ML320 with 180K. It shredded a belt about 1000 miles ago and the cause was obvious, since the idler pulley was broken. Replaced the pulley and and it ran fine for 1000 miles. I just did some repairs to fix some oil leaks, none of which touched any of the pulleys, but I did take off the fan (so of course the belt as well). I also replaced the MAF, which made a noticeable difference in increased power.

It was running great for a series of test drives for 50 miles or so. Then I accelerated pretty hard to see how it would do, and the belt came off and shredded. I'm in the process of checking everything now. There are no pulleys obviously broken this time. I've read that the harmonic balancer can fail over time so I plan to replace it as a matter of course, even if it wasn't the cause of this. I am also going through each pulley and checking to make sure there is nothing seized, nothing broken and no slop.

Is there anything that makes obvious sense to check since it came off during hard acceleration? Is there anything else I should change as a matter of course (fan clutch, tensioner, harmonic balancer)? Are there any potential issues with the power steering pump, water pump or alternator that I should look out for that could cause this problem under acceleration? Is it wise to replace the water pump as a matter of course, or to leave it alone if it is working? Similar question for the thermostat (if I end up replacing the pump)?

Thanks

 

Run the eng. with the belt off and look at the crank pulley and see if it wobbles. If it doesn't that's not the problem.

Spin pulleys 4 & 7 as fast as you can. If either spins freely, it must be replaced.

Check the others for side to side movement.

 

Thank you for that.

4 broke previously and was replaced. It still seems fine (passes the spin test). 7 also passes the spin test. I don't see any wobble in the crank pulley. No noticeable slop in the PS, AC or generator. Not sure what else to check at this point. Guess I'll put on the new belt and try it out.

 

Look for a Gates belt.

 

OK.

Just FYI: I didn't put on the first belt, so I don't know what it was. The belt that just shredded was a Continental ContiTech. I have a new AC Delco belt to try something different than the Conti. I'll go get the Gates and try it first.

 

If any of these two new belts shred, then there is something wrong with one of the components that the belt drives.

 

That is what I figure, but it's frustrating not knowing what to check. My guess would be AC first then PS since they should put the most load on the belt and the AC has a clutch that kicks in, but I'm not sure how to test either and they are both prohibitively expensive to change out with new parts just as a test. If the fan clutch failed I figure that would actually make it less likely to be the problem, as long as it spun true.

I have a belt tensioner pulley that I bought along with the idler pulley that broke. The tensioner itself seems fine, but I am not sure how to test it other than the spring still feels strong. Do tensioners lose spring strength over time or can they bind? That is a part that isn't too expensive so I could change it if it might be a problem.

 

What was the make of the tensioner and the idler pulleys?

 

Not Mercedes. I believe it was Bapdic. I threw away the box it came in. It was the same size as the broken one I took off and seems to be working fine. It's hard to see how that could cause the current problem, but I don't know what did cause it so I'm willing to change it out if it might help? Are any other pulleys acceptable, or just Mercedes? Gates? How about the tensioner itself? As I said before, it is running just a little rough at idle. I can see the tensioner move very slightly when the engine stutters. Is that OK, or is the tensioner too loose and should be replaced? it is definitely sprung tight enough that it is hard to hold it with one hand to put the belt on.

I've idled it for 10 minutes and then driven it for 20 miles stop and go on surface streets with the new belt with no issues so far. I'm going to try to look for vaccuum leaks this afternoon.

 

Here are the Gates part numbers you should buy. Fill in the info.

https://www.gates.com/us/en/power-tr...-pulleys/c/141

 

Thanks! I was going to ask if there was a recommended after market brand, and about gates in particular.

 

Aftermarket is anything other than the dealer. Gates is one of the best aftermarket company.

Why can't you research it yourself? Why do I have to tell you about it?

https://en.wikipedia.org/wiki/Gates_Corporation

 

You said one hand to hold the tensioner?
How long was your tool? Mine seemed to be pretty tough with a decent length ratchet on it.

Oh also there's a cool video on YouTube about replacing the grease with good grease in these pulleys (they typically are filled with the cheapest grease) to make them last an extra long time.

One possibility is when the belt was put on the first time it wasn't all the way put on. Like one spline off. I've seen this happen before, it's hard to tell because the chaff at the back of the belt hides one of the grooves sometimes.

Another possibility is that the water pump or power steering is about to go. It could be tensioner pulley.

I once let my tensioner pulley bearings get so bad it eventually sized up, broke the center out of the tensioner plastic tensioner pulley and threw the belt.

