MonteCarloSS.com
MonteCarloSS.com

CELEBRATING 20 YEARS!

Previous Thread
Next Thread
Print Thread
#1056103 - 02/26/18 06:03 PM Help identifying non-original rear end  
Joined: Oct 2015
Posts: 124
JesusCPenney Offline
Member
JesusCPenney  Offline
Member

Joined: Oct 2015
Posts: 124
Fort Worth, TX
Hey folks, I'm hoping someone here is good with axle stamps or knows where I can look up this info. My '85 SS doesn't have the original rear end, it's a non-posi unit that's stamped "9TZ" on the passenger side axle tube.

[Linked Image]

Any idea what it is? Google doesn't seem to be helping, and I'd like to know what my gear ratio is. I'd also like to figure out if I can convert this to the factory 3.73 posi or if the entire rear end would need to be swapped.

#1056127 - 02/27/18 06:49 PM Re: Help identifying non-original rear end [Re: JesusCPenney]  
Joined: Dec 1999
Posts: 12,363
PB86SS/87LS Offline
Administrator
20+ Year
PB86SS/87LS  Offline
Administrator
20+ Year

Member

Joined: Dec 1999
Posts: 12,363
New Berlin, WI
This is the only g-body axle codes that I've seen posted:

http://www.g-body.org/tnt/diffs/diff-codes.php

I'd be curious if you find out what it is. So your RPO code has G80 to know it was a factory posi rear?


-86'SS 383 CCC QJet- BRF 2004r-8.5" 3.42
-87'LS 350 MAF/SD TPI- CRF 2004r-7.5" 3.42
-81'Grand LeMans Safari Wagon 350 CCC Q-Jet/CZF 2004-r/8.5" 3.73
-07'TBSS Stockish daily driver
[Linked Image]
#1056129 - 02/27/18 07:18 PM Re: Help identifying non-original rear end [Re: JesusCPenney]  
Joined: Mar 2000
Posts: 5,651
upflying Offline
20+ Year
upflying  Offline
20+ Year
Member

Joined: Mar 2000
Posts: 5,651
Reno, NV
TZ sounds like you have an open diff with 2.56 gears. C is Buffalo assembly plant.
The other numbers are the date of manufacture on the second shift.
The 9 is "1979", just a guess.
But one of the charts says TZ is a code used in 1977.
http://rustynutscarclub.com/novaaxlecode.htm
http://novaresource.org/axle.htm

Last edited by upflying; 02/27/18 07:28 PM.

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

#1056132 - 02/27/18 09:45 PM Re: Help identifying non-original rear end [Re: JesusCPenney]  
Joined: Dec 1999
Posts: 12,363
PB86SS/87LS Offline
Administrator
20+ Year
PB86SS/87LS  Offline
Administrator
20+ Year

Member

Joined: Dec 1999
Posts: 12,363
New Berlin, WI
If it has metric or standard studs, that might help figure out if it's a 1978-1981 rear as well. My SS had a rear from that range when I bought it, standard studs, found out the hard way with lugs/wheel coming loose.

Last edited by PB86SS/87LS; 02/27/18 09:46 PM.

-86'SS 383 CCC QJet- BRF 2004r-8.5" 3.42
-87'LS 350 MAF/SD TPI- CRF 2004r-7.5" 3.42
-81'Grand LeMans Safari Wagon 350 CCC Q-Jet/CZF 2004-r/8.5" 3.73
-07'TBSS Stockish daily driver
[Linked Image]
#1056357 - 03/13/18 02:09 AM Re: Help identifying non-original rear end [Re: JesusCPenney]  
Joined: Oct 2015
Posts: 124
JesusCPenney Offline
Member
JesusCPenney  Offline
Member

Joined: Oct 2015
Posts: 124
Fort Worth, TX
Thanks folks. Someone with a copy of some GM literature showed me a chart saying TZ was 3.73 Posi but I'm not 100% sure. If it is a Positrac unit, then the limited slip components have failed for sure. It does have the metric studs, same ones as the front wheels.

