Author Topic: rear brake spring  (Read 7715 times)

Offline i-man

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rear brake spring
« on: October 22, 2014, 09:47:50 PM »
I've taken my k75 on a few short shake down runs and the clutch work seems to be working well. So i hope to get it registered and tagged soon. One odd thing--I have a spring left over. i'm 99% sure it goes with the rear brake assembly. It's of thin gage wire, about 2 inches long. i've looked through all the exploded views at bike bandit and bobs bmw, but no luck in figuring it out. Anyone have any ideas?

Offline Chaos

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Re: rear brake spring
« Reply #1 on: October 22, 2014, 10:05:31 PM »
Pics would help, I assume you have a rear drum?  Could be one of the springs from the sidestand retraction mechanism.
  • sw ohio
1987 K75S    VIN 0231
Original owner, Original litter
200,000 miles (plus or minus) and 5 paint jobs
sold 6/23
2023 Ural 2WD sidecar (BMW's bastard step child)

Offline rbm

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Re: rear brake spring
« Reply #2 on: October 22, 2014, 10:22:26 PM »
Have you tried the obvious, fitting the spring to the rear master?   If it is an expansion type and has large loops on each end, it probably is what you think.
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline bmw-rider

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Re: rear brake spring
« Reply #3 on: October 23, 2014, 04:24:23 AM »
Do you mean this one.



Offline i-man

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Re: rear brake spring
« Reply #4 on: October 23, 2014, 08:14:44 AM »
thanks all! esp. BMW rider, that tension spring was it. Seems it hooks in line with the center stand tension springs?

Offline bmw-rider

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Re: rear brake spring
« Reply #5 on: October 23, 2014, 03:24:49 PM »
thanks all! esp. BMW rider, that tension spring was it. Seems it hooks in line with the center stand tension springs?

I've found this foto




Offline Motorhobo

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Re: rear brake spring
« Reply #6 on: October 23, 2014, 04:47:33 PM »
Neither of my K75s have that spring and I don't think they ever have. I remember inquiring about it here a year or so ago...but I don't remember anybody telling me exactly what it's for. At any rate, I didn't run out and get the part and if I'd thought it critical based on the responses I would have done so.

So -- again, someone please refresh my memory -- what does it do and why hasn't the roof caved in for me not having it?
1994/1995 K75 ABS Frankenbike: original engine 136k miles, frame from Gary Weaver (RIP), 173k miles -- Current Odometer: 193k miles
1994 K75 since 2013, 76,000 mi (11k mine) w/California Sidecar Friendship II Sidecar & Black Lab 'Miss B'

Past: 1974 Honda 550/4 (first bike), 1994 K75 (sold), 1995 K75 ABS (parts bike), Sidecar Dog & Best Bud 'Bo' - RIP

Offline Photog

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Re: rear brake spring
« Reply #7 on: October 23, 2014, 05:24:32 PM »
It's the return spring for the brake pedal, without it there is some likely-hood of the rear brake dragging.
I've also found that replacing the 25 YO one on my bike with a brand new one made the rear brake seem a little less vague.

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Offline i-man

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Re: rear brake spring
« Reply #8 on: October 23, 2014, 06:01:15 PM »
based on the foto kindly provide by BMW-rider, I'd say I have mine in the correct place. A little hard to be sure form the angle the foto was taken, but I think that it hooks to the center stand. Someone please correct me if I'm wrong.

Offline rbm

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Re: rear brake spring
« Reply #9 on: October 23, 2014, 06:43:33 PM »
You're correct ... one end hooks to the post inbetween the two centre stand springs, and the other end to the L-bracket on the brake pedal.  The spring helps to maintain the gap between the master cylinder plunger and brake pedal actuator (2mm I believe).
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline i-man

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Re: rear brake spring
« Reply #10 on: October 23, 2014, 07:51:03 PM »
good to know! thanks everyone!

Offline Sigmakappa

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Re: rear brake spring
« Reply #11 on: November 21, 2017, 10:36:03 PM »
Can anyone tell me the length of the tension spring. Mine is missing but BMW wants $45 for the pleasure. I suspect my local hardware store would be able to sort for a few dollars
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Offline The Mighty Gryphon

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Re: rear brake spring
« Reply #12 on: November 22, 2017, 12:37:57 AM »
Can you give a bit more information on what spring you need?  Is it for drum or disc brakes.  What year is your K100?  A part number of the spring in question would be really nice.

I found two tension springs for the rear drum brake at MAX BMW 113mm and 95mm $3.08 US.  I suspect they are not what you are looking for.
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline Sigmakappa

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Re: rear brake spring
« Reply #13 on: November 22, 2017, 12:43:09 AM »
Attached
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Offline The Mighty Gryphon

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Re: rear brake spring
« Reply #14 on: November 22, 2017, 11:28:14 AM »
Wow, they sure are expensive in OZ!  It looks like that spring is used for the pedal return if I am not mistaken.  Might be a special spring rate for the job.  I will be going out this afternoon to putter about with my RT and will try to get a length measurement for you.

Max BMW in New England shows that spring on their parts fiche as being only $11.22US.  Be aware, though that the semi-annual 10% price hike is due in a couple weeks. 

You may want to investigate the possibility of copping one from a source in the US.  Postage shouldn't be too bad on such a small part if they put it in a padded envelope.
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline Inge K.

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Re: rear brake spring
« Reply #15 on: November 22, 2017, 11:46:38 AM »
From Max BMW:

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Offline rbm

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Re: rear brake spring
« Reply #16 on: November 22, 2017, 01:42:04 PM »
Spring rate is not critical; enough to pull the rear brake pedal back to its resting position.  A local supplier should be able to supply you with a close match.
  • Regards, Robert
Toronto, Ontario

1987 K75 - Build Blog @http://k75retro.blogspot.ca/

Offline Martin

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Re: rear brake spring
« Reply #17 on: November 22, 2017, 02:05:19 PM »
Try buying one of those assorted spring kits, can be had cheap at local Saturday Sunday markets. they also crop up at Aldi. I have now amassed quite a collection of various types of these kits. I buy them from Aldi when they come out, some I use all the time some I haven't used at all but priceless when you need some thing.  It would also help if you put a more specific location for your address.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline Sigmakappa

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Re: rear brake spring
« Reply #18 on: November 22, 2017, 05:10:01 PM »
Thank you so very much one and all. Exactly the information I needed. Have a great day!
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