Seen a mb throw a belt and then about 500-1000 later it threw the belt again because the power steering pump "had just seized" (and some how lost its fluid, I didnt work on this car but I fail to see how the mechanic couldn't tell...he claimed the belt was thrown the first time because of an idler or tensioner pulley..maybe he never filled the pump up with fluid)

Also it could be the water pump, if it's still neiwsh/ super good the thing should be pretty tight with a tiny bit of resistance.

It's hard to tell with bearings because you have to put them under load to really feel how good the bearings are.

Oh and the thermostat I believe you can change without removing the belt, but it's a pain. They seem to wear out every 100k or so. I wouldnt worry about it.

A miss at idle is hard to diagnose, but mine was problems with the wires, then leaky vacuum lines, egr vacuum lines, then other ignition components like a weakening coil, crank and cam sensors, on other non ML cars I've seen bad grounds, even failing ecus, or bad electric throttle body or throttle position sensor. Bad MAP sensor, Or even the intake tube not being on all the way at the back or on the MAF or PCV plugged, leaking. I suppose fuel injectors, or fuel pump and filter though youd get extra symptoms usually.

Theres also a chance you could have a break in the wiring. With the m113 and m113 if someone drove it an extended amount of time with bad engine mounts it can cause damage to the harness.

I suppose errand voltages in the intake air temperature sensor, or even coolant sensor or the alternator regulator could all be culprits. Or even a leak in the transmission TCU plug with the transmission fluid wicking up into the TCU and shorting it out which is a problem on the m112/m113.

But don't quote me on the perhaps and maybes just throwing things out there!

Good luck and let us know if you fixed it!

Btw gator belt is awesome I have one too!

 

Of course I know what aftermarket means. Yes, I know Gates is a good company, which doesn't mean they make parts that would be recommended here for use in place of genuine Mercedes parts in all cases. I have been researching it, that is why I am here searching the archives and asking questions. You don't have to tell me about it, you offered your opinion and I thanked you for it. Why did that upset you?

I'm very confused by your response.

 

I'm becoming suspicious of the tensioner, so I am going to swap it out. It isn't easy, but I can hold it with a standard 1/4" socket wrench with one hand so it may be weak. The tensioner pulley looks different than any of the pictures I can find, so I'm guessing it has been replaced and possibly the tensioner as well.

 

All fixed and running great!

Replaced the tensioner with a new one from Gates. Old one had Mercedes symbol and part number stamped on it (A1122000370), made by Litens with Litens part number 113, so I assume it was original. The new tensioner from Gates was stamped Litens 0113, so literally the same part from the same manufacturer as the original from 20 years ago! I finally found some pictures of what looked like original tensioners from around 1999 and they did in fact have the metal split pulley (looks like two pulleys riveted together). I'm not sure the expected lifespan of a tensioner, but the new one feels much stronger than the original and I don't notice the same movement I saw in the original during the rough idle.

The rough idle was an easy fix. After I replaced the crankcase gaskets, I accidentally ran one crankcase vent tube over another tube when it should have gone under, which caused the air hose connector to lift up and not seal. Reversed the route of those two hoses and the connector seals and idle is rock steady again.

No more oil leaks, running much smoother with much more power (thanks to new MAF and new fuel filter), and the belt seems rock steady. I'm very happy for now.

Thanks for all of the advice. It has been very much appreciated. This is my first Mercedes and I'm learning it's quirks. It's been very rewarding so far.

 

Nice job! Glad it all worked out for you. Working on the front of these engines can be such a pain. I used to have a 190e and you could just lift up the rad and place it on top of the engine with the hoses still connected and have full access, or things like replace the alternator regulator from underneath. Or have heated washer fluid. Or shut off the coolant from the HVAC... (I saw a guy who retrofit the same on his ML and he measured his A/C as 8 degrees cooler). In the 70s/80s you could even push start an MB with an automatic transmission. I guess they had to remove that feature to fit in an extra gear into the casing. At least our electric actuated transmissions are so smooth, too bad we cant easily check the fluid level without buying the special dipstick.

Btw beware of your window switches in the 99 they tend to stop functioning often and then you have to replace the entire switch panel. You can pull off the top of the switch and the white piece inside to get access to the springed contacts to push them with something plastic like the inside of a pen.

 

I'll keep an eye on the window switches. The power lock on the drivers door went out a little while back. The part looks expensive and the instructional video I have seen says you have to drill out rivets and reattach with bolts, so I am living with it for now (pushing it down manually, and using the key to open the door.).

