YZ dual leading shoe front brake

[Enginerd]

Gentlemen,

I am working on repairing a 1983 YZ 250 that a friend of mine recently bought.  His goal is to make a nice trail bike out of it, but we have a problem with the front brake, or the cable rather.

We just fitted a new Motion Pro front brake cable and cannot get enough adjustment in the cable at the wheel or at the lever to take up all the slack.  The wheel will stop when the lever is squeezed, but the wheel can be made to turn by hand, so we know the brakes will be insufficient whilst riding the bike.  

The brake shoes are factory Yamaha and appear to have about 75% of the factory thickness remaining.

Am I overlooking something in the adjustment here?  I have been working with bikes from the 70's & 80's for nearly 20 years, but this is the first dual leading shoe Yammie I have dealt with.

By the way, yes, I am from the US. 

I decided to ask this question here first because the members of this board seem to be honest, knowledgable, and practical.
I am hoping that some of you Yamaha experts familiar with the early 80's bikes might offer some advice.

Thanks!

Gary (Wyoming, US)

[mx250]

Welcome aboard Gazza .

I haven't mucked with the YZ twin leader but I've mucked with street twin leaders back in the day. It sounds to me the brake shoes are not moving in sync. With the backing plate off the bike adjust the two cams to make sure they are moving in sync. With things back together on the bike make the first adjustment at the backing plate and then at the cable. The adjuster at the backing plate has a left and right handed thread so be careful with the locking nuts.

Also, while twin leaders are powerful turning forward (the leading edge of both shoes gets dragged into the liner by the leading edge - self servo'ing), they are nearly useless when turning backwards (and stopping a bike rolling backwards on a hill ) - but that's why God gave us a death grip like a bear trap .

[DJRacing]

It sounds like your inner cable is to long.
Without the the cable on, measure the distance from where the cable hooks on to the brake arm and the top of the cable holder mount on the backing plate (while you are squeezing the brakes on) and then measure the distance at the brake lever where the cable is held (and with the cable adjuster still screw in) out to where the out cable is seated. Add the 2 measurements together. That measurement is about what should be showing out of the outer cable.
 

[Enginerd]

Thanks for the advice gents.  I knew that both cams weren't perfectly in sync, but they are only slightly out of sync. 
I will rectify that and it should help, but I have a funny feeling that my new cable might just be too long.

By the way Graeme, let me in on the joke.
What does Gazza mean?  I only speak American, not Aussie.

[mx250]

Thanks for the advice gents.  I knew that both cams weren't perfectly in sync, but they are only slightly out of sync. 
I will rectify that and it should help, but I have a funny feeling that my new cable might just be too long.

By the way Graehme, let me in on the joke.
What does Gazza mean?  I only speak American, not Aussie.

Michael = Mick, Charlie = Chazza, Barry = Bazza, Warrick = wazza, Garry = Gazza. Just a cheeky familiarity . When we get to know you and get really friendly we'll probably call you Septic .

[Enginerd]

Ahhh.......its all so clear to me now!

By the way Graehme, let me in on the joke.
What does Gazza mean?  I only speak American, not Aussie.

Michael = Mick, Charlie = Chazza, Barry = Bazza, Warrick = wazza, Garry = Gazza. Just a cheeky familiarity . When we get to know you and get really friendly we'll probably call you Septic .

[pancho]

i'm not familiar with the actual mechanism of the brake assembly you are looking at but there are a few basic essentials to check.the shoe linings need to be the same radius as the drum so that full area contact over the lining area is attained when the brake is applied.you may have to take the shoes to a brake specialist to have them radius ground to achieve this. next you need to have made certain that the backing plate assembly is centralised in the drum.i always apply the brake as i tighten the axle.this is critical if the backing plate has clearance on the axle....On some makes the brake cable outer is on one lever&the inner cable pulls the other lever towards the first lever.this ensures that the both shoes contact the drum in unison. on the type that has an adjustable rod between the two levers the common method would be to disconnect the rod, push the two levers with you fingers till the shoes each contact the drum and get an assistant to adjust the length of the rod so that the clevis pin can slide straight in. Twin leading shoe brakes can be savage when cold so the shoes are usually adjusted to drag slightly when cold, also as mx 250 said they don't work real well backwards, plus they tend to get erratic when cold  and fade when hot.cheers wally.

[Enginerd]

Thanks Wally!! Gret ideas!!!

i'm not familiar with the actual mechanism of the brake assembly you are looking at but there are a few basic essentials to check.the shoe linings need to be the same radius as the drum so that full area contact over the lining area is attained when the brake is applied.you may have to take the shoes to a brake specialist to have them radius ground to achieve this. next you need to have made certain that the backing plate assembly is centralised in the drum.i always apply the brake as i tighten the axle.this is critical if the backing plate has clearance on the axle....On some makes the brake cable outer is on one lever&the inner cable pulls the other lever towards the first lever.this ensures that the both shoes contact the drum in unison. on the type that has an adjustable rod between the two levers the common method would be to disconnect the rod, push the two levers with you fingers till the shoes each contact the drum and get an assistant to adjust the length of the rod so that the clevis pin can slide straight in. Twin leading shoe brakes can be savage when cold so the shoes are usually adjusted to drag slightly when cold, also as mx 250 said they don't work real well backwards, plus they tend to get erratic when cold  and fade when hot.cheers wally.