I have just purchased a 9 bolt rear from a 89 IROC It has the aluminum calipers 12 inch rotors and 3.27 gears and limited slip. It also came with the proportioning valve and master cyclinder. I would just like to know what I am getting into when I swap this out with my original 10 bolt rear 3.42 gears open diff. and drum brakes from an 85 firebird orginally with a 2.8 V6 and t-5 5 speed manual tranny. First I have 15 inch snowflake aluminum rims will these fit over the big 12 inch rotors and aluminum caliper or do I need to get 16 in rims? Also Is this borg warner 9 bolt stronger than the GM 10 bolt I have? Will it hold up to an occasional drag race from a 327 engine with 350 HP and 400 FT/LBS of torque and a richmond 6 speed. This is also a daily driver most of the time. Will the 3.42 to 3.27 gears slow my ET's much. I also spun my tires a little on start. Maybe I will get more traction? And the important thing to me how much better gas mileage? When parts start to wear out how hard will it be to get them like the posi unit and gears, since in the catalog I have not seen anyone making after market gears for the 9 bolt just 10 bolts. And last, any problems that I might run into in swapping this over? Thanks for all your help!! Erik

 

The only real knock against the 9-bolt is the fact that parts are $$$ when compared to the 10-bolt. As for strength, the 10-bolt doesn't hold a candle to the 9-bolt. I cannot say for sure if the 15" rims will clear... what size rims were on the 89?

As for your milage, it will get better. The 3.27s are a little low for a manual (ideal for a 700R4 though), so you may lose a little in the 60' times I think. Then again, your traction will be better with both the lower gearing and the posi differential.

For what it's worth, I am glad I did mine... and the proportioning valve I bought is still sitting in the tool box.

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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock... all the suspension stuff... 9-bolt posi disk is in... K&N filter... 93 octane...

-=ICON Motorsports=-

 

Thanks.... ummm i don't know what size rims were on the iroc it didn't have them. Also about how much do 9 bolt parts cost and where can I get them from? Since this rear came from an 89 it should have the better 28 spline shafts instead of the 26 right?

 

These rears are different from the 10-bolt. I don't know that they had 26-spline or 28-spline axles depending on the year like the 10-bolt. I don't think they have c-clips either (a good thing).

I am betting that they would fit under your stock 15" rims, but make sure with someone else. Madmax knows a lot about these rears.

check this place for parts:
http://www.nationaldrivetrain.com/

 

The 15 inch camaro rims fit over the brakes, I did the same swap as you and it was not a problem, you will need new brake lines a e-brake cables though, I am glad I did my swap.I have the 3.45 ratio though and I am glad that I have it, I know where there is a complete rear with only a few miles on it the car was wreck shortly after it was brought and has set in a friends feild since, the motor is gone but the rear is still there, It has the 3.27 ratio and if I need to Get a posi or gears I will just use that rear since the price for parts are expensive.

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86Z28, GM 350, Jet perf Q-jet & chip Dual snorkel air cleaner, Edelbrock performer intake, Edelbrock headers, Edelbrock cat-back, Off road pipe, MSD 6AL, Accel Super Coil, Taylor Spiro-pro wires, Rapid fire plugs, Jet fan switch, World class t-5, Hurst Short Throw Shifter, Ram Flywheel, Center force dual friction clutch,Aluminum drive shaft, BW disc rear 3.45's & a posi, PBR calipers, Earls braided brake lines, Polygrapite bushings all the way around, poly tranny mount & torque arm mount, Hotchkis lower control arms & panhard rod, Rancho limiter straps, KYB struts & shocks, Gm Wonderbar, Edelbrock strut tower brace, SSM sub frame connectors, Jamex lowering springs, Carbon metallic brake pads, Crossed drilled rotors, Mobil 1 Tranny fluid & motor oil, GM syntheic rear end oil, K&N, Grant stering wheel, 1,200 watt system, Jet Black Paint, 91 Z28 rims, 92 wing, Tinted windows.

 

YOUR BW ONLY HAS 26 SPLINES AND I WOULDNT TRUST ONE OF THOSE WITH EVEN MY S10. I WOULD GO WITH A 3.23 OR 3.42 LIMITED SLIP OUT OF A 90 OR NEWER F-BODY 28 SPLINES. AND THERE ARENT THAT MANY GEAR OPTIONS FOR THE 9BOLT.. AND 10 BOLTS HAVE TONS.. ALSO YOU WILL SAVE PROBABLY 3-6 MPH IN GAS .. BUT STILL NOT WORTH GIVING UP YOUR 60' TIMES. IF YOU HAD THE SAME GEARING AND A POSI UNIT BELIEVE ME YOU WOULDNT SPIN YOUR TIRES THE SAME AND YOU HAVE A CLUTCH WHY DO YOU SPIN YOUR TIRES AT ALL YOU CAN TOTALLY CONTROL ALL MOTION OF YOUR CAR.. HAVE FUN LEARNING .

