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Flathead replica springer problem

4K views 25 replies 14 participants last post by  geasy$ 
#1 ·
Hi all,
I am in the process of building my first semi custom bike (1997 heritage softail based).
I fitted a flathead springer replica on my bike (stock frame & springer length). Now everytime I apply front brake, the whole front end would try to fly up instead of diving like a normal shock would. The mech told me that all flathead replica have that tendency and it is normal. I personally dont like it and think it is dangerous. Is there any way to correct this tendency? Would fitting a friction ride control or shock absorber help?
Here is the specification of my suspension and tires:
F tire: 130/90/R16
R tire: 180/60/R16
Springer: 22" (bottom neck to bottom rear rocker hole)
Rear shock: stock height.

Thanks a million for taking the time to answer my questions, appreciate it.
 
#12 ·
No it is not tweaked. I have tried riding with it and it runs fine. The only problem is the extreme upward front end stop whenever I applied front brake. It feels like I am about to get thrown over the handlebar. I could only use the rear brake...
 
#15 ·
#23 ·
Geometry from anchor rod should be looked after again...and make sure everything is working "loose" with the correct bushings at pivot points... when the frontend comes up while braking it usually means something is "to tight" that should be not tight at all...

...What Danny F said, I think the Anchor rod geonetry he refers to are the pivot point on front of the rocker and axle point in relation to the rear pivot point on the rear springer leg"anchor" To "Rock" the front pivot point should be 1/8 to 1/4" higher (measruring vertically from the ground when the bike is standing with the wheel straight. If not, that combined with the nuts too tight or improper bushing fitmit, size, greasing can make the bike "Pogo" when it hits a bump on in breaking. Instead of the rocker "rocking" and compressing springs it "drives" the whole front end upward...or at least that 's what happended on mine.
ted
 
#16 ·
after comparing to so many different springer pictures, I noticed that the rebound spring (upper spring) is not compressed enough, so maybe when I applied front brake the momentum of the bike forced the front end to retract upward instead of diving because there is not enough pressure from the rebound spring..... Am I correct???
 
#18 ·
Hey uwiik,

I just got done working out similar problems on my springer, although my setup is using a front drum. I think this is what is causing your problem:

Think of your front end as a parallelogram. two sides are the two fork legs on your springer. One side is the line from your rocker bolt to your axle. The final side is the line from your brake stay fork anchor and the brake stay disc anchor.

The fork sides of the parallelogram are parallel naturally as your springer was built that way. It is CRITICAL that you brake stay and rocker are parallel.

If they aren't then you will experience very odd behavior when you apply your brakes. What exactly will depend on what type of misalignment you have. In your case, when you apply the front brake, the forward rotational force of your wheel will put huge load on your brake stay and that force will be transferred to your springer leg then compressing your springs.

If your brake stay is parallel to your rocker then the regardless of your front-end movement they will remain parallel and the force applied to your brake stay when you apply the brake will be pulling "straight" on your fork leg and will prevent your brake from rotating, thus keeping your front-end true.

Hope that makes sense! I don't have time to sketch out diagrams for you this morning but if you're still stuck I'll cad it out later today.
 
#22 ·
that brake stay/rocker parallel thing makes sense. seeing your home built springer is inspiring, but maybe you could move that anchor for the brake stay on the rear leg up towards the stem a bit. that should make the brake stay rod jut out parallel to the rocker. the fact that the stay rod is currently pointing up, away from the rocker would explain why you get that rising sensation when you brake.

good luck.
 
#24 ·
I think everyone is looking to much into this problem, is it me or do those springs look like they are not compressed at all. If you press down on your bike, is the front end real squishy? It looks like both the top and bottom springs need to be tighter, or "pre loaded" so that its not so loose.
 
#26 · (Edited)
Move the brake stay up on the back leg as stated several times already. The rod should be parallel to the ground. As it sits, when you apply the brake, the reaction you are feeling is from the rod, as it is being pulled foreward, it wants to "level out". If the rod was already parallel to the ground, it would be pulled foreward, instead of UP, which in turn forces the back leg UP, and you feel the bike going UP, as you brake.

Hope that explains it a little better.
 
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