the diaphragm type pressure plate spring do not have this adjustment.

The owner's manual tells you how to set this.

[jeffc280sl]

Let's address your questions one at a time.

Speedometer Bounce/Transmission noise

here is a pic of the rear of the transmission.  The just prior to the front universal joint, the tail shaft of the transmission has a large nut that provides tension on the internal gears of the transmission.  Inside the transmission this tension is fixed via spacer washers.  If the nut is loose the lack of proper tention can cause noise inside the box.  Another consequence of a loose tailshaft nut is a bouncing speedometer.  Look at the attached sketch.

Just inside the nut (#102) there is a worm gear (#75).  This worm gear spins with the revolutions of the transmission tail shaft.  If nut 102 is loose the worm gear can slip causing the speedo needle to jump around.  The worm gear meshes with another gear (#94) and turns the speedo cable.  A jumping speedo needle indicates you may have a loose tail shaft nut.  It is hard to tell from your description if this is the problem.  A 1mm jump in the needle does not seem very severe.  Does the needle jump more as you accelerate?

Worn Throw out bearing

With the clutch pedal out the clutch plate is in contact with the spinning engine flywheel.  The throwout bearing is at full stress in this state.  Half the bearing is spinning with the rotation of the engine and the other half is stationary with the two pronged fork.  As you depress the clutch pedal the fork pulls the throw out bearing and pressure plate away from the flywheel.  The pressure plate and transmission gears eventually stop spinning.  In this state neither the transmission or throw out bearing are spinning so there is no noise associated with a failing condition.

Transmission bearing

There are 4 bearings inside the transmission.  #32, #72, #26 and the unlabled bearing just in front of #24.  Experience with a bearing failure in my box was obvious.  The bearing came apart and the transmission was hard to shift.  It also went from no noise to a loud whinning noise.  The noise happened all at once as the bearing failed.

 

[JimVillers]

Richard .... Some sounds can normally come from the transmission.  Just because you can hear a change does not mean that anything is bad.  Rebuilding a transmission can be a difficult and expensive job.  Wait until you are sure that it needs to be done.

On you rear differential, that is also a big expensive project.  Start with wheel bearings.  Relatively inexpensive and not a bad job.  Also check your center drive shaft support bearing.  The rear axle bearings run in grease and after 50 years can easily fail if they have not been removed and greased.  The drive shaft support bearing is often overlooked when greasing the chassis.

Also closely inspect the U-joints for rust dust around the yokes indication that a bearings has failed.

Eliminate the easy jobs before deciding on rebuilding the transmission or the differential.

[richard230sl]

Hello,

Thank you for all your advice until now.

Last week I tracked down the previous owner of the vehicle and heard that the rear axle was replaced by another one before the car was sold. Only a few hundred kilometres were driven with the axle afterwards

Today I removed the driveshaft and felt that the rear axle flange was not turning smooth at all. Rotation torque for the flange (axles leveled, drums removed) was to high and the nut that preloads the bearings was obviously  tightened to much when the rear axle was replaced (such a shame....)

So just to find out if this was the cause of my rear axle trouble, I released the nut a little bit until the torque to drive the flange was approximately 2Nm (and turning smoothly). I took the car for a drive and the whine was gone!

So after this experiment I am planning to fit a new crush sleeve
(in order to pre load the bearings in the proper way) and front pignion bearing. I am starting to hope that this axle can still be used without the excessive whine...

I am now having the following questions:

1 How is the removal and refitting of the front pinion bearing done? (do I need special pullers?)
2 I suppose the rear pinion bearing cannot be removed with the axle on the car and I just have to cross my fingers that this bearing is able to cover some more miles after pre load is restored, am I right?
3 In order to get the right parts I need some help with identifying the rear axle. I have attached some pictures of the numbers on it. Is this a w110 axle with 3.5 ratio? And is the crush sleeve and front pinion bearing the same as a 230SL? (does anyone happen to know a SKF number for it?)
4 Might anyone in the netherlands be willing to lend out his torque measurement tool (in order to get the driveshaft turning torque right?) Today I did the measurement with a force measuring tool on a lever of 0.25m but this tool is not accurate enough to get a precise measurement of  the 1.8 to 2.9 nm. ( I will throw in some"koninginnedagtompoucen" as a thanks!)

Thanks a lot. I will keep this forum updated about my progress!

Kind Regards

Richard


Attachments: rear axle with numbers 110 35(7?) (the last number is not clear or just a dent)
other number on the axle: 282985

 

[George Des]

Richar,

I did a rebuild on a 230SL rear axle recently where I replaced the two pinion bearings and the crush sleeve. The pinion bearings are widely available std bearings on the axle I did. The numbers were HM 89449/M88048 and HM89411/M88010--these are the numbers for the cone and race respectively front and rear sets. They are around US $20-25 per set. I believe the crush sleeves are different between the 230 and 280 set ups but someone else will need to chime in here. Also, I'm not sure you can remove the front pinion bearings to get at the crush sleeve w/o going through a total dissassembly--I know this is true with the rear pinion bearing and race--hope this helps.

George Des