clunking noise when letting off throttle

mainejohn · August 23rd, 2010, 07:08 AM

Seeing if anyone might know what would be causing a clunking noise when i let off the throttle in my 92 5speed? It seems to be louder in or more obvious in 5 gear. i can feel it under my butt. could it be transmission mounts getting worn? i didn't think it is ujoint becuase i dont here any rotation noise.

orangestang42 · August 23rd, 2010, 07:56 AM

this can be many things, but for starters i would check these things out first

*excessive play in differential
*tranny mount, causes tranny to hit underside of the car
*bad u joints
*bad motor mounts

i actually had a firebird that had bad motor mounts and when you would get on the has a little bit the motor would lift up slightly and then when you let of the gas the motor would fall back down and made kind of a thud noise. The tranny mounts were also common to go bad on the firebirds. Start with those first and see what you come up with, hopefully its something simple, but your looking at around $500 for a rear end rebuild it thats the problem, but is there any whining noise at all from the rear? usually when the backlash in the rear starts to go out of wack the rear makes a distinctive wine sound. im leaning more towards u joints though, u dont really have to hear any rotation noise for it to be u joints. What might be happening is that when you get bad u joints there ends up being more play in them and when you let off the gas the driveshaft loses velocity and abruptly slows down and if the u joints arent tight it will make that noise. if it is u joints, that might be a good excuse to throw on a nice aluminum driveshaft, i bought one for my firebird completely assembled ready to bolt in for a little over $100...let us know what u find out

mainejohn · August 23rd, 2010, 08:29 AM

there is no whinning, when i'am running at higher rpm's i dont hear it, i hear it when iam 2000 or less and left off the throttle i feel it midway in the car under mt butt. thats why i was thinking tranny mount. whats the best way to test a tranny or motor mount? i will check the ujoints also.

flyin ryan · August 23rd, 2010, 09:30 AM

I had the same deal before in a fox... it turned out that the upper control arm bushings were shot in the passenger side one. I'd crawl under and check them out good with a flash light for any cracks or any play

mainejohn · August 23rd, 2010, 02:12 PM

okay, that makes some sense, i will check that also.

Dap1991 · August 23rd, 2010, 02:48 PM

Did you remove a wheel recently, seems kinda dumb but once i removed my wheel and replaced it and about a week later i heard a clunking noise, turns out my lug nuts loosened so the rim would bounce off them when i was off the throttle or breaks. Just a thought

mainejohn · August 23rd, 2010, 04:12 PM

well i crawled underneth the car and checked everything out. the you joints seemed okay, tranny mount it looked okay, i didnt notice anything different on the mounts. then i checked the control arms and the only thing i could see was that the bushings were starting to dry rot and crack. do you think with them starting to dry rot it would cause the cluncking noise? do they sell just the bushings? money is tight so i really dont want have replace the whole control arms.

orangestang42 · August 23rd, 2010, 05:03 PM

you can replace just the bushings...im leaning more towards driveline though...because it does it when you are letting off the gas

mainejohn · August 23rd, 2010, 06:09 PM

i guess not sure what to do. it makes the clunk when there isnt much of load on it. i will be cruising around 55 @ 1800 rpms and let off the gas and i can feel a soft clunk under my butt. i crawled under and twisted the drive shaft back and forth and couldn't feel any u joint slop. i did push on the shaft were it enters the tranny and there is very little play. Is that normal? is there any visuale things to look for on the tranny mount besides an obvious break?

autoarc94 · August 23rd, 2010, 06:42 PM

put a wrench on the bolts, just cuz you can't turn them by finger doesn't mean the aren't loose, the looser the are the more the tranny will sag putting pressure on the bolts still! i ran into the anyways, just another idea

(tranny/engine mount bolts)

mainejohn · August 23rd, 2010, 06:48 PM

okay will try right now. will let u know

mainejohn · August 23rd, 2010, 07:35 PM

okay i just checked all bolts and nuts seem to be tight. i took the drive shaft out and ujoints seem tight. so what the HELL else could it be?

orangestang42 · August 23rd, 2010, 08:18 PM

i forgot to suggest this if you havent checked it already...there are bolts that secure the driveshaft to the differential near the back, i do believe there are 4 of them. i hada clunk too a while back and then i looked under there and one was missing and 2 of them were loose, so check them out, again disregard if you have already...

mainejohn · August 23rd, 2010, 08:28 PM

yes bolts were tight when i took the drive shaft off!! i cant be the only one to ever hear this problem. and my car only has 85000 easy miles.

