Modern Vespa

I've been riding around breaking in a newly rebuilt engine and I've noticed when I approach stop signs or traffic lights and lean on the rear brake there is a weird pulsing to it. If it were a car with rotors I would describe it as a warped rotor.

Is this something I should be concerned about? Is it perhaps a sign at the brakes have not yet seated?

It hasn't created any hazards but I don't want to just ignore it

The front brake on my Super 10" conversion does that a little Not too bad at speed but no good when I slow down. Regardless, it can be dangerous and indicates that our drums are out round and should be replaced if they are too far gone to be saved by some guy on a lathe machining them true. I'll report back after getting into mine.

The back brake on my smallframe does that a lot. How and why is it dangerous?

My LML has this problem, I suspected a manufacturing defect in the hub causing it to wear in a slightly oval manner.

I swapped out the rear hub for a cheap new one, and it's sadly still present, though seemingly to a lesser degree.

Is the pad new? I assume it will take a while to seat.

I don't think it's dangerous as long as the bike still stops within a reasonable distance.

The brakes had no issues when the bike seized, requiring the rebuild, so they just came off and went back on once the engine was finished. The pads looked plenty fine so this is a matter of me removing them and then reinstalling, hence the mystery.

It doesn't seem dangerous in normal operations..I use both front and rear brakes in stopping and it only becomes noticeable shortly before stopping. But it's definitely not normal. It's interesting to see so many other folks with a similar issue.

Definitely more of a safety concern if it is the front brakes, trust me. I don't know what could cause the problem if before you had it apart, it was all fine. Maybe it had a favorite position on the splines and it's not there now? Shouldn't be that way though, but tolerance stackups can sometimes get you. Try pulling the hub and reinstalling it at 180 degrees from current on the axle?

Greetings:

Pulsations mean the braking surface is out of round (drum) or out of true (disc) There is no other explanation. In cars, it's sometimes the result of haphazard torquing of the lug nuts or bolts. Overheating on scooters - perhaps long downhills with the brakes applied - could explain the reason.

The pads or shoes "wearing in" will not compensate for this. The risk in mild cases is minimal. In the most severe cases, firm application of a drum brake in particular could cause wheel lockup in a panic stop situation. This could lead to Serious Injury or Death.

Drums and brake rotors can be turned or trued on a lathe if suitable equipment can be found, or replaced if not. I've had to replace a few Honda 50 rims over the years for this reason. Stock steel rims have 95mm drums built into the hub with a couple of my builds capable of speeds over 70 MPH. One hard stop from over 60 can distort a drum. New rim solves the problem immediately.

Asked about getting some hubs turned a few years ago and my machine guy nixed the idea. Said he could do it, but because of the relative lack of meat in a Vespa drum, making it thinner was not a great idea, and a potential liability issue for him. Just shell out for a new hub or find a better used one.

Pads are cheap...if this continues much longer I'll simply drop in a new pair and see what that does. I agree it's not something to ignore, but since it only shows up once I'm below 10 mph I'm not too freaked out about it.

I've had this happen on my Stella. It can be fixed by removing the rear wheel and cleaning the drum and brake pads. The drum surface should be cleaned with a clean rag and solvent. The pads can be cleaned by scuffing the surface with sand paper.

The problem is probably caused by an oil leak.

Could be something else f course...... but try this first and see if that fixes it.

Actually, there is..

If the person using the vehicle does use the brakes hard (A.K.A. Heavy foot) once the disk or drum overheat, some of the resins used in the production of the shoes/pads get transfer to the metal, making the surface uneven..

It is a very common situation and the easy way to fix it is to use a bit of wet and dry sand paper on the disk/drum to remove the leftover resin build up, and to replace the shoe/pads with sintered material (it does handle heat a lot better), while organic pads/shoes do tend to leave a lot more resin behind..

Slotted brake shoes help with this as well....you can even add slots yourself if needed but obviously the shoes have to be in fairly good condition

Good hubs are getting harder to find. I ended up doing a rear seal conversion and installing a P hub on my GT. Mainly because Chinese hubs are garbage and are what are carried by most domestic shops lately. I still have a small pulse in my front brake but, would rather that than have the cheap, pressed in studs break off on a poorly made replacement. I had just that happen on a Chinese rear hub. Nuts kept getting loose. Kept re-torquing them periodically (with a torque wrench, not a gorilla). Came to a stop after a brisk ride, bike dropped down, wheel came off. 3 Studs broken. 1 missing the nut. Scary but true!

Buy Quality hubs, Italian, German... That's the short version