I purchased a disc brake posi rearend from an '88 Iroc (still has 26 spline axles) and I do not like the calipers. I hear that the '91-'92 models use the 1LE calipers. Is this true? What do I have to do to use the 1LE calipers? New rotors? Adapter bracket?

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If you live in Southeastern US, check us out!
South East Thirdgen


ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey, 22# injectors,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
-->14.97 @ 94.9 MPH<--

'97 Bonneville SSE

 

I happen to have a 91 one sitting in my garage at the moment...

It looks like all you have to do is unbolt the "backing plates" from the later model housing and put them on the early rear. It looks like the housings are all the same among drum-equipped ones, the early disks, and the late disks. Obviously you have to take the axles out first to get to that point. I'm not sure about the rotors though; I don't have an early one to compare to right now.

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"So many Mustangs, so little time..."

 

The calipers are PBR dual piston on the 1LE.
Not sure if they're single or dual on the regular 91/92 but I'm pretty sure the dual piston caliper is 1LE/vette only.

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91 Formula
305 TPI 5speed
1LE/G92/WS6
Custom K&N cold air intake, SLP airfoil, ported & hi-polished plenum, March pulleys, TB coolant bypass, 180* stat, Crane AFPR (47psi),94 octane,Crane Extruded Alum. 1.6 full roller rockers, Timing set from 4*BTDC to 10*BTDC,MSD coil,MSD6AL, Holley 9mm Annihilator Laser shot 50 wires, Ac Delco cap,rotor and plugs, Bosch O2sensor, SLP 1 5/8 headers,SLP catback,3:73s,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.
Street legal with stock throttle body, runners,intake manifold,cam, and heads.

 

I have a 89 and it has the twin piston aluminum caliper with 12 in rotors

 

MKOS1980, in 1989 the specs for the 4wheel disc brakes were 10.5" rear and 10.5" front.

Theres no way you can have 12" rotors unless you have a turbo trans am or a 1LE

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91 Formula
305 TPI 5speed
1LE/G92/WS6
Custom K&N cold air intake, SLP airfoil, ported & hi-polished plenum, March pulleys, TB coolant bypass, 180* stat, Crane AFPR (47psi),94 octane,Crane Extruded Alum. 1.6 full roller rockers, Timing set from 4*BTDC to 10*BTDC,MSD coil,MSD6AL, Holley 9mm Annihilator Laser shot 50 wires, Ac Delco cap,rotor and plugs, Bosch O2sensor, SLP 1 5/8 headers,SLP catback,3:73s,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.
Street legal with stock throttle body, runners,intake manifold,cam, and heads.

[This message has been edited by theformula (edited January 06, 2001).]

 

All third generation cars came with front disk brakes,some with disks on the rear instead of drums.The standard front disk size (not counting 1LE) were 10.5",and used an iron caliper and hub assembly.If you had rear disks,the rotor size and brake pads are the same,but the caliper is slightly different (at least I think it is).I don't know the exact size of the brake drums offered,but drum cars used a slightly smaller master cylinder than rear disk cars.In 1989,GM introduced the rear 12" rotors for high performance models.These brakes were the best to come on the rears of third generation cars,and can be adapted (or rear swapped) to fit the older rears with 10.5" disks,the calipers are aluminum.


I measured and it was 12in. The info above came from the thirdgen tech section. My rear rotors are WAY bigger then the fronts when I went to change over to cross drilled.

 

You didnt need a 1LE or Turbo to get the bigger rears just the fronts.

 

I know you dont need 1le to get bigger rear brakes. I have a 1LE!

My info came from Hot Rod magazine where they tested a 1989 GTA 350 A4 and a 89 Trans Am 305 TPI. Both had 10.5" disc brakes front and rear. I have the article right in front of me. You said high performance models got the 12" rear rotors in 89. Any 350TPI equipped 3rd gen car is considered " high performance". What kind of car do you have? Not arguing with you, just trying to get this straightened out!
Later man

Rear drum brakes were 9.5x2-"

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91 Formula
305 TPI 5speed
1LE/G92/WS6
Custom K&N cold air intake, SLP airfoil, ported & hi-polished plenum, March pulleys, TB coolant bypass, 180* stat, Crane AFPR (47psi),94 octane,Crane Extruded Alum. 1.6 full roller rockers, Timing set from 4*BTDC to 10*BTDC,MSD coil,MSD6AL, Holley 9mm Annihilator Laser shot 50 wires, Ac Delco cap,rotor and plugs, Bosch O2sensor, SLP 1 5/8 headers,SLP catback,3:73s,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.
Street legal with stock throttle body, runners,intake manifold,cam, and heads.

