Rear Drum Brake Springs - MK2 850

thunderbolt

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Restoring a '74 MK2 850 Roadster. Got to the stage of fitting the rear brake pedal, rear brake light switch and Venhill brake cable. The problem that has arisen is that the brake pedal will not return up to the front footrest when released so the brake switch is inoperative because of this. When I take my foot off the brake pedal I can then still raise the pedal by hand another 1/2" to 3/4" which allows the brake arm on the rear drum to return further rearward to its normal position.

The external spring that goes around the rear brake arm on the drum is stainless steel and new. I cannot remember if I replaced the two springs inside the drum that go on the brake shoes.

Which of these springs are responsible for returning the brake arm back to its normal position when the brake pedal is released? I am thinking I may need to replace the brake shoe springs or the other possibility is that the stainless steel external spring is not as strong as the original that it replaced!

Thanks for any responses.

Cheers Don
 
'I cannot remember if I replaced the two springs inside the drum that go on the brake shoes.'

Do you mean 'replaced' or 'renewed'?? Don't ride the bike without checking they're in place...
 
thunderbolt said:
Which of these springs are responsible for returning the brake arm back to its normal position when the brake pedal is released?
Click to expand...


Mainly the brake arm spring I would have thought but assisted by the shoe springs.

Have you got the brake cable routed correctly over the Z-plate (not running below the Z-plate)?

There's also the later safety spring (not in the parts books) that should also assist in returning the pedal.

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thunderbolt said:
Restoring a '74 MK2 850 Roadster. Got to the stage of fitting the rear brake pedal, rear brake light switch and Venhill brake cable. The problem that has arisen is that the brake pedal will not return up to the front footrest when released so the brake switch is inoperative because of this. When I take my foot off the brake pedal I can then still raise the pedal by hand another 1/2" to 3/4" which allows the brake arm on the rear drum to return further rearward to its normal position.

The external spring that goes around the rear brake arm on the drum is stainless steel and new. I cannot remember if I replaced the two springs inside the drum that go on the brake shoes.

Which of these springs are responsible for returning the brake arm back to its normal position when the brake pedal is released? I am thinking I may need to replace the brake shoe springs or the other possibility is that the stainless steel external spring is not as strong as the original that it replaced!

Thanks for any responses.

Cheers Don
Click to expand...
Hi Don, Had the same issue on my identical model. Spring on brake arm appeared weak so added a couple of Heath Robinson but safe pieces to each abutment to increase it’s tension. By far the biggest improvement was in adding the AN safety pedal spring as mentioned elsewhere.
Steve
 
Stevo said:
Hi Don, Had the same issue on my identical model. Spring on brake arm appeared weak so added a couple of Heath Robinson but safe pieces to each abutment to increase it’s tension. By far the biggest improvement was in adding the AN safety pedal spring as mentioned elsewhere.
Steve
Click to expand...
Hi Stevo,
Do Heath Robinson's devices work better than Rube Goldberg's?

Ed
 
Is there any restriction when trying to move the drum lever by hand, with or without the cable attached? Shouldn't have any binding. Is the operation lobe correctly lubed, via external grease nipple(both at the foot lever and at the drum lever pivot)? Is the grease passage clear for the hub pivot lobe? Cable routing and freely moving correct?
 
Correctly lubed and assembled you should not be having this issue at all. To isolate the problem, unscrew the rearmost nut on the adjuster and remove the cable from the rear arm. Now work the arm - does it come right back when you move it forward? If not, you want to look at the internal brake springs and the level of lube for the cam. If fine, turn your attention to the cable, its routing, and the rest. Good luck, and do get that additional safety spring it is a nice bit of kit.
 
I cannot remember if I replaced the two springs inside the drum that go on the brake shoes.

Estuary Boy asked for an answer to this a few posts back.

Renewed or replaced?

I don't mean to be condescending but it is your braking system...you have to get that right and you gotta' resolve this before you do anything else.
I assume if you replaced the shoe/inner springs you would remember doing so?
If you left them out or they are banging around inside the hub things are going to get exciting in a hurry.
 
APRRSV said:
Hi Stevo,
Do Heath Robinson's devices work better than Rube Goldberg's?

Ed
Click to expand...
Lol,
Ed, I think HR’s devices were a precursor to Rube’s, not certain though. Perhaps Rube refined some of them and used the others just as they are, not pretty but usually get the job done.
 
