i recently bought a 92 civic cx hatch and it has rear disc brakes off an si hatch (idk what year). i was told that the rear disc brakes (complete trailing arm) was the only parts that was swapped. i was wondering if brake booster and prop valve will have to be switched to the si parts. 92-95 cx and si share the same honda part number for master cylinder so i know i won't have to swap that out. cx and si brake booster part numbers are different and same with the prop valve. can somebody confirm that the booster and prop valve has to be replace with si parts. as far as pedal feel it's a little soft and doesn't engage the brakes until close to the floor. it might just need to be bleed and i will do that soon.

 

Bleed the system and pick up a 50/50 propo valve if you that **** about it. Atleast you will have peace of mind.

 

i'm pretty sure all you need to do is swap the prop. valve

 

Honestly you don't even have to do that. I'm running the same setup as the OP. The Si does have a different prop valve though, 3040. My pedal is also low, but I wouldn't call it excessively low.

 

The main problem with discs over drums is the higher pressure & volume needed to get the same stopping power. The prop valve is said to give more pressure to the rear, and the larger master cylinder (attaches to brake booster) moves more fluid for the same amount of pedal travel.

Without the MC, the pedal will be softer and travel farther. Without the prop valve, you won't get the most out of your rear discs and will stress the front more. The later will lead to even worse braking than with the drums, since the CX has small 9.4" front rotors.

 

The 5th gen Si's use the same small front rotors (except the '94 ABS models) as the CXs. They also use the same 13/16MC.

 

Well yea you don't have to. I probably shouldn't have used the word "need" but rather "should".

Pretty sure though that if you don't swap it, the rear pads will wear more quickly than with the right prop. valve because the balance of how much the rear brakes get used compared to the front brakes when you push the pedal will be off and the rears will be getting used too much.

 

thanks everyone. i just picked up an eg si prop valve and will be installing it soon.