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Brake booster????

General Tech Talk

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Brake booster????

Post by fat496 »

Hi Guys.
Just a quick Q, i'm having serious brake issues at the moment. pedal goes almost to the floor before stopping the car, but ive bled brakes twice now and doesn't seem to be any air in them. pedal is firm until i start the car then almost hits the firewall when booster gets vacuum. tend to think i need a new booster, but if it's stuffed shouldn't the pedal be more firm than usual??? Forgive my ignorance, just want another opinion before i go buy a booster. Vehicle is 1990 Daihatsu Feroza and yes i should have posted this in the Daihatsu section but no one answers quick enough there :)
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Post by RAY185 »

Sounds like master cylinder is cactus.
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Post by lump_a_charcoal »

Yeah, you have a hole in your diaphragm maybe...
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Post by smithie »

If the feroza's have a dual piston master cylinder it sounds like the first piston is stuffed. I'd whip the MC off and open it up and check the seals. Should only need a set of circlip pliers to get into it.
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Re: Brake booster????

Post by mkpatrol »

fat496 wrote:Hi Guys.
Just a quick Q, i'm having serious brake issues at the moment. pedal goes almost to the floor before stopping the car, but ive bled brakes twice now and doesn't seem to be any air in them. pedal is firm until i start the car then almost hits the firewall when booster gets vacuum. tend to think i need a new booster, but if it's stuffed shouldn't the pedal be more firm than usual??? Forgive my ignorance, just want another opinion before i go buy a booster. Vehicle is 1990 Daihatsu Feroza and yes i should have posted this in the Daihatsu section but no one answers quick enough there :)

When you have the engine off, no vacuum left, if you hold your foot on the pedal does it slowly start to sink to the floor?

If it does its the master clyinder.

Once the booster has vacuum it will accellerate this process.
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Post by fat496 »

no doesn't sink to the floor, and also pumping brakes can hear hissing sound (Engine off), which leans me towards booster. if i'm driving and pump pedal a few times it firms up noticably.
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Post by mavzilla »

sounds like you broke the primary spring in the master cylinder ., or you have air in the system. it is not a booster problem with what you have described. blank of all brake lines with clamps and test, if ya got a full pedal ,release each clamp and test pedal pressure, when you notice a big drop in pedal you might have found the problem
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Post by Ruffy »

fat496 wrote:no doesn't sink to the floor, and also pumping brakes can hear hissing sound (Engine off), which leans me towards booster. if i'm driving and pump pedal a few times it firms up noticably.
They're both normal.
The cannot make your pedal travel further but it will excentuate a fault.
All your symptoms point to a master cylinder
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Post by fat496 »

had a play with it on the weekend rebled system but still same problem. basically it seems to me that there's still air in the system. have bled it twice now but it's like there is air in the actual master cyl still. shouldn't it bleed out when i'm cracking the bleed nipples at calipers/wheel cyls?
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Post by mkpatrol »

fat496 wrote:had a play with it on the weekend rebled system but still same problem. basically it seems to me that there's still air in the system. have bled it twice now but it's like there is air in the actual master cyl still. shouldn't it bleed out when i'm cracking the bleed nipples at calipers/wheel cyls?

Not always, sometimes you have to bleed the master first at the unions.

I always bench bleed a master cylinder before I fit it.

Same process as at the calipers, pushdown on the pedal, close union, release pedal, depress pedal, release uinon ect.
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