Thanks for the replies everyone. Appreciated.
The first thing to put straight is that when I said I couldn't remember if I replaced the shoe springs - I meant I couldn't remember if I replaced with new springs. Of course I did not put the drum brake back together without internal parts.
I have greased the brake shoe cam, etc. As well as the shaft the brake lever mounts upon.
I have installed a new Venhill rear brake cable and it is routed correctly.
I have fitted the safety spring on the brake pedal, but it is a loose fit - it doesn't hold the pedal up against the footrest but does prevent it dropping down to come in contact with the roadway, etc.
I have no idea what Heath Robinson devices are - could someone explain please?
I will follow the advice and tips given today when time permits, such as remove the cable and test the movement of the lever on the brake drum.
I can also replace the stainless external return spring that mounts over the lever with the original crappy one and see if that is any stronger.
Thanks again for all comments, etc.

Cheers Don
 
L.A.B. said:
en.m.wikipedia.org

W. Heath Robinson - Wikipedia

en.m.wikipedia.org en.m.wikipedia.org
Click to expand...
Thanks Les. haha

The stainless return spring on the short lever on the brake backing plate doesn't seem that strong and the Venhill brake cable seems to have excessive friction when mounted on the bike (it's okay when removed and lubricated). I will dig out the old cable and return spring and try them out before removing the rear wheel and disassembling the rear brake hub.
 
thunderbolt said:
Thanks Les. haha

The stainless return spring on the short lever on the brake backing plate doesn't seem that strong and the Venhill brake cable seems to have excessive friction when mounted on the bike (it's okay when removed and lubricated). I will dig out the old cable and return spring and try them out before removing the rear wheel and disassembling the rear brake hub.
Click to expand...
You have not mentioned whether you have the spring on the actual brake pedal - as mentioned in the latter part of Les's post #3.
That spring is quite strong on my bike and would, I am sure, remedy your issue.
Cheers
 
robs ss said:
You have not mentioned whether you have the spring on the actual brake pedal - as mentioned in the latter part of Les's post #3.
That spring is quite strong on my bike and would, I am sure, remedy your issue.
Cheers
Click to expand...
Rob, I did mention that in Post #10 about halfway down as well as other comments.
I have found that this safety spring does not hold the brake pedal up high enough to rest against the bottom of the footrest but does prevent it from falling lower to catch on the roadway if the rear cable breaks.
 
thunderbolt said:
...the Venhill brake cable seems to have excessive friction when mounted on the bike (it's okay when removed and lubricated).
Click to expand...

Venhill cables should not be lubricated as they are Teflon-lined:

Cable Installation and Maintenance

www.venhill.co.uk www.venhill.co.uk
"You do not need to lubricate Venhill cables with oil as this will increase friction between the inner wire and the Teflon tubing."
 
I did disassemble the rear of the bike this afternoon. I found the pivot pins and cam a bit dry of lube.
The stainless return spring is weaker than the original that came off the brake arm.
The internal springs that go on the brake shoes look okay.
There are some high spots on the brake linings, so I can linish them down a bit before it all goes back together (the linings are new and were bonded to my original shoes).
So there are a few things there that I can address which should improve things.
Needless to say I am not that impressed with Venhill cables.
 
IMO the majority of the work is done by the shoe springs.

If you think about it, if the brake arm spring was stronger than the shoe springs, it would force the cam over centre and make the shoes drag.

The pedal safety spring is only intended to prevent the brake pedal from dropping and causing an accident in the event of a snapped cable.

So it’s the shoe springs that have the main role in ensuring the shoes are centred (ie the cam is ‘flat’).

Then one thing thats not been discussed much is cable adjustment. If the cable is not adjusted correctly then the pedal will ‘droop’ even if the shoes are correctly centred.
 
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thunderbolt said:
Needless to say I am not that impressed with Venhill cables.
Click to expand...

Perhaps if you were to flush out the lubricant you might be more impressed, :) however, I suspect this is a weak brake lever return/shoe spring problem.
 
Failure to lubricate the shaft where it turns in the backer plate is very common.


Another case of "stainless jewelry" that is a downgrade.
Leave that stuff for fishing boats.
 
thunderbolt said:
Rob, I did mention that in Post #10 about halfway down as well as other comments.
I have found that this safety spring does not hold the brake pedal up high enough to rest against the bottom of the footrest but does prevent it from falling lower to catch on the roadway if the rear cable breaks.
Click to expand...
Sorry, I missed that.
My spring on the brake pedal is quite strong, requiring force to depress the pedal.
 
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