Light thump heard under accel/deceleration

gray87GT · 05-23-2001, 08:45 AM

Since I installed most everything in my sig I have about 30 miles on it, and I noticed a new noise. When I start to move, or am rolling and hit it or back off there is a light thump from the rear somewhere. It's not a U-joint sound, it's kind of like a pop. I am wondering if it is the subframes. I have FMS subframe connectors and when I installed them they were tight up against that low circular spot in the floor boards, could it be my floorboard popping up and down from flex??? Anybody have any ideas?? Thanks

------------------
87 GT, BBK shorty's, MAC High-Flow H-pipe, ASP pullies, BBK 70mm T.B., Cobra intake, no smog pump, Windsor Jr irons, Comp cams 1.6 rollers, F303 cam, FMS HD water pump, Tri-Ax, FMS subframes, Battle boxes, SSM liftbars, FMS King Cobra clutch, mass-air conversion, 73mm C&L, 24lb injectors, BBK AFPR, 3/8" no EGR spacer,MAC pro-dumps, FMS 3.73's, and other piddly sh*t.

SaleenGTS · 05-23-2001, 09:20 AM

My subframes pop when I hit a coner hard, but not under accel/decel...maybe a busted shock?

------------------
Dustin
89 GT(Saleen Clone) 392 rwhp UNTUNED(TFS Intake, spacer,Heads and #2 cam, BD-11A 9#(only boosting 6???WTF),1.6 rr's,BBK 70mm TB,FMS 70mm MAF,MSD 6BTM,FMS 9mm wires,BBK longtubes and H-Pipe,American Thunder cat back,3.55 lots more...

12.564@118.49 on street tires is my best so far. Still untuned

Mike_W · 05-23-2001, 11:44 AM

My SSM lift bars did that so I took them off. It felt like they were ripping my floor out. Although I heard that if you weld them they dont make that noise anymore.

------------------
90LX, T-5, Vortech V2-SQ, Holley, Twisted Wedge Stage1, X-303

blueneonman1 · 05-24-2001, 02:06 AM

429mustang · 05-25-2001, 01:39 AM

Hey, I think I know what noise your talking about. Does it make a thump sound almost like a quiet backfire somewhere around the rearend? My car usually makes it when I get on it at a low rpm or in 5th gear on the highway. I'm pretty sure it's not the trans mounts, I just had my motor/trans out and made sure everything was tight when I put it back in and it still does it every once and a while. If I get around to it I'll check my driveshaft and shocks, although if it were the shocks I'd almost think it would do it when you push down on the car a few times, and it doesn't. I'm pretty sure it has to be one of the rearend parts, if I find it I'll let you know.

jimberg · 05-25-2001, 02:32 AM

I have a similar thump. The transmission crossmember mounting holes have elongated on the driver side.

------------------
351W 89 Mustang GT Convertible

faststang90 · 05-25-2001, 06:27 AM

whats up i had a noise like that and it was my torque boxs that were the lower arms bolt to the body Had to cut out old ones and weld in southside torque boxes they tie into the sub frames connectors look at your boxs and see if they are missed up

