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AydinZ71

Drum brakes for a racing application

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Hi all! I have been doing some research on drum vs. disk since my expertise is not in braking or suspension. I purchase it as an SCCA group EP race car, and I am restoring it for the past 4 months (it was in rough shape). For the purpose of this discussion, I am specifically talking about the rear brakes since the fronts already have disks. 

 

From what I read, it clear drums are cheaper than disks but are much more inferior in handling heat with consistent high duty-cycle use. I also see some sources stating they are lighter, but this was not specific to an S30 chassis. The spec. line from the SCCA rule book does allow for disks in the rear: "(R) 258 or 269 Solid Disc. Discs and calipers from 280-ZX."

 

I am trying to determine if I should keep the car with drum brakes in the rear, of if it is worth the weight and expense of upgrading to the specific disks allowed by SCCA. The car already has a front/rear proportioning valve installed. If I keep the drums, I would be looking into adding my own modifications to improve cooling. Welding-in thin steel sheet metal on the rear side of the drum dust shield, as well as other cooling fins on the cast steel hub assembly itself. Would love to hear your input!

 

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It largely depends on what you plan to do with the front discs (if anything) and what type of events you plan to run....

 

Start by reading all the "brake upgrade" threads in this sub-forum and in the FAQs if you haven't already done so.  You'll find a TON of great info.

 

The stock front discs and rear drums are actually a pretty well-balanced system, and work ok for most types of short duration racing (e.g. time trials, auto-x, etc).  Longer events will quickly overheat the system and you will find yourself looking for better braking longevity during extended high-speed use.  You'll find the fronts overheating/fading (and possibly boiling the fluid) and the aluminum rear drums will expand and lost most of their effectiveness.  It's an old S30 trick to pull the rear parking brake up one or two clicks when this starts to happen.  Some people have preferred to go with cast iron drums in the rear because they expand less (but are significantly heavier than the stock ali drums.) 

 

If you're not planning to upgrade the fronts with bigger, vented rotors and calipers, you should probably leave the drums in the rear IMHO.  Don't forget that bigger calipers in the front and/or disc brakes in the rear will typically necessitate a larger bore MC.  If you leave the drums in the rear for now, Porterfields are probably some of the best shoes you can get....the generic off-the-shelf shoes (e.g. Centric, etc) from the auto parts chain stores are not worth your time.

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12 hours ago, jhm said:

If you're not planning to upgrade the fronts with bigger, vented rotors and calipers, you should probably leave the drums in the rear IMHO.  Don't forget that bigger calipers in the front and/or disc brakes in the rear will typically necessitate a larger bore MC.  If you leave the drums in the rear for now, Porterfields are probably some of the best shoes you can get....the generic off-the-shelf shoes (e.g. Centric, etc) from the auto parts chain stores are not worth your time.

Totally agree with this.

Also, the early 79-81 ZX rear disc is not an upgrade in stopping power over the drums. It is possible to get enough rear braking with the early ZX and the stock front calipers, but any front upgrade will overwhelm the rears. I had Toyota fronts and the early ZX and couldn't get enough rear braking, eventually put the stock front calipers back on and was able to dial it in, but then I would boil the brake fluid all the time. Got to the point where I no longer got an adrenaline rush when the pedal went to the floor. That's a bad sign LOL.

Also got the fronts so hot the brake pad lining just abandoned ship and a punched a hole through the backing plate. Rears had pad material coming off in chunks. To my discredit though, I was trying to run Porterfield's R4S street pad. Not a good idea...

I never tried the 82-83 rear brakes so I can't tell you if they're any better. Definitely lighter, those early calipers are HEAVY and the pads are TINY.  I would suggest looking at what other EP drivers are doing for brakes. Greg Ira is the 3x national champ. See if he has any recommendations for you. If you could use the ZX rotor and change out the caliper that might help. I don't think the heat capacity is as much of an issue in the rear, but the lack of clamping and pad surface area certainly is. 
 

r4spad.JPG

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Thanks so much for all your help! I can answer a few questions that you asked, and I copy-pasted the SCCA rule book for braking at the bottom. 

 

- I will be entering the car into group EP road racing, or sell the car to another driver for that intent. The way i purchased the car, it would not have been up-to-snuff, so my goal is to prepare the car to have the "bones" it needs to be tuned into a competitive vehicle. I may never race it myself, as I seem to enjoy the restoration/research. My day job is as an ME, so I naturally gravitate to the technical challenge. 

- According to the rule book, I have to keep the stock front caliper. They allow alt. ferrous material but the dimensions must remain the same. Therefore, no vented front rotor for me. The car is currently equipped with cross drilled rotors, but this seems like an unacceptable upgrade given OEM was not drilled. 

