Brakes locking up

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Originally posted by nazgul:
in your june 10 posting you said "don't see any bushing" there should be a rubber bushing (dust cover) or rubber guide to keep the actuating rod straight and in line...

There is a serrated rubber opening on the brake booster, that the rod comes out of, but not on the adapter plate itself. The adapter plate is just metal. Seems to me just acting as a spacer to make the Ford MC work. When the MC and plate are pulled away from the booster, the rod does not stay straight, it does angle a little bit down until the plate and MC are put back on.

quote:

as an aside, any chance that there maybe a vacuum leak on the booster, any sucking noise from any of the vacuum hoses???

Not that I can tell anyway. The last mechanic to look at it said it was fine. Remember, this whole problem is directly heat related. Winter comes along and the problem goes away.

My 2¢. I'm just rambling here, but all the standard problem issues seem to have been addressed, so perhaps it is time to really think outside the box on this one?

You said your proportioning valve was gutted. Any chance there is still an issue within it?

You say it is a summer, heat related issue. Bear in mind, it could be the ADDED heat of Summer that brings the problem to the forefront.

In that vein, a wobbly disc will create quite a bit of heat. Have you checked disc run out? I"m not sure how bad run out could give you your symptoms, but I don't recall the issue being previously addressed in this thread.

Have you checked inside cabin pedal height? Could linkage be binding, possibly with the added heat of the season?

If you can create the problem at will now in the summer heat, then go for a drive until you get the problem, but take a cooler filled with some bags of ice.

Once the issue pops up, grab an ice bag and plop it on your booster, or MC, or proportioning valve. See what happens. You may be able to locate the problem area more accurately.

I still think this is a length problem with your piston rod. But that has been addressed...

Larry

To add to Larry's deductive reasoning suggestions.

1. Expose the car to heat (leave it in the sun or drive it) then when you know the brakes are engaging, jack it up front and then rear to establish exactly which calipers are binding.

2. Do same with engine running and not running

If it is just front or rear (I assume a pair as you haven't indicated it pulls to one side) the problem is likely not in the MC/booster, conversely if all calipers are dragging it probably is an MC/booster issue. If it only happens with engine running it is more likely a booster issue.

If it is just front then it may be air in the system which is expanding with heat. I seem to recall issues with people not realizing that there are two bleed screws on the calipers and it can seem like all air is out of the system when it is in fact not if you don't bleed both ports and hence there remains an air pocket in the caliper. Someone correct me if I'm talking total jibberish here...I'm on too many forums now

If it is just rear then could something on the e-brake bind when hot? (although normally one would expect the cable to sag when hot)

Another possible if it is either front or rear only is the shuttle valve (different to proportioning valve, still in the trunk, but under the booster). When 'shuttled' (activated when brake pads are too thin) blocks off flow to either front or rear brakes. In doing so I suppose it can seal that side of the system and any internal expansion has nowhere to go other than apply the calipers. The shuttle valve can be activated from over zealous pumping when bleeding the brakes if a hard pump is applied when the bleed screw is open. It is a bit of a bitch to recenter and some people have done it with compressed air, but more often than not requires disassembly of the valve and manual recentering.

Good luck,

GhostRidr, The "serrated rubber" you refer to is a seal for the booster housing to master cylinder sleeve. The extended receiver tube from the master cylinder seals on the ID. of the seal and the booster housing seals on the OD. The pushrod moves through the center of the hole and will hang un-centered without the master cylinder receiver tube. That rubber seal maintains the vacuum in the booster, the adapter mounting plate should applied some pressure to the OD. of the seal against the booster housing. You will hear a hissing sound if this seal is not sealing properly.
I doubt it is related to your problem, I believe you have a master cylinder, booster or proportioning valve problem. Remove the master cylinder from the booster, then check the brakes. If the brakes are still holding that means the fluid cannot return to the MC reservoir, bad MC or proportioning valve. You can loosen the 2 fittings on the MC until fluid starts to leak out, then the brakes should be free.
If not brakes are NOT holding, then the pushrod/booster is not allowing the master cylinder spring to return completely. This can be a subtle problem, there must not be any mechanical force/binding on the master cylinder, the only mechanical energy to return the brake fluid is the return spring in the master cylinder.

Just because something is "new" doesn’t mean it’s operates perfectly or fits perfectly.