Opinions needed on my rear end

marcar1993

marcar1993

G-Body Guru
Aug 31, 2007
655
96
28
New Jersey
#1
Exactly as the title states, lol. I have an 8.8 in my car with some vibration issues. I'm honestly sick of dealing with it.
I was supposed to be picking up a 4.10 posi 8.5 last week, however while it does have 4.10 gears, its an open diff! So now I am kinda stuck. I planned to just throw it in and drive it, but I want the posi. So either I drop $400 on a 28 spline carrier then spend more later when I upgrade axles, or just jump for the 30 spline and then order axles, and get the housing cut for 9" ends. The issue is, do I want to drop that much cash into an 8.5? Is my money better spent on a quick performance 9" which already has bolt in axles, upgraded to a new center sections, ect ect for about $2500? What would I be looking at cost wise to upgrade my 8.5 to the level of the 9"? What is the difference in the power level of each rear? Which route should I go? I just want a rear that bolts in with 100% stock stuff and will hold up do some clutch dumps on slicks at the track hopefully into the 10's if I ever get there. (Right now its a high 12 second car at ~4000lbs).
I'm sick of doing it over and over again too!

Thanks guys!
 
pontiacgp

pontiacgp

Canadian Prime Minister
Mar 31, 2006
22,898
3,877
113
Kitchener, Ontario
#2
I would put the rear up on jackstands and run the car at the speed the vibration shows up and you should be able to see what is causing the vibration. It could be slightly bent ale or rim
 
marcar1993

marcar1993

G-Body Guru
Aug 31, 2007
655
96
28
New Jersey
#3
It has been a LONG time issue and I have done so much to check the vibe out. I think it could be a bearing in the rear at this point. I have set pinion angle to all different positions with little to no change, swapped axles, many different wheels, including sets that run true on other cars, a brand new driveshaft. It is something in the rear, and it just has driven me to my wits end.
 
ed1948

ed1948

Royal Smart Person
Aug 6, 2016
1,117
833
113
Toronto
#4
I've always wondered about testing for rear vibration - would the axle, being supported by axle stands, not show any vibration well due to being solidly supported? On the other hand, letting the springs/shocks hold it, would alter the driveline angles causing vibration?/
 
vanrah

vanrah

G-Body Guru
Apr 16, 2013
668
559
93
Near Afton, Wisconsin
#5
Greetings MarCar & all; I go around giving free advice & no takes it. Ya get what ya pay for! Looking for hidden problem & some hide better than others. When ya say ya got an 8.8, I'm just not sure if you're referring to a Ford (my best guess), a 8.875" GM 12 bolt, 8.625 (?) or some other unit I'm not familiar with? My first question is did ya get it out of a wreak & the housing is got slight mis alignment? Next who welded up the control arm mounts, & how the hell do you check them without a fixture? You have obviously checked drive shaft balance & angle? Have ya checked drum-rotor balance? Then ya ask the question, what should I do for the future? Ten guys will give ya 11 opinions! Anyway being that I'm not much of a drag racer as I only go once about every 3 years & I like to Auto-X also. I'm more concerned with Unsprung weight as most of my driving is on the street. If you're going drag racing a bunch, how can ya not have a 9" Ford, inexpensive parts & great availability? But I have read that the Ford 8.8" is nearly as bullet proof as the famed 9" unit & a bit lighter saving some unsprung weight. We just put one (8.8 F) in my buddies 1950 Chevy with disc brakes & I gotta say it seems to be a very well packaged unit assembly. But then we won't be dropin' the clutch at 5000 RRR's with slicks either. So to sum up my BS for free, if that is a Ford 8.8 I'd try to fix it by sending it out to a well equipped shop. Good Luck Ole' Bob.
Ps: I attached a picture of my 8.5 GM unit with gussets, 20 years of heavy use! Some would say abuse?
 

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565bbchevy

565bbchevy

Geezer
Aug 8, 2011
5,362
2,113
113
Michigan
#6
I would sell them both and get a bolt in 9".
 
DRIVEN

DRIVEN

Comic Book Super Hero
Apr 25, 2009
4,664
1,696
113
Owyhee County
#7
Opinion on your rearend? I think it makes your jeans look fat. :D
 
joesregalproject

joesregalproject

Royal Smart Person
Nov 4, 2012
2,198
715
113
Pittsburgh, PA
#8
The last time I gave someone an opinion on their rear end, she smacked me across the face :mrgreen:
 
motorheadmike

motorheadmike

Comic Book Super Hero
Nov 18, 2009
2,625
2,625
113
Ottawa, Ontario Canada
#9
Strange S60... Plenty enough rearend for most men.
 
lilbowtie

lilbowtie

Royal Smart Person
Jan 7, 2006
2,090
1,046
113
Canton Mi
#10
First of all is the vibration your getting in your 8.8 speed related or load related. If it's an rpm that it passes through it will be a balance issue. And if it changes with the load you put on it will be a bearing. You know the cheapest - easiest way right now will be to just put a posi in and it will take you a long way. If your to do more than that I would agree with 565 and go with the nine inch. $2500.00 is quite the rear end, you can get an axle/housing package in the $700.00 range and build or buy a nine inch on the cheap or buy a $1500.00 plus aluminum bolt through with the best of parts.
 

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