Composite brake rotors.

[ron350]

 

I found out the hard way that my 96 Regal requires composite brake rotors. Don’t know if it is because of the thick factory aluminum rims or if the car came with short wheel studs.

 I ordered a set of Full Cast rotors from the rock and because of the thicker flange I could only catch 3 lug nut threads.  Three threads are not acceptable so I finally talked the rock in to taking the Full Cast rotors back.

 

Went to the Dealership and ordered two rotors that were supposed to be composite but both turned out to be Full Cast. Ended up finding two correct composite GM rotors on ebay. The two NOS rotors I purchased are over 20 years old but were my only option.

 

Has any one run across this before?

 

 

[White93z34]

Composite? 

These cars are way way too mass market to require anything more exotic then cast.

You have stock wheels right?

It almost sounds like someone previously broke the studs and replaced them with short ones - this was done because you don't have to loosen the hub assembly to install them. It works with steel wheels, not so much with aluminium.

I'd examine the length of your studs and see what you can get your hands on. I probably have a few of the proper length out in the garage if you need an approximate measurement of how long they should be. Either way once you loosen the 4 hub bolts on the hub it will allow you the clearance to slide the proper ones in.

[ron350]

 Not sure you understand that most w’s came with composite rotors that have steel mounting flanges like in my picture above. Every GM car I have owned came from the factory with composite rotors.

My 96 Regal is all stock with factory aluminum rims and nothing has ever been changed out. With the factory composite rotors each lug nut catches 6 full threads.

Edited November 16, 2020 by ron350

[rich_e777]

I bought some off the shelf rotors from Autozone and put on a 95 Vert front and back and didnt have any issues, well they rusted quick on the edges.

[Cutlass350]

From:
https://www.aa1car.com/library/rotors1c.htm

==========

Composite brake rotors have been around since the early 1980s. When they were introduced, everyone was worried about soaring fuel prices (just like today), and auto makers were scrambling for ways to take weight out of their vehicles so they could meet government Corporate Average Fuel Economy (CAFE) standards. So one of the changes that was made was to replace heavy cast iron rotors with lightweight composite brake rotors.

COMPOSITE ROTORS SAVE WEIGHT

This type of rotor derived its name from the fact that it combined a stamped steel center hat with a cast iron rotor. Thus, it was a composite of two different materials. The new design proved to be about 20 percent lighter than a conventional one-piece cast rotor and saved up to a couple of pounds per rotor.

The composite design also allowed the rotor disc on some applications to be cast out of a special "dampened" gray cast iron for added noise suppression (dampened cost iron is not structurally suited for use in a one-piece cast rotor).

Some of these rotors also featured redesigned cooling fins for better heat management. Some were also directional for use on either the left or right side of the vehicle. Directional rotors are not interchangeable side-to-side because reversing the direction of rotation changes the cooling characteristics of the rotor.

COMPOSITE BRAKE ROTOR APPLICATIONS

Some of the earliest applications for composite rotors were the 1982 Lincoln Continental, 1984 Ford Mustang SVO, 1987 Ford Thunderbird Turbo Coupe, and 1988 Ford Taurus and General Motors front-wheel drive "W" body cars (Buick Regal, Oldsmobile Cutlass Supreme and Pontiac Grand Prix). Since then, the number of vehicle applications has continued to grow.
 

BRAKE SERVICE PRECAUTIONS

As the vehicles with composite rotors accumulated mileage and came out of warranty, the aftermarket discovered that composite rotors required some special service procedures. Because the stamped steel center hat is not as thick nor or rigid as that in a one-piece casting, the center hat on a composite rotor must be fully supported with special adapters or oversized bell caps when the rotor is resurfaced on a brake lathe. The other alternative is to bolt the rotor to the hub (with the lug nuts reversed to provide better support and to prevent deforming the center hat) and to then resurface the rotor with an on-car lathe.

If a composite rotor is not supported properly, it can wobble and flex creating runout and surface finish problems. Both sides of the center hat must also be clean and rust-free for the rotor to turn true.

ROTOR RECALLS

Some of the early composite rotors experienced corrosion problems and were recalled for replacement. Ford switched some of its models back to conventional one-piece cast rotors for awhile, and issued a service bulletin (#91-8-9) saying it was okay to replace composite rotors on the 1986 to 91 Taurus and 1988-91 Continental with one-piece cast rotors (P/N F10Y-1125-8). The corrosion problem is mostly history now because the OEMs now apply a protective coating to the stamped steel center of the rotor to inhibit rust. Aftermarket composite rotors typically use stainless steel for the center section to prevent rust, and the circumference of the center section is also dovetailed (notched) for increased strength where it mates with the rotor.

