Self-Levelling Q. (very noisy fanbelt)

[genphreak]

Hello all,

Mum's '95 525i touring (an M50/5HP18 auto) has developed a very noisy serpentine belt.

It seems from the screaching noise that the belt is slipping (but only when the car is laden). It can happen (a little) unladen, ie when taking off from rest uphill (and especially when the engine accelerates).

Clearly when the rear suspension switch causes a load to the SLS pump, the belt is slipping. Do I just need to change the belt and belt tensioner, or is it likely to be something worse like the pump being worn out so unable to maintain the correct pressure?

In my limited (I've no pressure gauge) testing the LAD appears to work fine- but it does not sound good under a heavy load. The car is:

- in good condition and has done about 200,000km (180,000miles)
- not throwing up any Suspn Levelling warnings on the dash
- the ride height seems good
- after being parked at night the rear sags a bit and the fluid height in the reservoir rises a bit above the mesh.
- when we got the car earlier this year it was doing this and it had red fluid (perhaps 7.1 or a mixture of that and Dexron). I changed at least 1.4L of fluid- replaced with CHF 11 as I thought that all LAD was CHF11, so now its a bit purplish. However the Bently lists 7.1 as the OE fluid (I've no handbook). Section 330-11 of the Bently covers the system in detail.

The problem is she's going on holiday and I only have a day or two to fix it before she goes... so far, all I've been able to buy is a tensioner and fan belt. Any advice would be appreciated... although I have to say I'm not keen try an SLS delete a few days before they go... (let alone find the bits- it would take a week minimum to get the parts)

The holiday is only 2000km of driving, so if I could just reduce it till they get back, that'd be a good result.

[shogun]

Clearly when the rear suspension switch causes a load to the SLS pump, the belt is slipping. Do I just need to change the belt and belt tensioner, or is it likely to be something worse like the pump being worn out so unable to maintain the correct pressure?

There is actually no load so to speak, the pump just delivers depending on what the engine speed is and what the belt delivers (not slipping).
In case the rear does not need a lift, the regulating valve just sends the oncoming fluid back to the Pentosin reservoir.
The pump has no brain, it just delivers what is can, that is all.

So just fix the belt, the belt tensoin, finished.

[bubba966]

The cap on the reservoir should say if it needs CHF11 or 7.1. I know my cap says it requires 11 (I've got SLS & EDC on my car). I would guess you also need 11. But you can run 11 when 7.1 is needed, but can't run 7.1 when 11 is needed. 11 is synthetic, 7.1 isn't.

[Elekta]

Dextron will kill your accumulators and the proportioning valve. Get that stuff out of there asap and flush the system. Dextron eats the internals of the accumulators.

I made the mistake of hitting a quick lube to change the oil on my maiden voyage from SF to Texas, and the guy topped up my CH11 reservoir with Dextron, and 3000 miles later I was replacing both accumulators and praying that my EDC would not fail. You have no EDC, but you can seriously damage your LAD/SLS

Flush that systems asap

[genphreak]

Dextron will kill your accumulators and the proportioning valve. Get that stuff out of there asap and flush the system. Dextron eats the internals of the accumulators.

I made the mistake of hitting a quick lube to change the oil on my maiden voyage from SF to Texas, and the guy topped up my CH11 reservoir with Dextron, and 3000 miles later I was replacing both accumulators and praying that my EDC would not fail. You have no EDC, but you can seriously damage your LAD/SLS

Flush that systems asap

Hi all, thank you for your replies.

Oh yes, the reservoir does say CHF11S. (No wonder I changed).

I will change the belt as I can and will post back my experiences. Makes me feel much better about it, the squeal is quite alarming to everyone, and I've read about some people removing inline filters/restrictions in the system to resolve problems that accumulator replacement et al do not. Having tread about the valve and accumulators etc, it seems to me the system charges a threshold 2000-3000 psi with minimal flow under no load. The valve simply allows more flow the lower the suspension goes- allowing more fluid to flow through to the shocks when the load increases- so from this point of view the load would have to present against the fanbelt. eg 1ml/min at 3000psi is nothing compared to 1/L/min at 3000psi.

It has to be the fanbelt countering gravity and raising the car.

I've a sneaking suspicion however that the problem is the belt itself or rather the last person to change it- everywhere I've tried I can only get a 1560mm belt and facrtory is 1555. The tensioner would deal with that new, but once the belt gets older it may loosen prematurely adn slip (ie before it would normally wear out).

Re the fluid, I think it had Dexron in there for sometime and it has survived The flush is not possible that I know- has anyone done this- all I did was a thorough drain, but I didn't get to teh accumulators or the shocks...

[shogun]

the belt lenght depends on the other items you have installed. On my E32 750 also no fan belt offered in the U.S. fits, as my car is the version for higher visco fan clutch speed for tropical countries, so maybe your country spec has the same. There is a different size of belt pulley. Buy the belt from your dealer if you cannot get the right size online.

[genphreak]

the belt lenght depends on the other items you have installed. On my E32 750 also no fan belt offered in the U.S. fits, as my car is the version for higher visco fan clutch speed for tropical countries, so maybe your country spec has the same. There is a different size of belt pulley. Buy the belt from your dealer if you cannot get the right size online.

Thanks Shogun, this is definately the case. Realoem and ETK says 6PK-1555 (ie a 6 rib, 1555mm belt).

Mum packed up the car and went anyway, reporting after 400km that the squealing was getting really, really bad.

Jumped in the car with a 1550 and a 1560mm belt. Got there 4 hours later tried to fit the 1550mm, but it seemed at least 2" long. The old belt had the numbers rubbed off, but the local spares shop had a measuring device; it was 1500mm long. I rang the local BMW dealer (McGuigan BMW) who were really helpful, helping a customer who simply wanted to confirm an M50 belt length. Spoke to the front desk parts guy who spent a put in a great effort to check my VIN required a 1555mm belt. Perhaps surprising since this was an Australian delivered car. The parts manager even got on the line and confirmed all M50s to be the like this AFAHK.

Hunted around for hours but couldn't find a 1500 anywhere, nearest thing that might fit was a 6PK-1510, which I tried but was too long. Went to the third parts place, Autpro in Tuncurry- who were just terrific and arranged for me to goto their distributor to collect it. Tried both 1500 and 1485mm belts there, as I reckon that the 1500 is a tad long. Looking at the throw of the tensioner, I reckon a 1495 or perhaps even 1490 is correct.

Comparing the pulleys to a non-vanos M50, there seems only one difference: The tensioner roller has a 45-torx nut instead of an 8mm female hex behind the dust cover. Grrr! It looks like Heinrich the Continuous Improvement engineer got in there and decided that rollers should be torx from now on. OK, so the main belt tensioner roller is slightly different, but the diameter looks the same. But looking closer, the tensioner is really different too: I can see it has different throw and looks perhaps stronger.

So I fitted the 6PK-1500 and the squeal mostly disappeared. Loaded the car with 5 adults and a full tank, and the noise did come back- but was almost all gone.

So now they will continue off on their holiday and we will see how it handles the pressure. I will measure the rollers and try to document the part numbers once they get back.

Has anyone ever done seen a tensioner like this before? It is not a little piston like the normal ones, it is more like a chunky alloy casting with a 16mm male hex cast into it- you can use a nice big wrench on it and relive the tension really easily without slipping and grating your hand on the radiator .

Of course, I only discovered this after struggling with the torx...

The moral of this story? if its different, otehr things will be- inc the procedure!) Sometimes I guess that Herman does a great job.

Nick