Vacuum brake booster bad (I think). Advice?

[Laurence MacNeill]

So I think I have a bad vacuum brake-booster in my ’68 Ford Galaxie. I thought it might be the low vacuum I get at idle with the camshaft I installed, but after installing a vacuum-reserve canister, I’m still having the same problems — no brake boosting at all when the engine is idling. I attached a MIty-Vac directly to my brake-booster and it will not hold any vacuum at all (I assume it *should* hold vacuum if the booster were good, yes?)

Assuming I’m correct that the booster is bad, can I replace just the booster without removing the master cylinder and opening up the can of worms that would accompany the removal of the master cylinder?

Or, should I just go ahead and replace the master-cylinder and brake-booster both at the same time and deal with the headache of bleeding the entire brake system? (The cost of a booster+master is not much more than the cost of a booster alone.)

Thanks for any advice you can give me.

Topic

[619DioFan]

Do you have a hard pedal yet no brakes – this will be the brake booster check valve. when you step on the brake pedal do you get a sound of air escaping – this would be a bad booster. do you see any wetness under the dash were the brake pedal push rod goes through the firewall – bad booster. I would do the booster / master as a unit. make sure to bench bleed the master prior to install. this would be a good time to flush the entire brake system and start with fresh parts and fluid.

[college man]

[quote=”619DioFan” post=66529]Do you have a hard pedal yet no brakes – this will be the brake booster check valve. when you step on the brake pedal do you get a sound of air escaping – this would be a bad booster. do you see any wetness under the dash were the brake pedal push rod goes through the firewall – bad booster. I would do the booster / master as a unit. make sure to bench bleed the master prior to install. this would be a good time to flush the entire brake system and start with fresh parts and fluid.[/quote]

++++1 on the above. Do the master and booster together
and flush the fluid.Brakes are to important.

[Laurence MacNeill]

Yes, the pedal is very hard and there are no brakes — I don’t hear the sound of air escaping or see any wetness under the dash. If I put the car in neutral and blip the gas-pedal, the brakes come back briefly, then get hard again — this is why I assumed it was a low-vacuum problem initially.

Yeah, I’ll go ahead and replace both the booster and the master-cylinder… I hate bleeding brakes, and was really hoping to avoid it, but you’re right — the brakes are too important.

Thanks,

[college man]

Keep us posted on your progress.
How about a couple pictures of the car. 🙂

[Laurence MacNeill]

She’s not quite picture-worthy yet. 🙂 Not one trim-piece on the whole car right now, although she is painted at least. Saving up the money to have the trim straightened up, polished, and re-anodized. (45 years have left the trim in pretty sad shape.)

I’m currently working on the interior — I have all the pieces for it, just need to get them installed. I’ve finished some of the interior — seats and carpet. I’m working on the door-panels and dashboard right now. Then I need to get the top squared away — it needs a lot of adjustment to get it to fit correctly, plus some tuning on the hydraulic mechanisms to make it raise and lower properly without assistance.

Hopefully in a few months I’ll have enough saved up to get all the trim done — which will take a good 3 to 6 months after I give them all the trim pieces, anyway.

And last, but not least, I want to get the factory A/C working again, and converted to R-134a while I’m at it — but at least that won’t affect its picture-worthiness. 🙂

So hopefully, this time next summer she’ll be picture-worthy and car-show worthy.

[619DioFan]

[quote=”LMacNeill” post=66578]Yes, the pedal is very hard and there are no brakes — I don’t hear the sound of air escaping or see any wetness under the dash. If I put the car in neutral and blip the gas-pedal, the brakes come back briefly, then get hard again — this is why I assumed it was a low-vacuum problem initially.

Yeah, I’ll go ahead and replace both the booster and the master-cylinder… I hate bleeding brakes, and was really hoping to avoid it, but you’re right — the brakes are too important.

Thanks,[/quote]

You might want to try replacing just the brake booster check valve. when they go bad they give you that hard pedal yet no brakes condition.( they are only a couple of bucks ) if you have already ruled out the check valve then do the booster / master combo.

[Laurence MacNeill]

I honestly think it’s the booster itself — when I attach my Mity-Vac directly to the booster, it holds no vacuum at all. Even if the check-valve were bad, it would still hold vacuum if the vacuum diaphragm inside the booster were good, yes?

[Bill]

You would need a Mity-Vac about twice it’s size to create enough vacuum to pull the booster into a vacuum.

I suggest to start the engine, remove the vacuum hose from the booster and quickly put your thumb over the fitting. After 10 seconds , remove your thumb. If there is no vacuum present you need to replace the booster.

[Author]

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