70 power brake booster help

Hey everyone. I got the carb back from my builder (he rebuilt it) but I’m still bogging on take off. I don’t think the power brake booster is even working, feels like manual brakes and it’s making a loud sucking noise at times. I’ve traced down all vacuum lines and they are good but the sound comes and goes, especially when hitting the brake pedal.

So, is that part of my bogging issue, cause the brake booster is creating a vacuum leak? I’ve never replaced a power brake booster so tell me how bad, what to do and not to do and give me all the tips you can.

Also are aftermarket brake booster ok or should I send the original off to get rebuilt? I’m scheduled to go to my first car show in about 3 weeks, so I’m really in a pinch to ship it off for 4 to 6 weeks.

You need a booster for sure! Give WCCC a call! They might have one rebuilt and ready ship back to you.The aftermarket boosters a junk! Stock motorcraft carb?

Stay away from one time use, Chinese boosters and DO NOT give up your original BENDIX core for a rebuilt until you confirm your are getting a correct booster in exchange. We have economy and premium in stock.


My stock carb got replaced sometime long ago by someone else. It’s an Edelbrock 1407 750 cfm now. I had it rebuilt (off the car) and I’m going to take the car to the guy and let him tune it on the car this week but I’m just wondering the the brake booster is creating a leak that’s causing my poor performance? I had someone suggest cap off the vacuum to the brake booster and see if it runs any better. I guess that wouldn’t hurt the brakes anymore than they are now. They just feel like manual brakes now.

I looked through about 8 pages of Repairs on here after searching brake booster but don’t see any guides or tips. Anybody want to share any???

I would advice against driving your car with the vacuumhose to your booster capped off. I had my old booster blow a hole and almost had a crash since the damn brakes were so hard I could not get the car to stop, even with 2 feet on the pedal.
The pedal is much harder to press on a powerbrake car (if the booster fails) than on one with manual brakes
Unless you have a nice wide stretch of road with no traffic, then you might give it a go at your own risk ofcourse :slight_smile:

One easy test is run your car for a minute, shut it off and return hours later and pull the plastic check valve out. It should give significant resistance and you should hear a loud “whoosh” sound when pulled. If it cannot hold vacuum after parked you have a bad diaphragm.


Its a tough job, all day and maybe into 2nd day. Pull drivers seat and console out, get a pillow and get cumffy

Actually… Should be about 3 hours unless things are really rusty. Just know that this bracket is double nutted and will cause grief if you do not know.


Seriously? Full day into the 2nd??? I see one screw head on the engine bay side. Can someone outline the steps on a 70? I thought I should see 4 bolts all on the engine bay side and then just unhook from the pedal on the inside…and of course the brake lines. Should I replace the master cylinder too?

Getting under the dash is a pain. Here is a video.


Thanks, Don.

Trust me, its all day. The nuts are tough to get at under the dash and the MC was a tough task also. I replaced the MC, it was $25 from auto zone, Both booster and MC were about $100 or so

Ok, gonna pull the trigger and order the parts from WCCC. Don, I’d appreciate you or anyone else double checking me on parts before I place the order.
I’ve got a 70 Eliminator, 351C, Auto with power disc up front and drums in back.

I’m ordering…

Bushings and hairpin. Should I replace anything else while I’m at it?

Also, WCCC doesn’t have a master cylinder in stock so how do I pick from the multitude the local auto parts place will have?

How about this one…

I saw some horror stories about brake lines not fitting certain master cylinders and having to re-flare the ends. I don’t want that.

If your Cougar has the OEM Bendix master cylinder, you might consider sending it to Booster Dewey for rebuild, or exchange. Does your local have O’Reilly Auto Parts nearby?..or multiple locations that are nearby? If so, spend some time checking to see if any of the stores have rebuilt master cylinder units in stock. If so, go to the stores and physically look at them to see if any are Bendix units. You might get lucky. I have found them in the past. Whatever you decide, consider keeping your original Bendix unit (if you have it). If you need to go short term with a generic rebuilt unit, you can still have your OEM Bendix master cylinder rebuilt for future use. Best of luck, and hope the end result turns out well.

YES!!! I finished removing everything in 1 hour and 15 mins. I might hurt all night from playing contortionist under the steering wheel, but it’s done. Here’s what all I did… removed air cleaner and unhooked vacuum hoses that were in the way. Siphoned brake fluid from master cylinder. Removed brake lines from master cylinder. Removed export braces. Removed master cylinder. Removed 4 brake booster bolts from under the dash and one on the outside. Removed brake light switch. I’ll post the pictures next. I assume the brake booster is the original but I’m guessing the master cylinder is a replacement.

Don Rush, you’ll be getting this brake booster soon!!! LOL

…and all bolts were 9/16. I used two 6 inch extensions with a swivel for the under dash bolts.

A secret…
Prop open the hood…
Remove the dr hood hinge spring & you won’t have to remove the export brace (or one side of the factory brace) to get the booster out.

That mastercylinder should work fine, eastwood has some brake fluid resistant paint I spray on my m/c so they don’t rust.

That Eastwood paint you’re referring to works very well indeed. As far as rattle can paints they have some good stuff.