lazy brake master cylinder

[bloodvette]

I have a problem that comes and goes. my argo is a 99 Response. the right hand brake lever has more travel than the left one sometimes. basically, I have to push it farther down than the left one to activate the brake. so naturally I suspected air in the system, so I bled the system. I actually completely bled both sides and flushed new oil and topped it up. anyways, it still happens. but not all the time. often after running for a while, the levers both have the same travel. I looked in my manual, and referred to the adjustment section. this section mentions that you should verify that the piston is retracting fully when you release the lever... and thats where my problem lies. I'm referring to the cylindrical piston inside the master cylinder that pushes the brake fluid. It is not always fully retracting when I release the brake lever. is there an actual return spring inside? I'm suspecting it has broken. I haven't openned it up to have a look yet. just wondering if anyone has come across these symptoms before.

john

[bloodvette]

just had a look at the exploded view parts diagram and I'm thinking return spring part number 162-02 is broken and I shall be in the market for an entire master cylinder rebuild kit.

[LarryW]

Thats cool you got it narrowed down at least, Keep us updated.

[Roger S]

There's not much in there.. a cup and spring, a gasket on top, if my memory from '98 is good. My new argo had a bad cup from the factory. I took it apart to fix, but argo sent a new Master cylinder.

I have one rotor with a little run out, it pushes the caliper piston back and makes one lever operate farther than the other. It will pump up.. sort of like your symtom.

[bloodvette]

With closer examination this afternoon, I determined that without that piston fully retracting, the port would not line up with the piston cavity so no fluid could be added to the brake line.

I took apart the master, cleaned up inside bore. slightly gunked up. but the piston (has 2 cups as previously mentioned) was STILL not fully retracting by the return spring. I could see this during "bench testing" before i even re-installed it. so I did a little modification. Assuming that the spring is old and weak, I dropped in 2 appropriately sized washers (ie. spacers) before the spring to add spring tension. this worked perfectly. I adjusted the brake lever cable adjustment. went for a drive... had to make one more adjustment, then it was great.

[mike bar]

Glad to hear your fixed and ready to go.Sometimes we have to improvise as our machines get older.My left brake lever will sometimes go all the to the bottom, without activating the brake when the machine gets hot MIKE

[bloodvette]

Glad to hear your fixed and ready to go.Sometimes we have to improvise as our machines get older.My left brake lever will sometimes go all the to the bottom, without activating the brake when the machine gets hot MIKE

after tearing apart my master cylinder the other day, I realized how simple they are. based on what you've described, I'd say one or both of your lip seals on your master cylinder piston need replacement. sounds like brake pressure is bypassing the lip. becuase it doesn't sound like you have a leak. and if the probem happens when its hot, its obvisouly heat related, and the rubber lip seals are certainly the only vulnerable parts in the there.

[Paul]

This exact thing happened to my conquest (the only breakdown I've had in two years). I replaced the master cylinder parts with a kit and it has worked well ever since. The system was full of gunk so realy I should have done both master and both slave because another one will let me down garenteed.

[mike bar]

Good to know guys, I'll get at it soon as i get a chance.Just finished my trailer for the argo 80"x144". Thanks,
Mike