Spongy Brakes
 

Can some-one help with this, my pedal has always been very spongy since i moved to a 7/8 master.. my brakes are manual , pedal ratio changed ,, just installed willwood 4 pot 'dynalite discs' and calipers up front and 'right stuff' single piston rear calipers .. Master is wilwood , and using a summit proportioning valve. I did email wilwood and they have suggested that the 7/8 master may not be enuf with the larger rear piston calipers..

could this be correct?? i need more pedal..


Gav

Was the pedal OK before the new master or did you install it when you installed the Wilwoods and Right Stuff discs? Were you ever able to get the parking brake adjusted so you had 1/2" or less travel of the park brake actuating levers on the calipers?

There are folks here who know far more than I ever will about brakes who might have answers for you but more info is required. Many knowledgeable people don't want to start a week long fishing expedition asking questions to get the info they need to help you. Take some time to list in detail everything you've installed and the methods you used to install & bleed include pics of everything. Then you may get the answer you need.

Was the master cylinder bench bled according to Wilwoods instructions before installation?

What method was used to bleed the system on the car?

Spongy usually equals air trapped in a high spot or pocket in somewhere in the system. Sometimes it's a real challenge. Altering the direction of fluid flow and push vs pull may remove a stubborn air pocket.

As Scott stated, spongy generally equals air. That said, an undersized MC relative to the caliper piston area can make the pedal feel "bouncy" for lack of a better word, which could be confused for "spongy". We can go back and forth over semantics, but that's probably not productive :catfight:

If you know your piston diameters or areas, please share, otherwise we're forced to make assumptions. My best guess is that your Wilwood Dynalites have 1.75" pistons and therefore 4.80 square inches of effective piston area. As for the rear calipers, are the RSD kits using the 78-85 Caddy calipers or something else? Just based on your front calipers, the 7/8" bore MC is on the small side of things...if the rear calipers have 3.00 square inches or more area, then you're definitely undersized on your MC. That's not to say that it won't work, it just may not provide the feel that you desire.

Tobin
KORE3

Tobin, this is the caliper RSB is sending. I'm building a 69 Camaro for a customer who had purchased these rear brakes and wanted them installed on the 12 bolt I built for the car.

http://i240.photobucket.com/albums/f...MVC-032F-1.jpg

http://i240.photobucket.com/albums/f...MVC-027F-1.jpg

Guys , im not sure on rear caliper make ,,right stuff kit with the adjustment arm for emergency brake, largish single piston,, i have bench bled master 3 times now out of frustration,, vacuum bleed, reverse bleed and good ol' 2 person bleed has been done prob 10 times with no luck.. found a couple of bad lines and replaced them,, changed pedal ratio.. I was running the wilwood 7/8 master with rear drums and stock camaro discs before i changed to this current setup and was never happy with the pedal.. it was always spongy and too close to the floor . The emergency brake is not fully adjusted ,, prob running 50% of what it could be.. thats another problem, getting these things to 'wind up' is an art in itself ive found. Would that solve my problem?
P.S. this is a manual setup as my injection runs very little vacuum for assist.
I have also tilted the rear caliper nipples upward when bleeding as per instructions just to squeeze that last bit of air from system.. every trick i can think of..

Short and simple. The master cylinder must displace as much (preferably more) fluid than the amount of fluid it takes to push the pistons out enough to apply good pressure to the pad / rotor combo.
My bet.... The m/c is too small.

This is the conumdrum.... :lostmarbles: some are saying it is,, others are telling me 7/8 is what i should be running? is there a difinitive answer?

I wouldn't do anything with respect to the master cylinder until you have the rear calipers set up properly, since that's more than likely exacerbating any perceived volumetric issues that you may or may not be experiencing. The rear pads should be virtually snug up against the rotors, but not tight. See link below.

http://www.pro-touring.com/cars-gene...rs-101288.html

While there are definitive answers with respect to MC sizing, your system should work, albeit with a somewhat longer pedal travel than some would like. If I were making a recommendation for your system from scratch, I would suggest a 15/16" bore unit for manual brakes with a 6:1 pedal ratio. That said, there is only a ~12% difference between that and a 7/8" or 1" bore unit and it sounds like your pedal travel issue is greater than 12%, making me believe you primarily have a rear caliper installation issue.

Tobin
KORE3

Here's a simple question. Anybody here running the 7/8" Wilwood master cylinder with a manual brake setup that doesn't feel a little spongy? I have that same setup and mine is slightly spongy also. I was doing some research on it a few months ago and it seems that it's a fairly common side effect as you reduce the bore size on a master cylinder in a manual setup(regardless of the calipers). As you increase the bore size, you get a harder pedal, but less brake pressure.

I'm sure there are plenty of people out there are running this master cylinder and bore size OR have done so in the past that could chime in. Would love to hear from someone who has this exact setup(Wilwood MC, 7/8", manual brakes, 4 disc) and can say they have a hard pedal.

I'm running a 7/8ths manual and have what I would consider a good pedal. I can stab it at 35-40 mph and chirp the fronts......if that means anything.

.........but I also have rear drums. :underchair:

Per usual, excellent point Ron.

We tend to forget that many of the younger generations may have never had any experience with manual brake systems.

My first muscle car ('66 GTO) had manual drums.......Fred Flintstone could stop faster than that car.

