Rear drums vs Rear disc

Thu Jun 30, 2005 11:59 pm

If you had the option of changing your drums for the bmw rear disc would you undertake this task or forget about on the grounds that it would be more trouble than its worth. My retired touring has rear discs and I am thinking of breaking it for spares. The engine was running rough with one cylinder having low compression (which went up when a little oil added giving indication of worn rings/cylinder).
My 316i has drum brakes. Would it be much hastle in swapping rear brake systems over.

Fri Jul 01, 2005 12:22 am

rear discs is definately a bonus dude, much better than drums no contest

Fri Jul 01, 2005 8:30 am

its not so much hassle but time consumin good days work but discs are the way to go

Fri Jul 01, 2005 9:27 am

Hmm I might leave it as it is for a bit.

Fri Jul 01, 2005 9:53 am

yer discs are the way forward...... They look mucho better too

Fri Jul 01, 2005 10:04 am

There is hardly any difference in braking performance between the two, they just look better.

Fri Jul 01, 2005 10:22 am

what planet u from then (no difference)

Fri Jul 01, 2005 10:34 am

If you cant be bothered to fit discs why don't you go down halfrods and by one of the fake disc kits, they'll look lush !!!! ha ha ha ha

Fri Jul 01, 2005 10:57 am

1.6i M40 for sale

Fri Jul 01, 2005 11:21 am

jonbuoy wrote:There is hardly any difference in braking performance between the two, they just look better.

I would have said there was a difference. But for higher speeds only and I don't realy do high speeds so maybe your statement is justified. And as for looking better I usualy keep my wheels on so no one would notice.

Fri Jul 01, 2005 11:32 am

ive done this before and wow what a difference!

Fri Jul 01, 2005 11:40 am

If your drum brakes are setup properly there's no difference.
I think BMW went to rear disks because of the heat build up.

Fri Jul 01, 2005 11:49 am

Martinaston wrote:If your drum brakes are setup properly there's no difference.
I think BMW went to rear disks because of the heat build up.

They become 'un' setup after a few miles, Disks are much much better!

Drums are shit!

A

Fri Jul 01, 2005 12:36 pm

I think there's just more movement in the peddle as the shoes wear.
As opposed to the disks where the caliper piston moves out more taking up the slack.

Fri Jul 01, 2005 12:42 pm

I'm changing my 320i over to discs - is there any difference in the brake compensation valve for drums compared to discs? - I understand the valve apportions braking effort around 60/40 (60% front, 40% rear.) Is there any difference between drum valve/disc valve?
sorry if I'm wandering off topic!!!

Fri Jul 01, 2005 1:32 pm

Treeman612 wrote:I'm changing my 320i over to discs - is there any difference in the brake compensation valve for drums compared to discs? - I understand the valve apportions braking effort around 60/40 (60% front, 40% rear.) Is there any difference between drum valve/disc valve?
sorry if I'm wandering off topic!!!

No!

A

Fri Jul 01, 2005 2:59 pm

Drums brake over a greater area so they are better at braking. That’s why coaches and lorry's use them.

However, discs dissipate heat much better and that’s mainly why discs are used.

People also like the look of rear discs through the alloy wheels. Makes the car look more sporty and modern.

Fri Jul 01, 2005 3:36 pm

I thought disk weren't used on lorries because they shatter ?

Fri Jul 01, 2005 4:22 pm

the only thing drums are good for is HGV`s

Fri Jul 01, 2005 8:52 pm

the reason drums are used is because they disapate heat better due to the larger surface area. they are also cheaper to make and drums also ahve a self servo effect, that is one shoe once it is applied to the drum gets pulled on by the rotation of the drum giving better brakoing efficency. on the truck front the vast majority of long haul trucks now use disk brakes as the do not need adjusting and on long hauls don't heat up cuasing warping/cracking plus servicing is vastly quicker with disks compared to drums

Sat Jul 02, 2005 4:58 pm

slideways wrote:the reason drums are used is because they disapate heat better due to the larger surface area. they are also cheaper to make and drums also ahve a self servo effect, that is one shoe once it is applied to the drum gets pulled on by the rotation of the drum giving better brakoing efficency. on the truck front the vast majority of long haul trucks now use disk brakes as the do not need adjusting and on long hauls don't heat up cuasing warping/cracking plus servicing is vastly quicker with disks compared to drums

Mate, drums dont disapate heat better than discs. Where did you get that info from?

Next time you see a truck check if it has discs. I'll think you'll find they still mainly use drums.

Sat Jul 02, 2005 5:26 pm

i'm a truck mechanic, and i look at the heaps all day ever day, virtually all new trucks excluding construction, have disks, as to the heat disipation we will have to agree to disagree, mate.

Sat Jul 02, 2005 10:53 pm

Disc brakes don't work by the pads"gripping" the discs and drum brakes don't work by the linings "pushing" against the inside of the drums.
Both types of brake work by converting the kinetic energy of the vehicle into heat and then dissapating that heat to the atmosphere. There is no great problem in providing the friction for either type of brake, but where disc brakes are vastly superior to drums is their ability to dissapate that heat into the atmosphere.

Sat Jul 02, 2005 11:03 pm

Ive seen modern lorries with both drums and discs

Should see the size of the components on an 8 axle lorry tho!

Wed Jul 06, 2005 7:26 pm

Hey, Brian, your answer makes so much sense - as an old school (!) engineer, is the difference mainly that a drum has to dissipate mainly by transferring heat right through the drum to atmos., whereas disc is 90% exposed to atmos. anyway, therefore much less heat build-up in disc as opposed 2 drum?

Wed Jul 06, 2005 7:29 pm

Treeman612 wrote:Hey, Brian, your answer makes so much sense - as an old school (!) engineer, is the difference mainly that a drum has to dissipate mainly by transferring heat right through the drum to atmos., whereas disc is 90% exposed to atmos. anyway, therefore much less heat build-up in disc as opposed 2 drum?

yeh but surely heat has to first dissipate from inside the drum to the outside first.... whereas with discs, the surface involved which is the disc face is directly nxt to atmosphere....

Wed Jul 06, 2005 7:34 pm

Brianmoooore wrote: Both types of brake work by converting the kinetic energy of the vehicle into heat and then dissapating that heat to the atmosphere....

Are you sure about that? My brakes seem to work by converting the kinetic energy of the vehicle into sound (ie squeeeeeel)

Wed Jul 06, 2005 7:36 pm

ok people what do u c on the track DISCS these r used coz they excell in brakin technology wid different disc composit ie ceramic u dont c a breakfast bowl on a formula 1 car do ya? u c dirty great fat dinner plates

Wed Jul 06, 2005 10:06 pm

Treeman612 wrote:Hey, Brian, your answer makes so much sense - as an old school (!) engineer, is the difference mainly that a drum has to dissipate mainly by transferring heat right through the drum to atmos., whereas disc is 90% exposed to atmos. anyway, therefore much less heat build-up in disc as opposed 2 drum?

Yes, it's all about getting rid of the heat. Taken further of course by the vented brake disc.