Vibration problems were also blamed on the design of the composite rotor. But the underlaying cause more often than not turned out to be improperly torqued lug nuts. Any rotor can warp if the loading on the lug nuts is not even. That is why an impact wrench should never be used to tighten lug nuts, unless it is used with a torque-limiting socket. Otherwise, a properly calibrated torque wrench should be used to tighten the lug nuts in a star or cross-pattern sequence.

REPLACE ROTOR

When worn or damaged composite rotors need to be replaced, be careful not to intermix rotor types side-to-side. Rotors should always be the same type on both sides. Replacing a composite rotor on only one side with a cast rotor may create a brake pull. So do not replace a composite rotor on one side of a vehicle with a cast rotor unless the rotors on both sides are being replaced.

Cast replacement rotors for vehicles that were originally equipped with composite rotors are available from various aftermarket suppliers. But other aftermarket suppliers recommend against substituting one type of rotor for another because the cross-section of the center hat on a cast rotor is significantly thicker than the stamped steel center hat on a composite rotor.

The difference may range from 1/8 to 1/4 inch or more depending on the application. This may not sound like much, but it does reposition the wheel slightly further out on the hub. This adds positive steering offset and alters the scrub radius of the steering geometry. The amount of change is not great, but neither is the amount of scrub radius that is designed into many vehicles. Scrub radius affects steering feel, steering effort and steering feedback. It also plays a role in the way braking and engine torque affect steering.

The change created by replacing a composite rotor with a one-piece cast rotor may be enough to alter the scrub radius from negative (which is the case on many front-wheel drive cars) to zero or positive offset. This, in turn, may create a noticeable difference in the way the steering feels and reacts, especially on cars with rack & pinion steering that are especially sensitive to steering feedback.

There is also a concern that substituting a thicker cast rotor reduces the overall length of the lug studs, which reduces the number of threads available for the lug nuts to retain the wheels (especially on thicker alloy wheels).

Suppliers who subscribe to the "replace same with same" philosophy say you are apt to encounter far fewer problems when you install replacement parts that are the same design and function as the original. Those who do not subscribe to this philosophy say there is often room for improvement over the OEM design.

===========

 

 

Good Luck!

Edited November 17, 2020 by Cutlass350

[jman093]

It does sound like there's something incorrect with your wheel studs. I have always tried to get factory composite rotors on mine, but the vast majority of first gens at this point in their life have plain cast rotors on them and there's no issue with thread engagement.

[Schurkey]

1.  I used to buy "all cast" rotors for my '92 Euro 3.4.  In the end, it didn't seem like those rotors made any real difference in rotor warpage.  I don't remember if I've got "all cast" or composite rotors on the vehicle now.  Never had a problem with stud length and OEM wheels/lug nuts.

2.  Look at most any GM brake drum from the last fifty or sixty years.  They're "composite" too--formed-steel center, cast-iron friction surface.  No one complained about them.  Buick used to have aluminum drums with an iron friction surface.

Edited November 17, 2020 by Schurkey

[ron350]

OK here is a picture of the rim and the studs. The studs measure 1.300” off the face of the hub. The studs have a smooth blank section on the end of each stud with no threads that measure 0.300” so that only leaves 1 inch of threads on each stud. All 20 studs are exactly the same.

 

 

[mfewtrail]

I just compared your studs to a factory one off a '94 Regal. They appear to be identical length, with the exception of the '94 stud not having the extra blank space at the end. There's only about 1 1/8'' worth of threads on the stud(measuring very top thread to very bottom). Have you compared the thickness of your factory composite rotor to the other ones you've tried?

[ron350]

Yes all of the steel center flanges on the composite rotors measure 0.100”or 1/10 inch.

The full cast Power Stop rotors measured 0.250” or ¼ inch thick.

 Looking at the lug nuts seams like the factory only wanted 6 (six) threads of engagement on each stud. Each lug nut only has 7 (seven) threads in each nut and the back section is hollow so that the nuts can’t be threaded on aluminum rims backwards.

Every thing will be fine now that I found the NOS composite rotors pictured above.

 

Edited November 19, 2020 by ron350

[mfewtrail]

Even though you've solved your problem, I've added a picture of the used(probably 220,000 miles) factory stud I removed. Maybe it'll help someone on a future search...

 

Edited November 19, 2020 by mfewtrail

[White93z34]

Guess I learn something new every day. I had no idea.

Granted it all seems to be academic at this point since I don't see any listings for composite style ones now.

I will say that in all the years I've been turning wrenches on these cars I've ever had a rotor fitment issue like what you describe, that is still really weird to me.