 

I am really glad I asked yall! I fell like there is a reflexive notion to automatically go disk in the rear. If I am reading your responses right, having the right shoes in the rear for a road race could keep the drums usable. Especially if the front caliper/rotor combo must remain. The car does not currently have a hand brake, but I am eying the hydraulic one sold by arizonazcar. I will spend more time looking in the FAQ's. You two obviously have a ton of experience so this was very helpful. I will look into Greg as well!

 

Unless i read something different, it seems like the way to go will be primarily upgrading the pads in the front and rear with R-4, or RD-4 Porterfield shoes and pads. The RD-4 seems to have a better bite at lower temperatures, which might be useful for my occasional drives on Angeles Crest Highway (I live a mile from the portal). 

 

 

"Brakes Level 1 and 2
a. Stock calipers must be retained. Cars fitted with integral hat brake rotors can convert to a two
piece design hat and brake rotor. The alternate design hat must be made of ferrous or aluminum
material. Alternate discs can be used, but must be made of ferrous material. Alternate drums can
be used, but must be made of a ferrous or aluminum material. Alternate discs and drums must be
the stock diameter, width and design. Brake rotors can not be cross drilled or slotted unless fitted
as stock.
b. Cars fitted with rear drum brakes, can convert to rear disc brakes. When converting from rear drum
brakes to rear disc brakes:
1. Rear brake rotors can be no larger in diameter than the largest permitted front brake rotor. Rear
brake rotors must be solid and made of a ferrous material. Rear brake rotors can not be cross
drilled or slotted.
2. Rear brake rotor hats can be made of a ferrous or aluminum material.
3. Rear calipers and mounting brackets are unrestricted but must be made of a ferrous or
aluminum material.
The standard and alternate brake listings on a vehicle’s specification line, does not prohibit a car
that was fitted with rear drum brakes as stock from converting to rear disc brakes under this rule."

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12 hours ago, AydinZ71 said:

The car is currently equipped with cross drilled rotors, but this seems like an unacceptable upgrade given OEM was not drilled. 

 

True statement IMO.  I have shied away from cross-drilled rotors, because I know too many people that have suffered cracked rotors due to the cross-drilling.  I like slotted rotors, but the plain-jane pancake rotors are fine too....just use some good pads.  I prefer Carbotech for track (and Porterfields for street), but that's just my own personal preference because I've found a good combination that works for me with my particular setup.  There are several good high-performance pads available to choose from.

 

13 hours ago, JMortensen said:

Got to the point where I no longer got an adrenaline rush when the pedal went to the floor. That's a bad sign LOL.

 

I'm not at that point yet....still get the clenched butt cheeks when the pedal goes to the floor.  :-)

Edited by jhm

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I did a quick check, and the stock front rotor is 10.6, so you'd want to get as close to that diameter as possible, since you can run up to the same diameter rotor. The early ZX is 10.5, later ZX is 10.2 according to rockauto.com. If you're going to make your caliper brackets, I'd use an early rotor and a late caliper. Or if possible find a rotor with a less deep hat. Early ZX has really deep one, the rotor is probably 3" back from the axle flange.

Also re: drilled rotors. I pushed the piston through that brake pad with drilled rotors. I was at the track and needed to drive home, so I went to the local parts store, bought their shittiest pad, slapped it on and drove home. Changed them before the next race, but never even surfaced the rotors and there were no cracks at all between the holes. I worked on Porsches at that time and we routinely replaced rotors when the cracks were nearing the next cross drilled hole, but mine never cracked at all, front or rear, after lots of abuse. I will say that they make a weird buzzing noise when you get them hot. My explanation is the heated air is being released from the holes as the rotor turns past the brake pads, successively venting each little hole along the way. Not a problem, but it's kinda strange. The bigger issue is that you're taking away material. I guess the idea is that the cross drilling helps to cool the rotor, but more mass means it can absorb more heat, so ??? If you're running stock brakes in front I'd suggest a couple of 3" vents per side. Katman, who prepped a lot of ITS cars, posted about using a soup can with a slot in it to get air to the outside of the rotor, and warned against cooling only the inside. You might be able to search his threads to find. Probably close to 20 years ago now.

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Just read your (sensible) brake rules, my response is that you could use dimpled solid rotors on the front if you wanted to and use two piece which may save some weight. On the rear the only restriction for a disc brake conversion concerns the solid rotor diameter which may be two piece and use any calipers. So there is a fair bit of scope there for improvement of the rears both in weight and effectiveness.. I'd be tossing the rear drum brakes for sure.

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