Aftermarket rear disc brake conversion that does not axle modifications
 

Merry Christmas all!

Is there a disc brake conversion that fits over the factory axle hub and requires no modifications to the axle flanges/hubs? Also, do they cause a track width change?

This is for an 8.5 10 bolt rear with Moser axles.

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.

Yes, our drum-in-hat setup will do this. It will move the wheel out 1/4" due to rotor thickness. You will need 15"+ wheels to clear.

You also will need longer studs as GM was very cheap here.

Edit: Like Skip said - the 1979-85 Caddy calipers can be problematic, hence our drum in hat setup which dispenses with them.

https://scarebird.com/image/cache/ca...ar-500x500.JPG

I have the same exact rear you do and used the right stuffs kit with no E brake provision. So it was really simple. Probably not the ratcheting calipers that are being discussed. They looked just like the chevelle calipers on the front IIRC.

It might have moved the wheels out a fraction. I can’t remember. It was a super easy install though. Way easier than the front. It certainly took me less time to install the complete retro kit than it would have to rebuild the drums. Might have been more affordable too than an all inclusive drum rebuild.

The hardest part is that stupid proportioning valve.

Blazer LS rear brakes...fits 15" wheels, has e-brake

If you have larger wheels(minimum of 17”) then you can buy a C6 based conversion system that Kore3 sells. I have F/R conversion kits that use the C6 Z51 brakes for a 73-77.
http://www.kore3.com/

The kit I used came from Pirate Jack's and at the time the same kit was offered through Inline Tube and Jegs as a "Bolt-on kit requiring only hand tools". The kit included a "love note" advisng the rear axle flanges required a corner radius to be machined for the rotors to mate with the axle flanges. Without the radius, the rotors did not fully seat. This may have been a BOP 8.2 10-bolt issue only.

They also neglected to mention you had to weld the tabs for the hardline-to-hose transition to the axle housing and also need to be able to shorten and double flare the rear axle brake lines. Just an FYI, that ain't ever going to work so you're going to have to buy a rear axle line set, shorten them and double flare the ends for connection in addition to welding the tabs in place. Pirate Jack's suggested I use hose clamps around the rear axle to secure the tabs in place or just eliminate them altogether and use nylon zip ties instead. I asked them if I couldn't just use told "bread twisties" for the full "ghetto engineering" effect.

Aside from requiring machining and welding, it was a bolt on installation lol. After I replaced the 2 leaking Eldorado rear calipers it worked out fine.

What I learned ... buy the caliper brackets from our Forumite and source the rest from reliable suppliers. Unless you're buying Wilwood, any component that can leak will leak, so buy your calipers and master cylinder from a store with a liberal over the counter return policy unless you're buying Wilwood and avoid no-name Chinese proportioning valves even if they look just like GM.


https://imagizer.imageshack.com/v2/6...924/b7BzTt.jpg https://imagizer.imageshack.com/v2/6...924/t60wzh.jpg

https://imagizer.imageshack.com/v2/3...924/P5iMEG.jpg

Any particular years? I assume no kits on market with components?

Wheels are 15x7" Rally II

Do you have factory style axles/flanges or Moser?

Clean install - Although it sounds like a PITA - I do expect to flare lines and have tabs welded

I have Moser 30 spline axles.

I did have to weld on tabs. And I just used a couple of hard lines from Napa and bent them. You could make it better if you cut and flare lines. Mine are a little wacky because it was too long.

FYI: I (easily) grafted discs Strange Dana 60; 70-79 Rear Hats, 84 T/A Calipers and Emerg Brake cables.

Seems odd that no issues whatso ever since install, yet those rear Calipers were known to lockup due to mech Emerg shaft rust. Great Brake response using the G-Body Master CYL.

Yeah, the tabs they furnished were radiused to match the rear axle. The stock termination location of the hardlines was too far outboard to mount up anyway but I thought they could have easily punched the brackets for them maintaining the stock alignment and requiring only shortening the hard line termination.

I had a good laugh over their hose clamp and ziptie suggestion. I thought man oh man, what am I dealing with here?

Is this the kit you used?
https://www.summitracing.com/parts/rsd-afxrdm1/reviews

When H-O made rear disc brake kits, we supplied a spacer to keep the axle end play from pushing the pad back into the caliper and creating a low or zero brake pedal. a floating caliper design will eliminate this problem, but none of the designs I see pictured seem to support this.

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.

OOPS ! I was thinking of our A Body conversion ! But check axle end play anyway

Yeah, I just looked up my old tracking email.

I used RSD-AFXRDM1 and RSD-PV72 for the prop valve.

Im fairly certain I didnt pay that much for it, but they may have been hit hard by overseas availability. I think I payed like $275. Oddly all that I can find is the tracking and not the order receipt with prices.

All in all though I installed it in 2019 and have had no problems with it.

Was yours an original front disc car? If so, did you swap the MC?

It was drum drum, but the car was a basketcase. Everything on it now is all new aftermarket.

So initially I bought a right stuff front kit, that came with a master and a prop valve for front disc rear drum.

Then I bought the rear kit when I swapped the 8.5 in. Kept the same master but switched to a disc disc valve.

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

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

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?

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

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.

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

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.

+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.

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

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

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.

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.


.

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.

Scare bird - I sent you a PM

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.

.

You can get a standard wheel stud to fit into a 1LE rotor. The studs I bought and installed were identical in overall size as the original metric stud. I popped out the old studs and installed the new 7/16" studs. I have had the brake set up on my '76 Firebird for 2 years now.

I use the 1LE front and rear rotors both 12". I didn't want standard studs in the rear and metric in the front. The only studs that would fit the later model rotors and be 7/16 were off a 1967 only F body fronts with drum brakes. Talk about a hard to find stud...they're one year only.

you mean THESE studs...

10 - Optional standard wheel studs (NAPA PN-6411560 or Dorman PN 610-114)

simple knock ins.

Scarebird - duplicate to e-mail I sent you

Is the 1/4" overall track-width or per side for total of 1/2"? Also, what length studs would one use that would still work with Rally II's and blind lug nuts. Do the studs fit holes in the GMC Jimmy rotors?

s the 1/4" overall track-width or per side for total of 1/2"?

Total of 1/4"

Also, what length studs would one use that would still work with Rally II's and blind lug nuts.

1/4" longer works well here

Do the studs fit holes in the GMC Jimmy rotors?

yes, same pilot and stud size.

Yes, not for nothing but the part number was easy...I had to order them twice to get all the same studs in the box. Lol Nobody where I'm from nobody had them in stock. I couldn't even find one where I could see if they would work before ordering.

FWIW I just measured some Moser 30 spline 8.5 10 bolt F body and the pilot is 2.760. Factory ones I have laying around are 2.770 another one 2.783.

That's because aftermarket wheels are lug centric. The hub can vary, and they want them to fit multiple cars.

.