Wiper dragging

[philharve]

Hi All

I fitted a new wiper blade a few weeks ago and during the past few days whenever I activate the wiper in rainy weather, the top 2 or 3 inches of blade has taken to dragging across the windscreen. Such is the level of friction that the dragging almost stalls the wiper motor.

Using the windscreen washer to clean/lubricate the surface of the windscreen doesn't really help. Even with a wet windscreen the wiper fails to glide smoothly across the surface.

There's no apparent reason why the wiper's upper edge should meet with such high levels of friction. Can the downforce pressure of the blade onto the windscreen be adjusted?

Is the 'dragging' possibly being caused by a wiper blade fault? Can the blade pressure be reduced so that it applies less down force onto the windscreen?

REGARDS Phil

 

[television]

I know you changed your wipers recently, Do the blades have the same contour as the screen.there could be too much preasure at the top

malcolm

 

[philharve]

Hi television

I'll check. I purchased the genuine replacement wiper insert and I'm sure I fitted it correctly. I thought the backing structure of rocking levers continuously adjusted the alignment of the edge of the blade to fit the screen's changing curvature? Maybe the top rocker isn't working correctly, perhaps it's stuck. I'll take a look today.

Thanks for suggesting a possible solution. It's something I hadn't considered. I was thinking the problem lay nearer the motor and the device that controls the broad sweeping action.

REGARDS Phil

 

[philharve]

An expensive lesson

Hi All

What I described as 'wiper dragging' was an incorrect diagnosis. I took the Merc' to my indie today after the wiper arm stalled at the 2 o'clock position on my way into work. Of course, it had to be raining.

My indie's initial diagnosis was that the wiper gearbox needed greasing because a 'dry' gearbox would increase the friction the wiper motor would have to overcome to move the wiper arm. A dry gearbox would produce the symptoms I described: slow moving arm and eventually stalling

However, upon closer investigation the indie found the increased friction had damaged the motor which now has to be replaced. Including fitting, I now face a bill of almost GBP290.00!!!

Had I correctly diagnosed the fault sooner and had the wiper gearbox regreased, the motor would not have been damaged and the bill would have been a fraction of what I must now pay. Had I taken the Merc' to a dealership my bill would have undoubtedly been very much higher.

So, if you wish to avoid big bills, have the wiper gearbox regreased as soon as the arm begins to slow its sweep across the windscreen. This is the first sign the wiper motor is struggling.

The wiper motor has a thermal cutout. If the motor struggles to move the wiper arm because of increased friction, the motor draws more current and it begins to overheat. A thermal cutout senses motor temoerature and shuts off current to the motor when it gets too hot. Unfortunately, the motor can still be damaged if it is used repeatedly in this damaged condition.

The indie stated the the wiper gearbox is not a service item and it should be regreased every few years. My wiper gearbox probably hadn't been regreased since it was manufactured almost six years ago. By not acting sooner I now face a huge bill.

REGARDS Phil

 

[television]

That's interesting as TOM 3075 is doing his, and now I will do mine.

Phil, are we talking here about the wiper motor gearbox, rather than the cam for the wiper arm, or both. I know that on the gear boxes that I have dismantled, the grease has long gone from the gears.

Malcolm

 

[Stulc]

I dont have dragging....it's the top 2-3" of the screen that get's missed, I need a new wiper.

 

[996jimbo]

Had I correctly diagnosed the fault sooner and had the wiper gearbox regreased, the motor would not have been damaged and the bill would have been a fraction of what I must now pay.

.....

So, if you wish to avoid big bills, have the wiper gearbox regreased as soon as the arm begins to slow its sweep across the windscreen. This is the first sign the wiper motor is struggling.

Even though the gearbox was dry I would still put my money on the slidey-in-out bit of the wiper arm causing the problem. The reason is the reverse leverage this has on the mechanism. The gearbox itself, even when dry, has leverage on it's side to work. But the wiper arm if it is getting sticky needs be much less sticky to stop moving.

