Forrest Posted July 23, 2006 Share Posted July 23, 2006 In light of my problems: http://forums.hybridz.org/showthread.php?t=113035 I've had 4 other members with AZC brakes + 79 master tell me they also had a spongy but linear pedal feel. It has been suggested that the 79 280zx master is not a large enough bore for our brakes. Before I go buy a 4th master cylinder, is there anyone who has AZC brakes on all 4 corners, is using the 79 master, and has a firm pedal? (At least as firm as stock anyway.) Please let me know if you are, thanks. -Forrest Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 23, 2006 Share Posted July 23, 2006 I ran that master with 4x4 front calipers and 280ZX rear calipers and had a firm pedal. That's a two piston caliper vs a 4 piston caliper in the back, and I am not sure but I think the piston size on the front of the Toyota piston is smaller in front too. Quote Link to comment Share on other sites More sharing options...
jt1 Posted July 23, 2006 Share Posted July 23, 2006 Forrest, check my post in the other thread. My setup isn't AZC, it's Design Products Racing, but similar. Is there a larger master that will work with the booster, or are you thinking of going to a non power setup? John Quote Link to comment Share on other sites More sharing options...
RedNeckZ Posted July 23, 2006 Share Posted July 23, 2006 I have the 300ZX brake rotors and toyota calibers on front and 280ZX Disc and calibers on the rear. Also have the 15/16th (280ZX) master cylinder on it. Also removed the brake bias unit from the rearend area for the drum brakes (just bent the line over and reconnected). Some people have put in a manual brake pressure adjuster unit in the rear line. But I have not done this at this time (did the back disc brake package in the 1990's). After bleeding the brakes, I had to adjust the length of the rod going into the master cylinder from the brake pedals. Before that it felt like soft brakes to me. After the adjustment are firm and nice. Only thing I have added since that time is speed bleeders. Good Luck, Rich. Quote Link to comment Share on other sites More sharing options...
TimZ Posted July 23, 2006 Share Posted July 23, 2006 I have the AZ Zcar brakes and I'm still using the stock '78Z master cylinder. My brakes are fine. When I first installed them I had problems similar to what you are describing - soft pedal, seemed like you had to stand on them to get the car to stop. Pretty much couldn't lock the wheels under any circumstances. Several years later I decided to try a different set of pads (carbon kevlar) - this time I properly bedded them in, and these pads made a world of difference - firm pedal, and I now had to be careful not to lock the wheels on hard decel. I've since changed over to Wilwood's 'Gator' pads and they work fine, too. I don't know if it's the pads, or the fact that I properly bedded the new pads in, but they work really well now. BTW, you won't be able to get away with not using the prop valve for long once you get things working properly - I have my rears backed all the way out, and it's just barely enough. One time a couple of years ago after working on the brakes I forgot that I had the prop valve misadjusted and put the car completely sideways when I tried to stop late for a red light. Had to sit at the front of the line with the car sideways in the lane until the light turned green. :shock: Quote Link to comment Share on other sites More sharing options...
TimZ Posted July 29, 2006 Share Posted July 29, 2006 Several years later I decided to try a different set of pads (carbon kevlar) - this time I properly bedded them in, and these pads made a world of difference - firm pedal, and I now had to be careful not to lock the wheels on hard decel. BTW - I'm pretty sure I still have the Carbon/Kevlar pads sitting in a box in my garage if you want to try something different. They didn't have more than a few hundred miles on them, they just tended to be a bit too squealy for my taste. Quote Link to comment Share on other sites More sharing options...
pete280z Posted July 29, 2006 Share Posted July 29, 2006 Thanks TimZ. I just ordered the AZC setup and was debating getting the ZX master cylinder or a 1" Wilwood tandem. My stock MC looks like it has had the same fluid in it for over 10 years, so I'll be swapping it when I do the brakes regardless. From what you're saying the 15/16" will definitely suffice if everything else is in order. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 29, 2006 Share Posted July 29, 2006 I'm a little confused. How do you figure that the pad gave you a squishy pedal? Did you have Nerf pads the first time, Tim? Or are you just saying that the pads worked better so you didn't have to push on the pedal as hard? Just doesn't make sense to me that by changing pads the pedal would get firmer. Quote Link to comment Share on other sites More sharing options...
