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With foot on brake and medium force, engine off, the pedal should be rock hard and high. Without releasing pedal pressure, start engine. Pedal should sink and become a little softer as booster receives vaccuum. If pedal doesn't change at all, stays stiff and high, you have no booster function.
I decided to tackle the issues. Prior to changing the master cylinder with a new one I made sure that the brake booster rod had proper clearance(0.2 inches). After install and bleed, pedal feel did not change. I took it to a performance shop and has them double check everything. They then reinstalled the MC checked the clearance and pedal still is the same. Both of us agreed that the booster is the culprit. It feels that its impossible to push the pedal after a certain distance. When I bleed the brakes the pedal can easily be pushed a lot lower.
Now before I purchase a new booster, I am honestly thinking about just deleting the booster entirely. Couple options available:
Slap the Honed booster delete kit with the 1" MC or a OEM MC. I do believe this would require way to much pedal effort.
Slap on the Fab9 kit, i really don't like the fact that its a 1 way system.
Follow some of the guides on this forum and do a custom duel MC system.
Or just fix the booster and call it a day.
Don't forget mazda used different ratio boosters in different models. I believe the lowest ratio is 1:4. A quick search should tell you which car to source from.
The Honed kit includes a template to drill a new hole in the pedal to improve the pedal ratio, but does not get it to stock (NA8) ratio. Also remember with a bigger master and no booster, it maybe harder to modulate the brakes. A bigger master will mean less pedal travel to modulate the pressure at the calipers.
A bigger master will mean less pedal travel to modulate the pressure at the calipers.
Ahh so your saying when you switch from boosted to manual brakes, a smaller MC is preferred as the pedal stiffness will be there, its just you want that flexibility of more pedal travel along with the stiff pedal?
Ahh so your saying when you switch from boosted to manual brakes, a smaller MC is preferred as the pedal stiffness will be there, its just you want that flexibility of more pedal travel along with the stiff pedal?
Basically yes. Too little travel and heal-toe braking becomes an issue.
This weekend I got hold of a working booster & valve and the time to put it in. Sadly.... issue remains the same. The pedal is just sponge until the last 20% of travel and that last bit can't lock race rubber. Running out of ideas here. However....
Something I noticed when reading step 2 in the instructions for the same kit on v8 roaster, "Check to make sure that the rod from the booster is slightly compressing the plunger in the new master at static(no pedal pressure). To check this for engagement use a small piece of molding clay on the tip of the rod. Install the master like normal, then remove and check to make sure the clay is completely compressed. If it is not, the difference in the clay will need to be added to the rod by adding a small amount of weld on the end of the booster rod. If the booster rod is not fully engaging you are only getting partial pressure from the new master." I put that in bold cause it feels like I'm getting partial pressure.
When I swapped in a master cylinder that was dry and not connected to any lines the pedal had so much travel before it bottoms out. If you hook up the lines and only have fluid in the system the pedal travel is limited by 3x, as in if I put all my strength into pushing the pedal I will hit a wall 1/3 of the stroke of the pedal with no lines connected to the MC. Could anyone explain to me why this is? Does a booster just have a maximum amount of that travel that it can build pressure?
Maybe v8 roadsters are right but from what I know a booster should make pressure no matter what, low pedal anything Sigh.... Getting to the point where I may just go back to the OEM MC and get a HOONED booster delete kit. This will just make the whole system even simpler. But part of me is starting to think that the MC or booster isn't the problem. Me and a reputable shop have done throughout inspections of components and nothing looks out of the ordinary. Might be time for swaptronics.
I would start by measuring the piston to flange distance of the oe mc that works and compare it to the wilwood unit. Its something I always do regardless if the replacement is an aftermarket or oe replacement. The welding of the op rod justs sounds dumb. It the distance is too great the adapter could be milled down. Sometimes when the mc is bolted on you can see if the piston moves though the fluid port holes in the bottom of the reservoirs.
I would start by measuring the piston to flange distance of the oe mc that works and compare it to the wilwood unit. Its something I always do regardless if the replacement is an aftermarket or oe replacement. The welding of the op rod just sounds dumb. It the distance is too great the adapter could be milled down. Sometimes when the mc is bolted on you can see if the piston moves though the fluid port holes in the bottom of the reservoirs.
Agreed, there way of fixing sounds really stupid. You could honestly just turn the nut on the rod and it will extend. More safety measure put some Loctite or just add a jam nut. I did measure both MC's. They are within 3 mm of each other. The rod to the MC piston measures 2mm. And they are measured in account for all differences in master cylinder bodies.
I decided to isolate each brake circuit until I could pinpoint an issue. Using only stuff I had in the garage I made some plugs:
I plugged the rear circuit. Pedal still felt garbage. I then plugged the front circuit with the rear open, the pedal is still garbage. Pugged both and that leaves the MC feeling like garbage. Well, I changed that 3 times. Then that leaves the booster. Ahh, well I changed that too. So then what the **** is wrong?
I decided to listen to V8roadsters instructions: just extend the rod at the booster until it was obvious that the MC was going to be preloaded. I kept repeating while adjusting the rod until the plunger was not being preloaded. And ya, that fixed it. It looks like it was extremely vital to make sure that the rod is adjusted with virtually no gap. I took it up some mountain roads to further test it. Been a while since I've driven the car there, was pretty nostalgic. Anyways...
I am assuming when I first put the MC, the rod was binding on the edges of the MC walls, when I got to the track that bind gave and now the MC was being compressed right. The same thing happened when I put the second MC in.
Overall this whole brake system feels great. Supermiata Boxmount + the 1" Willwood MC is definitely a nice upgrade. My track buddy drives a mustang GT and I was always jealous of how his pedal felt with those Brembo's. Now I am no longer jealous.
If anyone is planning to do a 1" Wilwood Master Cylinder, MAKE SURE THE BOOSTER ROD IS ADJUSTED TO JUST BE TOUCHING THE MASTER CYLINDER. If you just slap it on, odds are it won't work. Looks like Ed was the winner.
I will be probably making a post with install notes on these kits.
I'm glad you figured it out. There are two op-rod adjustments. One from the pedal to the booster and one from the booster to MC. The booster to MC is not an easy dimension to measure. It can have a very small amount of clearance to a small amount of pre-load as long as it does not cause the mc piston to block off the feed port from the reservoir.
This was the difference in length of the rod before I adjusted it. Never would have thought such a small gap could be the difference from garbage brakes to amazing brakes. Well I'll be damned!
02-04-2022, 06:38 PM
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