[Regal]

On 11/16/2020 at 7:54 PM, ron350 said:

For what it's worth now a few weeks later, I've owned 3 W body cars and this doesn't look out of the ordinary to me.

As far as brake rotors, I bought an EBC front kit for my '93 Regal of their "OE" rotor line with "red" (their mid level I believe) pads. Have been very happy with it. Not sure as to whether the rotors utilized composites or not but believe they are the best brakes I've bought. I had to wait some time for them which was fine as I actually believe they were made to order. They are made in England; rotors were finished in USA (rust prevention).

[GnatGoSplat]

What are composite brake rotors?  Anyone got a side-by-side comparison?

I know 2-piece rotors exist with the rotor part bolted to the hat, but I guess that's not what we're talking about.

 

[mfewtrail]

10 hours ago, GnatGoSplat said:

What are composite brake rotors?  Anyone got a side-by-side comparison?

I know 2-piece rotors exist with the rotor part bolted to the hat, but I guess that's not what we're talking about.

 

The pictures here cover it, but the article is pretty short as well.

http://www.remaninc.com/pdfs/compositevsfullcastrotors.pdf

 

 

[GnatGoSplat]

Huh, since they come out looking like 1-piece, I'm not sure I could tell a full-cast from a composite except maybe for the thickness of the hat.

I do remember those smooth-ended studs.  I had a low-mileage front hub pulled from a 96 Monte that was like that.

 

[ron350]

If you have the two types side by side it is easy to tell the difference. Every GM Composite rotor or drum I have seen has a raised retaining ring that holds the steel center. The Full cast rotors or drums do not have the retaining rings. The steel centers on a composite rotor and drum have a raise center lip that will cut your hand

If you ever replaced brake shoes on a GM vehicle from the 70’s you held a composite brake drum.

Edited January 19, 2021 by ron350

[GnatGoSplat]

I think I've only ever seen the composite ones.  All of my rotors have had the raised lip on the center bore.

I've never seen the full cast.  How thick are their hats?  Seems like it would be noticeably much thicker to lose that many threads on the studs.

 

[ron350]

 The full cast rotors I had to return had .250 -inch thick mounting flanges

The factory front rotors measure .100 –inch thick mounting flanges.

 

[GnatGoSplat]

I've definitely never seen the full cast rotors.  I needed 5mm spacers for my aftermarket front wheels to clear the calipers.  Turns out, I could have just used full-cast rotors instead!

Speaking of the spacers, I recall I had to push out the 96 style lugnuts and replace them with the ones from my old hub when I swapped to the 96 hub for the spacers to work.

 

[Schurkey]

Needed a "surprise" front brake job on my '98 Monte Carlo.  Ordered my usual pads, (Made in USA Performance Friction "Carbon Metallic" 0376.20) and found some "Genuine GM Original Equipment" 177-0972 brake rotors on Amazon.  The rotors came in GM-looking boxes (one box opened, rotor had very light surface rust, one box still sealed with the rotor in a sealed plastic bag inside.)

The new "original equipment" rotors were Made in China.  Bummer.  They're also full-cast which didn't bother me any, nor do I consider it an upgrade any more, which I once did.

The old rotors were on my driveway overnight, it rained, they rusted.  The braking surface wasn't rusty in-use, but the rest of the rotor was, as is usual.  The stamped-steel center vs. the cast-iron center is visible in the next photo.

 

I also took pictures of the lug studs with the all-cast rotor and the composite rotor:  First up, composite

About an inch and an eighth of stud sticking out, compared to about one inch for the all-cast rotor.

Looking at the lug nuts in the background, you can see that the composite rotor has about an eighth of an inch more protrusion than the all-cast rotor.  I have no idea how that eighth-inch can cause problems.

Of course, I wire-brushed the hub flange and around the lug-studs to remove loose rust before sliding the new rotors over the lug studs.

 

 

As is my proclivity, I also pulled the calipers apart for cleaning and inspection.  The most-contaminated brake fluid in a brake system is usually in the lowest point--the calipers or wheel cylinders.  I was concerned that the driver's side caliper might be sticky, as the pad was down to the rivets while the passenger side still had some life left in 'em.  In fact, the calipers looked fairly good inside, and slid easily on the pins.  God bless iron calipers!  I did this same job on my Trailblazer (Aluminum calipers) and the aluminum calipers tend to corrode behind the square-cut seal, leading to seized or at least stiff-moving pistons.  The iron calipers were beautiful inside, and the pistons were pristine behind the outer dust-seal.  The pistons were ugly on the part that sticks out of the dust seal, but that cleaned-up nicely on a wire wheel.  The part that sticks out doesn't really matter, but anything that would slide on the square-cut seal has to be perfect--no pitting, no flaking chrome.  I pulled the square-cut seals out for inspection and cleaning.  Sometimes the square-cut seals develop a hard "crust" from deposits in the caliper.  That crust would have to be peeled off with a fingernail.  These calipers didn't have any of that.  The seals were nice.  The dust seals are pressed into the caliper; they've got a metal reinforcement molded into the rubber.  I left them alone--removing them would likely wreck the metal reinforcement or tear the rubber.  I sprayed the bores with Brakleen, and wiped 'em out with paper towels.  Then lube the seals with clean brake fluid before reinstalling, and lube the pistons before trying to cram the pistons back in.

