Whenever I push the gas pedal to the floor at a dead stop I hear a single, loud *clunk* sound coming from the rear of the car. I have no idea what it could be. Drivetrain is stock with 700R4 automatic and 10 bolt rear end. If I am at any speed over 10mph then it won't make the sound. Any ideas or suggestions?

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1986 Iroc Z 305
3.23 posi-rear
ported mass-air
custom ram-air
removed air pump, converter, straight pipe no muffler
0-60 5.5 sec
1/4 mile at 102mph
top speed 160mph (racing a mustang)
est 285hp
fiberglass hood
$2000 Alpine stereo hit 135 in spl comp.

 

Dude, the only thing I can think off is check your U-Joint, My friends firebird had the same prob, we changed U joints and it was fine, give that a shot.

Nate

 

trans mount.

 

Could also be a link bolt on the rear sway bar is busted...

 

All trans mount.


19.95 from summit and it will never break again.

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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

Yeah get a poly trans mount

 

If you're replacing U-joints, go ahead and do both ends at the same time. It's a good safety measure if you don't know how old or what condition the joints are in. Ask some guys what breaking a u-joint at highway speed is like!

 

Has anybody mentioned the trans mount yet?

Those things are fragile... If I wanted to, I could break one the first time I took off after replacing it even when my car still had the 305 in it.

Get the Energy Suspension one and never have to worry about it again.

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"So many Mustangs, so little time..."
ICON Motorsports

 

it's definitely dangerous. i don't think this could happen on a third gen but once i saw a toyota previa van that had broken a u-joint on the freeway. the drive shaft spun around and ripped a hole in the gas tank!!! one little spark from that driveshaft and that van would have been TOAST.



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Dan
1990 3.1L RS
80 Series Flowmaster
It's fast(er than a 3 cyl metro)

 

no all of you guys are wrong. Its the trans mount

 

when i was in high school i had a 1972 cutlass 442 with 455 rocket in it. i was going down the x way at a how do i say this umm at a law breaking speed put it that way and my front u joint went out!! posted it into the road turned me all the way around bout 4 or 5 times came to a stop in the median on my side.. not any fun broken arm, broke ribs and cuts and scrapes. fix the u joints!!!! just a little something from some one who did it!! wish i had pix of that car after wards never even thought bout it!! live and learn all over trying to catch up to some girls who flashed me and buddy!!!


like my old man said **** or tires they both cost a lot of money!

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1988 firebird ws6 formula350tpi msd 6al box blaster 3 coil accel 8.8 race wires hooker shorty headers hooker cat back system pro shift light a pillar gauge pod and water temp and air/fuel ratio gauges autometer oil pressure gauge b&m mega console shifter, march underdrive pullies, tpis airfoil cvr high torque starter (love it)
best 1/4 mile run of 14.44@ 96.53
this run is before the new exhaust system

 

that clunk is the transmission mount.. i have the same problem in my car, just broke it, haven't changed it yet

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Webmaster: www.IROC-Z.org

 

Change or at least take a look at the torque arm mount as well, I just had mine replaced and the noise went away. The tranny mount gets a lifetime warranty at any parts store the price for the mount is like $7. The torque arm mount is hard to find at an auto parts store I had to get mine at the pontiac dealership after the moron told me to call a chevy dealership because they only sold parts for pontiacs...duh! anyway I bought the torque arm mount there for $20 or so

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88 IROC-Z,L98 350 TPI, 700R-4 Tranny 2.77, K&N Filters, 126K Miles runs great.

 

I saw a frt u joint go on a 72 nova making a 11 sec pass. Hit the ground bounced back up through the floor shot the yoke through the roof. Missed the guys elbow by inches. Man I should get a loop....

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87z 383,afr 190's, crane hyd roller(224/230-.509/.528,112 sep),Ported and polished mini ram, 30lb inj, 3.42 gears, strange 12 bolt, tremec 5spd, , 1,3/4" slp headers.
"Just remember children, no man can beat you once youv'e found the cliterous." 'chef'