RE Locking Brakes

[Sandy Duffy <sandy@pcnet.com>]

Johann:

Well I would have said replace the master cylinder as this exact problem
happened to me on my 1987 5KTQ but it appears as if you've already done it.
 Hate to say it, but could the master cylinder be defective?  Also have you
checked the parking brake for good release?  It possibly might not be
releasing all the way and when the brakes heat up they might grab a bit
Thereby displaying the symptoms you speak of.

Sandy