When I took the covers off mine to grease it (the wiper arm) I was surprised that there was no real appearance of distress and expected to find the problem was elsewhere. However the grease made a world of difference. It wouldn't surprise me at all that the additional load of a sticky wiper over just a short time could quickly knacker the gears.

Of course, I'm no mechanic...

 

[philharve]

Phil, are we talking here about the wiper motor gearbox, rather than the cam for the wiper arm, or both. I know that on the gear boxes that I have dismantled, the grease has long gone from the gears.

Malcolm

Hi Malcolm

My Merc' goes into my indie's garage tomorrow morning to have a new wiper motor fitted. It's less than an hours work so labour is just a fraction of the GBP286.00 I have to pay. I expect the indie will want to show me the old motor to justify the cost of replacement. I'll put your question to him and report back tomorrow.


Hi 996jimbo

QUOTE: "When I took the covers off mine to grease it (the wiper arm) I was surprised that there was no real appearance of distress and expected to find the problem was elsewhere. However the grease made a world of difference. It wouldn't surprise me at all that the additional load of a sticky wiper over just a short time could quickly knacker the gears."END QUOTE

Your final sentence interests me. I fitted a new wiper blade and shortly afterwards I noticed the wiper 'apparently' dragging. I assumed that if I did nothing the blade would 'bed in' and eventually glide across the windscreen more smoothly. I couldn't have been more wrong. But maybe the new blade initiated a series of events that knackered the motor. I'll ask the indie about this point too.

How easy is it to grease the cam/gearbox thingy at the base of the wiper arm and the bit that slides in and out? I don't see how you gain access to it.

REGARDS Phil

 

[television]

That's an interesting point Phil about the new blade, it must have more drag than the old otherwise we would not need to change it apart from damage.
Was the new blade the final straw.

Malcolm

 

[philharve]

Was the new blade the final straw.

Malcolm

Hi Malcolm

I have no idea but I'll inquire tomorrow about 'wiper dragging' and the possible effects on the motor, i.e. increasing the load, knackering gearboxes, etc.

You do get dragging if you activate the wiper in dry weather (dry blade on dry windscreen) but I've never experienced wiper motor damage/failure before. Seems like poor design to me.

REFARDS Phil

 

[turnipsock]

Is this a wiper blade bought from the stealers?

If you buy one from hellfords, there is a special one with a MB suffix you need. (not sure what the MB stands for)

 

[television]

Is this a wiper blade bought from the stealers?

If you buy one from hellfords, there is a special one with a MB suffix you need. (not sure what the MB stands for)

MB = mega bucks

 

[television]

Is this a wiper blade bought from the stealers?

If you buy one from hellfords, there is a special one with a MB suffix you need. (not sure what the MB stands for)

Being serious, I think the difference is the the blade fits the arm direct and
comes without the universal fitting kit.

malcolm

 

[philharve]

Update of wiper motor replacement

Hi All

I visited my indie this morning and he replaced the wiper motor in my ‘W’ reg. W202 for GBP286.47p, the greater portion of which was the cost of the motor itself. The motor was the only part that needed to be replaced. The whole job took around 90 minutes.

I asked what steps a typical M-B dealer would take if presented with the same wiper problem. The indie, who once worked for M-B, informed me that the dealer would replace the motor AND the drive plate between the motor and the wiper arm, as a preventative maintenance measure, at a total cost of around GBP700.00. The drive plate incorporates a solid coupling that transmits power from the motor to the wiper arm. By taking my problem to a friendly, neighbourhood indie I have potentially saved around GBP400.00.

After the repair had been completed I was shown the defective motor which I have retained as a paper weight. The indie then explained the operation of the wiper subsystem to me using components from a previous repair, possible from another C or E-class. The indie remarked that this kind of failure is common with the C-class. However, the E-class, which uses a similar wiper subsystem design rarely, if ever, gives problems.

