wierd knocking sound in the back

**notfastenuff** · 10-15-2007, 07:05 PM

hi I'm hearing some wierd knocking sounds in the back of my trans am. Do you guys have any idea as to what this may be? How often should we change the rear fluid anyway? All help is appreciated guys. Thanks

**0rion** · 10-15-2007, 09:27 PM

What conditions does it take to get it to knock back there? Any mods or work done back there recently? LCA's will pop if not torqued down correctly, if it sounds just underneath you it could be a tranny mount also. Any vibration in the car ever? Any other sounds besides the knock?
I change my rearend fluid at the beginning of every year. I'd have to look it up as to what the stock recommendations are.

**notfastenuff** · 10-15-2007, 09:43 PM

Originally Posted by 0rion

What conditions does it take to get it to knock back there? Any mods or work done back there recently? LCA's will pop if not torqued down correctly, if it sounds just underneath you it could be a tranny mount also. Any vibration in the car ever? Any other sounds besides the knock?
I change my rearend fluid at the beginning of every year. I'd have to look it up as to what the stock recommendations are.

thank you man, PLs let me know the stock recommendations when you can. My car is stock as can be 57k on the clock and it makes just a knocking sound when at low rpms probably 1000 - 2000? Bout 0-35 mph at first gear. Mine is an a4. Thanks

**0rion** · 10-15-2007, 09:49 PM

does the noise definitely come from the back of the car? Does it also sound like the rear or could it be a U-joint or something like that? LCA's will pop on take off and mine used to pop going over bumps when my sub frames were installed and the guy didn't torque the LCA's tight enough but it was side specific and you could hear it in the body.

rear differential fluid
Checked every 15k or 1 year whichever comes first
Changed every 30k or 2 years whichever comes first

**notfastenuff** · 10-15-2007, 10:04 PM

so it couldn't be a change needed in rear differntial fluid huh? It definitely sounds like its coming from the back. The passenger side to be exact. Do you know where i should take my car? Im not very knowledgable of vehicles just yet. Sorry , im just as new as they come. But the knocking in The back is really starting to get me worried and annoyed. I just hope something big isnt brewing back there.

**0rion** · 10-15-2007, 10:14 PM

man, it could be a whole slew of things from very minor to pretty major. Could just be the exhaust hitting your panhard bar back there. You're a mechanics wet dream.

Don't ever tell them you're not knowledgable. At least have some ideas of what might be wrong before you go in.
I would strongly suggest trying to find someone from the site to take a look at your car to give you an idea of what's wrong before taking it somewhere. Post up in the Western section and see if there's anyone that'll take a look at it for you.
Is it a low sounding knock or a higher "empty metal pipe" kinda sound? Is it speed dependant meaning does it increase and decrease with speed?

**notfastenuff** · 10-15-2007, 10:34 PM

yes it is speed dependabt! It increases and decreases with speed!! Its a low sound. And I feel like it has nothing to do with the exhaust. I'm not sure but I'm just saying.

**0rion** · 10-15-2007, 10:37 PM

speed dependent is not good. Doesn't mean the worse. Could still be something simple like a U-joint although those tend to "ping" or "clink" on take off when going bad. Might also be a tooth busted on the ring gear which would be considerably more expensive. Might be a wheel bearing also. Just some ideas.

**notfastenuff** · 10-15-2007, 10:37 PM

it doesnt sound like an empty metal pipe.

**0rion** · 10-15-2007, 10:38 PM

change your fluid and pull the cover and see if there's metal in there.

**notfastenuff** · 10-15-2007, 10:40 PM

oh wow. Sounds like i might have to drop some serious cash. Man!! What do you suspect may have caused this? Is this a pretty common prone problem to f bodies?

**0rion** · 10-15-2007, 10:48 PM

the stock rear is a pretty weak rear. Like I said. Don't expect the worse until you can have someone you trust to look at it. It's hard to help diagnose this stuff through the board.

**notfastenuff** · 10-15-2007, 11:17 PM

right. Well I'll see what I can do tomorrow and let you know what the low down is. Thanks man!

**sic2001** · 10-16-2007, 03:41 AM

Im in huntington beach, kinda far away but I have alot of tools and know the cars pretty well. my twin brother has a TA as well so we can have a look if ya bring it out here. Let us know what happens when ya pull the rear cover.

**notfastenuff** · 10-16-2007, 04:18 AM

I'm currently in lancaster California
(still in l.a. County) I appreciate your offer. I'll let you know when I'm around the areA. Maybe during my next trip to la which I do about once a week. Thanks

**notfastenuff** · 10-19-2007, 01:02 PM

okay I just got back from good year and this cool guy who has friends with ls1 cars and who was really into the f body scene went on a free test drive with me and 5 seconds in to it he heard and knew what the problem was. U joint! This guy was an expert!he really knew his f body stuff. He really seemed nice and was really trying to help a fellow enthusiast out, so I basically didnt feel like he was trying to rip me off. He spoke to his manager and said that $200 oughta take care of it. So I said I'd come back later, so I can talk to you guys first. Do you think that $200 is fair? Is good year the way to go? Thanks for all your help guys. Really appreciate all your continuing help. Again, I'm still in my early stage of being a car nut, so I'm not quite up to par when it comes to u joints etc. So I really appreciate all your help. Im learning. Thanks

**0rion** · 10-19-2007, 01:39 PM

There is no way I'd pay $200 to have a U-joint repaired. Do you own any tools at all? There are only a few bolts that have to be taken off and the u-joint comes right out and the new one in. I think they're 10mm bolts. Not kidding, you can do a U-joint by yourself in less than a half hour even it's your first time doing it. I'm leaving town right now until Sunday. If someone else doesn't chime in here and help you I'll do a detailed write up on changing the u-joint. My wife could do it.

edit:
If it's the front u-joint you'll probably have to pay someone $20 to press it out but the rear is cake. I was just assuming the rear joint.

**notfastenuff** · 10-19-2007, 01:44 PM

Sweet man! I'll hold off till you get back. And attempt to do it myself. Thanks and Enjoy your weekend! How much would you pay for a u joint job though? What would you think is fair?

**0rion** · 10-19-2007, 01:48 PM

the U-joint is ~$15 here from advanced auto. Let's say 1 hour labor @$60 so $75-$85 would seem about right. It's so easy though you can do it yourself for $15.