How to fix thunk in lower control arm - Prothane bushing
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Cruising
Joined: Sep 2014
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How to fix thunk in lower control arm - Prothane bushing
I installed Prothane bushings in the control arms back in 2011. Starting this season (2017) I have a thunk sound on braking coming from the lower control arm bushing.
With the wheel off, I can shift the control arm up and down with a screwdriver by about 1/8".
Yesterday, I removed the control arm and noted the metal sleeves could not be turned easily inside the bushings. I took the sleeves out, cleaned and regreased with lithium grease then re-installed. I tightened the bolts as much as I could without breaking the wrench. The thunk went away for about 5 miles, then came back.
Any idea how to solve this problem? I could try to replace the bushings but they look OK so I doubt that would make any difference. They sell replacement bolts on ebay that look a little wider in the middle. These might make for less movement. Seems like the stock bolt fits too loosely inside the aftermarket bushing sleeve.
With the wheel off, I can shift the control arm up and down with a screwdriver by about 1/8".
Yesterday, I removed the control arm and noted the metal sleeves could not be turned easily inside the bushings. I took the sleeves out, cleaned and regreased with lithium grease then re-installed. I tightened the bolts as much as I could without breaking the wrench. The thunk went away for about 5 miles, then came back.
Any idea how to solve this problem? I could try to replace the bushings but they look OK so I doubt that would make any difference. They sell replacement bolts on ebay that look a little wider in the middle. These might make for less movement. Seems like the stock bolt fits too loosely inside the aftermarket bushing sleeve.
Thread Starter
Cruising
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Melting Slicks
Joined: Dec 2008
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From: Mystic CT
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Do you have a dial caliper to measure the ID of the sleeve and the OD of the bolt ? I would do so and then call Prothane to see if there was an inadvertent mismatch of parts. That seems like a lot of play.
Measure the parts and post the dimensions up to share. There might be someone on the forum that has a set not yet installed that they could compare the measurements to.
If you don't have a dial caliper, a cheap a** Harbor Freight one would be close enough but you would be better off to have a better grade one in your tool box.
I have had a set for 40 yrs that I purchased from Sears. Of course they were not made by Sears, but simply sold under the Craftsman name. They have been as good as any I encountered when I worked doing precision machine work years ago when I was younger.
http://www.sears.com/tools-layout-me...and&sbv=Fowler
Measure the parts and post the dimensions up to share. There might be someone on the forum that has a set not yet installed that they could compare the measurements to.
If you don't have a dial caliper, a cheap a** Harbor Freight one would be close enough but you would be better off to have a better grade one in your tool box.
I have had a set for 40 yrs that I purchased from Sears. Of course they were not made by Sears, but simply sold under the Craftsman name. They have been as good as any I encountered when I worked doing precision machine work years ago when I was younger.
http://www.sears.com/tools-layout-me...and&sbv=Fowler
Last edited by drcook; Oct 30, 2017 at 11:17 AM.
Melting Slicks
Joined: Jul 2008
Posts: 2,269
Likes: 142
From: Ottawa Ontario
Are you detecting the thunk in just one side or both? Do both sides have the same movement? If both sides have the same movement, maybe the thunk you feel is actually a lower ball joint going bad.
Thread Starter
Cruising
Joined: Sep 2014
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I threw out the original bushings and sleeves back in 2011 so I can't say how the original GM sleeves fit the bolts. These are original GM bolts with aftermarket bushings and sleeves from Prothane. The original GM bolts fit the GM frame snugly.
Thread Starter
Cruising
Joined: Sep 2014
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Just one side. I replaced the upper and lower ball joints on that side. The old ball joints were fine, but it was my first guess at the cause of the noise.
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Thread Starter
Cruising
Joined: Sep 2014
Posts: 11
Likes: 0
Do you have a dial caliper to measure the ID of the sleeve and the OD of the bolt ? I would do so and then call Prothane to see if there was an inadvertent mismatch of parts. That seems like a lot of play.
Measure the parts and post the dimensions up to share. There might be someone on the forum that has a set not yet installed that they could compare the measurements to.
If you don't have a dial caliper, a cheap a** Harbor Freight one would be close enough but you would be better off to have a better grade one in your tool box.
I have had a set for 40 yrs that I purchased from Sears. Of course they were not made by Sears, but simply sold under the Craftsman name. They have been as good as any I encountered when I worked doing precision machine work years ago when I was younger.
http://www.sears.com/tools-layout-me...and&sbv=Fowler
Measure the parts and post the dimensions up to share. There might be someone on the forum that has a set not yet installed that they could compare the measurements to.
If you don't have a dial caliper, a cheap a** Harbor Freight one would be close enough but you would be better off to have a better grade one in your tool box.
I have had a set for 40 yrs that I purchased from Sears. Of course they were not made by Sears, but simply sold under the Craftsman name. They have been as good as any I encountered when I worked doing precision machine work years ago when I was younger.
http://www.sears.com/tools-layout-me...and&sbv=Fowler