Need help diagnosing some engine & chassis noises
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Laughing Gas
Joined: Feb 2015
Posts: 765
Likes: 1
Need help diagnosing some engine & chassis noises
1991 Ford F150
5.0 V8
Auto / 2WD
Single cab/short bed
I'll start with the engine. On a cold start up after the engine revs down to normal idle, i hear what sounds like a very light knock. I don't know how to explain it other than it sounds kind of like a diesel engine does ... Seems to quiet, if not disappear after it reaches operating temperature. It doesn't make a lot of excessive vibration when cold, but after running it for awhile the engine seems to shake a little more than seems normal. Drives/shifts ok.
As for the chassis noises, there are two I'd like to share: One is a popping noise that occurs during a low speed, sharp turn either left or right. Only happens once during the turn, almost sounds like a weight transfer of some kind. I don't think it's the front bearings, they have less than 15,000 miles on them since I last replaced and greased them.
The other is a similar noise that occurs during braking, between 5 and 0 mph. I think it may be the radius arm bushings but I would love any other suggestions as to what it might be.
Thanks, guys!
5.0 V8
Auto / 2WD
Single cab/short bed
I'll start with the engine. On a cold start up after the engine revs down to normal idle, i hear what sounds like a very light knock. I don't know how to explain it other than it sounds kind of like a diesel engine does ... Seems to quiet, if not disappear after it reaches operating temperature. It doesn't make a lot of excessive vibration when cold, but after running it for awhile the engine seems to shake a little more than seems normal. Drives/shifts ok.
As for the chassis noises, there are two I'd like to share: One is a popping noise that occurs during a low speed, sharp turn either left or right. Only happens once during the turn, almost sounds like a weight transfer of some kind. I don't think it's the front bearings, they have less than 15,000 miles on them since I last replaced and greased them.
The other is a similar noise that occurs during braking, between 5 and 0 mph. I think it may be the radius arm bushings but I would love any other suggestions as to what it might be.
Thanks, guys!
Postmaster
Joined: Nov 2011
Posts: 3,533
Likes: 17
From: SW Florida
Does the tapping last just a few seconds or does it stick around for a few minutes? If it's just a few seconds then it could be your hydraulic lifters have bled down overnight. And if it stays for a few minutes or more it's probably just piston slap as the motor gets some wear on it. How many miles and what oil weight you running?
Suspension noise could be your sway bar bushings, I'd start by looking there and at the rest of the bushings as well. Don't forget the axle pivot bushings.
Suspension noise could be your sway bar bushings, I'd start by looking there and at the rest of the bushings as well. Don't forget the axle pivot bushings.
Thread Starter
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Laughing Gas
Joined: Feb 2015
Posts: 765
Likes: 1
Does the tapping last just a few seconds or does it stick around for a few minutes? If it's just a few seconds then it could be your hydraulic lifters have bled down overnight. And if it stays for a few minutes or more it's probably just piston slap as the motor gets some wear on it. How many miles and what oil weight you running?
EDIT: The frequency is about 6-8 times a second. Again, it does not feel like it shakes the engine when cold. But the engine does shake a little more when warm, but the noise is almost completely gone.
I have rear sway bars but not in the front. I added some from a PNP donor to the rear but I haven't gotten around to doing the front yet.
And when you say axle pivot bushings, are you talking about the ones where the I-beams join to the frame by the K member?
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
Another recent thread on a similar topic: https://www.ford-trucks.com/forums/1...le-repair.html
Postmaster
Joined: Nov 2011
Posts: 3,533
Likes: 17
From: SW Florida
As long as the vibration is not severe, I wouldn't worry about it. Remember once the engine warms up the computer will lower the idle speed and it might just be that with your particular truck the warm idle RPM happens to cause a little more shake than the faster cold idle RPM. Mine shakes too, so did every other Ford I've owned. I actually like it.
Thanks rla! 
I'll answer for dixie...Yes!
Another recent thread on a similar topic: https://www.ford-trucks.com/forums/1...le-repair.html
Another recent thread on a similar topic: https://www.ford-trucks.com/forums/1...le-repair.html
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jd460
1987 - 1996 F150 & Larger F-Series Trucks
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