Viscous clutch/fan repair

[LeaUK]

Here's some info specific to repairing the SL clutch that I wanted to share. An explanation of operation can be found in the Tech Help forum so for this, it’s best to search there first.

My car is a '93 500SL and has the classic symptoms of no fluid remaining within the clutch. ie you can easily spin the fan blades by hand.

Here’s what I’ve completed so far:

1. Removed all plastic cowling – 2 minutes

2. Removed fan blade assy.

3. Removed clutch – there’s a hex cap head bolt (M8/M10) through the centre (standard thread) this needs a long lever and plenty of force

4. Removed the bi-metallic strip and pin – push the strip down at one end (inspection reveals which end) and slide. Remove pin with fingers.

5. Refill clutch (30ml – not sure how much to use as all clutches are potentially different) with Dow Corning 12,500CST silicone fluid by using a 5ml syringe. Force the fluid down the hole that the pin originally sat within.

6. Reassemble

The clutch feels much tighter now and next week my plan is to measure the RPM at:

idle
<95degC @3000RPM
>95degC @3000RPM.

I’ll let you know the results soon...

Here are some pics for info too:

[LeaUK]

Update:

Refitted clutch and fan blade assay.

Engine RPM Fan Blade RPM

804 370
1100 490
1800 540

Had to suspend testing as the bi-metallic strip started to operate and my twins needed feeding

Anyhow, the clutch now seems to operate correctly. After a period of standing the fan resists movement, and at startup will 'whoosh' quite significantly. Then after 30 seconds or so will return back to normal running (quite, fan RPM about 1/2 engine RPM).

At a certain temperature (I think this is 95deg F according to several on the Tech Help forum) the clutch engages and the whooshing returns - wow, some serious air is being moved as the fan is rotating at nearly engine RPM - up until around 3000RPM where the clutch starts slipping again. This is by design.

So from these tests it seems like 30ml of 12,500CST was indeed a good choice of volume and viscosity. This fluid can be purchased in the UK from R W Greeff. Min order 1KG @ 10UKP!!! enough to refill everyone's bad clutch in the UK!!

However, I have one question which I hope someone can answer; my clutch doesn't seem to engage at higher RPM - say 2500, even though 95DegF has been reached. However as soon as the RPM reduces (around 1000) it engages and operates up to 3000RPM as it should. Is this correct? Maybe someone could test their known working MB clutch/fan for me (prefereably '89-'95) and let me know if theirs is similar.


Thanks

[DavidSoine]

I admit I haven't looked into this issue yet...but my question is: What happened to the original fluid?

best,

Dave

[LeaUK]

Dave

Must have leaked out - which unfortunately implies that a seal is worn somewhere. Never had this problem with my previous 190E which is still going strong and is 15 years old! But maybe one of the previous owners had changed the clutch? Who knows!

Can one of you helpful chaps with '89-'95 129s do a test for me?

Whilst stationary rev car to 2500 until she warms up and let me know if your fan starts to suddenly pull heaps more air.

Or once she's warmed up do you need to return to idle to witness greater air flow.

Would be much appreciated.

Cheers
Lea

[LeaUK]

Cross post on TechHelp forum if anyone's interested, find it here

Lea