Strange brake problem - what's the MTBF for this one? (Page 1/1)
sanderson231
APR 17, 06:12 PM
I'm finishing up a 4.9L swap for a friend who has health problems. The car has been off the road for about 10 years but mostly inside or under cover.
I rebuilt the brakes and went to bleed them. I hooked up the pressure bleeder at the master cylinder with 40 psig of pressure. I went to the passengers side rear caliper, opened the bleeder and nothing came out. Went to the driver side rear and got fluid. So I know the line is open from the master cylinder to the splitter manifold by the passenger side caliper. Downstream of that is a short piece of metal tubing which then transitions to the brake hose going to the caliper. I unbolted the hose from the caliper - still nothing. So either the metal tubing or brake hose has an obstruction in it. Took the assembly off and separated the metal tubing from the hose. Blew air through the metal tubing and it's open. So the hose has an obstruction. Ran a 1/16" welding rod down the hose and found an obstruction where the bracket that attaches the hose to the knuckle is clamped on. Pried the bracket off and saw that the hose was oval shaped. Cut the hose apart and sure enough it was pinched shut completely. What appears to have happened is that the bracket was initially clamped on a little tight. Then there was corrosion on the underside of the bracket. Since the volume of corrosion product was greater than the metal loss this was the final straw that pinched off the hose. Perhaps if I bled the brakes with the pedal, there would have been enough pressure to get past the pinched section in the hose but then I don't think that the caliper would have released after letting off the pedal.
After 39 years of Fiero ownership I thought I had seen it all. Unfortunately Mr. Murphy is still out there.
------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
sleek fiero
APR 17, 07:59 PM
Murphy is always hanging around .just can't trust that guy. good to know about the clamp. I will check mine. I once had a rubber line separate inside and blocked the banjo fitting. thanks sleek
theogre
APR 17, 08:01 PM
Yes, The support bracket can rust and rust then crushes the hose shut. Many live w/ high road salt have seen this problem many times over the decades.
Hoses can swell shut too. Oil etc gets on them and gets thru outside layer and attack inside layer and swells it but cord layer won't let inside growth so only way to swell shut.
Use hose rated SAE J1401 on top of DOT 106. Same setup as OEM so BS of SS but much better "rubber" hose. see http://www.fiero.nl/forum/Forum2/HTML/129208.html rubber brake lines vs stainless steel
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
