[grivera]

Originally Posted by Schurkey

What brakes do you have now? Typical 9.5" drums from an older compact/intermediate axle?

If so, consider merely upgrading to the 11.x drums from a newer intermediate like a 73--77, or a full-size car.

You get better, stronger brakes than what you have now, retain the park brake, zero issues with wheel compatibility, and they practically give away the parts at the Treasure Yard.

Verify or replace the springs and adjuster, cut the drums and replace the shoes as needed. Biggest problem is swapping the backing plates; and assuring that the shoe-contact pads on the backing plate aren't excessively worn. If they are, you can have the wear-grooves welded up and smoothed-out for little money.

Pretty-much all the advantages of the typical disc conversion, few problems.

Originally Posted by jerry455

I used a 1LE front brake set up for my 1976 Firebird. I also installed the 11" drum set up on the rear. It makes a big improvement for a lot less money. I went from 11" front to 12" front and 9.5" rear drums to 11" rear drums. I used a 1977 Lemans as a donor for the rear.

Intriguing for sure

[grivera]

Does upgrading front from 11” to 12” disc require different spindles or caliper brackets?

[Scarebird]

yes, and only works on 1970-81 Firebirds.

[Schurkey]

Originally Posted by grivera

Does upgrading front from 11” to 12” disc require different spindles or caliper brackets?

Originally Posted by Scarebird

yes, and only works on 1970-81 Firebirds.

For the record, the " spindle" is the steel "rod" that's pressed-into the iron casting; together they're called the "Steering Knuckle". The iron casting also includes the caliper mount, if we're talking about the OEM GM A/F/X/B/C steering knuckle design--essentially the same geometry although several different casting numbers/part numbers owing to different bearing sizes or casting revisions. The 12" knuckle/rotor system fits heaps and piles of GM vehicles including those retrofitted with the H-O Racing "Tall Spindle" disc brake conversion for '64--'72 A-body.

[grivera]

Originally Posted by Scarebird

yes, and only works on 1970-81 Firebirds.

Originally Posted by Schurkey

For the record, the " spindle" is the steel "rod" that's pressed-into the iron casting; together they're called the "Steering Knuckle". The iron casting also includes the caliper mount, if we're talking about the OEM GM A/F/X/B/C steering knuckle design--essentially the same geometry although several different casting numbers/part numbers owing to different bearing sizes or casting revisions. The 12" knuckle/rotor system fits heaps and piles of GM vehicles including those retrofitted with the H-O Racing "Tall Spindle" disc brake conversion for '64--'72 A-body.

So this means upgrading a 1st gen bird to 12" front disc brakes from a late 70's A body would require swapping in the steering knuckle - is geometry the same?

["QUICK-SILVER"]

Originally Posted by grivera

So this means upgrading a 1st gen bird to 12" front disc brakes from a late 70's A body would require swapping in the steering knuckle - is geometry the same?

I was thinking 72 was the last year for two piece steering knuckle. For first gen birds, the bolt on arm, for tie-rod, has to be retained. You swap the arms to convert from front steer to rear steer.

Seems like wheels set to the outside an inch or so further after the swap.

Clay

[Skip Fix]

That kit uses the TA/Caddy rear calipers and they are floating. Still betting your Moser brake pilot barely sticks out the rotor.

1le/B body spindles(yea I know Shurkey steering knuckle-but most folks use spindle) have a cast in caliper bracket. Swapping to aftermarket or C5/6 you cut it off and use a bracket so 11 spindles ok for that route. The term 1LE is from the 12" rotors use on the 1LE option road race third gen F bodies-metric studs. 12" B body rotors use a large diameter wheel bolt pattern. Speedway does have the 12" rotor with 7/16 studs.

And yes HO and Global West did that swap on A bodies also either with a lot of shims or a different upper arm from Global.

[Scarebird]

The 1LE spindle conversion is best reserved for 73-77 A's and 70-81 F's.

Using it in 64-72 A's causes more issues than it solves; ie. turn radius is much larger, bump steer issues - this even with the specialized upper arms. I know, I sold 60+ spindle pairs Morse reamed to fit the A's in the early 00's until I learned of the issues.

First Gen birds are rear steer - this will not work at all.

As far as the axle pilot goes, we had a pair of rings laser cut from 1/4 steel with an OD of 2.781" and an ID of 2.25". We would simply use a hose clamp to center it on the existing pilots and use a MIG to put a few heavy tacks to secure on the inside diameter. You do not even need to pull the axle to do this. These rings can be ordered from Send-cut-send or other online cutters or made from thicker material if desired.

[Skip Fix]

Speedway has the 7/16 12" rotors listed as replacements for their dropped spindle Impala kit.

[Gator67]

Timely thread. Trying to decide what to do about front and rear brakes for my son's 79 TA. Came with drum brake rear end but have a disc brake rear end as well.

[67Fbird]

Originally Posted by Skip Fix

Grivera most of the kits out there use the 79-81 Trans Am/Cadillac ratchet calipers-sometime problematic. The problem I have found with Moser axles is the rear axle brake pilot it too short to locate a hubcentric wheel and a rotor-as they are thicker than a drum. The rotors being thicker might increased the track 1/8". I think whatever kit you might see that issue.

+2 on the hubcentric issue. MOSER axles hubs are MACHINED SHORT to allow clearance for ANY WHEEL. Well that's great until you MUST have a hubcentric axle DUE to the factory set up. Been there done that...cost 2 extra weeks as I had to send the mosers (stock replacement) axles back.

