would i need a new proportioning valve if i was to put disks from a 90 or 91 crx on my 89?

 

Yes, you should change the prop valve as the brake bias is very off if you keep the old disc/drum valve om a car now equipped with disc/disc. I learned the lesson by destroying two brand sticker Hoosier race tires with huge flat spots in one big front brake lockup. Without the right valve, the rear discs will do almost nothing. It would be a good idea but not as mandatory to change to the larger master cylinder as well to keep the pedal level higher.

 

As Lee said, definently change the out the prop valve.

When it comes to the master cylinder, you can leave it stock. A rear disc CRX, and a rear drum CRX both come with the same master cylinder from the factory. A master cylinder upgrade is only required when you go to larger front brakes (but thats a whole different mess).

If your pedal is mushy after your rear disc swap, it could be one of two things:
1- Air still left in the brake lines
2- One of your brake line fittings is NOT fully tightened down.

I have experienced both situations. After fixing those problems I have a rock hard brake pedal...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94eg! &raquo;</TD></TR><TR><TD CLASS="quote">A rear disc CRX, and a rear drum CRX both come with the same master cylinder from the factory. </TD></TR></TABLE>
You might check on this as the many drum cars I have owned were smaller in bore than the few disc rear cars and the disc donor car by 1/16th inch I beleive. I can't verify this as my drum rear '89 CRX now has a several size larger MC since my Integra/Civic EX upgrade. The bore size is cast into the side of the MC body.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94eg! &raquo;</TD></TR><TR><TD CLASS="quote">When it comes to the master cylinder, you can leave it stock. A rear disc CRX, and a rear drum CRX both come with the same master cylinder from the factory. A master cylinder upgrade is only required when you go to larger front brakes (but thats a whole different mess).
</TD></TR></TABLE>

definatley not true at all.

the 88-89 Si had a 13/16" MC, and the 90-91 Si had a 7/8" MC. prop valves are different, 1725 and 2040 respectively. the front piston area grew larger as well.


http://www.norcalcrx.org/tyson/brakepartslist.xls

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by teler86 &raquo;</TD></TR><TR><TD CLASS="quote">would i need a new proportioning valve if i was to put disks from a 90 or 91 crx on my 89?</TD></TR></TABLE>

my general advice is that if youre going to swap brake parts, swap the whole system. mismatching parts is not a good idea in my opinion.

 

Thats odd. I know the rear disc 94 civic Si has the same 13/16" master cylinder as the 94 cx/dx/vx (rear drum). I guess I just asumed that it would be the same for the CRX. My conversion was on a 94cx and it works great with the small MC.

Does the 90-91 Si have different front brakes than the 88-89 Si?

I wonder why Honda stoped using the larger MC for rear discs? It must have been for cost cutting...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94eg! &raquo;</TD></TR><TR><TD CLASS="quote">Does the 90-91 Si have different front brakes than the 88-89 Si?
</TD></TR></TABLE>

yes.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94eg! &raquo;</TD></TR><TR><TD CLASS="quote">I know the rear disc 94 civic Si has the same 13/16" master cylinder as the 94 cx/dx/vx (rear drum). </TD></TR></TABLE>

that is interesting to know tho.