I keep having a problem throwing both the fan and the alt belt on my 1978 Ford F250. What would cause this to happen??? The only thing that i could think of, would be that i have to much movement of the motor....

any advice or suggestions would be very helpful, i'm tired of going to the Napa to get belts every week.

thanks

Sethro

 

Seth,
The motor could jump out of the truck and it shouldn't throw the belts. Is one belt coming off causing the other to throw? Are you getting your belts tight? Is every thing factory on this rig? Are you racing this motor? Check your water pump and fan for loosness. Give me some more details.
KingFisher

 

Couple of things to check, are the pulleys lined up? You can take a straight edge like a ruler and check to see if the "V's" line up. Also check that you don't have a bent one, same thing to check, just do it across the "face" of the pulley with the ruler flat at several different places around the outside.

 

I managed to get the pickup from a guy who rebuilt it from the ground up. (not the greatest job, but the motor is strong), not everything is stock.

It has a 1970 Ford 460 motor along with 1971 Lincoln heads. I needed to find the alternator bracket for it, but the water pump on my motor has different bolt holes than the motors i was trying to steal parts from, so i just bought the adjustment arm and kinda made my own. (i kinda have an electrical, charging problem, but not sure if this is the reason why....still trying to finger that out)

When the belts fall off, it usually happens when i gam accelerating from 2nd to 3rd gear.

I have the power steering pump and the alternator ligned up pretty straight, althought i will check with the ruler. The power steering belts is extremely tight, but the alternator belt isn't tight tight, but tight enough to keep the alt spinning.

i just thought the motor moving and twisting, might have something to do with the belts comming off.

Sethro

 

Is the belt, Too Wide for the pulley's ?
I had a friend who had the same problem,He ended up having a 15A wide belt as opposed to an 11A.


Dennis
78 F-150 429CJ C6 ,Silver w/Explorer Pkge
641/2 Mustang,Pre-World's Fair Car #8092
64 Fairlane S/C waiting for a 390-4spd.
68-Mustang.Sunlit Gold 80,000 miles

 

I'm going to lean towards the alt. belt being the problem (it's the closest to the engine?), I would try to get the alt. bracket sorted out, making sure that the alt. pulley isn't cocked to one side, in other words, is "leaning" in some direction, be it left-right or up and down as you look from the top. You may also want to try a belt that is an inch or so smaller if the lack of tightness is due to running out of adjustment. Having the alt. belt tight will not cure a misaligment but may at least keep it on (but will eventually destroy the belt or take out a bearing), I think it happens when you are changing gears because the belt "slaps", when your on the power, the engine is pulling the belt to turn the alt. and keeping it tight on one side (can be top or bottom depending on which side it's mounted and which direction the engine turns), when you let off to shift, the alt. is trying to pull the engine so to speak (engine revs drop quicker than the alt. slows from spinning) and causes the slack to be on the other side of the belt allowing it to jump from the now slack side. Oh, and no to your question of cause, even a broken motor mount allowing the engine to jump all over won't throw a belt because everything is mounted to the engine and the belts are moving around just the same as the engine is.

 

i wasn't sure about the engine twist at all....

I will take what you have suggested to me and try to get the alt aligned as straight as possible. At first i had a problem with the belts being to wide, so i went to a smaller belt (might have to go down one more size)


thanks for all your help.


Sethro

 

I had a buddy who had an electrical problem which caused the belt to turn and throw. I don't remember much, but he had built a 51 ford from the frame up and did the wiring himself. I think the problem was his wiring to his alternator which caused it to magnitize and screw it all up.

 

I broke two alternator belts then found that the nut holding on the crank pulley had come loose. This let the crank pulley back out and misalign with the alternator pulley.