05-23-2001, 08:45 AM	#1
gray87GT Registered Member Join Date: Jan 2001 Location: Minnesota Posts: 177	Light thump heard under accel/deceleration Since I installed most everything in my sig I have about 30 miles on it, and I noticed a new noise. When I start to move, or am rolling and hit it or back off there is a light thump from the rear somewhere. It's not a U-joint sound, it's kind of like a pop. I am wondering if it is the subframes. I have FMS subframe connectors and when I installed them they were tight up against that low circular spot in the floor boards, could it be my floorboard popping up and down from flex??? Anybody have any ideas?? Thanks ------------------ 87 GT, BBK shorty's, MAC High-Flow H-pipe, ASP pullies, BBK 70mm T.B., Cobra intake, no smog pump, Windsor Jr irons, Comp cams 1.6 rollers, F303 cam, FMS HD water pump, Tri-Ax, FMS subframes, Battle boxes, SSM liftbars, FMS King Cobra clutch, mass-air conversion, 73mm C&L, 24lb injectors, BBK AFPR, 3/8" no EGR spacer,MAC pro-dumps, FMS 3.73's, and other piddly sh*t.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
head light problem	crazyi	Windsor Power	5	12-17-2003 06:37 PM
Brake Problem/Warning Light Update with more info	twilightcall	Windsor Power	1	06-06-2003 09:24 AM
Check Engine Light	96GTPRT	Modular Madness	5	05-20-2002 07:48 PM
Emissions related? Check Engine Light	Coupe Devil	Windsor Power	2	05-09-2002 11:49 AM
Dome light will not shut off.	Chris_H	Windsor Power	1	08-30-2001 03:16 PM

05-23-2001, 09:20 AM	#2
SaleenGTS RICE taste like Chicken Join Date: Jun 2000 Location: Edmond, OK Posts: 687	My subframes pop when I hit a coner hard, but not under accel/decel...maybe a busted shock? ------------------ Dustin 89 GT(Saleen Clone) 392 rwhp UNTUNED(TFS Intake, spacer,Heads and #2 cam, BD-11A 9#(only boosting 6???WTF),1.6 rr's,BBK 70mm TB,FMS 70mm MAF,MSD 6BTM,FMS 9mm wires,BBK longtubes and H-Pipe,American Thunder cat back,3.55 lots more... 12.564@118.49 on street tires is my best so far. Still untuned

05-23-2001, 11:44 AM	#3
Mike_W Registered Member Join Date: Apr 2001 Location: Sterling Hgts, MI, U.S. Posts: 64	My SSM lift bars did that so I took them off. It felt like they were ripping my floor out. Although I heard that if you weld them they dont make that noise anymore. ------------------ 90LX, T-5, Vortech V2-SQ, Holley, Twisted Wedge Stage1, X-303

05-24-2001, 02:06 AM	#4
blueneonman1 Registered Member Join Date: Mar 2001 Location: Palm Harbor, FL Posts: 208	Sure it's not the tranny mount? ------------------ Blueneonman - '95 5.0L Mustang GT Convertible \| K&N Custom Cold Air Intake \| FMS 9mm Wires \| Hollow Cats \| Flowmaster 2 Chambers \| BBK Subframes \| 6-pt Rollcage \| 14deg Timing \| King Cobra Clutch \| FMS Adjustable Clutch Cable \| Coolest Neon Lighting on a Mustang EVER! Homepage: http://www16.brinkster.com/blueneonman/ Best time: 14.578 @96.20mph

05-25-2001, 01:39 AM	#5
429mustang Registered Member Join Date: May 2001 Location: westerville, OH USA Posts: 618	Hey, I think I know what noise your talking about. Does it make a thump sound almost like a quiet backfire somewhere around the rearend? My car usually makes it when I get on it at a low rpm or in 5th gear on the highway. I'm pretty sure it's not the trans mounts, I just had my motor/trans out and made sure everything was tight when I put it back in and it still does it every once and a while. If I get around to it I'll check my driveshaft and shocks, although if it were the shocks I'd almost think it would do it when you push down on the car a few times, and it doesn't. I'm pretty sure it has to be one of the rearend parts, if I find it I'll let you know.

05-25-2001, 02:32 AM	#6
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	I have a similar thump. The transmission crossmember mounting holes have elongated on the driver side. ------------------ 351W 89 Mustang GT Convertible

05-25-2001, 06:27 AM	#7
faststang90 Registered Member Join Date: May 2001 Location: baytown,tx,us Posts: 128	whats up i had a noise like that and it was my torque boxs that were the lower arms bolt to the body Had to cut out old ones and weld in southside torque boxes they tie into the sub frames connectors look at your boxs and see if they are missed up