Hey everyone, I'm trying to understand the reason for experiencing weak braking performance on a fresh 1989 CRX build I've been working on. The rear has been converted to disc. I vacuum bled the system as I've done before on other cars, I have a nice firm pedal, I've driven the car through a brake-in cycle, but I still get weak stopping performance. I can press hard on the pedal, which stays hard midway down, but the car brakes relatively weak where I should be locking wheels at that pressure.

After various drive cycles, brake performance is mediocre, only slightly improving once they have warmed up. I'm suspecting perhaps an issue with either the brake master cylinder, or maybe the proportioning valve. Either then that, can't really think of anything else. For the exception of the brake booster and the proportioning valve, everything else is basically new.

Here's all the components:
-- Rotors (Front/Rear) - Stoptech Sport Slotted Cryo-treated rotors
-- Pads (Front/Rear) - Hawk HPS Street/Sport Pads
-- Calipers (Front/Rear) Centric Remanufactured Calipers
-- Lines (Front/Rear) - Goodridge G-Stop Brakeline Kit
-- Booster, Original
-- Master Cylinder - Changed to 15/16" from the EX sedan
-- Brake Proportioning Valve - 30/40 from an EG civic

Any feedback/thoughts/suggestions would be appreciated, as this issue is pretty different from most other common issues.

Thanks!

 

I assume you are talking about the HPS pads. They need heat to work. I will typically drag the brakes for about the first 30 seconds to a minute of driving to build up heat in the pads and rotors. Otherwise, the car doesn't want to stop.

 

I assume you are aware that by putting in a 15/16" master cylinder over the stock 13/16 one you have made it so you have to press the pedal harder for the same braking force?

A=πR²
3.14 * ((13/16)/2)² = 0.51822265625
3.14 * ((15/16)/2)² = 0.68994140625

0.51822265625 / 0.68994140625 ~ 0.75
0.68994140625 / 0.51822265625 ~ 1.33

So a compared to a 13/16 mastercylinder a 15/16 is going to have about 75% of the travel distance and require 133% of the pedal pressure to generate the same braking force.

Personally I prefer to stick with the stock 13/16 and do a booster delete, but other opinions vary.

 

The HPS 5.0 pads work pretty well when cold but add some heat and they really bite.

The earlier HPS pads needed a lot of heat to get half decent performance. They really didn't like being wet!

 

Hey TacoCat, yes my bad, HPS pads. I updated the original post to make sense.

I have an older set of more aggressive Hawk pads on my track car and definitely don't experience the lack of braking power there, even cold.

 

Hey Joel,

So yes, I have a firmer brake pedal due to the larger bore master cylinder. However, this should also result in less pedal effort with more fluid moving through the brake system.

I've ordered a 2040 proportioning valve, which is what the Si CRX's originally had with rear disc brakes. If that doesn't help then perhaps I'll step down to the 7/8" bore master cylinder, which is also what the Si model had.

 

Hydraulics 101, bigger bore on the master means more displacement for a shorter stroke but the pedal pressure is going to be higher to get the same pressure at the calipers when compared to a smaller bore.

 

Not how it works, there is no such thing as a free lunch here.

Exactly. Think of it like a lever where you have the load side, the fulcrum (pivot point) and the effort side:


If you cut the distance between the pivot and the load to half its current length, the difficultly to move the load will be cut in half, but you will need to move the effort side twice as far to move the load same distance.

Same thing with hydraulics, you make your master cylinder bore half the surface area, and the difficulty will be cut in half, and the travel distance will double. You went from a 13/16" bore master cylinder to a 15/16" bore master cylinder, so you increased your bore surface area by about 133%, so you increased the difficulty to press by about 133% and reduced your travel by about 75%.

Honestly for these cars I would far preferred Honda had made them completely manual brakes and given them smaller master cylinder options, ~5/8" master cylinder bore size and no brake booster would have probably been just about perfect for these cars for just normal OEM use. Unless you are dealing with something super heavy I personally think boosted brakes are just a marketing gimmick.

 

I have a chase bays booster delete kit that came installed on my crx and I can't get it to stop well at all. I am flexing the entire brake pedal assembly and firewall just to slow down. Tried Hawk DTC and HPS. It's not safe for street or track atm. You really think manual brakes work well? ​​​​

This thread sounds kinda like my woes too. My old cx brakes on my EK hatch stop way better than my crx. Hoping removing the booster delete kit helps.

Same issue tho, (was already rear disc), vac bled, firm pedal, can't lock em up. In for suggestions

 

What size bore is the master cylinder that is in your kit? Manual brake systems on relative light cars like this work fantastic if you use a correctly sized master cylinder, but it sounds like yours is far too large.

My brake booster deletes just involved a stock 13/16" master cylinder and parts out of a stock vacuum booster, which worked just fine for me, but as I said I am a pretty big guy. Unless you are getting a kit that involves a master cylinder smaller than 13/16" or about 20.6mm I cant see any point in buying a kit and not just reusing the stock 13/16" master cylinder just bolted to the firewall with the center shaft from a stock brake booster.

 

It's a rather small wilwood single piston. I can't find the size marked on it nor on chase bays website.