I inquired about the possible causes of wiper motor failure and the indie explained that in my particular case the wiper gearbox, specifically the cam+slider mechanism that enables the wiper arm to ‘reach out’ into the corners of the windscreen had seized. Apparently the slider mechanism, comprising 3 steel rods - 1 big central one, two smaller ones held in supporting bushes - can become dry due to exposure to the elements. The lack of lubrication eventually prevents the rods from sliding smoothly in their bushes and the wiper arm will struggle to reach out into the corners of the windscreen. The biggest rod, because of its greater diameter, exerts the greatest frictional force when dry. Without lubrication there is a tendency for the rods to ‘stick’ in their bushes and the motor has to work even harder to free them. If it fails to free them the motor will cutout after 10 – 15 seconds. The wiper arm will cease to move, having stalled.

The weakest link in the M-B wiper subsystem is the nylon gears. One set (worm & wheel) is attached to the output shaft of the motor. The other set is in the cam+slider gearbox which forms the bottom end of the wiper arm assembly. Both sets of gears are greased and ‘sealed for life’. They are not normally serviceable. Because Nylon is not as durable as steel, the gearboxes (either) often fail when the wiper arm ‘stalls’. Teeth are stripped from the worm or pinions and the motor rotates freely. That’s the loud ‘groaning’ sound you hear when the drive is damaged. It lasts about 10 – 15 seconds.

More often than not, when the wiper arm stalls, it’s usually the motor gearbox that loses its teeth, not the cam+slider gearbox. The only ‘effective’ remedy is to replace the expensive wiper motor.

The indie commented that some owners, maintaining their M-B on a tight budget, seek a cheaper solution, one which only works if the motor has not been irrepairably damaged. It’s a crude solution but it works. What they do (or have done for them) is spot welds are placed on the 3 rods so their sliding range is restricted. Consequently the wiper arm is prevented from reaching into the corners of the windscreen during a wipe. In other words the wiper is forced to behave like a conventional wiper; it describes a simple arc. Now you see why I say it’s crude.

If buying an M-B, observing wiper behaviour might be a clue as to how well the vehicle has been looked after by the previous owner.

In order to avoid huge repair costs all that is necessary is to note two things: firstly, when the wiper arm begins to slow or ‘drag’; and secondly, when the wiper fails to reach out into the corners of the windscreen. These 2 symptoms mean the cam+slider needs greasing – and soon.

In an emergency a few drops of light oil applied to the big rod will free it sufficiently for the wiper arm to do its business and relieve the frictional stresses upon the motor. However, this is only a temporary solution and my indie recommends the car be booked in for a wiper service ASAP. It takes around 45 minutes.

Yes, it is a DIY job BUT there is a hazard. In order to grease the rods properly you really need to remove the wiper arm and cam+slider assembly. The removal process does not require special tools but because the wiper arm is spring-loaded in order to force the wiper blade onto the windscreen surface, there is a real risk the windscreen could be broken in the removal process. If you’ve done it once successfully, you know the hazard and you can remove it again without trouble. If you’re not a mechanic or never removed the assembly before, it’s a job best left to a specialist, like an indie.

Finally, greasing the cam+slider is not a regular M-B service task but because it is a known ‘weakness’ in some models, an indie or a dealer will (should) look out for the symptoms described above and grease the cam+slider is wiper movement is suspect. This simple, cheap maintenance measure should prevent gearbox failures or the motor burning out. The latter is unlikely because there is a thermal cutout which switches off current to the motor if it gets hot as a result of trying to move a stalled wiper arm.

I asked the indie why fit Nylon gearboxes in the first place because it’s an obvious weak point in the wiper subsystem. His answer was predictable. Nylon is cheaper than steel, doesn’t rust and, in the context of a gearbox, is quieter in operation. However, if wiper subsystems were ‘unbustable’, M-B would never sell any wiper subsystem components at a nice fat profit.

I have driven many cars in almost 40 years but never have I had to replace a wiper motor. I have occasionally activated a wiper inadvertently in freezing weather when the blade has stuck to the screen or been embedded in as thick layer of snow. The wiper never budged – how could it - and the motor always cutout after a few seconds. No wiper damage was ever sustained to any of my cars.

