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08-19-2015, 06:35 AM
Hello all...got a brake issue here. 1970 Mach 1 with DRUM brakes front and rear. All brake hardware and shoes are new, master cylinder new, all lines new Except front 2 Hard lines. Ok......system is bled, pedal stops (like against metal stoppage) halfway to floor, when I open Rear bleeders the pedal goes all the way to the floor. If I release Front bleeders the pedal does NOT go to floor but still stops halfway as stated above. This cant be correct as my pedal height is about 8+ inches from the floor and is too high to be used safely. Any tips/ideas???????
Thank you, Neilhttp://mach1club.com/images/smilies/Smiles72110/sSig_help.gif
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First, I believe when you bleed either the front or rear on a dual piston master cylinder system the pedal shouldn't go to the floor. When you bleed the fronts the pedal travel seems normal. There may be air trapped in the lines or master cylinder for the front brakes because when you bleed the rears the pedal travel seems incorrect. Did you bench bleed the master cylinder before installing it? Also, are the brakes adjusted correctly? Brake adjustment has an impact on brake pedal travel.
I would make certain the brakes are adjusted correctly. Then bleed the brakes some more. Manually bleeding the brakes by pumping the brake pedal can be impossible some times. There are DIY pressure bleeding kits like the popular one Motive Products sells,
http://www.motiveproducts.com/ . I use a Mityvac vacuum brake bleeder,
http://www.mityvac.com/pages/products_bcbe.asp . It's a pain but has always worked and is not messy. Mityvac also has vaccum brake bleeders that use compressed air to operate.
If bleeding and adjusting has no affect I would exchange the master cylinder. Do not buy a rebuilt master cylinder.
The brake pedal height is odd. Was it fine before this work? Are these power drum brakes or manual drum brakes? On manual brake systems the pedal is usually higher than power brake systems. I'll measure my pedal height on my 69 Mach 1 and post it but mine are power disk brakes.
Regards,
Mike
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Thank you so much....in my shop manual it states that the pedal height should be about 6.5 - 7.5 inches from floor metal. These are Manual brakes...I did bench bleed the master cylinder. Ill try your suggestions.
Neil
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It sounds like the pedal height is not too far off. Let us know what happens. I haven't seen too many manual brake Mach 1's (actually never). I think the rod from the pedal to master cylinder is adjustable to set the brake pedal height.
Four wheel manual drum brakes. Last vehicle I had like that was a 1956 F100 pick up. Make certain they are adjusted correctly. Just in case, hang on to the steering wheel when stopping.
Regards,
Mike
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(08-19-2015, 06:35 AM)neilsonnewby Wrote: Hello all...got a brake issue here. 1970 Mach 1 with DRUM brakes front and rear. All brake hardware and shoes are new, master cylinder new, all lines new Except front 2 Hard lines. Ok......system is bled, pedal stops (like against metal stoppage) halfway to floor, when I open Rear bleeders the pedal goes all the way to the floor. If I release Front bleeders the pedal does NOT go to floor but still stops halfway as stated above. This cant be correct as my pedal height is about 8+ inches from the floor and is too high to be used safely. Any tips/ideas???????
Thank you, Neilhttp://mach1club.com/images/smilies/Smiles72110/sSig_help.gif
Just to add. I installed a so called rebuilt master cylinder and had no end of problems. Turned out the master cylinder was faulty and once i re-kited all good. Slim chance i know...but thought i would add.
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Yeah, rebuilt master cylinders or brake cylinders are often not very good. It all depends on the condition of the bore before the rebuild. Also, the honed finish in the bores of rebuilt master and brake cylinders are much rougher than in new brake and master cylinders.
Regards,
Mike
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Joined: May 2015
(08-20-2015, 06:30 AM)1969_Mach1 Wrote: It sounds like the pedal height is not too far off. Let us know what happens. I haven't seen too many manual brake Mach 1's (actually never). I think the rod from the pedal to master cylinder is adjustable to set the brake pedal height.
Four wheel manual drum brakes. Last vehicle I had like that was a 1956 F100 pick up. Make certain they are adjusted correctly. Just in case, hang on to the steering wheel when stopping.
Regards,
Mike
Thank you Mike....actually ive only seen a few Mach 1's with power brakes....I inherited this from my dad so I am essentially second owner....it isn't even drilled to mount a booster so I don't know.
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It is unusual to have a booster on drum brakes due to reasons I know but are too complex for a simple reply.
In a split system the pedal should not hit the floor if either half of the system fails.
That said, I would suspect the master in some way, maybe the input push rod is the wrong one? Maybe fix that and then go on to the other problems.
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