 

I have a 89 Formula 350. Now I found something that said they switched over early in 89 to the 12 inch. I think Jan of 89 was the last for the origional 10.5 J65 option.

 

That would explain it then. Thanks

 

GMT,

Join the "Caliper-Haters Club". The '88 and earlier calipers are a disgrace, and I've got plenty of examples. Find the correct anchor brackets and install some good calipers/rotors if you can.

I would think that you could find some brackets easier than most of us, since you have a direct line into the B&H system. I know the brackets for later 'B' cars with rear discs are available from aftermarkets, since I've replaced a couple (guide pins worn into them).

You might be lucky enough to find some for 'F' cars as well, meaning that the prices would probably be a little better.

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Later,
Vader
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"I cannot take this any more... Saying everything that I've said before..."
Adobe Acrobat Reader 4.0

 

So to make a long story short, I need:

• Twin Piston Calipers
• 12" Rotors
• New backing plates

I guess what my question was, do I need to be looking for 1LE brakes, or can I just look up, say, '92 GTA brakes? and is that the only three things I need?

------------------
If you live in Southeastern US, check us out!
South East Thirdgen


ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey, 22# injectors,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
-->14.97 @ 94.9 MPH<--

'97 Bonneville SSE

 

GMT,

Cables? Steel lines? Hoses the same? Prop valve? (Maybe a little different for the larger swept area and piston volume of the two-piston calipers.) And of course, pads.

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Later,
Vader
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"I cannot take this any more... Saying everything that I've said before..."
Adobe Acrobat Reader 4.0

[This message has been edited by Vader (edited January 07, 2001).]

 

That stuff is chump change, I plan on bending new lines any way, I already budgeted for a new prop valve, etc...

I was just worried about the "bulk" of the items, and what really was different, i.e. mounting.

------------------
If you live in Southeastern US, check us out!
South East Thirdgen


ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey, 22# injectors,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
-->14.97 @ 94.9 MPH<--

'97 Bonneville SSE

 

I have a 91 rear in my 92Z28 convertible. The rear disc's are only single piston aluminum PBR's. The front on 1LE's and TTA's are the dual piston.

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Convertible, L98, Mini-ram, ZZ9 cam, Comp Cams 1.52/1.6 steel roller rockers, Trick Flow 23* heads, K&N's with chopped airboxes, March underdive pulleys, Edelbrock ceramic coated TES, Flowmaster cat-back exhaust, Dynomax high flow converter, MAC subframe connectors, Accel box & coil, 3.23 rear gears, white face gagues, and NOS!
When I get back from Kosovo I will be installing these on-order items!

 

Okay gm tech you have helped me alot now I will help you, just so you know I know what I am talking about, my 86 starterd out as a drum brake rear, I then switch to a 88 iroc rear (9 bolt) with disc, but they where the early verison and they sucked, so I got a hold of some 89 backing plates for the 9 bolt (the only year they made them) and 2 aluminum calipers they are only single piston and they are the same ones used on 1les and all 89 and up rear disc packages. I then got 2 rotors which measure 11.65 in, the master cylinder is the same for the 89 and up rear disc and the drum cars of all years, the 88 and early rear disc used a diffrent one. You are going to need new brake lines ( earls braid lines is what I used) and new e brake cables. You can get all of this stuff used from http://www.tacreationsusa.com/

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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.

 

If you're good at fabrication you can make your own backing plates and then run off the shelf 2/4 piston calipers and as big of rotors you can find. 1LE brakes were good in '92 but if I was doing a full overhaul today I'd go bigger and would for sure have 4 piston calipers.

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1984 WS6 Trans Am Hartop
Former L69 Car under restoration
1984 WS6 Trans Am T-top car
4-bolt main 350, headers, Holley 650, T-5 and 3.23's.
Daily driver and restoration
13.98 @ 101