Question on 4th gen rearend,noise? - PY Online Forums

Father&Son73T/A · #1 12-17-2009, 08:30 PM

My 99 had the rearend replaced by Pontiac through my warrenty at 30k,and I did not thrash the car when purchased with 16k miles on her.
Clunk around slow turns is what it was doing,the Poncho dealer told me it was going.
When they rebuilt it I had them put synthetic fluid in the rear.
However,now at 45k miles,it is clunking/thumping at 1-2 and 2-3 shifts,with fair acceleration.
I've been told by word of mouth do not use synthetic in the rear ends,please tell me a simple changing of the fluid will fix this......
I run M1 XP in the engine,but have also been told it's ok,but dont run syn in the trans or rear end.

disc0monkey · #2 12-18-2009, 06:08 PM

well its really going to depend on which differential you have. i have the gear one so i use synthetic and friction modifier doesnt do anything with these. for the clutch type you should use normal diff fluid and use just enough friction mod so i wont chatter around turns.

after i do i hard run sometimes i get a lot of clicking and such after two hundred miles of driving it really easy it goes away. 42k miles on mine too.

Father&Son73T/A · #3 12-20-2009, 12:45 AM

Quote:

Originally Posted by disc0monkey

well its really going to depend on which differential you have. i have the gear one so i use synthetic and friction modifier doesnt do anything with these. for the clutch type you should use normal diff fluid and use just enough friction mod so i wont chatter around turns.

after i do i hard run sometimes i get a lot of clicking and such after two hundred miles of driving it really easy it goes away. 42k miles on mine too.

Gear one?
I take it was the new rear for the 00's?

disc0monkey · #4 12-20-2009, 09:17 PM

yea i think the gear locking was made by auburn clutch type was eaton. i heard the auburn was better for manuals but im not impressed. the eaton hd in my gto is 100x better. i dont know the years they switched but mine is auburn.(late '00 car, 241 heads, ls6 clutch and 01-02 clutch master/slave)

n20ta2 · #5 12-21-2009, 10:10 AM

Had the same problem on my old 95,switched to 3.73 gears and filled with synthetic.After switching to stock spec gm lube with posi additive it went away.

Father&Son73T/A · #6 12-21-2009, 11:15 AM

Quote:

Originally Posted by n20ta2

Had the same problem on my old 95,switched to 3.73 gears and filled with synthetic.After switching to stock spec gm lube with posi additive it went away.

This is not like the last time when going around a corner slowly and a clunk,but it's doing it from 1st through 3rd gear on medium accelaration,more if you push it,was wondering if it could be the U joints?

I am not driving the car now,it's stored for winters,trying to get a jump on idea's for spring.

n20ta2 · #7 12-21-2009, 05:31 PM

climb under the car and try rotating he driveshaft with the trans in nuetral should be aparent if there toast.

Father&Son73T/A · #8 12-21-2009, 05:47 PM

Quote:

Originally Posted by n20ta2

climb under the car and try rotating he driveshaft with the trans in nuetral should be aparent if there toast.

Thanks,I'll wait till May when it's at least 60 out,and bring my butter and jelly

Father&Son73T/A · #9 12-21-2009, 05:47 PM

Could it be the rear end acting like this and not the u joints?

n20ta2 · #10 12-21-2009, 11:27 PM

could be suspension related as well,might want to look for loose bolts on the torque arm and lower controll arms as the rear end was replaced.Maybe the gm dealership did not torque to specs.

Father&Son73T/A · #11 12-22-2009, 04:07 AM

Quote:

Originally Posted by n20ta2

could be suspension related as well,might want to look for loose bolts on the torque arm and lower controll arms as the rear end was replaced.Maybe the gm dealership did not torque to specs.

Thanks,I'm hoping it's something as simple and easy as this.

disc0monkey · #12 12-22-2009, 06:51 PM

i would put any amount its the rear they suck when they are setup right. its VERY rare to find someone to be dead on when setting up a rear. with these rears with enough torque applied they just flex like crazy and thats the end. it is what it is.

disc0monkey · #13 12-22-2009, 06:53 PM

if its a manual with good tires you have to be a real grandma not to bust it. :/

Father&Son73T/A · #14 12-22-2009, 07:47 PM

It's an auto car,however tires have maybe 5k on them and I was accelerating hard passing someone at about 45 mph and let off (a car in was infront)then nailed it again when I felt a bang not usual to the car,first time this ever happend.

n20ta2 · #15 12-27-2009, 09:47 AM

That should not have broke that rear that easily,I was running low 10's in the quarter with my 7.5 rear for a year with a 3500 stall and 325 drag radials.I was spraying a 175 shot of nitrous off the line and that converter hit violently.It eventualy stripped a few teeth of the pinion but it did work for over 50 passes,I switched to a 9" ford after building a 800hp dart 420.

n20ta2 · #16 01-08-2010, 01:07 PM

I might add that the 7.5 is a junk rear end and weak at best but it should hold up for a while with a stock LS1

Father&Son73T/A · #17 01-08-2010, 07:57 PM

OK,what would you suggest if it is broke.
I mean,if it's the gears again,can't I just replace them with a quality set of gears,for not a gizillion dollars,I mean less than a G?,..installed?
I would just want something to hold up to the stock LS1 again and maybe a 3:73 or 4:10 and still be streetable with an A4....

Old Blue 66 · #18 01-10-2010, 06:31 PM

Quote:

Originally Posted by n20ta2

could be suspension related as well,might want to look for loose bolts on the torque arm and lower controll arms as the rear end was replaced.Maybe the gm dealership did not torque to specs.

First time Im seeing this thread Duane. And this was my first thought was well. If not the problem, Id change the gear fluid and see what others thin about adding a 50/50 mix of Lucas and a stock GM lube.

Although now at all close to the same gears, I had this with my 66 and it went away. If the syn was not the right path to take, the dealer should have known enough to tell you.

n20ta2 · #19 01-10-2010, 11:50 PM

Yeah take a look at the bolts first.If that checks out pop the cover off the diff and try a visual inspection,it should be apparent if its gone.Motive gears are good and I have heard that they are quieter then most replacements,should be able to get out of it for less then 800 installed.A4go with a 3.73 gear, 6 speed 4.10 is best.

Father&Son73T/A · #20 03-21-2010, 06:26 PM

Guess what guys,it was the trans mount,nothing wrong so far with the rear.
And the shop I had look at checked the torsion arm bolts,all fine.
The also showed me on their computer GM DOES requir synthetic fluid as a replacement with the correct posi additive.
My baby is all fine,parent too.
Thanks for the help guys,there's interesting info in this thread regarding the rear ends of these cars.