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B210 brake problem


B210GX

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Ok problem is the pedal goes nearly to the floor( not all the time), but only when the motor is in a "NON vacuum" state ie.. not  accelerating or decelerating.

 

bled(several times)  New shoes on the rear, adjusted up nicely.  I have the 280zx brakes up front.  all in all the car will stop just great, until say, you are coasting.

 

I bought a new check valve thinking it may be bad.  I went out tonight unhooked the original, it still had vacuum stored in the booster from nearly a week ago.

 

So can it still be bad?

 

 

I am stumped, the weather is getting nice..It's time to get the Datsun out and be DRIVEN.

 

 

 

 

 

 

 

 

 

 

 

 

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Isn't idle ( not accelerating or decelerating )  the point of highest vacuum ??  maybe there is a problem with your springs inside the vacuum canister..   So when you push on brake ,, the weak springs allow vacuum to pull to hard..... Although if that happened i would think the brakes would lock up... Unless the vacuum chamber stays compressed slightly and doesn't fill all the way up so the brakes might seem to be closer to the floor and/or mushy feeling..

 

 

now i'm more confused then when i started trying to help you.

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Idle is 16-18 inches of vacuum. A 'big cam' will drop this to 12 or less.

Full throttle accelerating is very low vacuum.

Deceleration is very high vacuum 22 or more.

 

 

So I'm also confused by it's "non vacuum state. not  accelerating or decelerating"

 

If there was residual vacuum stored after two weeks this is totally normal and why the one way valve is there, and working. This is to allow at least one use of the boosted brakes if your engine should stall while driving and your vacuum source is lost.

 

Another test is to pump brakes several times to exhaust any residual vacuum from the system.

Now apply the foot brake and hold.

Start engine.

Pedal should drop towards the floor slightly as vacuum builds. This would be considered normal operation.

 

 

 

If everything is working properly and adjusted and you still excessive pedal travel....

 

You have to realize that the front disc brake on a B210 is extremely small and has a correspondingly small 3/4" master cylinder to operate it. The zx calipers are massively large and use a 15/16" master to operate them. If you use a 3/4" master it will have to travel farther to move the same amount of fluid the 15/16" master will move. Your B-210 pedal will feel mushy but it will work, but also you will need to keep the rear shoes well adjusted to reduce pedal travel to the minimum also.

 

 It is law that a larger master will be harder to push than a smaller one in order to get the same output pressure. It's called the "You can't get something for nothing" law. Moving more fluid will require more effort. The good news is that you have a brake booster so it will do most of the hard work of moving a larger amount of fluid. A 7/8 or even a 13/16" will improve your pedal feel if you can't source a 15/16" master.

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Would I hate it If  I removed the booster all together?   thing is, I have the Hitachi SU set up including the air cleaner.  

 

Being a LHD  the booster is in the way of the air cleaner to begin with.   Are there filters still available for the GX air cleaners?

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Edelbrock Air Filter dimensions suppose to fit 1974 B210, http://store.moparshop.de/en/oxid/Air-Filter-Element-oval-13-500-x-7-000-x-2-500.htmlI don't think so...

Measured my 1200 gx air filter element 12.00 x 6.00 x 2.00

A parts store in Yakima, listed GX element on Ebay for months and it's not listed now! How many parts stores are there in Yakima?

Steve at ZTherapy, makes a custom air filter assembly for the A series dual Hitachi carb set-up. Uses off the shelf air cleaner element and flows much better than stock. And no I haven't had him do one for my setup yet.

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The 1200 does not have a booster, but the car is also lighter. Assist is always a good idea it simply multiplies your foot effort on the pedal.

 

Hey if you want to see what running without a brake booster is like pull the vacuum hose off the engine and plug the fitting on the intake. You may be able to get away with it but expect a big surprise.... and try it in the driveway first!!!!!

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