Brake drag

[reborn55]

Took the ragtop for a cruise Sat. night---Noticed it pulled to left gradually and then pretty noticeable when brakes applied at road speed.  Left wheel was hotter than the right.  so i opted to put some calipers on---relatively inexpensive.  I have a single pot underfloor m/c with Midland booster and residual valves.  after bleeding brakes the front rotors seemed very hard to turn by hand--no wheels on yet.  I don't think there is a problem--won't know til tomorrow when I drive it.  Just curious as to if with this system there is more brake drag than usual.  Pretty sure it was like this before I changed calipers.  It should be all right when I start driving.  thanks

[wayne petty]

try loosening a bleeder screw to see if the caliper loosens its grip...

if it does... you might need to do something..

theory behind caliper retraction...

leaving a tiny bit of freeplay in the wheel bearing ajustment ..  this allows the rotor face to be slightly angled so when the brake pressure is released.. the rotor pushes the pads apart and the piston back..

what the brake designers also have done is to put a tiny angle on the outside of the seal groove...   what happens with that is the seal is flexed slightly as the brakes are applied.. the seal then tries to straighten back up pulling the piston back slightly..      for a few years they tried really hard to reduce drag and needed special master cylinders with quick take up functions.. like a duel sized bore.. and weird secondary bores..

you might try removing the rp valves to the front brakes and see if you loose any brake function...  i was always under the impression that they were to hold a tiny bit of pressure on the rear wheel cylinders seal faces so they are always pushed out against the pistons...   the return springs retract them...

[enjenjo]

If you have a single pot master cylinder, it was likely for drum brakes, and will have a 10 psi residual valve, which may cause some drag on the front calipers.

[reborn55]

Thanks guys--Changed both calipers and right brake hose(left was misboxed), rebled and test drove.  Stopped straight as an arrow, goo dpedal and wheels felt close to same as far a heat goes--left heat gun at work.  so on to next project and then on to Louisville.

[bucketmouth]

Good that you sorted the problem out. It reminded me of another time when someone said they had a similar problem. It wasn't until later I heard he had spun his disc in a lathe to clean them up a bit. But what he didn't realise was that brake discs have a couple of th runout to throw the caliper pistons back.