Fan Belt Vibration 88 F250 7.3L
 

My belts on the Alternator to Fan and Power Steering Pump to Fan both have alot of vibration in them at idle. I changed all the belts tonight and they seem pretty tight but still vibrate alot. I can deflect them less than half an inch so not much slack. Looks like they move back and forth when its running about an inch. Is this pretty normal or do I need to try and get them tighter?

Thanks..

That sounds normal. The alt belt jumps the most. Carry extras you can throw a belt sometimes. Try to use premium belts , they stay on longer. Most of the flop is caused by the vaccum pump, they should smooth out with an increase in engine speed

Mine do the same thing. Hope someone else chimes in but from what I understand it's normal for a diesel to do that

it is due to the large span.
if there was an idler pulley in there, it would go away.

Mine to do that, they smooth out as RPM's are increased. Don't worry about it.


Make sure to have spare belts and hoses in the truck at all times and your set.

Yeah the span is to long and the vacuum pump causes the jump. We bought this truck cheap several years ago because they couldn't hold the alt belt on it. I tried several things like new pulleys on alt and crankshaft but it didn't help. I finally fabricated an Idler pulley. Used the alterantor tensioner bracket bolt holes where it mounts to the water pump and mounted it there. Used a v-belt idler off a 70's something Ford Ac setup. This stopped the belt jump for aprox 4 years. I had it happen yesterday and the reason was the bearing went bad in the idler pressed new bearing in and put it back togather. Hopefully good for awhile. If anyone is interested I will be glad to email a picture of the Idler I made.

Yeah, anything that "pulses" will cause that, and long spans amplify the effect. The vacuum pump has high then low resistance to turning, and the engine pulses as each cylinder fires. As RPM goes up, there is less time between pulses, and things seem to smooth out...

x3,4,5,6 or whatever it is.....I have the same slop in my 7.3, and all three of my 6.9s(including my dad's 86)

Out of curiousity (warning: slightly OT), has anyone ever looked into installing the serpentine system off a 92-94 IDI to an older truck? Just wondering what would be involved........

Mike

Been done alot actually. Search it in the forum.

Please post up the picture, I'm sure a lot of us would be interested.

Alternator belt jumping....
 

Can you post the pictures of this belt tension modification.Just replaced belt and don't want the new one to get ruined.

Mine on my MH are very long and flap real bad at idle but smooth out at cruise PM