I therefore find it curious that a prestigious marque, like M-B, should choose to incorporate a component in one of its models that is known to fail under certain circumstances. If it had been a Toyota wiper subsystem, the company would have redesigned the component and replaced it the next time it failed. My previous car was a Toyota and on 4 occasions I recall fitting an ‘upgraded’ component.

Cost cutting doesn’t necessarily cut costs.

The indie remarked, as I left his establishment, that M-B have gone back to the 2-wiper system in newer models because it’s much less trouble. Looked at another way, there’s now twice as much to go wrong.

REGARDS Phil

 

[television]

Thank you very much for the supurb run down Phil, I wish I was as good as you with words. The first day of spring, mine will be serviced, thank's a million.

Malcolm

 

[C220GJS]

Phil,
As you have given such a comprehensive report on the faults with this wiper system I thought I could add a bit more that might be useful to anyone willing to attempt to repair their own system.
In my experience of failures with this wiper system ,the most common fault has been when the wiper continued to work but started to go out of syncronisation, the end of the blade would start to slap the trim at the side of the windscreen eventually getting jammed at the side of the screen and scratching the trim. This is caused by the nylon gear in the wiper head gearbox slipping on its shaft ;or in the worst case the gear teeth stripping; the stripped gear cannot be replaced and a new gearbox is required. If the gear has slipped on its shaft and is otherwise undamaged , drill a 3mm hole through the gear and shaft and fit a suitable pin with an interference fit, ensure the pin is short enough to clear the root of the gear teeth. Reassemble using grease on all shafts and sliding surfaces and you should have no further problems.
Sorry to hijack your thread Phil.

 

[philharve]

If the gear has slipped on its shaft and is otherwise undamaged , drill a 3mm hole through the gear and shaft and fit a suitable pin with an interference fit, ensure the pin is short enough to clear the root of the gear teeth. Reassemble using grease on all shafts and sliding surfaces and you should have no further problems.

Hi C220GJS

Ok, I understand. But how does the gear manage to slip on its shaft in the first place? Having not seen inside the gearbox at the base of the wiper, I can only assume its some kind of interference fit, or possibly a keyed system. I've used a similar type of repair in other situations where gears have become detached from their shafts. I drill a radial hole through both an use a drift to insert a hollow pin with a gap along its length. I can't think for the moment what this pin is called but it is very common.

To perform the repair you describe requires taking the gearbox apart, doesn't it?

I have seen this 'out-of-sync' condition but didn't realize it could damage the surrounding bodywork.

The indie showed me a wiper gearbox and drive shaft assembly and I formed the impression it was one component. He described this component as costing well over GBP300.00. He said I was lucky it wasn't damaged too.

Of course, in my case the damage occured to the motor gearbox. It would have made sense to make this a replaceable component but M-B have got to make money somehow so you have to replace both motor AND gearbox.

REGARDS Phil

 

[television]

Phil,sinse these motors are probably made by bosch I wonder if bosch supply the gear. In many cases on our cars where MB only supply a new complete unit, bosch do have exchange units and parts. Just for reference do you have the part number of the wiper motor and I will check with Bosch.

Regards and thanks again for info.

Malcolm

 

[philharve]

... do you have the part number of the wiper motor and I will check with Bosch.

Hi Malcolm

You're having an evening hitting the keyboard too, I see?

The indie gave me the damaged motor which he put in my boot. I wonder if the Part No. is stamped on it? I'll take a look tomorrow.

The Part No. may have been on my bill but when I climpsed the total at the bottom, everything else on the bill went out of focus. I guess I was suffering from shock. The bill's in the car log book but I'll take a look tomorrow.

Failing this, I could always ring my indie on Monday for the Part No.

REGARDS Phil

 

[turnipsock]

Being serious, I think the difference is the the blade fits the arm direct and
comes without the universal fitting kit.

malcolm

It's actually a different pivot point from other blades, that is, it's not in the middle.