Another Hydroboost question

[rkwhite61]

Ok, just picked up an '95 Astrovan hydroboost unit and a Chevynut adapater plate for my '57 Belair. Been searching around as to which master cylinder size I should be using. Everything I find states to match the bore size to that of the caliper. However, I'm using a big bore CPP kit (p/n CP412526-B) and I cannot figure out which master cylinder I should be using - cause the specs on the caliper show the bore size of 2.75". ????

I'd like to use a Wilwood MC. Which one of these would work, if either?

Wilwood 260-8556 1 1/8" bore
http://www.jegs.com/i/Wilwood/950/26...rentProductId=

or

Wiwood 260-8555 1" bore
http://www.jegs.com/i/Wilwood/950/26...rentProductId=

Thanks in advance!

[56-210Sedan]

The part of the caliper size and master cylinder size is correct you want those two to match up.

If i were doing this setup i would use the 1 1/8" bore this is more of a standard size with calipers on the market, just my opinion.

you will also need to know if you use a early or late bore when ordering your master cylinder, if you scroll to the very bottom of this link you will see what i am talking about http://www.hydratechbraking.com/Chev..._Fullsize.html

[Rick_L]

X2, a 1-1/8" master cylinder matches the 2.75" calipers correctly if you have power assist (and obviously you do with hydroboost).

The pushrod in a stock 95 Astro van hydroboost does not match up perfectly with either the typical shallow or deep GM master cylinders. I had to modify the pushrod for a shallow GM master cylinder depth, it was a bit long.

[chevynut]

X3, I'd use the 1 1/8" bore with the hydroboost and the large caliper pistons. Like the other said, make sure the internal pushrod fits the master cylinder correctly. I think I had to cut mine off a bit.

[rkwhite61]

One more question. When you say the internal pushrod needs to be shortened, are we talking about the pushrod going to the pedal? I understand I need to cut/thread the rod to the pedal. I'm very "green" with this stuff obviously.

[chevynut]

We're talking about the pushrod between the hydrobooster and the master cylinder. It doesn't necessarily need to be shortened, it may have to be lengthened. The point is it has to be the right length. It all depends on your MC. This is what I had to do to get a C4 MC to work:

07240008.jpg 07240009.jpg 07240013.jpg

What you need to do is measure the depth of the MC hole from the mounting face with a caliper. Then make the length of the pushrod that length as measured from the mounting face of the hydroboost. If you remove the "star" retainer, the pushrod will come out.

[chevynut]

FYI, here's what I did to make the pedal pushrod work.

08080004.jpg

[rkwhite61]

Ok so.. essentially the rod end from the booster should be touching the inside surface of the mc in it's normal position (before pushing the brake pedal)?

I'm sure I'll have more questions once I start the actual install. Stay tuned.

Off to purchase the Wilwood 1 1/8 MC!

Thanks all and thanks for the pics chevynut. Visuals help tremendously.

[toms57]

You will want to make it just a fraction shorter than the measured distance so the MC piston will fully retract with the pedal up. I had mine a little long and the fluid was trapped and the brakes started locking up when the fluid started heating up and expanding. I didn't have to grind much off to make a difference.

Tom

[rkwhite61]

You will want to make it just a fraction shorter than the measured distance so the MC piston will fully retract with the pedal up. I had mine a little long and the fluid was trapped and the brakes started locking up when the fluid started heating up and expanding. I didn't have to grind much off to make a difference.

Tom

Thanks Tom