I found on the forums...
It's smaller than a 1in for sure.

I'm fairly average size. Got some leg muscle strength from playing hockey and more. I can flex the heck out of the pedal assembly and watch the firewall flex easily. But the car doesn't really stop.

 

3/4" to 1" is a HUGE range for master cylinders. That is 12/16-16/16. Honda only does 13/16-15/16 for these cars as far as I am aware.

3/4" is about 0.442 square inches, 1" is about 0.785 square inches, you are talking about close to 1.8 times the effort there.

From my experience 13/16" is the very far end of what you would want for manual brakes in these cars and that was with Integra sized front disks, and a big guy. As I said 5/8" would probably be reasonable for these cars for brakes that felt powered, maybe 1/2” for the smaller brake versions.

Can you post a pic of your setup? Does the master cylinder have any part numbers?

 

The MC needs to be sized right for the calipers you have. For the OP, the 7/8" MC would work. @theYBLEGAL What calipers are you using?

Personally, I have DC2 integra calipers all around, a 4040 valve and 15/16 MC, and it feels great. Its using the 11" rotor kit from fastbrakes, so I needed the DC2 calipers.

Also, You don't want to push too hard against the firewall w/ manual brakes, something may give out eventually. The Hardrace MC bracket does a good job at stiffening up the pedal for me, it transfers some of the load from the firewall to the shock tower.

 

I know people say this about the firewall, but I have actually put a camera on the passenger side watching that firewall and dumped easily 500+lbs onto the brake pedal of an 88 CRX HF and that firewall BARELY flexes at all, I am wondering if what people are feeling flexing is the pedal assembly most often, either the pedals themselves or loose mounting bolts.

You really just need to make sure the volume of fluid your master cylinder can move is sufficient for your calipers, but in a well maintained and bled system with good brake lines you shouldnt need a ton of volume, just pressure changes for the most part. IMO as long as the volume is sufficient the master cylinder bore size should be tailored around the driver and the effort range they can learn to be comfortable with. A 240lb powerlifter with 11" rotors and an 85lb couch potato with 10.3" rotors are very likely going to benefit from different bore size master cylinders, even if they use the exact same calipers in a car that is otherwise the same.

I say try out a booster delete on a stock 13/16" mastercylinder and see how it goes before you commit to some expensive brake delete kit, then you can have a good idea how you should size your mastercylinder, or you might be happy with the stock master cylinder. Here are two crusty CRXs I did deletes on with the stock MC, one of them got a stock EG clutch MC added to run a hydro transmission.

 

Stock front and rear size rotors and calipers I do believe. That's a 15in rim

 

Is that number .75? Like .75" maybe? Also, I see you have an adjustable proportioning valve, can you take a picture of the plumbing going into that and coming out? Where does the line coming out of the valve go? Directly to the front brake lines? Directly to the rear brake lines? Somewhere else?

 

It is indeed an 0.75 as far as I can tell. The single output of the MC goes to a 3 way splitter, one leg goes to the adjustable prop valve, that then splits to the rear of the vehicle. The other 2 legs that split pre-prop valve go to the front wheels. I didn't build this one, but it was plumbed correctly. I got this crx at the end of last year and have been prepping it for an extra track car for this year. But it came with this booster delete kit and so far it been nothing but crap. I can't even drive the car around town safely. I acquired an oem booster to replace the delete kit, and going to get a reman oem MC; planning to remove it when I pull the trans to put in an LSD in a month or 2 (b16a/j1). Unless you have some other suggestion, it's looking like just a show piece.

 

Honestly if that is a 3/4" brake master cylinder with the stock pedal assembly ratios and everything is working correctly it should work great. Can you lock up the tires when you really lean into the pedal? It shouldnt be easy, but it should be possible. One of the benefits on non ABS cars to a stiffer manual brake setup is it isnt easy to accidently lock up the tires, you should have to try for it, which makes it safer on the street. Although it does take some getting used to because if you have only ever driven with power brakes it FEELS unsafe, because assisted brakes give you a false sense of security that manual brakes dont.

That being said those do look like stock 9.5" brakes, so something like the pretty affordable Fastbrakes 11" kit would be a definite upgrade for you by make braking easier, heat dissipation better, and fit under your 15" wheels: https://www.fastbrakes.com/product_p...rotor-kit-.htm

If you really decide you don't want to keep that, let me know, I would definitely be interested in it and I have a CRX with a completely functional stock setup, so I could send you the entire package with the lines from the master cylinder to the proportioning valve, the proportioning valve, the booster, and master cylinder and toss in some cash on top.

EDIT: Here is another option to consider, it looks like Wilwood makes that same master cylinder from the Chase Bays kit in 5/8" bore size as well:

https://www.summitracing.com/parts/wil-260-10371


Compared to your current setup that would reduce braking effort to ~69% of what it currently is,

If you were just considering the front brakes going from 9.5" rotors to 11" rotors would reduce braking effort to around 86% of current. So a 5/8" master cylinder and 11" brakes would get you somewhere in the ballpark of 60% of your current braking effort, and that would be a pretty sweet setup.