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1990 IROC-Z L98 350 TPI
AFPR 49PSI, GUTTED AIR BOXES, K&N, RAM AIR, PORTED PLENUM, B&M SHIFTER, 3.23 LIMITED SLIP, DUAL CATS, STOCK SUPER TURBO EXHAUST, COOPER COBRA XST's

MUSTANGS...ONLY 4 LUGS....HAHA THAT IS HILARIOUS.

 

Thanks for all the information you guys have given me so far! I'm glad the 15 inch rims will fit because I like the 2nd gen trans am snowflakes and i just bought some pretty expensive BF's theat are 28" tall for the rear. It would suck to have to replace them all. As for the e-brake cable the rear is coming with the with the two from the calipers. From what I was told as long as I have those 2 it will work with the single one that comes from the e-brake handle all I have to do it connect the three. Is that correct? As for the 9 bolt to 10 bolt stuff, I think I need the 9 bolt's strength. With my 327 I dropped in there (which is pretty much a summit racing motor... lots of goodies)I have already went through a muncie 4 speed not to mention the the T-5 I destroyed with the orignial 2.8 V-6!! Thats why I went with a richmond 6 speed. I'm afraid I will go through the 10 bolt too. Plus the one thats in here has 162,000 miles. So I think i will stick with the 9 bolt unless anyone knows where I can find a Dana 44 out of a 3rd gen f-body?? I only just started drag racing and will do it probally once or twice a year. I've only did it once so far and the car pulled a 9.4 in the 1/8 with street tires... Maybe with slicks I can break into the high 8's I hope to go to a 1/4 track and see what it will do there. But the big thing since this is a daily driver I want to be able to drive it home from the track so I dont want a 10 bolt to go out on me. As for the spinning tires your right I need to practice more on that one. I thank all you for your help... Thanks.. Erik

 

I'm doing that same swap now.
I'm using a 9 bolt from my crashed 88 IROC to my 87 IROC.
I'm rebuilding the 9 bolt now, here's what i've found. (you might want to open yours up to check)
PARTS ARE NON EXISTANT
the dealer only sells the posi unit as a whole @ $1000+ you can get spider gears and i think side gears and a spring kit that's all i've been able to find (correct me if i'm wrong cuz i still need parts).
what i did was, first, read the tech article on this board about them (https://www.thirdgen.org/newdesign/tech/9boltservice.shtml). when i opened up the posi unit i found that my cones were just starting to bottom out, you can tell by the wear marks. Since new cones are unavailable i took my existing cones and housings to a machine shop, neighbor lucky me. We cut the outer edge and the center near the splines down so the cone would contact the sides again and not bottom out. We cut one down .090" and the other only needed .070". Now to get the correct shim combination and we'll be good as new again.
no more chicken leg for me!!!

good luck....btw do we need to replace the proportioning valve for the drum to disc swap????

 

Hey thanks for the info, I will definatly check it out before I install it. From looking at old posts in this forum so faf I have found that strange engineering carries parts. I don't know their phone # or internet address. If someone knows this please let me know. Also Reider racing carries pars and from what I hear they are the cheapest. Their phone # is 1-800-356-1330 Also in an earlier post under this topic is National drive train's internet address. Oh and yes you need the proportioning valve and master cyclinder for the swap from drums to disc. The prop valve will give you the correct brake bias. If you use the old one i hear you will lock up either your front or rear brakes before the other will be applied. And the master cyclinder bore on the disc's is bigger than the drums. So you do need both.

 

It is true that you need a new proportioning valve to convert the older pre 89 drum brake cars to rear disc. The p.v. on the pre 89 drum cars has a brake line coming from the front of it. The disc p.v. has both brake lines coming from below. Re-bending your one brake line (carefully) will be necessary. From what I am reading the older drum brake cars have the same A50 master cylinder p/n 18006814 as the 89 and older disc/disc and disc/drum cars. The pre-89 disc/disc cars had a A65 master cylinder, which has a 1" bore diameter vs the 1.25" of the A50. However GM has now substituted the A50 for the previous pre-89 disc/disc application. Oh, btw, you will need the emercency brake cables for the disc brake rear end also as they are different than the drum brake ones. Good luck, Lon.

