serp belt problem
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New User
Joined: Jul 2003
Posts: 10
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From: Michigan
serp belt problem
i have recently purchased 1989 F250 4X4 with 7.5 and C6. however i can't seem to get it to keep the serp belt from running off the front it's the crank,water pump, tensioner, A/C, powersteering, doesn't seem to have any side to side play in any of the pulley's. how can i check for proper alignment of all pulleys... i realize eyesight can be deceiving. 1 belt well last me almost 11 miles...not a good thing i've tried different brand of belts...all the same thing 10.4 to 11 miles and they are off and tore up...it's getting expensive...not to mention aggravating.
Junior User
Joined: Jul 2003
Posts: 51
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From: Far Hills, NJ
serp belt problem
First, check that the belt is on the correct way. There is a diagram on the front cross member that shows the correct installation.
Second, the A/C and alternator are mounted in rubber bushings. These deteriorate after a while (on an '89, they may be shot), thus causing the A/C or alternator to 'drop' slightly. This is enough to make the belt slip off. I would remove the A/C and alternator and replace the rubber bushings.
Third, the crankshaft pulley on some V-8s is composed of an outer metal ring with a rubber isolation ring sandwiched underneath. This is to absord vibration from the engine. Often this rubber isolation ring will start to fail on high mileage/old vehicles. You might want to check the crankshaft pulley for rubber deterioration, and replace if necessary.
Fourth, the tensioner pulley on many Fords is a plastic pulley that can break down over time. NAPA has an all metal tensioner pulley as a replacement.
Bottom line is that all you need is a millimeter of off center play in the belt and it will slip off. So check the setup carefully, and I think you'll find the problem.
Second, the A/C and alternator are mounted in rubber bushings. These deteriorate after a while (on an '89, they may be shot), thus causing the A/C or alternator to 'drop' slightly. This is enough to make the belt slip off. I would remove the A/C and alternator and replace the rubber bushings.
Third, the crankshaft pulley on some V-8s is composed of an outer metal ring with a rubber isolation ring sandwiched underneath. This is to absord vibration from the engine. Often this rubber isolation ring will start to fail on high mileage/old vehicles. You might want to check the crankshaft pulley for rubber deterioration, and replace if necessary.
Fourth, the tensioner pulley on many Fords is a plastic pulley that can break down over time. NAPA has an all metal tensioner pulley as a replacement.
Bottom line is that all you need is a millimeter of off center play in the belt and it will slip off. So check the setup carefully, and I think you'll find the problem.
Freshman User
Joined: Sep 2002
Posts: 47
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From: Friendswood
serp belt problem
I too have been having problems with the belt not riding in the pulleys right. I have a 91 F150 with a 5.0L and it seems like the problem started when I replaced the A/C compressor. It appears to be to far back but there is not adjustment in the bolt holes or any where else to move it forward. Can the pulley be shimmied and if so, how is it removed.
Junior User
Joined: Jul 2003
Posts: 51
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From: Far Hills, NJ
serp belt problem
You might have forgotten to replace one of the rubber bushings, or the compressor might be different from the one it replaced.
The pulley shouldn't be shimmed, since it is handling all the load and also has an internal clutch. I'd check the mounting bushings and washers to make sure they were all replaced in the correct order and if any of them look cracked and flattened down. Also, cross check the replacement A/C compressor to make sure it is the correct part for your specific truck.
The pulley shouldn't be shimmed, since it is handling all the load and also has an internal clutch. I'd check the mounting bushings and washers to make sure they were all replaced in the correct order and if any of them look cracked and flattened down. Also, cross check the replacement A/C compressor to make sure it is the correct part for your specific truck.
Freshman User
Joined: Sep 2002
Posts: 47
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From: Friendswood
serp belt problem
The compressor does not site on any rubber bushings. It bolts straight down to the bracket that also holds the power stearing pump. This then bolts to the front of the block and there are no spacers there as well. I will have to double check part numbers on the compressor but I hope that is not the problem as i don't want to have to evac the system. Thanks for the insight.
Junior User
Joined: Jul 2003
Posts: 51
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From: Far Hills, NJ
serp belt problem
Just a thought, but if the compressor bolts straight to the bracket, did you maybe put the compressor on the backside of the bracket instead of the front? That would explain it being too far back. I don't know the V-8s too well, so I am just grabbing for straws on that one.
Junior User
Joined: Apr 2003
Posts: 92
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From: Oklahoma
serp belt problem
I had the same problem with my 91 I 6. I found that it was the tensioner. The surface of replacement pulley that i bought was not true. It was sloped out a little. I took the pulley off and turned it over and now it is just fine.
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New User
Joined: Jul 2003
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From: Michigan
serp belt problem
ok belt is on correct way according to the diag. so was the old one. but right out of the tensioner to the A/C it is being thrown off the front on the A/C pulley it is a 6 rib serp....the old one i took off only had 2 ribs left and was being slowly worked off the front also...can i get replacement pulleys or do i have to change the whole tensioner?? how do i figure what is out of line??
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