Why drums?

Why drum brakes? Somebody must have a decent explanation about why drum brakes are still being used. Mechanically, it seems to me that discs are so much easier and don't have as many issues. I'm just wondering in these wee hours of the mornin'.

Cost.

yup, cost, plus some vehicles such as older xj's dont have abs, its kinda law(in virginia) to have drums without abs!!! plus....do you mud? then you know you like rippin that handle!!!

drums are more effective with less input force. Sort of moot with
power brake boosters, but at least if they are adjusted properly
the dums give you a better emergency/parking brake.

Related to that, the parking brake mechanism on a disk set up needs
to be a complicated ($$) arrangement to hold the high pressure,
on the drum its just a cable to the shoe..

Which is why ZJs have cable actuated handbrake shoes working in the inside surface of the disk, rather than a caliper-related system.

trashedxj said:

its kinda law(in virginia) to have drums without abs!!!

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Source, please?

This makes no sense whatsoever, as there are many vehicles on the road that were sold with 4-wheel disc brakes and no ABS. Even in VA.

Marketing, one of the major selling points of the ZJ and WJ vs the XJ was 4 wheel disc brakes. When they introduced the KJ it had rear drums, now it has 4 wheel disc and considering it has always had a 8.25 same as the XJ it was no big deal. What suprises me is they don't offer 4 wheel disc on the TJ's 'yet', consider also that all the unlimited's come with a LSD.

The biggest reason for drums still be used on the rear wheels? aside from cost, the other MAJOR issue is the PARKING BRAKE.

It's much easier/cheaper to implement a parking brake into the design of drum brakes than it is for disc brakes, and the parking brake is almost always on the rear wheels.

Take a look some time at all the different methods the auto makers have used to get a parking brake to work in conjunction with disc brakes in the back. Then look at the ways they implement parking brakes on drum type rear brakes.

You will find that most everyone uses the same approach for drum-type parking brakes, but there are oodles of approaches for the disc-type parking brake, and NONE of them are as reliable or as cheap to create as that drum type.

That, more than anything else, has been the main reason for sticking with drum brakes in the back.

Chancer said:

Which is why ZJs have cable actuated handbrake shoes working in the inside surface of the disk, rather than a caliper-related system.

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IMO it is a simpler (to work on) and a better desgin... I have seen too many poor desgins, and less holding power for the emergency brake that are incorporated into the caliper than if the caliper and ebrake are seperate items...

FYI - Most newer larger trucks (1500/2500/3500/F350/250 -etc.) have the parking brake as a drum inside disk setup...

Will.

Just a point of interest. GM is going back to drums on the rear of there 1/2 ton pickups. They are saying better pedal feel and stopping power for the change. I'm sure cost is also a concern, but not a good selling point.

tompatjr said:

Just a point of interest. GM is going back to drums on the rear of there 1/2 ton pickups. They are saying better pedal feel and stopping power for the change. I'm sure cost is also a concern, but not a good selling point.

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As long as the bean counters and those who benefit financally have input on what is supplied on vehicles any 'improvements' should be taken with a grain of salt...
If the better stopping power and better feel were true they would be putting drum brakes on high end MB's, Porches, Lincolns, vettes and caddys...

All new TJ's w/ a Dana 44 rr. also include disc brakes on the rr. axle. This started in the '03 model year w/ the intro of the Rubicon package.
Also the the 44's from the factory had limited slip, since 97.

RichP said:

Marketing, one of the major selling points of the ZJ and WJ vs the XJ was 4 wheel disc brakes. When they introduced the KJ it had rear drums, now it has 4 wheel disc and considering it has always had a 8.25 same as the XJ it was no big deal. What suprises me is they don't offer 4 wheel disc on the TJ's 'yet', consider also that all the unlimited's come with a LSD.

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explorer said:

All new TJ's w/ a Dana 44 rr. also include disc brakes on the rr. axle. This started in the '03 model year w/ the intro of the Rubicon package.
Also the the 44's from the factory had limited slip, since 97.

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To qualify that, AFAIK the D44 option was the only way to get a LSD on a TJ. It also cancelled out ABS if you ordered the D44 LSD. Sons friend two houses down has two 98TJs w/D44s, one 2.5 and a 4.0. As far as I know only the rubicon's with the E lockers have rear discs. I'm going to have to look closer at whats out there. I'm hoping, money wise, that I can order an unlimited this spring, rear discs would be nice.