TimZ Posted July 30, 2006 Share Posted July 30, 2006 I'm a little confused. How do you figure that the pad gave you a squishy pedal? Did you have Nerf pads the first time, Tim? Or are you just saying that the pads worked better so you didn't have to push on the pedal as hard? Just doesn't make sense to me that by changing pads the pedal would get firmer. I don't know whether technically the 'squishyness' of the pedal was any different before/after as far as pedal travel vs. applied force goes, but the difference in decel vs. applied force (and hence travel) was remarkably different. It literally went from not being able to lock the wheels no matter how hard I stood on it to having to be careful not to. I'd estimate that the pedal force to decel ratio improved by a factor of ~2-3. It's always seemed strange to me too - the original pads were never bedded in properly (I was much younger then and didn't know better - the internet didn't exist yet ) so that might have been part of it, but the difference was pretty huge. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 30, 2006 Share Posted July 30, 2006 That sounds to me like you went from a race pad that needs heat to work to a street pad that works at any temp. Bedding in the pads also makes a difference, but I think you're main issue was the wrong pad the first time. A quick stomp on the pedal with the car off will tell the rest of us if you have a lot of pedal movement or not. Quote Link to comment Share on other sites More sharing options...
TimZ Posted July 30, 2006 Share Posted July 30, 2006 That sounds to me like you went from a race pad that needs heat to work to a street pad that works at any temp. Bedding in the pads also makes a difference, but I think you're main issue was the wrong pad the first time. A quick stomp on the pedal with the car off will tell the rest of us if you have a lot of pedal movement or not. Sounds reasonable, Jon - the pads I have now are definitely more biased towards street driving - not sure about the carbon/kevlars. The original pads were what Dave supplied with the calipers. I don't know what gets supplied these days, I got mine shortly after they became available back in the late 80's. I'm out of town right now - I'll check on the pedal travel when I get home. Quote Link to comment Share on other sites More sharing options...
primer&rust Posted July 31, 2006 Share Posted July 31, 2006 I don't know why a bigger master cylinder 15/16" is considered better since it will actually produce less pressure and a softer pedal. If any of you have driven a Volvo these cars have small master cylinders and the brake pedal is rock hard and very responsive. I have 4 wheel disc on my Z, the stock small master cylinder and steel braided lines. The pedal in my car is not soft and it seems to work fine. I think I could use an adjustable proportioning though as the rear rotors don't appear to wear much compared to the fronts. Also remember when you bleed these brakes (280zx ones at least) to turn them upside down so all of the air can be bleed out. Mityvac works great for doing this. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 31, 2006 Share Posted July 31, 2006 I don't know why a bigger master cylinder 15/16" is considered better since it will actually produce less pressure and a softer pedal. If any of you have driven a Volvo these cars have small master cylinders and the brake pedal is rock hard and very responsive. I have 4 wheel disc on my Z, the stock small master cylinder and steel braided lines. The pedal in my car is not soft and it seems to work fine. I think I could use an adjustable proportioning though as the rear rotors don't appear to wear much compared to the fronts. Also remember when you bleed these brakes (280zx ones at least) to turn them upside down so all of the air can be bleed out. Mityvac works great for doing this. Wrong, wrong, wrong. In general terms a larger master does produce less pressure, but it will have a stiffer pedal. But comparing the master cylinder from one car to another is a bad idea. There are many things going on here. The leverage ratio of the pedal assy, the amount of assist from the booster, the size of the master, and the size of the pistons or wheel cylinders in the calipers or drums. You also don't need to turn the brakes upside down, unless they were mounted upside down in the first place. The bleeder goes on top, which is where the air in the system will go as well. Quote Link to comment Share on other sites More sharing options...
