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Author: Subject: BMW handbrake design - is it just me that thinks it is poor?
stevegough

posted on 4/7/22 at 05:43 PM Reply With Quote
BMW handbrake design - is it just me that thinks it is poor?

It's been a very long time since I turned to Locostbuilders - kit car got built, used for 3 years, MOT-d and then sold. During which time, I was seriously grateful for all the engineering knowledge on here!!!

Anyway, Grandson (that's him, in the photo!)(who is 18 and was only 6 when Kitcar was being built!!) has bought a 2003 BMW 3 series which has, amongst other issues, an ineffective handbrake.
So he bought some new cables and brake shoes. I helped him fit them and was astounded how poor
the design appeared to be. Firstly, they are shoes and use the inside of the disc 'rotor' as the drum.
The shoes are fitted to the backplates which were rusted where the bayonet fitting were located.
So we had to replace the backplates as well. So all was okay, but there seems to be a lack of 'fixing'
for the brake shoes - they are held in place with the sprung bayonet-tipped clips and the pressed-steel
two piece pivot attached to the handbrake cable lug. Bottom line - they aren't solidly fixed to anything.

So I was wondering if anyone else has come across these patheticly-designed brakes?







Luego Locost C20XE.
Build start: October 6th 2008.
IVA passed Jan 28th 2011.
First drive Feb 10th 2011.
First show: Stoneleigh 1st/2nd May 2011.
'Used up' first engine may 3rd 2011!
Back on the road with 2nd engine may 24th
First PASA mad drive 26/7/11
Sold to Mike in Methyr Tydvil 19/03/14

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theconrodkid

posted on 4/7/22 at 07:01 PM Reply With Quote
lots of cars have that design, it,s not that bad, i does away with the problems they had with the calipers when the calipers did both jobs, the shoes are semi floating and easy to adjust so whats not to like ?





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indykid

posted on 4/7/22 at 10:09 PM Reply With Quote
There's nothing to load the shoes away from the backplate, all the reaction is rotational/circumferential and there's no way the shoes can escape unless you lost a wheel....and a caliper carrier.

SWMBO's CRV has the same setup. I think it's great. The handbrake never gets used as a service brake so it's all squeaky clean and never wears. The calipers are just calipers with no handbrake mechanism to seize, nothing to struggle winding back. Also, being drums, the bite on the handbrake is brilliant.






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ReMan

posted on 4/7/22 at 11:14 PM Reply With Quote
As said, I've never had a BM but what you describe is the same as most I've ever come across.
I always dress/chammfer new shoes on all edges to help with bedding them in and you may find you need to do some handbrake stopping to quicken the process, but beyond that they are never going to work as well as primary drum brakes due to the low pressure applied by a single sided cable operation, but should be good enough as parking only brake





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nick205

posted on 5/7/22 at 07:37 AM Reply With Quote
I believe the design approach is fairly common on modern cars to have rear discs/calipers for the service brakes with shoes inside the rear discs for the parking brakes. Never examined BMW's execution of the design myself so can't comment on their particular approach. With quite a few car makers using this type of setup it though it can't be ineffective or it would be a persistent parking brake/MOT fail.

I'd hazard a guess the increasing number of cars moving to electronic parking brakes may use this type of system. You'd not want to keep the brake fluid under pressure for the parking brake. I believe most operate by pulling a cable.

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JAG

posted on 5/7/22 at 08:03 AM Reply With Quote
This design is called a Duo Servo Drumbrake.

It provides a very powerful park brake (for the size and cost) and it avoids lot's of other issues that occur when you have the Service brake caliper performing the Park Brake function.

Fix it properly and you'll find it works very well as a Park Brake.





Justin


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Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!

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coyoteboy

posted on 5/7/22 at 08:04 AM Reply With Quote
I hate drum brakes at the best of times, they never work properly. Hated them on my pug 205, hated them used as you described on my ST185. The most awful archaic design of ratty spring loaded, spring clip fitted sheet metal.

