Brakes lock up when hot outside

[mrmurray]

Abstract:
Just thought I would see if anyone knows a common culprit for brakes locking up when hot?

Discussion:
Series IIa, 1967 88" 2.25 gas engine. M/C and all 4 wheel cylinders rebuilt by PO. New flex lines and pipes installed by me. Pads and shoes are a mix of new/old as many new drums I bought would not fit with new pads installed (I have new pads with old drums, or vice versa). Seems you have to turn even new drums and campher the new pads, which is on the agenda for a later date, but I digress...

Brakes are adjusted properly at the wheel (when cold)

I suspected the M/C actuator rod adjustment (rod and pedal stop), so I backed them way, way off (to the point where I have almost no pedal when cold, goes nearly to floor but still stops vehicle). Once the ambient temperature comes up (in the 90s here now), pedal is very firm and the brakes drag very badly. I let the system cool down, and once again, very little pedal. When its hot outside, I can drive maybe 10 minutes before the brakes start to drag.

Proposed solution:
I suspect the M/C and can buy a new one (I don't trust the PO rebuild).

Thank you!

[SafeAirOne]

I think you're on the right track, unless there's a nugget of debris blocking one of the orifices in the plumbing somewhere. If the valve to the reservoir isn't opening properly (usually because the MC piston doesn't fully retract), fluid cant freely return to the reservoir when you're not using the brakes.

Also, from what I understand, there are virtually NO brake shoes made nowadays that correctly fit these Rovers except for the...I want to say 'Mintex"...brand shoes (verify this info--there have been plenty of recent 'brakes bind with new shoes' stories on the internet, that have been cured only with a certain brand of shoes). So you might check your new shoes.

Which brakes/wheels are scorching hot when they finally start dragging? If it's ALL of them, then I'd obviously start with those brake items common to the entire system, and so on and so forth.

[I Leak Oil]

If it's truely heat related then you need to think about what is expanding as it gets hot. Does sound like a MC issue though. Fluid not returning to the reservoir. Even hot fluid should be returning to it.
Are the brake springs all installed correctly? Are the pistons on the wheel cylinders retracting? Have you clamped off any of the flex lines to see if the condition changes? What happens if you back the snail cams off a click on the back wheels then the front wheels then all the wheels? Any change?

[parrie]

How long have you owned the truck? Has the issue been on going or did it start after you replaced pipes & shoes? Does sound MCish but you also mention having trouble w/ the pads/drums fitting properly...is it possible they are too tight? Once had an old Chevy p/u with the same symptoms. I managed to get things together thinking things would "wear-in" but not the case...it got hot enough to boil the brake fluid then finally lock-up.

You also mention PO had "re-built" the wheel cylinders...I've never gone the rebuilding wheel cylinder route, to me makes more sense to just replace them unless you know for sure they are actually operating properly.

[siii8873]

probably a MC but did you replace hoses, I've had them swell to where fluid would not return thus locking up brake.

[mrmurray]

Hello, I wanted to post a followup in case anyone else runs into this issue. Seems that a number of issues can cause this condition, but in my situation, adjusting the master cylinder (M/C) linkages fixed the issue. I first adjusted the pedal height (using the 7/16-head bolt) per the green bible to a height of 6.25" from the floor to the bottom of the pedal. I then adjusted the M/C pushrod (the 1/2 inch head nut) to have 1/4 inch of free play before contacting the M/C. Brakes work great now. I am embarrassed that I didn't start with factory specifications. Thank you to everyone for the input on this and other issues I've had, y'all are a great community here! Cheers, Mike