1995 M50 threw alternator belt -WHY?

[Russell]

My 95 525i threw the alternator, power steering, water pump belt in traffic this evening. Had it flat bedded to my indy. No one has looked at it yet. However, what could have caused the problem?.

About 4 months ago I had all the pullies and belts replaced. I am thinking a "new" pulley failed. The alternator pulley spins ok as does the power steering pulley. So I guess they are not the problem. Did not get under to check the water pump pulley. BTW, It never overheated. When the old belt was pulled out of the way, it started and purred like a kitten.

Could the power steering pump have failed? Never noticed a problem beforehand. Hope not, as they may be expensive.

TIA

[Russell]

Any thoughts?

[billb]

Any thoughts?

Perhaps the spring broke? When mine threw the belt, it was because the water pump had disintegrated and the bearings let go. Not sure why it would throw one without either a tensioner letting go or a pulley bolt breaking/being loose.

[Russell]

BTW, your car looks just like mine.

Perhaps the spring broke? When mine threw the belt, it was because the water pump had disintegrated and the bearings let go. Not sure why it would throw one without either a tensioner letting go or a pulley bolt breaking/being loose.

[philbyil]

they should have replaced the water pump and tensioner at the same time...check your bill!

Don't laugh about the belt....it happens!

[Russell]

Purcased a Conti belt 1555 from BMA and my indy installed. All Pulleys were replaced, but not the tensioners. Should have done so! This belt lasted only about 4,000 miles.

Water pump was specifically checked, and apppreared to be functioning fine. I even put a metal thermostat cover on during the upgrade. As usual, on assumes they thought of everything.

Thanks

they should have replaced the water pump and tensioner at the same time...check your bill!

Don't laugh about the belt....it happens!

[Bill R.]

top and spin it by hand to see if it sounds bad and then try to wiggle it up and down and in and out.. If not then i would take a look at the tensioners as suggested. You can have either type of tensioner based on your production date either the type like Bill has with the spring loaded tensioner or the one with the little gas shock to push the tensioner out...In either case it only takes one wobbly pulley or bearing to pitch one belt which then gets tangled up in the other belts and takes them out too...

Purcased a Conti belt 1555 from BMA and my indy installed. All Pulleys were replaced, but not the tensioners. Should have done so! This belt lasted only about 4,000 miles.

Water pump was specifically checked, and apppreared to be functioning fine. I even put a metal thermostat cover on during the upgrade. As usual, on assumes they thought of everything.

Thanks

[Russell]

I knew I should have replaced the water pump when I had the belts and idler pulleys replaced. But NO! My indy also said the water pump pulley looked damaged and he is replacing that as well.

This car has a history of water pump, belts and pulley failures. The water pump, some pulleys and belts were first repalced around 40-50,000 miles. it now has 105,000 miles. So I guess it was about due.

Thansk for advice. I hope this experience encourages others, IMO, to replace the water pump as preventive maintenance.

top and spin it by hand to see if it sounds bad and then try to wiggle it up and down and in and out.. If not then i would take a look at the tensioners as suggested. You can have either type of tensioner based on your production date either the type like Bill has with the spring loaded tensioner or the one with the little gas shock to push the tensioner out...In either case it only takes one wobbly pulley or bearing to pitch one belt which then gets tangled up in the other belts and takes them out too...

[billb]

I knew I should have replaced the water pump when I had the belts and idler pulleys replaced. But NO! My indy also said the water pump pulley looked damaged and he is replacing that as well.

This car has a history of water pump, belts and pulley failures. The water pump, some pulleys and belts were first repalced around 40-50,000 miles. it now has 105,000 miles. So I guess it was about due.

Thansk for advice. I hope this experience encourages others, IMO, to replace the water pump as preventive maintenance.

You got lucky. My wife was driving ours when it let go in stop and go traffic. It was right around 60k miles. At 120k miles (late last fall), I replaced it again as preventative maintenance, again with a metal blade pump. That is part of my oil change routine underhood check (check for play in water pump). And make sure the right length belt is put back on (6K 1555 or 6PK 1555), sounds like the right one was put back on last time anyway. Too tight a belt will accelerate bearing failure on the pump.

Glad you figured it out. I'd recommend a thermostat when you do the water pump too (even if you just did it when you put the aluminum t-stat housing on). Cheap insurance.