 

Not true. The rivets at the window rail must be drilled out and replaced. Rivet gun required.

 

Haha yeah there's something wrong with the design of the locks on these 99 trucks. Not a single lock works on mine. Either they have broken micro switches, broken pieces/springs that keep the lock down and in the lock position, or they don't allow you to open it on the inside, and in the case of the lift door, the lock mechanism is ridiculously hard to move by hand, and the outside handle pops unhooked if you dont open it just right.

The truck also always thinks (due to a microswitch in the lock mechanism) that the front passenger door (I believe) is always open therefore the front overhead lights stay on and so I had to remove its bulbs to turn it off lol. All the solenoid/electric motor mechanisms still work surprisingly enough however when I hit lock I just get the dreaded machine gun sound.

I've seen now that they sell little plastic pieces on ebay to fix part of the lock however I don't think that's ur problem.

You need to find a self serve pick and pull yard if you wana spend almost nothing on parts. Especially small parts and at least a rivet gun kit can be has for as little as $20

Oh also, while we're talking about the interior, beware of the rear switches and the rear cup holders. Everytime I go to the yard they're almost always broken. New passengers are almost always confused by the switches and press too hard on the wrong side and they also brake in the same way internally as the fronts. The cup holders just have such a tiny bit of plastic tab for a hinge I'm sure they'd break if you looked at them sideways. I was able to fix mine by reattaching the tabs using a dremel to shape a few spare pieces of plastic as supports and then riveting and epoxying them all together. The thing is still weak as shiet.

Oh also the brake light switch tends to break lots, part of the vent selection dial that attaches to a bicycle brake cable like thing at the top. (It can be glued too). The wire for the FM antenna tends to break too from too much repeated flexing...it brakes right at the top were it goes from the roof into the rear lift gate. I know I'm forgetting something else here.

Tbh pretty much everything on the interior or made with plastic is super fragile.

Caution long rant below:

I've always wondered as to why...
was it due to an inexperienced new automotive designer/engineer?
Was the design rushed?
Was the wrong plastic chosen,
or the plastic changed for the production vehicle?
Maybe the plastic was manufactured incorrectly,
or perhaps it dries out quickly making it brittle.

Could it be they just didn't care expecting to replace nearly all of it by 2000, two years later.

I've also entertained the idea it was done on purpose...hoping the stuff would last long enough to surpass the warranty period so they could sell you extra expensive oem parts for the life of the vehicle. Maybe the design for the switches, etc was great but the aftermarket / OEM supplier weakened them again to sell more parts.

It also might have been done deliberately to cause the 2000 and up models to have much more of a night and day difference as compared to the 98-99, in order to goad 98-99 ML owners to find it almost impossible not to want to trade in or upgrade.

That might explain why they left out so many features at first, features which had been standard on E, even C classes since the late 1980's. Even inexpensive features.

I think they thought since it was a new segment for them, any mb loyal customer who either wanted an suv or who just wanted the newest mb vehicle type, would buy one regardless of how crap it is, and the same could he said for any car buyer who was aroused by the idea of a "MB" suv.

However if they wanted to attract E or C class buyers away from their car purchases and leases, the truck would need to be nicer and have everything plus more as compared to those cars. Hence the innumerable changes in 2000/01/02, etc.

Very sneaky.

I wonder how many people went to buy one in 98-99 and thought they'd hold off when they realized it didnt have auto dual zone climate control, no valve to prevent hot coolant from warming up the a/c evaporator your HVAC unit, no folding mirrors, no headlight washers, no HID's or advanced headlights, no heated windshield washer fluid or nozzles, no seat memory which is on a minimum way adjustable seat, no steering wheel buttons, no automatic lengthy antenna, no chrome door sills, no hood struts, no tool kit, no single articulating wiper, no tweeters, no suspension leveling or shock adjustment, no mechanical differential lock(s) no aesthetic soft door side-air bag cover, no backup sonar, no main electric radiator fan, no lower body cladding, no compass, no good sun visors.

I wonder how many people also stayed away when they noticed the undersized brakes, the lack of skid plate on the fuel tank that hangs down and is in the way for virtually all obstacles, the back seats that get stuck down all the time, the sound of leaky door seals, and the road noise from barely any sound deadening, how so much of the interior was plastic, thin, weak, and gross and the whole thing is a rattle box not to mention the bumpers and front grill are barely attached and can make all sorts of noises.