My back brake won't...

Here's one for the gurus... When I replaced my rear tire last year on VooDoo, I also replaced the rear brakes. Now mind you, I have never had the rear brakes working well with my forward controls, but I thought with new rear brakes and a good cleaning, I should be set. Not so. The brakes 'work', in that they will slow the bike down, a little, but there is no way to generate enough braking power to stop with the rear alone or to lock the rear up. Not sure where the problem lies, if it's in the brakes them self, or in my linkage/leverage system. Here's a couple side views of the rear setup..




This was before I flipped the mounting plates over, but it show the alignment of the connector rod...



It feels like I can't generate enough pressure when pushing the brake pedal...I wonder if I need a longer armature at the stock pivot on the frame, if that might help.... any thoughts??

 

De-Glaze the Rear Brake DRUM and SHOES.
Scrub away Glaze with 320 Grit Sand Paper.
De-Glaze and Chamfer New Pads.

Pre Position Brake Lever.
Adjust Brakes:
Adjust the Rear Brake Arm to a sufficient angle to activate the Cam (under slight force) to remove any Slack and allow for the Brakes to be closely adjusted.

Adjust the Forward Rod for position AFTER setting the Pivot for Maximum Movement with the Forward Rod.

Begin by Positioning the REAR Arm on the Splines of the Cam with pressure on the Brake Shoe Springs.

Arrange what can be adjusted for Comfort and Free Play.

 

So... cleaning the drum with brake cleaner isn't sufficient? That was my original approach, and I am guessing the glaze on the drum glazed my new pads.. correct?

 

The problem I see is the rod linking the front pedal to the rear. The rod is under compression when the brake is applied ,in other words the rod is pushed to apply the brake and it should be PULLED. You are using most of your braking effort to bend the rod and not apply the brake. I strongly suggest re-designing the linkage so the rod is being pulled.

I can see that the connecting rod is slightly bent. Sit on the bike and push the pedal and watch the rod, I bet you will see it bend.

 

I don't know about your brakes ....but that is one fine looking custom XJ Maxim.....

 

Thanks five
From what I can tell (and recall..)the original setup uses compression, so I don't think that is the issue... but the armature on the stock pedal is shorter. When I think about fulcrums and levers it seems like the shorter armature on the stock break pedal could generate more torque than the longer armature I have on mine with the same footpounds of pressure... get foot-pounds lolol but I digress, sorry.... I thought the rod looked bent in the pics too so I went and checked it on the bike and it's straight. I'll have to give set up a video sighted along the rod to see if I get any deflection with pressure on the brake...

 

Longer armature would create more force but require more distance traveled. Think of how a breaker bar works.

 

No
Compression is pushing together
Tension is pulling apart
The original brake rod is under tension(being pulled) while braking
Your extension rod for the forward control is being compressed while braking. I looks like it is bending while you are braking. A thicker and stronger rod may help

 

..

 

mlew is right; as soon as you put either rod under compression it's gotta be hell-for-strong or your braking force will be going to flexing the rod. This stock rear rod is fine being thin, it's under tension.

As long as that forward rod is, it looks like it's going to need to be about twice the diameter it currently is to resist flexing.

It's hard to tell from the pic, what is the forward link? A solid rod, tube, or ?? Aluminum, steel, ??

How long is it exactly? There may be a ready-made part out there somewhere in race car/bike/aftermarket land.

 

yeah, beautiful stuff...........I agree with the probability of that rod flexing.

Dave f

 

The forward link is a stock ready made .. (ahem) Harley part.. Chrome plated 1/8" steel.

I'm confident there is no flexing going on there...
The forward connecting rod is 3/8 solid aluminum rod drilled and tapped on the ends.
I agree the front rod is under compression, but it HAS to be compressed so that as fitz noted, it ok for the rear connecting rod to be thin since it's being pulled...to accomplish that the front linkage is compressed, the 180pivot armature converts that compression into tension on the rear connecting rod.
The stock brake pedal and front linking rod look like this, note the armature on the bottom of the pedal.

Then you have the configuration of the stock pivot armature looking like this...


So my weak link at this point is the front connecting rod, but I think my drum (and now pads?) might be glazed. I'll have to look into a ready made rod and see what I can find. Thanks for the replies, it helps me trouble shoot when I see things from the perspective of others. I'll keep you posted on the results..

 

Sorry, I was asking about the forward ROD, whether it's solid or a tube, what it's made of and how long it is.

There may very well be a ready-made, much less flexy part out there.

 

I realized that after I posted my reply.. I went back and edited it to add the 3/8" solid alum rod

also I need to 'print' a retraction of an earlier statement... upon closer inspection, the rod does have a slight deflection (read bend) in it... my bad

 

The other guys have given you some good ideas but I'd just like to add...with the foot brake applied, make sure that the cam lever at the drum is at a right angle (90 degrees) to the linkage for maximum brake shoe force. This gives the most leverage at the point of shoe contact.

 

Thanks Ski! every little bit helps

 

OK, it's only 3/8" and it's a solid aluminum rod? How long?

Looks to be about 20" maybe 22" long, or longer?

Send these guys an email; have them spec you something in a stiff aluminum tube with nice metric Heim joint ends. I'll bet it wouldn't cost an arm and a leg. http://www.cablecraft.com/products_custom_linkages.html

 

Mine has a 5/16" all thread incased in a steel tubing, cranked at both ends with backing nuts, it was a "universal" kit, but has zero flex and I believe it pushed too (compression), rear tire locks up like a champ, lol.

 

Thanks guys!