#1056362 - 03/13/18 11:48 AM Re: Help identifying non-original rear end [Re: JesusCPenney]  
Joined: Aug 2007
Posts: 1,786
88ss408 Offline
10+ Year
88ss408  Offline
10+ Year
Member

Joined: Aug 2007
Posts: 1,786
miramichi, NB
The studs are easy to change. It could still be a older rear with newer studs. But easyest way to tell is to pop the cover. The stampings is on the ring gear for the ratio and you will see the differential. All it will cost is gear oil and gasket.


1988 monte carlo ss 408 sbc
-----------------------------------------------------
1984 monte carlo cs 400 sbc
#1056521 - 03/21/18 01:50 PM Re: Help identifying non-original rear end [Re: 88ss408]  
Joined: Mar 2000
Posts: 5,651
upflying Offline
20+ Year
upflying  Offline
20+ Year
Member

Joined: Mar 2000
Posts: 5,651
Reno, NV
Originally Posted by 88ss408
The studs are easy to change. It could still be a older rear with newer studs. But easyest way to tell is to pop the cover. The stampings is on the ring gear for the ratio and you will see the differential. All it will cost is gear oil and gasket.

You can also turn the yoke, count the number of turns to revolve the axle(s) once. 3 3/4 turns and you have a 3.73, both axles turn in the same direction and you have a posi. The yoke will only turn 2 1/2 times with 2.56 gears.

Last edited by upflying; 03/21/18 01:52 PM.

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

#1056536 - 03/21/18 06:08 PM Re: Help identifying non-original rear end [Re: upflying]  
Joined: May 2009
Posts: 2,012
Richie Cat Offline
10+ Year
Richie Cat  Offline
10+ Year
Member

Joined: May 2009
Posts: 2,012
Lake Ronkonkoma, N.Y.
Originally Posted by upflying
[quote=88ss408]The studs are easy to change. It could still be a older rear with newer studs. But easyest way to tell is to pop the cover. The stampings is on the ring gear for the ratio and you will see the differential. All it will cost is gear oil and gasket.


Yes do it this way, no questions after that.


83 SC, 355 w/TPI
#1056541 - 03/21/18 07:57 PM Re: Help identifying non-original rear end [Re: JesusCPenney]  
Joined: Jun 2006
Posts: 1,851
Travis Jones Offline
10+ Year
Travis Jones  Offline
10+ Year
Member

Joined: Jun 2006
Posts: 1,851
Ferndale, MI
Also pop the cover, it's due for a fluid change for sure and inspect the splined spider gears for lateral play. that's how i lost an axle at 70mph... an old worn out posi unit...


86 SS 6.2l LS3, Ilmor intake, Summit Stage 4 Cam, Stainless long tube headers, Stainless 3in exhaust, Tremec T-56 Magnum 6 speed, Eaton Truetrac 8.8 LSD, UMI Cornermax Front Suspension, 3-link Rear suspension w/ UMI Control Arms, UMI Front & Rear Braces, Brembo Brakes
#1056607 - 03/24/18 11:07 PM Re: Help identifying non-original rear end [Re: Travis Jones]  
Joined: Dec 2005
Posts: 2,752
84LS1T56SS Offline
Member
84LS1T56SS  Offline
Member

Joined: Dec 2005
Posts: 2,752
Central, Arkansas
Originally Posted by thepezking639
that's how i lost an axle at 70mph... an old worn out posi unit...



I'll bet that was exciting.



85 MCSS, 02 5.3/4L60E stock daily driver,84 MCSS, Another stock 5.3/60E.

Random Images
500/thumbs/81_MC6.jpg
by MikePEI
500/thumbs/535507_10200670135264234_53312840_n.jpg
by JAWSS
509/thumbs/85_radio.jpg
by 85_SS
500/thumbs/100_1400.JPG
by 85RESTOSS
1126/thumbs/1986_6.jpg
by Rich S
Help MonteCarloSS.com


Recent Contributors
86BlackSuperSport
dns87ss
Authorized Vendors
Tell them you saw it
on MonteCarloSS.com!


CustomMonteSSParts.com
Dixie Monte Carlo Depot
GSI Interiors
HRpartsNstuff
Mikes Montes
Savitske Classic & Custom
Powered by UBB.threads™ PHP Forum Software 7.6.0