RoadRocket L98

Well my car has been acting up lately and when I launch it hard or light em up I hear (and feel) a loud thumping noise that seems to be coming from the rear of the car. My guess is either a Ujoint or a posi clutch. I do know that it only does one-legged burnouts now and when up on the rack, the rear wheels dont require much effort to turn, but Im not sure if limited slips are supposed to do that or not. Ive also noticed a high-pitched whine from the rear at crusing speeds. Can anyone identify this? Thanks alot!

------------------
'83 Firebird 2.8
'89 Firebird Formula 350
2nd owner, red/grey, t-tops, dual cats, and a 3.27:1 rear
K&N, TB bypass, No MAF screens, CAI, full Accel ignition

Pukka

For starters I'd check/replace your diff fluid. While you're at it check the u-joints....could be the cause of the thump sound but you didn't say anything about vibrations. If all that checks out, your problem is the gears inside the diff

------------------
92 Camaro RS LO3, 5-spd, T-tops
Performance:
SLP 1 3/4" Headers (Coated by Paul Barry Motorsports), Flowmaster Catback Exhaust, Fastchip Performance PROM, Centerforce Dual Friction Clutch, Xact 8mm wires, Open Air Element w/K&N Filter, Z28 Grille w/aftmkt fog lamps
Electronics:
Alpine 8030 Alarm System, Valentine One Radar Detector (How did I ever drive without one?), Pioneer DEH 7450 Head Unit w/6-pack CD changer, Pioneer DEQ 7600 Sound Processor, 2 Kenwood KAC-846 Amps powering 2 12" Pro Red subs, 2 Pioneer 6x9 and 2 MTX 4x6 speakers.
NEXT UP: TBI mods, Edelbrock performer intake

farm-kid/88camaro

From what i've heard a broken tranny mount will cause that type of noise, check it out, its worth a try

3RDGENFRANK

It's probably one of your rear sway bar end links. They rust out and break. I've heard and seen it many times before

------------------
1992 Camaro Z28; Engine:383 w/Ported Edelbrock RPM heads. Lunati Solid Roller Cam 224/232 .502/.502, Fluidampr, Comp Cams 1.5 Roller rockers and lifters, Comp Cams Triple Valvesprings, SVO 30 lb injectors. Holley/Walbro 255 lph in-tank pump, Haltech E6GM DFI, SLP 1 3/4" headers, 4" Mufflex, T56, SLP Clutch, Pro-5.0 Shifter, 4.10 Gear, Auburn Offroad Pro Posi. Super Ram. 17" X 9.5" Ronal FireHawk Rims w/ 275 40ZR17 Bridgestone RE 730's up front and Nitto Drag NT 555R's out back.

Double-Pump This! EFI Rules!

Desert86Roc

My vote is for tranny mount...very common problem.

------------------
Mike Metzler (Desert86Roc)[*] Webmaster: SpeedWorldMotorplex.com[*] Click Here For 86 IROC 305 TPI (406 build in progress) Page

ET's @ 1250 ft[*] 14.28 @ 95.461 mph (uncorrected, NOS, no headers)[*] 15.365 @ 86.785 mph (uncorrected, headers, no NOS)

85f-bird

when my tranny mount broke, i would hear a loud thumping sound, feel it too. Plus there was a whinning sound, but it didn't come from the back, as much as it did from the center console, that's also where the thumping was coming from.

elevario

Ok, I'm really confused. My car does the thumping thing too and makes the car hesitate. How exactly will a trans mount fix this? Isn't a trans mount the thing you mount the transmission on? How would this cause knocking sounds and hesitation? Thanks if anyone can help.

Dana92RS

I don't know about the hesitation, but if indeed you tranny mount is broken, it means your tranny is no longer being held down onto the crossmember. The thumping noise is the tranny lifting up and hitting the underside of your transmission tunnel.

RoadRocket L98

Okay, I can understand how a loose tranny mount would cause the thumping, but the car still does one-legged burnouts and the rear wheels turn without much resistance when up on the rack. Maybe limited slips are supposed to do this?

------------------
'83 Firebird 2.8
'89 Firebird Formula 350
2nd owner, red/grey, t-tops, dual cats, and a 3.27:1 rear
K&N, TB bypass, No MAF screens, CAI, full Accel ignition

vortecfcar

limited slips are NOT supposed to do that. YOU shoudnt be able to turn the tires by hand. Are you sure you have a limited slip? tranny mount is really easy to check, just push up on trans and look to see if rubber is torn.

------------------
91 RS W/carbed 350, Vortec heads, performer rpm, Comp cams Xtreme energy 224/230 duration and .477/.480 lift. BFG Drag radials. 3.42 posi,Corvette servoed 700r4, 3000 stallconverter. Edelbrock TES, 3inch cat, flowmaster with single 2.5 inch exit.
Best time yet to come
12's?? :crossthumbs:

This is a Pic of my car in race trim www.tbns.net/billyjay/camero.jpg

Yes I know how to spell camaro- so dont ask. I didnt make the link

Ed1LE

iTrader: (39)

Don't forget about the rear control arm bushing. If the car has high miles or hard miles, the stock rubber bushings may be worn...this happened on my friends 91 T-bird SuperCoupe.

------------------
'91 Z28 1LE; 355, Sportsman II heads, Edelbrock TPI w/ 58mm TB, Tremec TKO 5-speed, 3.73's & much, much more

'87FAKE-IROC-Z

Yeah, maybe some minor wheel-hop goin on causing the thumping.
My car with an open diff. and stock LCAs wheel-hopped bad, felt like the thing was shaking to pieces.


------------------
'88 RS (originally 2.8)
New 350, .040 over, ported vette L98s, ported stock tpi.
Old 305 injectors & chip
TES headers, 3.73 gears, 700r4.
Best with 2.8-17.4@77mph
Best with 305-15.0@93mph
Best with 356-13.7@101mph
(Damn the 2.8!)

JoelOl75

Could be the aformentioned...

Or bottoming on the bump stops, or a exhaust contacting somewhere.

vortech305

definitly tranny mount had same problem ordered a new one and problem went away with the old mount

RoadRocket L98

Thanks alot for the help guys. I replaced the mount and the noise/bumping went away. Any tips on keeping it from breaking again. It still only spins one wheel though.

------------------
'83 Firebird 2.8
'89 Firebird Formula 350
2nd owner, red/grey, t-tops, dual cats, and a 3.27:1 rear
K&N, TB bypass, No MAF screens, CAI, full Accel ignition

JoelOl75

Use an interlocking poly mount from energy/prothane. The mount could never seperate even if the material gave way.

I blew 3 trans mounts in my weak *** 2.8 and never tore one up in the 5.7? Go figure....

It really is true!?!?