stevegough
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| posted on 4/7/22 at 05:43 PM |
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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
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| posted on 4/7/22 at 07:01 PM |
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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 ?
who cares who wins
pass the pork pies
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indykid
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| posted on 4/7/22 at 10:09 PM |
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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
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| posted on 4/7/22 at 11:14 PM |
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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
www.plusnine.co.uk
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nick205
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| posted on 5/7/22 at 07:37 AM |
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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
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| posted on 5/7/22 at 08:03 AM |
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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
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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coyoteboy
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| posted on 5/7/22 at 08:04 AM |
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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
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| posted on 5/7/22 at 12:19 PM |
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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
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| posted on 5/7/22 at 02:09 PM |
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I’ve an E90 08 year, it’s 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 it’s just passed the test. The discs are originals, 100k miles perhaps
I’ll 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
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| posted on 5/7/22 at 02:42 PM |
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quote:
Originally posted by Dingz
I’ve an E90 08 year, it’s 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 it’s just passed the test. The discs are originals, 100k miles perhaps
I’ll 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
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| posted on 5/7/22 at 06:50 PM |
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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
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| posted on 6/7/22 at 09:43 AM |
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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
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| posted on 6/7/22 at 11:06 AM |
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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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