Another Brake Booster question too much boost?

[MN69Grande 203]

Hi Everyone,

I haven't had the Mustang out this summer as I was working on some of the front suspension.  When I finished I needed to bleed the brakes.  Everything went fine the pedal is hard with the car off hard to push to the floor.  When I start the car there is no brake feel very easy to push to the floor.  I re-bled the brakes to the point I've now flushed the system twice with the same results.  With the car off plenty of brake feel, with it running no brake feel.  When I turn it off again the pressure/brake feel returns. 

I removed vacuum from the booster and started the car plenty of brake feel - same as with the car off.  I've been hesitant to actually put the car in reverse as I worry that I'll have any stopping power.  I've read in some places this could be a failed valve in the booster?  I've never liked the feel of the system, there was never a lot of feed back and the pedal has always been easy to push - but I could feel the brakes bite a little now nothing with the booster having vacuum.  I can push the pedal to the floor with no pressure back.  I did try a new check valve with no change in results.

Some specs.  1969 Grande (Early 69 build date lots of 68 parts on the car) originally 4 wheel drum.  CSRP Kelsey Hayes conversion done 10 years ago, GM style Prop valve.  Originally Midland style booster, when replaced 10 years ago replaced with Bendix style from Cardone https://www.cardone.com/product/vacuum-power-brake-booster-54-73222. Over the last 10 years I've replaced the calipers when the pistons started to leak (I don't know if this is normal - because of the MN freeze/heat cycle every year).  I also replaced the flex lines this year when I was in working on the suspension.

Any thoughts?  Do I replace the booster?  I was just reading about this guy on WestCoastCougars https://secure.cougarpartscatalog.com/17969/32082/brake-booster-power-midland-style-repro-1967-1969-mercury-cougar-1967-1969-ford-mustang.html?sessionthemeid=26

I might put rams and blocks behind the wheels and try the brakes with the vacuum disconnected - possibly manual mode will work so I can at least move it.

[kblagron 20]

Sounds like the brake booster has failed, but I am no expert.  You could put a wheel (or multiple wheels) up on a jack and with the car running, have someone spin the wheel while in neutral and see if they stop when you press on the brakes.

[buening 63]

Doesn't sound like the booster.  If a booster fails you have no assist on the brakes, and would be like pressing the pedal with the engine off. 

I'm not familiar with the CRSP conversion, but double check that you don't have a manual brake pedal in a power brake setup.  The pedal hanger on the pedal arm is higher up on a power brake pedal. This will give a ton of brake pedal travel.  See here for pedal differences: https://mustangsteve.com/brake-pedals-identification-faq/

If the brakes worked fine previously, then odds are you still have air in the lines.  Make sure you tap the brake lines as you are bleeding them in case bubbles get stuck, look for any leaks (look at rear wheel cylinders if rear drums), and make sure you have the calipers on the correct sides (reversed can have the bleeder being in wrong location and trap air). I also like using the Motive pressure bleeder system, as it really helps pushing those stubborn air bubbles out.

 

Couple things to look into!

[RPM 1,190]

I fixed my power brake issues by going to manual brakes.