Belts flipping over and coming off?????
 

Here's a new one for me.

I replaced all the belts on my 1987 420SEL a few weeks ago. This would be the air pump belt, the ac belt, the alternator belt, and the two ps belts.

Last week, the alternator belt rolled over. I figured I probably made it too tight, as that is easy to do with the set up. So I tighted it up a little less.

Yesterday, all the belts came off! None damaged.

The accessories all turn freely, the pulleys are in fine condition, there's nothing in the grooves, none of the bearings on the pulleys are loose or wobbly.

Any idea what is going on?

I'm thinking I am making the belts too tight or too loose. Does somebody have a detailed procedure I can review?

I must have put a few hundred v-belts on in my life and have never had anything like this happen.

Thanks in advance!

Perhaps one of the pulleys is out of alignment (offset) with the others.

Nothing has been moved and everything is lined up.

Belt flipping
 

The correct way to tension these belts is to tension them up and then try and turn them 90 degrees. If that is all they will go then they are correct.

In other words: After the belt is installed take your fingers and grab the belt somewhere that it is streached out between pullies. Turn the belt towards you. The groove part shoud now face you. If it will turn further it is too loose, if will not turn that much it is too tight.

If one belt walks loose it will slap against the others and throw them off, too.

Pooka

So I completely removed the air pump and ac belts.

Drove a few miles. The alternator belt flipped again. The old cracked one did not flip. Only started when I replaced the belts (all of them). I've replaced the alternator belt twice.

Any ideas?

Here is a link I found. I would definitely look very closely at the pulleys.

http://www.thirskauto.net/Fan_Belts.html

I had this happen with belts that were too narrow, any chance of that? ,also the alignment is key , any wobble in the pulleys ( bearings/shaft?)

Check the width of the belt. I got a set of belts for the 300SD at the dealer that were too thin and they slipped, and walked as they drove themselves deeper into the pulley groove and lost tension.

I was thinking the belts are too wide.
The bearings on the pulleys seem fine. Nothing in the grooves of the sheaves, nothing bent, everything lines up. Nothing has been changed but the belts themselves.

When you said you changed it twice I assumed you didn't put the same exact belt in twice... If so then definitely try another brand.

The original was cracked and needing replacement. I went to the local Autozone and bought an unknown brand belt; probably made in China. The second belt I bought was a GoodYear.

Are you sure the belt tensioner is good and strong? I'm not sure if yours is the type you tighten manually or if it has a spring, or both. If it has a spring, make sure it is good and strong. If the spring is iffy, it could let the belt go under higher RPM.

It may be that the old belt was so worn that it didn't matter, and the new one is stiff and has creases in it still and might not be getting enough tension.

Pull the tensioner back (if it is a spring type) and see if it goes back into position properly and with enough force. It should be smooth and firm. If it catches or sticks in places, that might be your issue.

It wouldn't hurt to give all the pulleys a turn by hand and make sure that the bearings are in good shape.

Always disconnect the battery when working with belts. You probably like having all your fingers.


Good luck.

No automatic tensioner on this old beast. The alternator and air pump use a gear type adjuster, the ps pump uses and allen head to adjust, and the ac compressor uses a swiveling idler/

I've removed the air pump and ac belts to see if they were the cause. Nope. Alternator belt flips over, then the first ps belt flips.

I ordered some of the proper import belts from the local import shop. Metric measurements. This can't be anything but the wrong cross section belts, cross referenced by the parts counter guys.

The old belts have been on there for at least 6 years, and were cracked and needing replacement before they broke. If those crusty old belts did not come off, the proper new belts should not as well.

Probably the issue, I use the Conti belts. No issues on my 560.

I'm scratching my head as well.
I'm using the Conti belts on my SEC, and have had no issues with them.
My SD has Goodyear belts if I remember correctly, and again, no issues.

I'd never had any suspicion that V-belt systems could be as picky as that link above suggests, either.

Mine have always been just about trouble free, other than one car that I bought that the pulleys were misaligned on, and even then it worked, mostly...