Alright, background:
Replaced MC with Prelude MC (15/16ths) but kept the HF booster.

Eventually, my brakes wouldn't quite work so well and would require the brakes to be bled every week.

It got so bad that even bleeding them did nothing. I figured it was the booster.

Upgrade time.

Replaced HF booster for SI booster (bigger).

While I was at it, I replaced the Prelude MC under warranty (autozone rules) and got another remanufractured Prelude MC along with my Reman. Booster.

Installed both today.

At first, brakes worked great. modulation was great. Brakes felt like top of the line stuff.

after 10mins of driving... the pedal got harder to push. Bring it back to the garage and the car virtually stops without me touching the brakes.

Turn the car off, leave it out of gear and the ebrake off. tried to push the car, won't budge. Brakes are engaged without the brake pedal being applied.

15minutes later, the brakes disengage slowly. I drive it around. test brakes. same thing occurs.


What could it be? Is it a faulty MC or a faulty Booster?

 

calipers?

 

figure out which wheel was locked. individually, it would be a caliper problem i bet. all together, something wrong with MC.

 

Did you file down the piston for the MC? If you are using a 3rd or 4th gen civic and a prelude MC, you need to file down the piston for the MC ever so slightly so that it won't bind.

Edit: Always quote your sources
From redpepperracing.com
Q: What is the best upgrade for the Master Cylinder?
A: This answer comes from Scott Mullin http://www.mullinator.com/crx
The '88-'91 Prelude MC (15/16" diameter) fits right up to the stock
lines. Perfectly. CarParts.com and WrenchHead.com have good prices on
rebuilt units, FWIW. The end that fits into the booster requires a little machining, though. It's aluminum, so a hand file and an hour does just fine. I don't think power tools would be any better, BTW. TIP: If possible, I would recommend you secure the MC in a vice during the machining (and the initial bench bleeding). I would bet that would cut your time in half. The part of the MC that fits into the stock power booster is about 3/16" thick, it's a cylinder with a 15/16" inner diameter. You have to machine the outer 1/8" to make it fit. All it takes is patience and a bastard file. Use some blue RTV sealant as a final gasket and you're done. The MC is obviously slightly thicker than the stock one, but not appreciably longer. As I mentioned above, the brake line fittings are in exactly the same place as the stocker.
The fluid reservoir is quite a bit wider, but with the stock fuel injection, there were no clearance problems. The reservoir is not appreciably taller, as I remember. There were also no clearance problems with my aftermarket strut bar.
TIPS: When you buy your MC (or pick it up at a junkyard and rebuild it
You), buy an MC bench bleeding kit. I got mine at PepBoys for next to nothing. It's just a couple of bits of plastic and a few instructions. I had to ask for it at the parts counter, though; it wasn't on the floor. Also buy some brake fluid-- get DOT3 or DOT4, DOT5 is not compatible with the factory system. I recommend going to the Ford dealer (yes, the Ford dealer) and buying some of their Ford HD Brake Fluid. They may have changed the name in the past month or two, but whatever they give you is the right stuff. If you're **** like me, you should consider flushing your brake system during this process. DOT3/4 fluid absorbs some water, over time. You'll want to bleed your car at all four corners about a week after the install. That'll clean out any last little bits of air. It wasn't until the final bleed that I got the maximum benefit.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .RJ &raquo;</TD></TR><TR><TD CLASS="quote">calipers?</TD></TR></TABLE>
Nope. wilwood calipers in the front.

all four wheels are locked.

About the machining of the prelude MC. I had it installed previously and didn't have this problem (of course, I had a different, smaller booster). Plus, that article refers to a 1g CRX, i have a 2g CRX. but, good find!





Modified by Driven at 7:40 AM 7/11/2003

 

Sounds like the MC preload adjustment might be too tight. I believe there is a thread in here somewhere about it. Basically if it's too tight, there is a bit of drag, which heats everything up until it locks solid. Leave it for awhile until it cools down, voila, brakes work again, until it gets hot, wash, rinse, repeat.

The procedure to adjust I know of is for the 1G, not sure if the 2G is the same. Basically there is a locknut inside on the back of the booster, loosen that, rotate the rod, then tighten the lock nut back up. Find a service manual though, because I don't know if that's all there is to it.

Tom

 

The booster is the problem... I've seen the same thing happen before.

 

...Well, i got another reman MC, haven't installed it yet.


i was thinking it might be the booster rod that connects to the brake pedal...

but, wouldn't it lock the brakes from the start?

 

figured it out.

the booster rod that connects to the pedal wasn't adjusted.

an hour later of fiddling with it, car stops on a dime.