E body Power brake pedal problems?
#2705879
10/11/19 12:18 PM
10/11/19 12:18 PM
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Joined: Nov 2003
Posts: 333 Forest Lake, Minnesota
superbeejim
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Been working on friends 1970 Hemi Challenger repairing different items for over 20 years. He has had it for almost 40 years. 38,000 miles original car. Brings car over because it wont stop very well. I replaced front pads,calipers, and rotors. replaced rear wheel cylinders and shoes. When I went to bleed system,RF caliper wouldn't bleed. Found rubber hyd hose collapsed inside. Replaced all 3 rubber hoses. All wheels bleed fine. While in it, I suggest replace anything rubber. Bought new master cylinder and sent booster out to get rebuilt. When I open bleeders with helper pushing brake pedal, it goes all the way to floor. that's good. When done bleeding system it has high, hard pedal. But when road testing it, the car slowly stops even when standing hard on pedal. pedal goes down about and inch and is rock hard just like you but a 2x4 under the pedal. When put in reverse and standing hard on the pedal, car will slowly creep backward. So far everything in the brake system has been replaced except the 2 brass safety valves under the master cyl. I just ordered both new, will come next week. What am I missing?? Will the safety valves do something like that? Need ideas! thanks ahead, Jim
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Re: E body Power brake pedal problems?
[Re: Andrewh]
#2706035
10/11/19 08:41 PM
10/11/19 08:41 PM
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Joined: May 2006
Posts: 1,757 Phila
PhillyRag
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Phila
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start the car press the brake pedal. see how easy it is and how far down it goes. I believe it's 1-press pedal until it's "hard" 2-then while holding said pedal, start car. 3-pedal should drop maybe an inch or so.
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Re: E body Power brake pedal problems?
[Re: RapidRobert]
#2706151
10/12/19 11:04 AM
10/12/19 11:04 AM
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Joined: Nov 2003
Posts: 333 Forest Lake, Minnesota
superbeejim
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Booster/check valve issue. Before I sent the booster in, I connected the booster only in my hand to a different vacume source from my daily driver. When I pushed on the rod with vacumme, I could push it easy. When they rebuilt the one I sent them, they said it wasn't bad, but we decieded that it has 50 year old rubber parts in it, so it was good to do. They sent a new check valve with it and I checked it by sucking and blowing on it. The hard pedal was there before I had the master cylinder replaced and booster rebuilt.
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Re: E body Power brake pedal problems?
[Re: PhillyRag]
#2706155
10/12/19 11:09 AM
10/12/19 11:09 AM
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Joined: Nov 2003
Posts: 333 Forest Lake, Minnesota
superbeejim
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start the car press the brake pedal. see how easy it is and how far down it goes. I believe it's 1-press pedal until it's "hard" 2-then while holding said pedal, start car. 3-pedal should drop maybe an inch or so. I did do that and the pedal did go down a bit after I started it. A weird thing I noticed is when I hold the brake pedal down hard and rev the engine, I could feel the pedal go up and down about 1/4" as I was varying the throddle. The vacume changes with throddle opening, but I never noticed that before.
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Re: E body Power brake pedal problems?
[Re: DAYCLONA]
#2706156
10/12/19 11:14 AM
10/12/19 11:14 AM
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Joined: Nov 2003
Posts: 333 Forest Lake, Minnesota
superbeejim
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Another item to check off your list, ....sounds like you haven't confirmed the booster to master pushrod clearance when you replaced the master... generally .020 to .060 clearance This is another weird problem is with the new master cylinder and original booster and the rod screwed in to make it the shortest, I still had to put 4 flat washers on each booster stud to get a little clearance. So now the master is about 1/4" away from the face of the booster.
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Re: E body Power brake pedal problems?
[Re: superbeejim]
#2706167
10/12/19 11:54 AM
10/12/19 11:54 AM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Lincoln Nebraska
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another MC might be in order & not sure if haveing the MC not sealed to the booster is a (vacuum) problem or not. & on the pushrod I would shoot for .020"
live every 24 hour block of time like it's your last day on earth
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Re: E body Power brake pedal problems?
[Re: Andrewh]
#2706181
10/12/19 12:36 PM
10/12/19 12:36 PM
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Joined: Nov 2003
Posts: 333 Forest Lake, Minnesota
superbeejim
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if it happened before you sent it in, then there is probably another issue. the fact the master doesn't work without shims is concerning.
I would guess you don't generate enough vacuum. And you have the wrong master.
have you tested the vacuum that motor makes? I just did the math on both MC and the bore depth for the pushrod is the same on both MC. The one on the car wasn't original, it was replaced with an aftermarket one. The new one I got was from NAPA. The original one had 3 thick paper gaskets between the MC and the booster and that is about the thickness of my 4 washers. The Hemi has 15" to 16" of vacume at idle and my Daily Driver has about 20"
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Re: E body Power brake pedal problems?
[Re: Andrewh]
#2706345
10/13/19 09:25 AM
10/13/19 09:25 AM
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Joined: Nov 2003
Posts: 333 Forest Lake, Minnesota
superbeejim
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that sounds low for vacuum. also what is the part number on the master? you say it isn't original, but is it correct? It is not a Bendex, The one on the car has no casting #. The new one from NAPA also has no #. All I know for sure is the Hemi Master has the lines facing the fender and they use a 1-1/8" bore, so that much is correct. I think I read that the correct Bendex MC with the correct # for a Hemi is the rarest and most expensive MC out there.
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Re: E body Power brake pedal problems?
[Re: DoctorDiff]
#2706610
10/14/19 08:26 AM
10/14/19 08:26 AM
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Joined: Nov 2003
Posts: 333 Forest Lake, Minnesota
superbeejim
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Does the piston protrude past the mounting surface of the new master cylinder?
If so, you must adjust the push rod so the piston becomes FLUSH with the master cylinder during assembly. The piston is out about an 1/8". The screw in the bottom of the MC holds the piston from coming all the way out, but if I adjust it so the piston is flush, the piston will be forward of the brake fluid feed hole?
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Re: E body Power brake pedal problems?
[Re: superbeejim]
#2706699
10/14/19 01:06 PM
10/14/19 01:06 PM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
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Lincoln Nebraska
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I'd put a cheap parts house rebuilt M/C on there just to diagnose. You likely wouldn't keep it on there but at least you'd know if it was the M/C or not for not much money. I usually dont shotgun parts at a problem but I (just me) think I would here on this one.
live every 24 hour block of time like it's your last day on earth
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