But still work better than the damn screw-piston-on-disc handbrakes on my pug 306 disc rear end, which literally fails the MOT every year and every year I have an argument and have to replace both rear rotors, both rear pads, both cables (and last year the caliper too) and STILL have it fail the brake efficiency test.





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nick205

posted on 5/7/22 at 12:19 PM Reply With Quote
quote:
Originally posted by coyoteboy
I hate drum brakes at the best of times, they never work properly. Hated them on my pug 205, hated them used as you described on my ST185. The most awful archaic design of ratty spring loaded, spring clip fitted sheet metal.

But still work better than the damn screw-piston-on-disc handbrakes on my pug 306 disc rear end, which literally fails the MOT every year and every year I have an argument and have to replace both rear rotors, both rear pads, both cables (and last year the caliper too) and STILL have it fail the brake efficiency test.




Intersting...

I've had several 205 1.6 GTIs which have drums on the rear. They worked fine for me and were easily mainainted as well. I still have a 205 1.9 GTI which has discs of the rear. They work equally well and are easy enough to service too.

I had a 306 2.0 HDI for a good few years which had discs on the rear. No issues with it operationally or maintainance wise. Went through it's MOTs just fine too. The clutch cable had to be replaced. This apparently is down to it passing close to the exhaust, which dries out the lube inside it (an issue on right hand drive versions, but not left hand drive versions of the car).

[Edited on 5/7/22 by nick205]

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Dingz

posted on 5/7/22 at 02:09 PM Reply With Quote
Iíve an E90 08 year, itís just failed mot on handbrake. Tester said BMW and Mercs have same problem/design. I took it apart it was full of dust and rust. Cleaned it all up, the shoes have very little wear, adjusted them and itís just passed the test. The discs are originals, 100k miles perhaps Iíll change them next year.





Phoned the local ramblers club today, but the bloke who answered just
went on and on.

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nick205

posted on 5/7/22 at 02:42 PM Reply With Quote
quote:
Originally posted by Dingz
Iíve an E90 08 year, itís just failed mot on handbrake. Tester said BMW and Mercs have same problem/design. I took it apart it was full of dust and rust. Cleaned it all up, the shoes have very little wear, adjusted them and itís just passed the test. The discs are originals, 100k miles perhaps Iíll change them next year.



My 57 plate Passat estate got to around 85k miles on it's original rear discs. Admittedly the car was never asked to carry much weight or driven particularly hard.

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MarcV

posted on 5/7/22 at 06:50 PM Reply With Quote
The BMW handbrakes are rather bad. Like others mentioned you probably shouldn't regard it as an emergency brake (it won't really help you, will it?) but as a parking brake instead. And that it does well provided you park nose up and let the shoes wedge themselves.

Before an MOT I am used to driving around a bit with the brake pulled to get past the loud grinding noises and back to having some contact between drum and shoe. The big issue is indeed corrosion as my handbrake doesn't get used all year, except at MOT.

But that aside, I never had a lot of work or cost on the mechanism and I am on my 4th BMW already.

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nick205

posted on 6/7/22 at 09:43 AM Reply With Quote
I don't think the "parking" brake is meant to be regarded as an "emergency" brake.

Pretty sure the MOT wording refers to vehicle brakes as:


Service brakes - those operated by the brake pedal

Parking brake(s) - those operated by the parking brake lever or EPB (Electronic Parking Brake) switch


In fact when driving my old Passat which had an EPB, pressing the EPB button on the dash didn't actuate the parking brakes above about 10mph. I tried it in an empty car par park out of curiosity.


[Edited on 6/7/22 by nick205]

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coyoteboy

posted on 6/7/22 at 11:06 AM Reply With Quote
I think the reason it's tested on rollers for brake efficiency in the MOT (and not just a static test) is because it's meant to be a safety brake option in an emergency. Better than nothing, so to speak, but on a wet road, with no other brakes, I'm not sure most drivers should be trusted to use the brake as an emergency brake.

My 306 annually fails the handbrake efficiency test, it will happily hold itself on a hill but does almost nothing once moving.

[Edited on 6/7/22 by coyoteboy]





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