RichP said:

As long as the bean counters and those who benefit financally have input on what is supplied on vehicles any 'improvements' should be taken with a grain of salt...
If the better stopping power and better feel were true they would be putting drum brakes on high end MB's, Porches, Lincolns, vettes and caddys...

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I sure don't want to get into a pissing contest with you over this...so, I agree. I think disk are better for the most part. But I think a drum and disk will brake about the same until the drum heats up and fades. This is the primary reason disk are favored, they don't fade as easily. Anyway I'll be sticking with the drums fot the time being.

Also, Semi's may soon be changing to a air disk. Extra expense, but much improved resistance to fade.

Early Range Rovers have a drum parking brake on the rear driveline... cool idea if you ask me.

Tompatjr is correct. Braking effectiveness basically is a factor of swept area. Back in the late 60s when I was crewing on a short track modified stock car, ALL the cars ran drum brakes off full-size Lincoln sedans. The brakes were huge, and without any power assist they could smoke all four (big) racing tires in the middle of the back straight with no trouble at all.

Discs are not inherently better than drums in terms of stopping power when sized appropriately. Discs are better at dissipating heat. In a road racing type of vehicle, that will be seeing a lot of heavy brake use, this is an issue. I guess GM figures that a half-ton PU isn't going to see that much heavy-duty break use, and probably won't be doing extended towing of heavy trailers, so the drums may in fact be better than small-ish discs.

When's the last time you saw an 18-wheeler with disc brakes?

LSD was available on 35's, I specifically had to tell them I didn't want it when I ordered mine because I already had a Lockright waiting. D44 w/ 2.5? Was it swapped? That was another thing I'm pretty sure would be blocked when ordering the vehicle.

And just to stay on topic, the effectiveness of the brake depends on alot of things other than disc or drum. My dad had a Z34 Lumina w/ rr. disc that wore through rr. pads amazingly quickly while seemingly having no braking power at the rr. wheels. Frt. was the same for that matter. Later models of the Lumina went back to drum brakes for some period of time. Better braking and less trouble when they switched to the drums. As for as brake fade, yeah drums typically do that. But go drive a ZJ w/ the same brakes as your XJ, and do some moderate to heavy braking from high speeds. Then tell me discs never fade. Fade has everything to do with the amount of heat the brake can absorb. If the brake is undersized for the application, it will fade, disc or drum. All that aside. For my TJ I'm currently swapping to rr. discs on my new axle. It wasn't necessarily for more braking power. They are just much better a shedding dirt and mud and easier to clean and maintain and more consistent in varying conditions.

RichP said:

To qualify that, AFAIK the D44 option was the only way to get a LSD on a TJ. It also cancelled out ABS if you ordered the D44 LSD. Sons friend two houses down has two 98TJs w/D44s, one 2.5 and a 4.0. As far as I know only the rubicon's with the E lockers have rear discs. I'm going to have to look closer at whats out there. I'm hoping, money wise, that I can order an unlimited this spring, rear discs would be nice.

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Oh, yeah. fade.

The original 1968 and 1969 AMX had solid (non-ventilated) rotors in front. It had disc brakes, all right, but they weren't any better than the drum brakes on the base level Javelins of the same years. I fixed mine by using the vented rotors (with corresponding axles, hubs and calipers) from a '73 Matador.

Eagle said:

When's the last time you saw an 18-wheeler with disc brakes?

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They are coming! I have read test comparing them and the disk. European countries have been using them for sometime now.

tompatjr said:

I sure don't want to get into a pissing contest with you over this...so, I agree. I think disk are better for the most part. But I think a drum and disk will brake about the same until the drum heats up and fades. This is the primary reason disk are favored, they don't fade as easily. Anyway I'll be sticking with the drums fot the time being.

Also, Semi's may soon be changing to a air disk. Extra expense, but much improved resistance to fade.

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Good lord, semi's, man they lock them up now as it is, what do they need MORE brakes for, wonder if they also will put them on the trailers, those are what I usually see lock up out on the interstate...
On our old M151's we had an emergency brake that was basically a band setup of some kind around the driveshaft. You had to be stopped to use it, if you were rolling and pulled that handle up it would snap and no eb after that.
I've also seen an emergency disc brake on the rear diff, small 6" or so disc attached to the pinion, this was on a vette, totally mechanical caliper and I thought it was a neat idea till I thought about it coming down on a rock.
My main reason for liking disc in addition to better braking is ease of maintenance, they are just flat out cleaner to work on.