Chris951 · August 23rd, 2010, 10:52 PM

My car did this exact same thing! I never figured it out though. I did notice that my bellhousing had a nice crack going across the side of it. dont know if the thud caused it. i sold the car but i always wondered what it was

mainejohn · August 24th, 2010, 07:11 AM

well thats a comforting thought!! I hope its not my bell housing!

mainejohn · August 24th, 2010, 01:58 PM

just took the ujoints out and seem to be just like new!!! any other suggestions?

brody904 · September 1st, 2010, 07:15 PM

Originally Posted by mainejohn

just took the ujoints out and seem to be just like new!!! any other suggestions?

Could be the rear end? That would be my guess. I had a really bad clunking in my rear end of my 2000 GT and just had everything in it replaced this past week. Carrier berrings, clutches, gears, everything. There was no whining whatsoever, only clunking.
I'm not familiar with the fox bodies but if they have posi traction diffs then my guess would be the clutches in there are bad. No telling till it is apart though...

nolife · September 1st, 2010, 07:46 PM

Originally Posted by mainejohn

Seeing if anyone might know what would be causing a clunking noise when i let off the throttle in my 92 5speed? It seems to be louder in or more obvious in 5 gear. i can feel it under my butt. could it be transmission mounts getting worn? i didn't think it is ujoint becuase i dont here any rotation noise.

Based on what you have already checked, is this a new noise? All three of my Mustangs make a slight clunking on and off the gas in 5th. My 91 did it since it was brand new, the other two since at least I've owned them. I just assumed that was normal and a just a combination of play in the trans and rear

ryanw · September 1st, 2010, 08:59 PM

I have had a nosie problem where a bracket on my sway bar broke

August 23rd, 2010, 07:08 AM	#1
mainejohn Regular 1992 GT Join Date: Oct 2009 Location: MAINE Posts: 60 iTrader: 0 reviews	clunking noise when letting off throttle Seeing if anyone might know what would be causing a clunking noise when i let off the throttle in my 92 5speed? It seems to be louder in or more obvious in 5 gear. i can feel it under my butt. could it be transmission mounts getting worn? i didn't think it is ujoint becuase i dont here any rotation noise.

August 23rd, 2010, 07:56 AM	#2
orangestang42 Enthusiast 1995 Mustang GT Join Date: May 2010 Location: Port Charlotte, Florida Posts: 816 iTrader: 0 reviews	this can be many things, but for starters i would check these things out first excessive play in differential tranny mount, causes tranny to hit underside of the car bad u joints bad motor mounts i actually had a firebird that had bad motor mounts and when you would get on the has a little bit the motor would lift up slightly and then when you let of the gas the motor would fall back down and made kind of a thud noise. The tranny mounts were also common to go bad on the firebirds. Start with those first and see what you come up with, hopefully its something simple, but your looking at around $500 for a rear end rebuild it thats the problem, but is there any whining noise at all from the rear? usually when the backlash in the rear starts to go out of wack the rear makes a distinctive wine sound. im leaning more towards u joints though, u dont really have to hear any rotation noise for it to be u joints. What might be happening is that when you get bad u joints there ends up being more play in them and when you let off the gas the driveshaft loses velocity and abruptly slows down and if the u joints arent tight it will make that noise. if it is u joints, that might be a good excuse to throw on a nice aluminum driveshaft, i bought one for my firebird completely assembled ready to bolt in for a little over $100...let us know what u find out Last edited by orangestang42; August 23rd, 2010 at 07:59 AM.

August 23rd, 2010, 06:42 PM	#10
autoarc94 Newbie 1994 mustang gt vert n/a Join Date: Jul 2010 Location: soCal Posts: 34 iTrader: 0 reviews	put a wrench on the bolts, just cuz you can't turn them by finger doesn't mean the aren't loose, the looser the are the more the tranny will sag putting pressure on the bolts still! i ran into the anyways, just another idea (tranny/engine mount bolts) Last edited by autoarc94; August 23rd, 2010 at 06:42 PM. Reason: left out

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August 23rd, 2010, 08:29 AM	#3
mainejohn Regular 1992 GT Join Date: Oct 2009 Location: MAINE Posts: 60 iTrader: 0 reviews	there is no whinning, when i'am running at higher rpm's i dont hear it, i hear it when iam 2000 or less and left off the throttle i feel it midway in the car under mt butt. thats why i was thinking tranny mount. whats the best way to test a tranny or motor mount? i will check the ujoints also.

August 23rd, 2010, 09:30 AM	#4
flyin ryan Banned Join Date: Jun 2008 Posts: 3,387 iTrader: 0 reviews	I had the same deal before in a fox... it turned out that the upper control arm bushings were shot in the passenger side one. I'd crawl under and check them out good with a flash light for any cracks or any play

August 23rd, 2010, 02:12 PM	#5
mainejohn Regular 1992 GT Join Date: Oct 2009 Location: MAINE Posts: 60 iTrader: 0 reviews	okay, that makes some sense, i will check that also.