:rofl:

I can lock up my brakes also and my car now stops beautifully, so my setup is now working better than ever. I had that same problem described by the original poster with my previous brake system. Had 13" discs with Baer 4-piston calipers up front with 1-piston 13" setup in the back and could never get enough braking power no matter which MC I tried. When I upgraded the fronts to the 14" 6-piston Wilwood setup with BP-10 pads, it was a huge improvement. The BP-10 pads are grippy when they get warmed up, and that's a big contributing factor. My first response was geared towards the actual pedal feeling slightly spongy. I agree with everything Ron wrote, which is why I like the manual setup and the extra control, but I also feel a little 'sponginess' in mine, and I know there's no air in the system and I'm using stainless lines(flex and hard) all around. I read a post somewhere, I think it was a Wilwood rep or someone extremely familiar with Wilwood MC's and manual setups, that stated that you should expect a little more sponginess in a manual setup as you decrease bore size. Part of that 'sponginess' you're perceiving is just extra pedal travel which is expected(and desired by people who want that extra modulation). For me, the feel is not a problem, I was just trying to help the original poster with 'feel' expectations on his setup. (that he could have everything matched up perfectly, high grip pads, no air in the system, and might still have a slight 'spongy' feel). Now, if he needs more actual breaking power beyond just the spongy feel, then Ron's write-up is perfect for resolving that. I'd start with upgrading the pads first. And get some extra rags to wipe the extra brake dust off.

ok,, i have now wound up the rear calipers so my emergency brake now works.. I have re bled the system ,,no air in lines that is visible and my brake pedal bottoms out on carpet still. very little resistence.. I have bench bled the master several times and was confident it was done correctly.. I will try one more time ..I can pump them up a bit but even at that the car will not stop under braking. It has to be in the master ? air or could the piston stroke be dodgy? Wilwood lists 1.10 inches .. so how much is sufficient ?- Note -- this camaro has been converted to RHD in Australia and the pedal box is foreign to the car.

You have a BAD master cylinder.... swap it out.

Agreed - It's sounding like a bad seal on the piston. I believe Wilwood has a rebuild kit available.

What is your pedal ratio?

Tobin
KORE3

6-1 i believe or there abouts Tobin,, it was a standard ratio pedal and i have moved it up (pivot point) approx 3/4 inch.. The brakes were pretty much the same (bottoming out) before ratio change. When i pump them up i get a drag on rotors at best.. Im thinking now that maybe the master rod has damaged the master cyl seals ? pushed in too far ? or ? I will check the stroke today..

Up (closer to pivot point) on the pedal shaft reduces the leverage ratio!

no the pivot point is at the top and the rod has moved up 3/4 " from the original position:confused18:

i just measured im only getting just over 3/4 inch of push from my piston on the master then im hard on the floor... Wilwoods have 1.10" stroke so im underdone..
Now how to increase the stroke ?? i cant lengthen the rod and the pedal is against the stop in 'rest position'..any ideas?

You must be careful not to get your rod to far out of alignment, especially with a 7/8 Wilwood as the rod design is different than the 1". It will cause increased bore wear. It's doubtful it's causing your immediate issues but will cause long term problems.

When you bench bleed, you must make sure you have leak proof connections and your tubes are immersed in brake fluid. Otherwise, even the smallest leak will cause air to be trapped in the cylinder.

I have to agree with Chris and Tobin. I ran a 7/8 and 1" in my car. I always felt the 7/8 was a little to spongy for my taste. The 1" was great on the race track with some heat in the brakes. You had to treat the brake pedal like a red headed step child but the modulation was great. I learned to almost like them on the street. ha Where I agree with Tobin is on the 15/16th being the perfect size for a protouring car. When you want good drivability on the street and track with manual brakes, I think it's the right bore. Especially if you are running a realistic street compound. Clearly, your caliper bore sizes dictate but I've seen this discussion over and over in the protouring segment. Bottom line, if I wasn't a racer, I'd run a booster set up. Racer, a manual set up. As usual with protouring, you have to make a compromise.

thanx Todd,, the reason im running non assist is low vacuum with stack injection,, it was just easier and a cleaner look.. should my setup work with the 3/4 " max stroke i have regardless of bore size? Is this why im not getting it to bleed up properly? or because a 1" bore would it need less stroke?

Good morning, 3/4" of stroke isn't enough. If I recall correctly, the cylinder has just over an inch of stroke. Also, keep in mind that the higher you raise the rod, the shorter distance the piston will move with foot input. I moved my rod up the minimum amount by leaving just enough material between the factory and new hole in the pedal arm. I did this after switching to a 1". I'd put the rod in the factory position and see if you can get the brakes functional. Then you can move it up a hair.

My bad........old brain errored again.....sorry. You'd think after using a lever and fulcrum a couple of times last week it would be elementary. :sieg:

I just measured my travel and it's 3/4" also. I don't think travel length is the solution. I'll assume there needs to be a certain amount of reserve piston travel in the master for safety. The Right Stuff calipers would be my primary suspect. Based on forum observation there's a lot of people running the 7/8" Wilwood with stock pedals with no problems, though this is the first system I can recall (for what that's worth now) using the Right Stuff rear calipers. I do recall issues attempting to use another style of OEM parking brake caliper, possibly a metric?
:headscratch:

Stroke is 1.1". http://www.wilwood.com/MasterCylinde...inderList.aspx