Power Brake Booster Tech Question

My wagon came with a Mexican 302 V8, when I swapped it out for a 200 CID I6. I kept the V8 booster. The donor car has a smaller I6 booster. HandyAndy's Fairmont I6 runs a stock I6 booster, and stops quite nicely. On mine, it also stops very well, but the pedal isn't as firm. New discs, and shoes on both cars, and we've bled them both together. My booster was replaced when I did the last major resto on it, 5 years ago.

The V8 would definitely generate more vacuum than the I6, and it is deeper than the I6 booster. Mine has 10" drums on the back, the Zephyr has 9" drums. The disc brakes on the front are 10" on both.

Would a smaller booster be more effective or does the bigger really make it easier to brake?

 

I don't think it would make much difference Norm, the size of the booster diaphram would not be much different. Did you try bleeding the brakes with the engine running? A power bleed they call it. I had to do that on my Satty once to get my pedal back. I can't really think of any real advantage to a bigger booster would be, other than vaccum force on the master cylinder linkage. I'm thinking that weight to booster diaphram size is not an issue.

 

She also has AC. All the vacuum switches that run the plenums doors run off vacuum, so it has a larger vacuum reservoir than the Zephyr. I kept the AC, but I'll be getting it all rebuilt too.

I can't see the booster being a major issue, but I do want the pedal action to be crisper. Power bleeding eh? Nope, never did that, but it sounds like the thing to do. They don't mention that in the Ford shop manuals. Good tip. Thanks.

 

Never heard of power brake bleeding but it can't hurt to try it.
From what I understand about boosters is the smaller the harder the pedal is to push. Don't know but there must be a reason in larger and double diaphram boosters. Kind of like cubic inches bigger is better.

 

OK, the wagons had the bigger booster regardless of engine size due to the bigger rear brakes and weight-hauling capability. FYI, my first car was a 2-door Fairmont sedan from my dad who bought it new. No P/S, no A/C, no PB. Since the car was free, I guess I couldn't bitch.

 

Thanks guys. I'll do the Power Bleed. It makes sense, and it can't hurt. With the tri-power carb, headers and cam, I should get closer to V8 power, so the bigger booster might work better.

 

If the brake pedal is spongy, check the flex lines. How old are they? If much more than 5 years, invest in new ones. The fronts are less than 20 each at Canadian Tire, and the rear is not much more. If you really want to firm it up, get braided steel. They firm the brakes well.

 

You have probably hit the nail on the head, Mike! Those are the originals! Thanks! Between that the power bleed, I should be able to stop on 1980 Dime, and get one Cent back - inflationary economics does make our money worthless.

 

I believe Mike got it right. It's time to change all the flex hoses and check the metal lines closely. You'll at least be able to stop on a Canadian Quarter.

 

Thanks guys. Lucky for us Fox body owners that Mustang parts fit up to 1988. Not so sure about the rear flex hoses, but that's just a measurement issue. 10" discs front, 10" drums on the back. Different lengths, maybe.

http://www.americanmuscle.com/mustang-brake-lines-hoses-7993.html

http://www.cjponyparts.com/catalog/category/view/category/60030041/id/1640

I've dealt with CJ Pony. Good products, decent prices, and excellent service to Canada.

 

Got the new flexlines coming in from RockAuto - all Bendix lines. Thanks Mike. Almost forgot about the one to the rear axle, but its coming too. Going to make new lines at the Master Cylinder to the proportioning valve and at the rear axle lines. Andy had a double flaring kit and a line bending tool.

 

Good luck. Let's hope it works! Be sure to let us know how it goes.

 

My neighbor just went through an issue with his Jeep Cherokee. Soft pedal. He had swapped in all Grand Wagoneer (the big jeep) parts and it was not working right. We bled those brakes half a dozen times at least and still soft. He replaced every part, and the master cylinder three times, and still the same. Yesterday he swapped it all back to the original stuff and suddenly he has good brakes.

I will suggest the power bleed to him when he gets back from his weekend of mountain climbing. I've never heard of doing the bleed with the engine running but it is worth a try. I know he really wants the bigger brakes for the type of back country they travel though.

 

When the brakes were swapped on that Heep, was the MC also changed? A mismatch in the hydraulic stats can cause a soft or hard pedal. That's why everything needs to be changed when it's done.

 

On most Disc brake upgrades for the Fox body cars, the guys have to upgrade the proportioning valve as well. Just a thought...