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| | | | Joined: Jan 2016 Posts: 7 New Guy | | New Guy Joined: Jan 2016 Posts: 7 | Hello and please help. I have restored a 1955 Chevrolet 6400 1.5T. I installed a reman Hydro Vac unit from A1 Cardone and now the rear brakes are locking up. Pressure is not returning to the Master Cylinder. I have to crack a bleeder screw at the unit to "unlock" the rear brakes. Is it possible they did not remam it right? I'm at a lose right now as how to fix it. | | | | | Joined: Apr 2015 Posts: 113 Shop Shark | | Shop Shark Joined: Apr 2015 Posts: 113 | i am sure more knowledgeable people will be along shortly, but once you press the pedal, the brakes lock up, does the pedal stay soft? is it both sides that lock up? are all of the return springs intact?
1959 Chevy 8500 - Spartan 80
366 BBC
| | | | | Joined: Jan 2016 Posts: 7 New Guy | | New Guy Joined: Jan 2016 Posts: 7 | The pedal remains rock hard and both rears lock up. I'm wondering if the Hydro Vac unit I got from A1 Cardone has a residual check valve in it. There is no way to release them unless you crack a bleeder screw and then the fluid comes out under pressure. | | | | | Joined: Mar 2004 Posts: 6,236 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,236 | Check the rubber brake hose at the rear...is it new? If not they can fail and act like a check valve when they go bad... At this point in the trucks life I hope ALL of the brake line have been replaces, both steel and rubber. Mike B  | | | | | Joined: Jan 2016 Posts: 7 New Guy | | New Guy Joined: Jan 2016 Posts: 7 | Everything in the truck braking system is new. This is a fully restored truck. | | | | | Joined: Mar 2004 Posts: 6,236 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,236 | Are the front wheels locking up? What happens if you lock it up and try bleed a front wheel first, does it release the rear wheels? If bleeding the front doesn't release both rear wheels then I'd look at the rubber line serving the rear axle. Mike B | | | | | Joined: Jan 2016 Posts: 7 New Guy | | New Guy Joined: Jan 2016 Posts: 7 | We did replace the rear rubber line with a new one, but I'll check that again. The fronts never seem to lock up. | | | | | Joined: Jan 2016 Posts: 7 New Guy | | New Guy Joined: Jan 2016 Posts: 7 | We are going to try that this morning. I'll let you know
| | | | | Joined: Jan 2016 Posts: 7 New Guy | | New Guy Joined: Jan 2016 Posts: 7 | OK WE just tried and if we bleed off the front brakes the rears release. So that makes it the hydro vac unit holding brake pressure all the time. Arghh ANy one with any thoughts on this? | | | | | Joined: Dec 2015 Posts: 2,063 Big Bolt Forum Moderator | | Big Bolt Forum Moderator Joined: Dec 2015 Posts: 2,063 | to recap,
1. you press the brakes, the rears lock up, (front must be stuck on as well but, smaller shoes and don't do near the braking the rears do on a big bolt, your 6400 is a 2-ton BTW, not 1 1/2 ton).
2. You can bleed pressure off at either front or rear and the rear brakes release.
Do you have the proper free-play at the brake pedal (so it is not holding the master cyl down at all? I think you want 1/2-3/4" of pedal free-play if I recall off the top of my head).
If you loosen the line coming out of the master cylinder, does that release the brakes as well? | | |
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