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More braking power needed
(05-19-2019, 12:24 PM)Don C Wrote: Is the first part of your last post missing?

Have you verified that the problem is the booster and not a connection, or even an internal leak in the pump?

I am now 99% sure that the booster is  somewhat leaking . I renewed the  check valve and the  rubber grommet - no change. The pump continues in tiny burst when connected to the  booster...

I have  noticed that there  are many offerings for a 9 " booster  ( four  bolts connection) but what would you recommend for the 71  Mach 1 with original front disc brakes ?
I want to be 100 % sure that it fits  the car  and the  newish master cylinder.
I have one from LEED brakes: https://leedbrakes.com/i-21155650-9-inch...black.html
You may have mentioned this earlier, but did you try capping (with finger works) the hose to the booster to make sure the leak is not somewhere else? During my install I had one leak that was a nightmare and after a lot of troubleshooting I figured it was one of my customized metal fittings that had a cracked.

[Image: 20160929_171923_edit2_small.jpg]

1971 M-Code Mach 1 w/Ram Air, 408 stroker, 285/291 0.558" roller cam, Blue Thunder intake, TKO600, Hooker headers with electric cut-offs, FiTech EFI w/ RobBMC PowerSurge pump
Strange center section with Truetrac, 3.5 gear and 31 spline axles, 4-wheel disc brakes
(05-13-2019, 03:05 PM)c9zx Wrote: +1 on Don C's posts. Here are some easy tests. "Booster Function Test: Check pedal feel and vacuum booster function while test-driving the vehicle. With the engine off, apply the brake pedal repeatedly with medium pressure until the booster reserve is depleted. At least two brake applications should have a power-assisted feel before the pedal hardens noticeably. If the pedal feels hard immediately, or after only one brake application, it may indicate a vacuum leak or a low level of engine vacuum. Inspect the vacuum hose to the booster for kinks, cracks or other damage. Check vacuum at idle with a vacuum gauge. [img=375x0]https://s3.amazonaws.com/assets.knowyourparts.com/app/uploads/2016/09/automotive-vacuum-booster.jpg[/img]To test booster function once the reserve is depleted, hold moderate pressure on the brake pedal and start the engine. If the booster is working properly, the pedal will drop slightly."
Also, 20 in/hg is a lot of manifold vacuum for a modified 429 engine to generate at idle. Is idle speed high, or timing too far advanced, do you have another vacuum gauge to compare results? I currently have a 1969 Cougar and a 1972 Mach 1 that have aggressive cams and make 11.5-12.0 in/hg and still run the booster although these numbers are near the edge of not working with the OEM single diaphragm booster. Chuck

Hi Don,

well......there was a small leak  in the booster so I replaced it with a Leeds  Brakes 9" booster for 71 Mach 1. When changing the booster I noticed that  the old booster was  a 11" booster - maybe  for a bigger Ford - anyway the  bolt pattern was the same. I checked the  dimension  for the  rods for the pedal and the MC ( 145 mm / 25 mm) and the MC  cylinder diamameter  and stroke I checked , too ( 12 mm / 35 mm ) which was the same  as the old one  I replaced a year ago.
I also decided to buy new brake pads ( C-Tek Metallic pads = standard pads ?) . This change was important as the old pads  - altough hardly used - > 30 years old ? were about to crack and partly loose ( riveted pads !) so now this is OK.
After  priming the air out from the  MC connection I made  the test ride: First the  brakes did not  seem to be much better than before  but when I made  more stops they start to bite better. After  ab. 5 miles I was back at the garage and  noticed the smell from the front pads and saw that the  rotors were dark blue....= very hot !

I jacked up the front  and turned the front wheels by hand . They  could be turned without too much  effort but  my question now is: How much force  is accepted to use when  deciding what is too much when turn the wheel by hand ? 
If the  pads are too close what would you check first ?

The  new vacuum system works with the new booster otherwise fine.
Were the rotors new, or freshly machined for a break-in surface? If not they should have been scuffed. New pads on used rotors that were not prepared cause the pads to glaze, resulting in high temperatures and poor braking.

“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
Did you check pushrod length when you swapped your brake booster?

The reason I ask is because if the pushrod is too long it can result in dragging brakes.

See this neat little brake setup paper from Jegs https://www.jegs.com/installationinstruc...10-116.pdf
[When changing the booster I noticed that the old booster was a 11" booster - maybe for a bigger Ford ]
Same here, I still have the old 71 11 inch that I might attempt to restore one (far far away) day, for now, I had to do with the 9 inch as the shipping costs to Booster Dewey and back + repair would have made it idiotic. They are indeed identical aside the diameter. More space is this crowded corner isn't that bad Smile

[How much force is accepted to use when deciding what is too much when turn the wheel by hand ? ]
Practically zero. tho depends on wheel weight to get started. but once it turns, it should stay turning on its own for a few, only noise would be may be a tad of friction on new pads but not really succeeding on stopping the wheel.
Considering your question and the dark blue tint, looks like the pads are always under pressure, never at rest. Chances are now also high the rotors are no longer flat and needs be turned or replaced. Sad

73 modified Grandé 351C. Almost done. 
71 429CJ. In progress
Check the valve in the distribuiton block, If it stuck your front brakes will drag.

For knowing your limit you have to pass it thumb
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