The 4wd rear disc on a blazer centerhub thickness is .264" I would assume a drun hub thickness is probably .187"....so MAYBE 1/8" total track width addition.

[Skip Fix]

Dutchman can make a longer pilot, Moser laughed at me thought I was crazy for not going lugcentric.

[grivera]

Are rally IIs hub centric? If so can they be used lug centric?

[Scarebird]

Stuff we send to the EU has to be hub centric.

[67Fbird]

TYPICALLY any wheel is usually LUG-CENTRIC. meaning it is located/centered BY the taper on the lug nuts. Any wheel that uses TAPER seat lug nuts can be mounted via LUG-CENTRIC methodology. Now a wheel that uses SHANK TYPE lug nuts and a flat washer is one of those COULD BE type things. with the appropriate lug nuts YES this type of wheel is considered LUG-CENTRIC. Some wheels have NO taper seat and NO shank type lug nut, they use a big nut with a flat washer. The ONLY thing that this type of mounting system CAN DO is clamp one flat surface to another!!!! it OFFERS ZERO locating ability and MUST rely on a centering pilot in order to locate the wheel on centerline.

[HWYSTR455]

On my LeMans, I have Moser axles, and the axle hub sticks out far enough to go thru the rotor completely. I have a 'Touring Brake Specialties' 'hybrid' kit, which uses the late 90s SS camaro calipers. Those were for a while hard to get, but now are being reproduced. Fronts are C5/C6.

I have the Right Stuff rear kit on the 442, and Dutchman axles. The hub was cut down by Dutchman for free. It too sticks out far enough to go completely thru the rotor.

Some who offer rear kits also offer rotors with the center cut so you don't need to mod the axles, but, you are stuck sourcing rotors that need to be cut.

Rotor thicknesses on the rear I have found push the wheel out @ 1/4" per side, depending on the rotor. (more with some kits). If you're getting a housing made, order it 1/2" shorter on each side to compensate.

You need an E-brake.

Drums center well on the studs, so you could cut the hub on the axles and still use drum brakes, until you upgrade.

Any decent brake upgrade uses larger than OE rotors, and all but maybe 2 kits require at min 16" wheel (Baer SS is one such kit that works with 15" wheels, but there is very little performance improvement). Since tire selection is poor for 16s, 17s is the next sensible option, but 18" these days is the 'norm'. Much better tire selection.

Disc calipers require a certain amount of fluid moved to work properly, so you need to change the master. And, of course, the combo valve too. Depending on your booster/mc combo currently, you may need to swap your booster too.

It's best to get a booster/master/valve 'kit', to avoid any confusing or mismatch. They are not expensive, and have had great luck with Pirate Jack. (Believe they are affiliated with Master Power Brakes).

Disc wheel studs are roughly 1/4" longer than drums, but depending on the rotors/kit, you may need longer ones. Make sure you measure so the lug nut doesn't bottom out before fully tightened, and has enough thread engaged.


.

[Skip Fix]

My Weld Prostars that are lugcentric there is about 0.010 difference in shank vs wheel lug holes. An F body snowflake/turbo wheel has a .750 hole and factory lugnuts are .705ish so lots of room to flop around. I was going to use some of those wheels in the Camaro IA project to roll around the shop it uses 79-81 TA rear rotors and a metric D154 caliper(no e brake). With Moser axles short pilot and to get a lugnut to fut 1/2" studs standard mag shank lugnuts are 0/680! Lots of room to get out of round but was OK for pushing around the shop.
Factory F body rear disc axles use about a .720 length 2.78 pilot.

[Scarebird]

Originally Posted by HWYSTR455

Some who offer rear kits also offer rotors with the center cut so you don't need to mod the axles, but you are stuck sourcing rotors that need to be cut.

Not true.

Our drum-in-hat setup does not require ANY machine work, nor do I suspect any other DIH setup does to the rotor. The drum section of the rotor is much bigger than the axle shaft flange.

Ours is also compatible with BOP bolt-in axles, unlike other kits which require shims and/or have some goofy stack of spacers and brackets. We use a formed steel center the same thickness as the drum backing plate to keep the bearing preload the same.

[grivera]

Scare bird - I sent you a PM

[HWYSTR455]

Lug centric wheels do have larger holes than the stud, are conical, the lug tightened down centers the hole over the stud. There's no flopping around. (Unless the wheel is damaged)

Some OE wheels have a different degree conical seat, which requires matching lugs for the wheel. I believe snowflakes are one of those type wheels. So the WHEEL is what determines if it's lug or hub centric, not the axles or anything else.

As far as I know, there are no pre-80s Pontiac cars that used hub centric wheels, but I could be wrong. A think no GM pre-80s car used hub centric wheels, but don't hold me to that.

I've owned a number of BOP cars, none used hub centric wheels. And have used a variety of aftermarket wheels on those cars, lug centric wheels, never had a problem. Now of course, that doesn't mean that offshore cars might require hub centric wheels. Or adapters.

As for rotors requiring the axle hub be a certain diameter, it's to allow use of off the shelf rotors, most of the time from a number of applications. That reduces cost of the rotors. If you don't think that's common, look at some of the directions on the kits being offered, they specifically provide a hub diameter measurement.

Now I'm not saying that all rotors won't fit the standard hub, I suspect there are rotors out there that have larger center holes. Which is why I said 'some' offer the rotors already cut.

.