Rear Brake Cam Lever alignment = slack pedal (Triumph T120 67') - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 31 (permalink) Old 04-14-2019, 10:55 AM Thread Starter
Grand Prix 125
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Rear Brake Cam Lever alignment = slack pedal (Triumph T120 67')

Hi all. I recently stripped my rear wheel, including removing and refitting the lever that connects the rear brake linkage to the rear brake cam shaft. Upon reassembly I found that the travel in the brake pedal was extremely excessive, to the point it almost touched the ground, something clearly wasn't right. I am at a complete blank as to what the problem is, after all there isn't much to these things. I can only think it's something to do with the indexing of the rear brake cam lever to the cam spindle. There are only two positions that I can think that it could go, see both pictures, in one position there is no pre-tension in the spring, in the other the spring tension causes the cam to open up, this effectively results in the brake shoes retracting when the lever is operated rather than expanding. Both positions result in extreme brake pedal movement. Can anyone advise what the correct assembly method is for the lever please?
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post #2 of 31 (permalink) Old 04-14-2019, 11:56 AM
wol
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In the "correct" position the spring pushes the cam the wrong way as in your second picture - when the assembly goes into the wheel and on the bike ,adjusting the brake rod should pull the lever foreward and you should be able to achieve the correct adjustment - if not maybe turning the lever on the brake cam may give a better postion (although the lever has a slight set in it so only has one correct way round)-- cant recall if the square on the came has a bias such that rotating 180 degs may give a better position
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post #3 of 31 (permalink) Old 04-14-2019, 12:11 PM Thread Starter
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Thanks. Yes I assumed the second picture seemed the better solution. The problem I'm having is that when assembled like this in the frame, there is far too much movement in the brake lever i.e. the rod adjustment is fully tightened and the lever still hits the floor. The only solution I can think of therefore is to run a die down the threaded end of the rod to increase the adjustment. This seems crazy though as it was fine before I stripped it. I will have a go at indexing the cam through 180 degrees but have a feeling I tried this earlier with the same results
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post #4 of 31 (permalink) Old 04-14-2019, 12:22 PM
wol
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I am in the process of rebuilding my 1970 T120R - just looked at my brake plate - it is currently in the frame but does not yet have the external spring fitted- - with the cam held just by the tension of the brake shoe springs - with a straight edge from the centre anchor bolt to the cam pivot my, arm is almost on that line - leaning slightly rearward
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post #5 of 31 (permalink) Old 04-14-2019, 12:33 PM Thread Starter
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I have attached a picture of my rear wheel setup from a while ago (when everything was working fine). It looks similar to your description, lever in line with the centre nut to cam pivot, granted mine has the external spring fitted. I'm puzzled as to why I can't replicate this now
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post #6 of 31 (permalink) Old 04-14-2019, 12:36 PM
wol
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yes that exactly like mine - try to replicate that postion but without the external spring - it may be confusing the situation - your arm may need to rotate one flat to the rear
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post #7 of 31 (permalink) Old 04-14-2019, 12:43 PM Thread Starter
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Okay that's good to know. I'll have another play around with the indexing.
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post #8 of 31 (permalink) Old 04-14-2019, 02:41 PM
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Quote:
Originally Posted by matteus101 View Post
I'm puzzled as to why I can't replicate this now
Did you find that in that position the brake was quite firmly on with the wheel out of the bike? On my T100R that is the case because the lever arm spring takes the cam over centre and applies the brake 'backwards'. I've done exactly the same as you today, took it all apart to clean/grease without marking where the lever should be replaced. The pics are where I think it was before I took it apart and it works putting the brake plate back in the hub but I can't be certain until the wheel's back in.
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post #9 of 31 (permalink) Old 04-14-2019, 02:59 PM
wol
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Rusty1 - i think your arm may need to move "backwards" by one flat on the cam pivot -- the angle it is now in relation to the backplate is how it should look wnen in the wheel and the brake adjusted on the pull rod - but the arm has to move foreward to get the cam into "neutral" between the shoes - once it gets there the arm will be too far foreward - one flat looks like it will get it "indexed " right
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post #10 of 31 (permalink) Old 04-15-2019, 01:31 PM Thread Starter
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I have assembled the brake as shown in the first image. All seems fine when fitted however it still results in excessive pedal travel, see pic. This is with the adjuster wound all the way in. There is plenty of meat on the shoes and it worked fine before taking it apart. I'm clearly missing something. Does anyone have any other ideas?
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