OP
UTC

Enthusiast
Piaggio MP3 500
Joined: UTC
Posts: 56
Location: Los Angeles
 
Enthusiast
Piaggio MP3 500
Joined: UTC
Posts: 56
Location: Los Angeles
UTC quote
Anybody know what can possibly cause front wheels to lock up, the front brake lever to go stiff while riding?

I was riding around and all the sudden the bike locked up like that, to the point where I can't even turn the bike off and push it. I started the bike back up, let the bike rest for a bit, then the lever would loosen up slightly, and I tried revving real hard to overcome the brakes, sometimes it would allow me to do so for a while, and I'd be able to move the bike forward for a while, but as the bike decelerates, it would almost always start to stiffen and lock up entirely again.

Any clues what can be causing this problem?

I also hear some sort of small grinding noise in the front.
@steelbytes avatar
UTC

Veni, Vidi, Posti
2019 GTS300 Supertech E3 59,000km
Joined: UTC
Posts: 5547
Location: Batmania aka Melbourne, Australia
 
Veni, Vidi, Posti
@steelbytes avatar
2019 GTS300 Supertech E3 59,000km
Joined: UTC
Posts: 5547
Location: Batmania aka Melbourne, Australia
UTC quote
ABS unit failure?
@maksor avatar
UTC

Ossessionato
Gilera Fuoco 500ie
Joined: UTC
Posts: 4542
Location: Netherlands Olst
 
Ossessionato
@maksor avatar
Gilera Fuoco 500ie
Joined: UTC
Posts: 4542
Location: Netherlands Olst
UTC quote
aftermarket or left brake lever on the right handside
@dariusz avatar
UTC

Hooked
2007 MP3 250ie / 2022 MP3 500HPE SA
Joined: UTC
Posts: 216
Location: CCS-Vzla
 
Hooked
@dariusz avatar
2007 MP3 250ie / 2022 MP3 500HPE SA
Joined: UTC
Posts: 216
Location: CCS-Vzla
UTC quote
Other possible causes, extra to what Maksor says:

1- Brake fluid contaminated / overheated in some point and create a emulsion gel.
Easy way to check: if all returns to "normal" or is better with the brakes completely cold.
Solution: remove and replace all the brake fluid

2- Mix of DOT 5 (silicon base) brake fluid with the DOT 3-4 actual fluid. It generate a gel that leaves the calipers locked.
Easy way to check: only know if happens in a service or by mistake
Solution: remove and replace all the brake fluid (good flush is very important)

3- The level is installed wrong don't avoiding the pressure return (happens to me in the Ducati ones)
Easy way to check: remove the brake level, if the brakes become loose you are in
Solution: Install brake level correctly
@web-tech avatar
UTC

Veni, Vidi, Posti
2008 MP3 500, 2013 BV350, 2020 Vespa Sei Giorni, 2008 Vespa S150
Joined: UTC
Posts: 8951
Location: Ashburn, Va. Home to the Internet
 
Veni, Vidi, Posti
@web-tech avatar
2008 MP3 500, 2013 BV350, 2020 Vespa Sei Giorni, 2008 Vespa S150
Joined: UTC
Posts: 8951
Location: Ashburn, Va. Home to the Internet
UTC quote
One of your calipers is stuck. It's heating up and locking up.
@old_as_dirt avatar
UTC

Veni, Vidi, Posti
2007 GTS
Joined: UTC
Posts: 22483
Location: Harriman, Tennessee, Tn
 
Veni, Vidi, Posti
@old_as_dirt avatar
2007 GTS
Joined: UTC
Posts: 22483
Location: Harriman, Tennessee, Tn
UTC quote
did you wear the pads completely to the plates and weld the plates to the rotor?
@rank_bajin avatar
UTC

Hooked
MP3 - 500
Joined: UTC
Posts: 427
Location: Alabama, USA
 
Hooked
@rank_bajin avatar
MP3 - 500
Joined: UTC
Posts: 427
Location: Alabama, USA
UTC quote
perhaps open the bleeder valves and pull the brake lever a few times, letting out a portion of brake fluid, have rags handy in place, to catch the expelled fluid. tighten up the bleeder screws, check the b.f. level and fill up if low. Repeating several times may cure the issue

Good luck
UTC

Member
Piaggio MP3 500
Joined: UTC
Posts: 22
Location: Upstate, New York
 
Member
Piaggio MP3 500
Joined: UTC
Posts: 22
Location: Upstate, New York
UTC quote
My money's on a blocked/clogged compensation port in the master cylinder. If the front wheels free-up when you loosen the brake line on the master cylinder (relieving pressure), that will confirm the problem. If you have a bit of free play in the lever, it's a compensation port clog from dirty fluid, etc. If there's no play, you have a lever issue as mentioned by others. Good luck.
@rank_bajin avatar
UTC

Hooked
MP3 - 500
Joined: UTC
Posts: 427
Location: Alabama, USA
 
Hooked
@rank_bajin avatar
MP3 - 500
Joined: UTC
Posts: 427
Location: Alabama, USA
UTC quote
Any pics. or diagrams of the compensation port would be helpful

Thanks
UTC

Member
Piaggio MP3 500
Joined: UTC
Posts: 22
Location: Upstate, New York
 
Member
Piaggio MP3 500
Joined: UTC
Posts: 22
Location: Upstate, New York
UTC quote
The compensation port is a small hole in the top of the master cylinder bore. When you release the brake lever, the piston/seals retracts to uncover this hole, which releases any residual pressure in the brake line. If this hole is plugged or blocked (sometimes the piston rod is misadjusted), pressure can remain in the brake line, which causes the brakes to drag or lockup. The compensation port is also called a vent port or by-pass port. Hope this helps.
Forum member supplied image with no explanatory text
@web-tech avatar
UTC

Veni, Vidi, Posti
2008 MP3 500, 2013 BV350, 2020 Vespa Sei Giorni, 2008 Vespa S150
Joined: UTC
Posts: 8951
Location: Ashburn, Va. Home to the Internet
 
Veni, Vidi, Posti
@web-tech avatar
2008 MP3 500, 2013 BV350, 2020 Vespa Sei Giorni, 2008 Vespa S150
Joined: UTC
Posts: 8951
Location: Ashburn, Va. Home to the Internet
UTC quote
You can easily test the compensation port by removing a front wheel and see if if you can pry the inside brake pad in with a screwdriver away from the rotor, i.e. compressing the piston back into the caliper.

Pump the brakes to make sure the pads on both sides are seated against the rotors then see if you can pry one of the inside pads away from the rotor.
@rank_bajin avatar
UTC

Hooked
MP3 - 500
Joined: UTC
Posts: 427
Location: Alabama, USA
 
Hooked
@rank_bajin avatar
MP3 - 500
Joined: UTC
Posts: 427
Location: Alabama, USA
UTC quote
Terrific illustration plus advice on fixing faulty brakes.

The diagram sure removed a whole bunch of questions about how these things work.

Kinda miss the old cables though, where a spot of grease in the right spot could get things going again........

Many thanks for all the input.
DoubleGood Design banner

Modern Vespa is the premier site for modern Vespa and Piaggio scooters. Vespa GTS300, GTS250, GTV, GT200, LX150, LXS, ET4, ET2, MP3, Fuoco, Elettrica and more.

Buy Me A Coffee
 

Shop on Amazon with Modern Vespa

Modern Vespa is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com


All Content Copyright 2005-2024 by Modern Vespa.
All Rights Reserved.


[ Time: 0.0158s ][ Queries: 4 (0.0097s) ][ live ][ 313 ][ ThingOne ]