brakes

J

jbeboatman

Low Mileage
i have a 1981 x1/9 and when it sits in the sun or heat with the top on the brake pedal gets very hard and all four wheels start to lock up. sometimes not allowing car to move, pedal when cold feels fine i think poss air in brakes heats up and locks brakes. any other ideas thank jeff new member from michigan
 
Air won't lock the brakes - it makes them mushy. If all four wheels are locked, it's you master cylinder.
 
jbeboatman said:
thanks i was thinking that but how come brake pedal is so hard when car gets hot very strange
Click to expand...

It is indeed strange... But the m/c is inside the passenger compartment under the dash, so if it's going to jam when stuff expands....

In any case, the master is the only common point between the front and rear circuits, so it will be the problem if all four wheels are locking up.
 
You could see this if the pedal does not return completely after you take your foot of the brakes. The master cylinder has ports that connect to the fluid reservoir; In the relaxed state these ports are open, and excess fluid in the system will be pushed up into the reservoir. As you step on the pedal, these ports get blocked by the pistons in the master cylinder. In this case, if the fluid expands (e.g. thermal expansion) the fluid has no place to go and pressure will build up.

I believe the brake light switch sets the pedal height on the X1/9 (although I have not actually looked at it). Perhaps you can back out the switch a bit and see if that fixes the problem?

If adjusting the brake light switch does not work, have a look at the linkage between the pedal and the master cylinder. Perhaps someting here is causing the pistons in the master to not retract fully.
 
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Not much to offer on help here (I'd look at the brake light switch before going to deep though, as suggested) BUT, from another Jeff in Michigan (the west coast) Welcome!
 
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