 

Hey Lon, when we swapped Nick Steel's 92 Z28 from drum to disc, we used the e-brake cables from the disc rear end, and when we swapped my dad's 92 RS from drum to disc, we used the same cables that were on the disc rear end. But that is probably because both swaps were with 89-92 disc brakes, while yours is an 82-88 disc brake setup.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

Kevin, What you describe confirms what I was trying to say. You must use the e-brake line that is correct for that disc brake setup. If you swap in a pre-89 disc rear end you must order the correct e-brake cables if you don't get them with the rear end. You can't try and re-use your drum brake e-brake cables. Same holds for the 89 and up disc brake rear end also. Your dad's e-brake pull-up is nice and firm. Mine is a little soft by comparison, but I will correct it with a small spacer crimped behind the ball end. Unfortunately there is no adjustment at the saddle where the 2 lines combine on a 89 and newer. My 88 Iroc has a long threaded rod which allows adjustment at the saddle.

 

I am switch the pre 89 prop valve with drum brakes with a prop valve from an 89 with disc brakes. You said about rebending the line from the front. My question is which port does the rebent line from the front go in to? The one on the bottom that is the most forward? Does it matter? My front line is coiled twice and has plenty of extra would it be easier to cut it, re-flare it and then install it.

 

Keep a loop in it, as it reduces shock to the line. I believe it goes to the front fitting on the bottom of the p.v.

 

At lonsal's advice I will keep the loop and just try to bend it. Its dosn't look corroded at all so the line should be easy to bend carfully. Also if anyone else was looking for parts for a 9 bolt on here, I have found the number for Stange Engineering that I was looking for. Its (847)869-7010. Well just yesterday I finally picked up my nine bolt. I can't wait to start messing with it. DOES ANYONE KNOW a way to test the posi before installing it and without tearing it apart to see if its still strong? Maybe by spinning the axles and having pressure put on the other one? I don't want to get it in there and then have to pull it out and I would rater not take it apart if I don't have to besides pulling the rear cover. I don't mind that. Thanks for the help. Erik

 

use a torque wrench on one wheel with the other on the ground and the car in gear. Measure how much torque it takes to turn the axle. I dont know the specs for a nine bolt, but someone must(?)

 

Checking Limited Slip Operation: GM makes tools that atach to the lug nuts. J 2619-01 slide hammer with 1/2-13 adapter and a J 21579 axle shaft remover. You may be able to rent the equivalent at an Auto Parts store. Place the car in "Park" if an automatic or in gear if a manual. Raise rear of car until one wheel is off ground and remove tire. Attach the tools you rented and check the torque req'd to rotate the axle shaft. If it measures less than 48 N-m (35 lb-ft) than the unit needs to be repaired. There is a tech article by Karl Hunter on this board on how to repair and shim the cones of the posi. If you can't find it I can e-mail it to you. Good luck, Lon.

 

Can someone tell me if the break line fittings are the same connecting up to the brake line attached to the rear end? The 10 bolt that came on the 83 T/A had disc brakes as does the 89 9 Bolt I want to install. Everything else looks like an easy swap, even my factory 15" wheels clear the calipers (not by much).

 

No.

83 had SAE fittings; 89 has metric.

83 had the Delco-Moraine brake system; 89 has PBR. Aside from the fittings hoses and lines on and around the rear itself, the hydraulic requirements of the 2 systems are different, so the master cyl and proportioning valve are different as well, and will need to be changed out. And at that point, you're in the same boat: SAE lines on the car, metric fittings on the parts.

That said, the 89 brakes are a YYYYYYYYYUUUUUUUUUUUUUUJJJJJJJJJJJJJJJJJJJJE upgrade over the crappy 83 system; well worth overcoming the differences. It'll be a major undertaking but well worth it once successfully completed. It'll probably require either fabricating some lines where your existing SAE stuff will have to bolt to metric, or, probably the smartest thing you can do, just replace all the steel lines, rubber hoses, and the front calipers, at the same time you replace the rear calipers, rear rubber hoses, master cyl, and proportioning valve. No sense replacing 2/3 of your brake system, then alternate-ethnically-engineering around some sort of hack so that you can keep your existing almost-40-yr-old rusty dirty wore-out crap hooked up to it.

 

@sofakingdom
I would hope an SAE to metric connector could be fabricated w/o too much trouble. Your information was exactly what I was looking for & I thank you.

 

They can and are, as far as that goes.

Fitting them into a space on your car where things are made the exact size shape length etc. that they need to be, without hitting something else or getting in the way of something or otherwise being unusable, is potentially a whole other matter.

 

There are a few threads here for a good diff upgrade to use with the 9bolt for 500ish. Don't waste money on a factory diff or even rebuild the old one.

 

Summit has all kinds of these (very short) adapters. Now I just have to figure out what the SAE size is. So it's up on the lift to get at it. Thanks again everyone.

Update:
I found an adapter that goes between the SAE brake line connection on the car to the T-brake hose (metric) on the rear end. It's 3/8"- 24 X 12 MM 1.0 TP. Got mine on e-bay but had to order several. Now, getting that brake line loose is another story.