Upgrade brake vacuum booster?

Hello mate,

Recently, feeling brake weak.

Replaced the pads and caliper upgrade to pot 4, but still not got strong brake.

I heard may try to upgrade brake vacuum booster.

So what type booter I can replace ot.

Did you put in new brake lines? Also, I would re-bleed the lines. The brake booster does not boost the power of the brakes, it reduces the power needed to press the brake pedal. If you did not replace the lines I would suggest stainless braided. They helped change the entire feel of my car. Also, if the 4 pot have more surface area in their pistons than the ones you took off they can actually have less braking force.

 

In a hydraulic system if you have two pistons of equal size and you push one the other should move the same distance as the one you pushed. But if you double the area of one of the pistons, when you push the first piston the larger piston moves half as far. If however the second piston had half the area of the first piston and you pushed it the smaller piston would move twice as far.

 

In this situation the master cylinder is the pushing piston. And the calipers are the pushed piston. If you make the pushed piston (calipers) larger then you lose some of the movement.

 

This is the link to how I did my brake upgrade.

 

https://legacygt.com/forums/showthread.php?p=5461728

 

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Edited March 28, 2020 by choover1101

I second a full fluid flush and re-bleed using the correct procedure, which I can't remember.

You might be able to use a newer Subaru model like wrx/stinor Forrester. They may or may not even be different, but be warned the master cylinder and pedal box bolt onto the brake booster. If the booster studs are different you may need to modify the firewall and pedal box bracket and/or use the master cylinder from the new booster.

 

I know for certain that an 08 wrx master cylinder bolts on just fine.

I know for certain a 1998 Forester master cylinder bolts on and uses the same brake lines leading to slave cylinder

 

Look up part numbers for different models and check junkyards if you can to see what is the same.

Idk much about your climate or work methods, but grease or lubricants can contaminate pad material permanently. Also clean your rotors before and after installation.

 

Check that you didn't twist your calipers the wrong way twisting your brake lines. This causes some strange brake behavior and sometimes doesn't, but a good technician will always spot this and judge pretty hard lol

 

You could look at the specs of master cylinders to see if a sports model or SUV model may have a larger diameter piston. I know the wrx has a +1mm diameter slave piston. It's not a direct bolt on but it works and gives less clutch pedal effort.

Agree with the guys above. Start with the basics

 

If you have ABS, you more than likely have a two stage booster. If you want to keep the power brakes, about the only thing you can do to improve “feel” is to swap to single stage booster. The single stage is commonly found in non-abs cars and does feel better. You’ll want to pull the hard lines as well and delete the ABS.

 

I did this on an older build and it definitely felt better.

 

My current build is going to go to manual brakes with the help of a “Chase Bays” brake booster delete

Edited April 11, 2020 by DN1911

Non abs in my subaru,so single stage booster . Single and two stage booter ,look like different. If installed two stage ,should be modified brake line?

Non abs in my subaru,so single stage booster . Single and two stage booter ,look like different. If installed two stage ,should be modified brake line?

 

The Single stage is a much smaller and thinner unit. It is also the better one. Two stage boosters are softer and more vague feeling

Finally, replaced double stage vacuum brakes and 5 gen legacy front brake calipers(316mm) . Satisfied with this brakes performance.

Finally, replaced double stage vacuum brakes and 5 gen legacy front brake calipers(316mm) . Satisfied with this brakes performance.

 

So you took out a non-ABS single stage booster and put in a dual?

So you took out a non-ABS single stage booster and put in a dual?

 

 

Correct