primer&rust Posted July 31, 2006 Share Posted July 31, 2006 Mounting 280zx calipers on an early Z with Maxima brackets require you to turn them upside down since they are mounted at the front of the strut instead of the rear like the 280zx. The bleeders on my calipers are on the bottom of the calipers. Master Cylinders "The size of the master cylinders' piston has a direct result on brake fluid pressure. However, it may not work like you would think... higher line pressure will build up on a smaller master cylinder piston to react the force applied by the pedal. A smaller master cylinder will create more brake fluid pressure but will also increase brake pedal travel. The smaller diameter cylinder requires a longer stroke to move the volume of fluid necessary to move the caliper pistons during braking. Larger master cylinders will create less pressure but will require less travel" Quoted from http://sports.racer.net/brake_bias.htm I was wrong about pedal stiffness but not the line pressure. The mechanical pedal input force will be the same between the two, same pedal and booster, but the output force and line pressure will be higher with the smaller cylinder. From my old college automotive class worksheets I have found Line Pressure= Mechanical Input Pressure divided by Master Cylinder bore size. So with say 100LBS of input the stock 7/8 would have 114 psi and the 15/16 would have 106psi. Output force = Caliper Piston bore size (lets say 2" for an example) divided by our master cylinder bores (7/8, 15/16) than multipied by our 100LBS input pressure. In this example the 7/8 cylinder creats a output of 228LBS. The 15/16 cylinder creats a output force would be 213LBS. With the 1/16 differents in the master cylinder sizes it would probibly not be worth the effort of the swap. The Volvo must have a longer stroke to the master cylinder, bigger booster or greater mechanical force since it is about the same size as the early Z making up for its smaller volume. I will be staying with my smaller master cylinder. jmortensen Thanks for correcting me on the pedal stiffness factor where you were correct. Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted July 31, 2006 Share Posted July 31, 2006 Can't you swap the left and right calipers to get the bleeders on top? The larger MC is practically a requirement to get the larger displacement of fluid for the larger brake calipers. It is not so much I wanted the larger diameter, it is just the smaller MC will run out of volume without it. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 31, 2006 Share Posted July 31, 2006 OK, primer&rust, you figured most of this out. If that's what you meant by "turning them upside down" (swapping sides) well then I'm in agreement. Having to literally take the caliper off and flip it to bleed every time isn't a very good option, that's what I thought you were saying. Pop is right on the master size issue as well. Having driven a Z with Toyota calipers in front and with the stock master and stock rear drum brakes, I can tell you the pedal travel is excessive. Having driven my own car for years with the same fronts and rear disc which displace a lot more fluid than the drums, I can say the 15/16 master was a good upgrade. With the 4 piston calipers front and rear there will be still more fluid moving, which may require another larger master. The three things I was taking issue with were the pressure/pedal/size issue, the idea that you would have to dismount the caliper and turn it upside down to bleed it, and the comparison to a Volvo, which is totally useless without knowing ALL of the specs on the pedal box, booster, and caliper piston sizes. In rereading my post did look a bit harsh though, didn't mean it that way... Quote Link to comment Share on other sites More sharing options...
TimZ Posted July 31, 2006 Share Posted July 31, 2006 Just to clarify on my data point above - my Wilwoods have the smaller 1.38" pistons all around. The MC has been replaced with what I thought to be another stock 280Z MC (which I believe is 7/8"), and I do not feel the pedal travel to be excessive. Is there an easy way to check to see if my replacement MC was realy the 280Z piece, short of taking it apart? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted July 31, 2006 Share Posted July 31, 2006 Tim, they usually have the size cast right into the side of the master. The 1.38" pistons in your case is a pretty significant difference and that alone might explain why you're OK with the smaller master. Quote Link to comment Share on other sites More sharing options...
TimZ Posted August 1, 2006 Share Posted August 1, 2006 Tim, they usually have the size cast right into the side of the master. The 1.38" pistons in your case is a pretty significant difference and that alone might explain why you're OK with the smaller master. OK - I'll check tomorrow. Since it worked okay for me, I never really had a reason to check. Thanks, Jon. Quote Link to comment Share on other sites More sharing options...
GAZRNR Posted August 1, 2006 Share Posted August 1, 2006 Yes, I am running disc brakes on all 4 corners and have a firm pedal. 15/16 master cylinder, 8 inch power booster (stock 1978Z), wilwood NDL 1.75 calipers front and 240sx single piston calipers rear, wilwood proprotiong valve in rear line to balance system. My issue is brake performance, my Integra and Taraus out brake the Z. I swapped out the wilwood Q compound street pads for hawk hp pads and finally had a much harder bite I was looking for, but the squeal was so bad I replaced them with hawk hps pads to get rid of the squeal , now the car stops only slightly better that with the wilwood Q compound pads. In short if I tried to slam on the brakes and lock the wheels it will not happen. This is what I am needing to fix before I need to make a hard stop in a short distance that ends badly. I contacted hawk and was told there was no quiet pad for the street. I contacted wilwood tech and was told that with an 8 in power booster and 15/16 master cylinder I should be using 1.38 piston calipers. I am not generating enough clamping force with the 1.75 pistons. To use the 1.75's I would need a 1 1/4 master cylinder with a 8 in power booster or 1 1/16 master with non assisted brakes. I plan on ordering the NDL 1.38 piston calipers and will report back after I make the change. Rusty Quote Link to comment Share on other sites More sharing options...
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