??

 

I would guess at rotors as there is less weight ???? same meterial (alum???) I don't know, Im just guessing.

 

I thought the rotors were like cast or steel?

 

Rotors are cast iron and some of them have a steel middle component (where it meets the axle or hub flange) and an iron outer disc. Those are called composite rotors and are the lightest style of rotor out there. I would guess that a drum system is going to be heavier no matter what since the brake drum has to have a cast iron friction surface even if it has an aluminum housing and that is going to be pretty heavy. I'm not really sure though........ they (al drum vs. iron disc) would be pretty close on rotating mass I bet. The other thing to consider is that the drum's mass is farther away from the center axis of the axle or hub compared to a disc, which is undesirable......

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But, drums fully release from the contact surface, where-as there is some amount of drag between a rotor and pad setup, which is undesirable and a reasom many drag racers use drum brakes.

 

In the case of disc vs. drum, both being iron, the disc setup will always be heavier than the drum setup. Remember you have the disc itself (which has more mass than a drum), the caliper, brackets, etc ... While the drum has only the drum (less mass), and some srpings with the support being the axle plate. I have two 10-bolt rear ends (one disc and one drum) and the disc are very noticably heavier than the drum rear end. Now if you are comparing the aluminum drum to disc, it's a no brainer ... Al drums are lighter. This setup is ideal for drag racing (in a limited budget class), but disc are better for road racing.

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FYI, the '89-'92 rear disc brake setup is MUCH MUCH lighter than the earlier setup. I weighed them and seem to remember roughly about 9-10 lbs per side less. The calipers are aluminum vs. iron, and the rotors, while larger in diameter, are much lighter (I assume because they are thinner).

That setup seems to weigh less than cast iron drums and all the associated drum hardware.

 

I guess i'll stick with the aluminum drums. Anyone know the P/N for these????????

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92 RSS,
Aluminum Drums: 1255496

Cast Iron Drums: 1249146

Those are GM part numbers and they should be valid.

FYI.......I tried to get the aluminum drums thru AutoZone. They don't carry them.....have to go to GM for those I believe. Cast iron......many places sell aftermarket ones. Hope this helps.

Mike

 

Advance auto has the aluminum drums. I think they were around $45 a piece.

 

I re-read your post and I really ain't buying... Maybe aftermarket disc setups. I agree 100%, but the factory rear disc setup really sucks. BTW, the calipers are cast iron. I know, I have two cars with them. One is supposed to have them, the other I converted to discs. After converting I noticed NO IMPROVEMENT in stopping. none. zero. ditto. The back brakes are not stressed very much so therefore fade isn't a huge issue with them.

Also, neither car has an e-brake that works proper. I hooked the cables up, got new ones, got new calipers, and the best the lever does is a very light lock, not even enough to stop the car on a very steep hill. With the drums, 'dem babies were locked!

Another point: The drum brakes are cheaper to service, and ALOT easier to change. For those who do the brakejobs and would think the discs would be easier, remember, they are NOT anything like the fronts. The piston has to be pressed and turned at the same time and you must align a notch in the piston with the nub on the pad. A PIA to say the least.

THE ONLY THING FACTORY REAR DISC BRAKES HAVE ARE GOOD LOOKS THROUGH 'WIDE OPEN' MAGS

 

Look, you obviously have the older style ('82-'88) rear discs. Yes, they suck. Yes, they are cast iron. They also have nothing in common with the '89-'92 brakes which are the same as the brakes on the the LT1 4thgens. Those brakes work pretty damn well, and the calipers ARE aluminum.

If you don't believe me, ask some other people on here.

 

yeah but with disc breaks the ONLY rotating mass is the disc, not the caliper and pads, etc.

-Brian

 

I did call my local dealer about the aluminum drums and the were like $160 each!!

Advanced auto $45?? I'll have to check that out.

Thanks for the replys,
I believe the aluminum drums will be lighter than the rotors.

 

Well.... being in my 4th year of Mechanical Engineering, basics show you that drums would have more rotating weight. True that they may weigh less on the scale... but you get them rotating at 1000RPM... the drums weight a lot more rotating weight. All the material on a drum is 4-6" from the center, thus creating a force greater than that of a rotor that the material is almost uniform from center to edge. Plus... you can get some drilled and slotted rotors that will bring weight down even more. I would stick with the disc breaks, expecially if you are driving this on the road as well.

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I'll be damned. Somehow I missed the whole "rotating" part of the original question! Absolutely the 89-92 rear rotors are much lighter than iron drums. I would think the '82-'88 rotors are close.

I've never weighed or even picked up aluminum drums so I have no idea how much they weigh...

But this also begs the question, why is the original person worried about rotating weight? I assume there is a reason behind asking the question.

 

The same reason you put on an aluminum driveshaft and rails run tiny, skinny tires on the front: It takes power to get them moving.

Also, they act like a flywheel when braking.

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Yes, but that doesn't take into account the drag from disc brakes.