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Wilson Offline OP
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Since I cannot find a 8.5 differential, I am looking to build a 9". Many different builders Moser being the most popular. Strange builds a really nice piece with some added expense. Quick Performance is about the most economical. Has anyone used their brand of axles? Looking for some options. Thanks


1987 Monte Carlo SS. 355 SBC, Pro Systems carb. 2004R non lock up 10" PTC converter
UMI front and rear control arms. Strange 9 Inch, 31 Spline Axles, 3.89 TruTrac.
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Why not a 12 bolt? Keep it GM.

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I have run a quick performance 9" for at least 10 years. As with everything else, it's kind of you get what you pay for. IF you are willing to work on and fix a few of the QP's low spots, it's a better economical choice. The hgiher end Strange, Moser, etc housings are nicer and more complete...but that comes with a price.

What I found when shopping for an upgrade mainly hinged upon brake choice. The Ford Explorer rear disc kit that can come with the QP 9 is a fantastic economical brake upgrade while disc brake choices for the 12 bolt tend to be a bit more spendy.


Lance
1985 Monte Carlo SS Street Car
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I also have a QP 9" with disk brakes. I had to have custom parking brake cables built.


-'87 Monte SS LS 2/4L65e Quick Perf. 9" w/disk brakes
-'89 Iroc Z28 Stock 5.7 Edelb. TES headers, Borla Exhaust90K
-'77 Trans Am 468(Stroked) Doug's Headers Flowmaster catback
B & M shift Kit 400 Turbo trans. Edel brock Performer
RPM Intake Sean Murphy built Rochester Carb. Restored
in '08. 3K
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Hi Wilson - I think we need to stop fixating on ring gear diameter and look at pinion gear diameter instead. The latter overwhelms the former in terms of stress imparted to the teeth. Beyond that, bearings and metallurgy. Beyond that, brakes, etc.

A 2.19:1 rear might work fine with a 7.5" OE ring gear, for example. But 4.11:1 will require a more expensive solution and a big ring gear.

I know that's not much help but it's all I've got - apologies. I had a GN 3.42:1 8.5" rear that gave zero trouble, but that's just anecdotal data.

Best - MAP

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Wilson Offline OP
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Correct. That is why I am looking into replacing it with a 9 inch.
If I could find a 8.5 I go that route. They are really scarce anymore.


1987 Monte Carlo SS. 355 SBC, Pro Systems carb. 2004R non lock up 10" PTC converter
UMI front and rear control arms. Strange 9 Inch, 31 Spline Axles, 3.89 TruTrac.
Joined: Jul 2000
Posts: 2,755
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Try pemracing.com

I just got this one: https://www.shoppemracing.com/product-p/stfhnm290290-tt.htm

Add your own brake kit or use their's.


88 SS Black/Oxblood. Power Tour car
80 Malibu 2dr. Drag Week car
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No problems with my QP 9". As mentioned in another thread, I had to clock the Explorer calipers at 4 o'clock to clear the frame. Long parking brake cables wrap around the top of the axles. Changing the proportioning valve to run rear discs was a knucklebuster.

Last edited by upflying; 01/25/21 02:39 PM.

86 MCSS Notchback coupe, LS3, 4L65E, QP 9", Eaton Truetrac, 4 wheel disc, column shift, Dakota Digital, silver with maroon bench interior

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I'd like to see pictures of your set up, Upflying.


-'87 Monte SS LS 2/4L65e Quick Perf. 9" w/disk brakes
-'89 Iroc Z28 Stock 5.7 Edelb. TES headers, Borla Exhaust90K
-'77 Trans Am 468(Stroked) Doug's Headers Flowmaster catback
B & M shift Kit 400 Turbo trans. Edel brock Performer
RPM Intake Sean Murphy built Rochester Carb. Restored
in '08. 3K
Joined: Mar 2000
Posts: 5,681
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Posts: 5,681
I wish I knew how to post pics, past attempts was a struggle and I failed. I guess I'll have to revisit the photo hosting process.
Other forums have a little paperclip thingy that makes posting photos easy.

Last edited by upflying; 02/01/21 03:36 PM.

86 MCSS Notchback coupe, LS3, 4L65E, QP 9", Eaton Truetrac, 4 wheel disc, column shift, Dakota Digital, silver with maroon bench interior

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Posts: 647
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I was warned about the frame making contact with the calipers but I didn't clock them differently and yes, I've had issues....it also doesn't help any that QP didn't add bump stops. I've yet to remove them from the stock diff and weld them on or possibly source them elsewhere.


-'87 Monte SS LS 2/4L65e Quick Perf. 9" w/disk brakes
-'89 Iroc Z28 Stock 5.7 Edelb. TES headers, Borla Exhaust90K
-'77 Trans Am 468(Stroked) Doug's Headers Flowmaster catback
B & M shift Kit 400 Turbo trans. Edel brock Performer
RPM Intake Sean Murphy built Rochester Carb. Restored
in '08. 3K
Joined: Aug 2016
Posts: 128
Wilson Offline OP
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Anothe question would be rear brakes. I know disc brakes are the hot setup but are they worth the headache over drums? Wilwood vs other brands?
If I were to go to wilwood or another brand then have to replace the fronts. Sigh!!!


1987 Monte Carlo SS. 355 SBC, Pro Systems carb. 2004R non lock up 10" PTC converter
UMI front and rear control arms. Strange 9 Inch, 31 Spline Axles, 3.89 TruTrac.
Joined: Nov 2010
Posts: 833
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I have been running a 9" for over 10 years.

Quick Performance Housing, Moser 31 Spline Axles, Strange S Case, Detroit TruTrac Diff, Richmond 3.89 Gears, Aluminum Daytona Pinion Support with 1350 Chromeoly Yoke. LT1 Fbody Rear Disc Brakes on it. I prefer Discs because they are simple.

[Linked Image]


1984 MONTE CARLO SS 6spd
6.HO | LS6 INTAKE | CUSTOM CAM | BUILT T56 | CUSTOM 9" REAR | 3.89 GEARS
2002 EBM C5 Z06 | FREE MODS | BOLTONS WITH TUNE
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Wilson Offline OP
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That is the exact same setup gear ratio case and trutrac that i have ordered. Haven't ordered housing yet deciding what brake setup going with yet.


1987 Monte Carlo SS. 355 SBC, Pro Systems carb. 2004R non lock up 10" PTC converter
UMI front and rear control arms. Strange 9 Inch, 31 Spline Axles, 3.89 TruTrac.

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