My 1970 v8 was bought as a restoration project and has been off the road for 32 years. I'm working through various jobs but the brakes have me scratching my head! The car has recon front and rear calipers, known good master cylinder, servo overhaul kit and new flexi hoses. I bled the brakes and ran the car up and down my drive yesterday but the brakes were sticking. Jacking it up confirmed that all four were sticking. Working from the master cylinder, releasing the unions had no effect until I loosened the servo to brass 4 way coupling Union on the inner wing. A good squirt of fluid when the union was released resulted in the brakes freeing off. Having had a similar issue with another p6, I suspected the air control valve piston to be at fault. So, off came the servo again. It was seized (forgot to check first time round) so I unseized it, cleaned the bore, renewed the piston rubber, checked for satisfactory movement and reassembled. I re bled the system today but they're still sticking on all four! I used the same Union releasing sequence as before and again, releasing the servo to 4 way coupling Union freed off the brakes. Have I still got a servo related fault? The only other explanation is that the 4 way coupling could be blocked after so many years laid up? Any suggestions greatly received!
Sticking brakes
- Thread starter badrover
- Start date
clive P62
Active Member
Have had same fault with servo being the fault/ when hot sticking got worse.
Rebuilt a few of these now and in the kit of seals is a pack of silicone grease.
Instructions in kit say to put silicone grease on retraction valve piston and plastic bearing on main piston, i dont know use the red rubber grease to lube seals just clean brake fluid.
Do not use new old stock seals as sell buy date now way out.
I get all my brake seals/parts from a company called power track/mail order only but the main man there is Paul Hunt and what he doesnt know about girling/lockheed parts/fitment i cant fault.
Had no probs with the servos repaired since.
Hope this may be some help.
Clive.
Rebuilt a few of these now and in the kit of seals is a pack of silicone grease.
Instructions in kit say to put silicone grease on retraction valve piston and plastic bearing on main piston, i dont know use the red rubber grease to lube seals just clean brake fluid.
Do not use new old stock seals as sell buy date now way out.
I get all my brake seals/parts from a company called power track/mail order only but the main man there is Paul Hunt and what he doesnt know about girling/lockheed parts/fitment i cant fault.
Had no probs with the servos repaired since.
Hope this may be some help.
Clive.
roverp480
Active Member
I had exactly the same issue on my P4 Rover, it is the hydraulic cylinder not returning in the servo and holding the brakes on. Either the spring is weak , its assembled incorrectly or the seals in the cylinder are sticking. Its the same effect as not having clearance on your master cylinder push rod when at rest.
codekiddie
Active Member
Under normal conditions, pressure from the master cylinder at the input of the servo will give you greater pressure at its output.
When the same thing happened to me, the words of the wise Harvey were:
"Next time it happens, slacken the brake pipe in to the servo, if the brakes free off it's the master cylinder, if they don't it's the servo".
What he was saying is that if you undo this input pipe you are removing any pressure from the master cylinder, so if it frees off it must be the master at fault, but if the pressure at the output remains, the fault must be in the servo.
I too used a servo overhaul kit, and new air control valve, but finally went for a reconditioned servo from Winns, which cured the fault completely
When the same thing happened to me, the words of the wise Harvey were:
"Next time it happens, slacken the brake pipe in to the servo, if the brakes free off it's the master cylinder, if they don't it's the servo".
What he was saying is that if you undo this input pipe you are removing any pressure from the master cylinder, so if it frees off it must be the master at fault, but if the pressure at the output remains, the fault must be in the servo.
I too used a servo overhaul kit, and new air control valve, but finally went for a reconditioned servo from Winns, which cured the fault completely
mrtask
Well-Known Member
I had this problem last Xmas. I 'd replaced the servo for one which I reconditioned myself (albeit under the guidance and observation of a mate who is a proper mechanic, unlike myself!), but I failed to notice that there was no spring in the air control valve! Couldn't believe that such a weak spring, which seemed about as strong as a paper clip, could bring a whole car firmly to a standstill! To determine that the fault lay in the servo, on the advice of our esteemed mentor Harvey, I loosened the brake line just after the servo, a length of hard line before the four way junction, and it freed up the brakes.
Thanks for all contribution. I feel as though I've cheated and taken the easy way out but I just want to get an mot on it so I've fitted a fully reconitioned master cylinder and fully reconditioned servo, just to make sure and get the thing moved on. I'll be bleeding them at the weekend. I would have liked to have pin pointed the problem but there comes a point where paying out is a better option than further frustration and wasted time!
classicalgreen
Active Member
had same issue with brakes sticking on and only being released when undoing union in front of servo. removed servo for exchange ( wins international) and found master cylinder was leaking into servo. about a half litre in it. new servo and master cylinder exchange units cured all though this servo needs a touch more pressure the brakes work decently ( apart from handbrake)