Just like any other multi-piston caliper, it's a pain in the ass to get both pistons out, and worse getting them back in again.  Compressed air will usually blow the pistons out, (put a piece of wood against the piston, so it doesn't bang into the iron of the caliper when it pops out) but one pops free before the other--and then you've got a big hole in the caliper so you can't build pressure to force the second piston out.  One piston has to be stuffed partially in-place to sort-of seal the hole, while using compressed air to remove the second piston, or to inflate the dust seal over the other piston during re-assembly.  Then you have to secure the partially-installed piston so it doesn't blow back out when you try to inflate the dust boot over the other piston.  I found that my C-clamp vice grip was not shaped properly for these pistons.  I needed to drop a pair of 3/4 steel nuts into the pistons so the vice grip would press on the bottom instead of the side of the vice-grip pushing on the top rim of the piston.

This photo shows one piston held in place to prevent air leakage, just before inflating the boot over the closer piston.  Wear leather gloves, the piston will get pushed away from the bore as the boot inflates, and your fingers will get kinda pinched against the outer edge of the caliper.  It's not bad, but gloves help some.

Once the pistons are started in the bores (with the bottom edge past the square-cut seal) they ought to press the rest of the way down with hand pressure.  I lube the pins with brake caliper grease, and I apply anti-seize to the threads of the various fasteners EXCEPT the banjo bolt for the brake hose.

 

I've had exceptional luck re-using all rubber seals, copper washers, etc.  These parts are not always re-usable, check them carefully for signs of wear, cracking of rubber, etc.

 

Time to quit typing, and flush the brake fluid, then put the wheels back on...

Edited August 13, 2021 by Schurkey

[Schurkey]

Just to finish this up, I pulled the rear drums, verified that the rear brakes were in altogether too perfect condition--41K miles, the shoes look like they were installed two months ago.  The rear brakes must hardly work, which explains why the front pads haven't lasted.  (second set down to the rivets!)

I dicked with the rear adjusters, tightened them up some.  They're supposed to self-adjust when the park brake is used...but it's a fookin' automatic transmission, I don't use the park brake.  The Leading/Trailing shoe brake design is piss-poor engineering as far as I'm concerned, 'cause I'm not the only person who doesn't stamp the park brake--which means the rear shoes never adjust.

Adding insult to injury, the damned rear drums are less than 9 inches in diameter, with narrow shoes.  How powerful could they be?  Fookin' GM, cutting corners on the 2nd Gen W-bodies by making disc rear brakes optional when the older cars had decent rear discs as standard equipment.

Anyway, I flushed brake fluid through six bleeder valves--one at each wheel, plus two on the ABS unit.  Flushed until I got nice, virgin-clear fluid at each one.  One of the ABS bleeder valves sputtered a little before giving me a solid stream of fluid.  Pedal height is improved.

Performed my usual after-brake-job test drive to burnish the new pads. Three hard "slows" from 40 mph to 10--15 mph, then several hard "slows" from 70 mph to 40 mph.  At that point, the pads seemed nicely bedded; the car didn't shift side-to-side any more when slowing; and the pedal effort for a hard stop reduced considerably.  Nice and predictable.  I also began to smell the brakes a little.  I continued at highway speed for a couple miles, then slowed hard from 90 to 40.  Powerful, sure, stable.  Good to go!

 

I don't allow the wheels to "stop" when bedding brake frictions--finned drums and vented rotors are centrifugal air pumps; and I want as much cooling air flow as practical--especially when braking from high speed.  Going from 90 to 0, and allowing the brakes to roast with no air flow is brutal--keep the speed up if possible so the air flow carries the heat away.  Of course, if traffic conditions require a full stop, that's what you do--but don't hold heavy pressure on the brake pedal while stopped.  Release as much pressure as possible while keeping the vehicle stationary.  This reduces the heat put into the pads, and therefore the heat put into the calipers and fluid.  And the pads/shoes don't "weld" to the rotors/drums.  The rotors and drums are designed to get hot; ideally the pads or shoes, calipers, rubber seals, and fluid should be kept cool if practical.