August 23rd, 2010, 02:48 PM	#6
Dap1991 Hardcore Enthusiast 91 GT 90 LX 5.0 Join Date: Aug 2009 Location: youngstown, ohio Posts: 1,025 iTrader: 0 reviews	Did you remove a wheel recently, seems kinda dumb but once i removed my wheel and replaced it and about a week later i heard a clunking noise, turns out my lug nuts loosened so the rim would bounce off them when i was off the throttle or breaks. Just a thought

August 23rd, 2010, 04:12 PM	#7
mainejohn Regular 1992 GT Join Date: Oct 2009 Location: MAINE Posts: 60 iTrader: 0 reviews	well i crawled underneth the car and checked everything out. the you joints seemed okay, tranny mount it looked okay, i didnt notice anything different on the mounts. then i checked the control arms and the only thing i could see was that the bushings were starting to dry rot and crack. do you think with them starting to dry rot it would cause the cluncking noise? do they sell just the bushings? money is tight so i really dont want have replace the whole control arms.

August 23rd, 2010, 05:03 PM	#8
orangestang42 Enthusiast 1995 Mustang GT Join Date: May 2010 Location: Port Charlotte, Florida Posts: 816 iTrader: 0 reviews	you can replace just the bushings...im leaning more towards driveline though...because it does it when you are letting off the gas

August 23rd, 2010, 06:09 PM	#9
mainejohn Regular 1992 GT Join Date: Oct 2009 Location: MAINE Posts: 60 iTrader: 0 reviews	i guess not sure what to do. it makes the clunk when there isnt much of load on it. i will be cruising around 55 @ 1800 rpms and let off the gas and i can feel a soft clunk under my butt. i crawled under and twisted the drive shaft back and forth and couldn't feel any u joint slop. i did push on the shaft were it enters the tranny and there is very little play. Is that normal? is there any visuale things to look for on the tranny mount besides an obvious break?

August 23rd, 2010, 06:48 PM	#11
mainejohn Regular 1992 GT Join Date: Oct 2009 Location: MAINE Posts: 60 iTrader: 0 reviews	okay will try right now. will let u know

August 23rd, 2010, 07:35 PM	#12
mainejohn Regular 1992 GT Join Date: Oct 2009 Location: MAINE Posts: 60 iTrader: 0 reviews	okay i just checked all bolts and nuts seem to be tight. i took the drive shaft out and ujoints seem tight. so what the HELL else could it be?

August 23rd, 2010, 08:18 PM	#13
orangestang42 Enthusiast 1995 Mustang GT Join Date: May 2010 Location: Port Charlotte, Florida Posts: 816 iTrader: 0 reviews	i forgot to suggest this if you havent checked it already...there are bolts that secure the driveshaft to the differential near the back, i do believe there are 4 of them. i hada clunk too a while back and then i looked under there and one was missing and 2 of them were loose, so check them out, again disregard if you have already...

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August 23rd, 2010, 08:28 PM	#14
mainejohn Regular 1992 GT Join Date: Oct 2009 Location: MAINE Posts: 60 iTrader: 0 reviews	yes bolts were tight when i took the drive shaft off!! i cant be the only one to ever hear this problem. and my car only has 85000 easy miles.

August 23rd, 2010, 10:52 PM	#15
Chris951 Hardcore Enthusiast 1991 mustang 5.0 Join Date: Aug 2007 Location: Mesa, AZ Posts: 1,938 iTrader: 0 reviews	My car did this exact same thing! I never figured it out though. I did notice that my bellhousing had a nice crack going across the side of it. dont know if the thud caused it. i sold the car but i always wondered what it was

August 24th, 2010, 07:11 AM	#16
mainejohn Regular 1992 GT Join Date: Oct 2009 Location: MAINE Posts: 60 iTrader: 0 reviews	well thats a comforting thought!! I hope its not my bell housing!

August 24th, 2010, 01:58 PM	#17
mainejohn Regular 1992 GT Join Date: Oct 2009 Location: MAINE Posts: 60 iTrader: 0 reviews	just took the ujoints out and seem to be just like new!!! any other suggestions?

September 1st, 2010, 08:59 PM	#20
ryanw I Post Entirely Way Too Much 1991 Ford Mustang GT Join Date: May 2007 Location: San Diego, California Posts: 6,061 iTrader: 0 reviews	I have had a nosie problem where a bracket on my sway bar broke

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