johngeorge Posted November 10, 2009 Posted November 10, 2009 Not sure this is the right place to ask but here it goes... Ffr st2 trim with sn95 front spindles, wilwood 6piston calipers up front, 9" Torino axle ends welded onto 8.8 rearend, wilwood 4piston rear calipers. We are getting what it seems to me is pad knockback and want to know if you guys have experienced this with fixed (not floating) calipers and if so how did you fix it? The mastercylinder is a CNC dual with 7/8" front and 3/4" rear sizes along with 2lb residual valves on front and rear. We are going to try a new set of front and rear bearings, rear are tapered type. Any help would be much appreciated as we are setting up the car for the Nasa25hr race. Quote
ST#97 Posted November 10, 2009 Posted November 10, 2009 Not sure this is the right place to ask but here it goes... Ffr st2 trim with sn95 front spindles, wilwood 6piston calipers up front, 9" Torino axle ends welded onto 8.8 rearend, wilwood 4piston rear calipers. We are getting what it seems to me is pad knockback and want to know if you guys have experienced this with fixed (not floating) calipers and if so how did you fix it? The mastercylinder is a CNC dual with 7/8" front and 3/4" rear sizes along with 2lb residual valves on front and rear. We are going to try a new set of front and rear bearings, rear are tapered type. Any help would be much appreciated as we are setting up the car for the Nasa25hr race. Drove a wilwood equipped SN95 last year for 3 hours in an enduro...it had terrible knockback and required a pump or two after every turn....for 3 hours. Fixed caliper requires a floating rotor....however, I ran the brembo 2000R setup for years with fixed rotor and fixed caliper and had ZERO knock back. What did you torque the front hubs to so the bearing is pre-loaded? Quote
johngeorge Posted November 10, 2009 Author Posted November 10, 2009 That I do not know. We are changing the bearings tomorrow.. What torque should they be at? Quote
ST#97 Posted November 10, 2009 Posted November 10, 2009 That I do not know. We are changing the bearings tomorrow.. What torque should they be at? One time use nut...so they say, torqued to 254 foot pounds. Quote
nape Posted November 11, 2009 Posted November 11, 2009 I'd bet on the hubs or 9" ends. I have fixed Wilwoods all around on my car with fixed rotors and I have no issues, but my front hubs are easily rebuildable/checkable and the rears are GN circle track floating hubs. Quote
b_tone Posted November 11, 2009 Posted November 11, 2009 Have you tried a residual pressure valve, if one is not already installed? http://www.wilwood.com/products/006-MasterCylinders/010-RPV/index.asp Quote
johngeorge Posted November 11, 2009 Author Posted November 11, 2009 I'd bet on the hubs or 9" ends. I have fixed Wilwoods all around on my car with fixed rotors and I have no issues, but my front hubs are easily rebuildable/checkable and the rears are GN circle track floating hubs. What are GN circle track rear floating hubs? Yes 2lb res valves are installed. Quote
nape Posted November 11, 2009 Posted November 11, 2009 http://stockcarproducts.com/rear12e.htm You cut the end of the axle tube off, weld on a snout, and then the wheel bearings ride on the outside of the snout just like an old spindle pin. I'm pretty sure they only make the snouts for 3" axle tubes unless you do something custom. Quote
bmrracing Posted November 11, 2009 Posted November 11, 2009 You also can check out Coleman Products IMCA Sportsman housing. I also use Wilwood fixed calipers with no problems Quote
Members Jay A. Posted November 13, 2009 Members Posted November 13, 2009 Front: Check the old bearings before you replace them. Check by torquing the wheel like normal. Jack up the front to get the load off the tires. Grab the top and the bottom and carefully push top, pull bottom then alternate. If you feel a slight tick or hear a slight clicking then the bearing is bad. Usually if there is pad knock back in the front the bearings are really worn. Floating rotors are designed to expand (float) radialy as they get hot independently of the hat. The floating part has little to do with runout or knockback. Severe gator curbing at turn exit can cause knockback at some tracks and some turns but not others. Same on the rear. Check for bearing play in the old bearings prior to replacing them. Be sure the bearing retainer is keeping the bearings in place and no spacers are missing. With the 9” axle the axle flange at the outer end is pretty strong but under cornering load you could be getting axle flex or the flange is flexing where it connects to the axle. In stock 8.8 axles this is very common is the main cause of piston knockback in the rear calipers. This is why many guys still using the 8.8 axles still use the stock floating rear calipers. If the rear axle is flexing there is not much to be done about it. The 9” outer floating bearing with the snout welded to the end puts all the load on the outer axle tube rather than the axle flange. That is the best set up but more work to put it together. Jay Quote
Members Al F. Posted November 16, 2009 Members Posted November 16, 2009 Knockback is not exclusive to fixed calipers, though they do make the situation worse. Floating rotors doesnt help, as those are designed to allow movement but not movement in the direction that is causing the knockback in the first place (dont take my word for it, that is what Wilwood and Stoptech told me when I was trying to resolve my issues). I put in a residual pressure valve in my car and had zero improvement, ymmv. The only solutions are to reduce the flex in the spindle/axle and learn to put a little pressure on the brakes with your left foot. Quote
ST#97 Posted November 16, 2009 Posted November 16, 2009 for the record, my 2000R brembos with the TCE/Coleman rotor setup and the stock hydroboost setup has ZERO knockback even with my liberal use of curbs and the Racecraft Drop spindles. Now, HEAT is another issue! LOL!!! Over the years I have heard of knockback problems with Wilwoods and some stoptechs (actually were fixed with different parts on the floating rotors), but have NEVER heard of the problem with ANY brembo whether fixed or floating. YMMV... Quote
Members Jay A. Posted November 16, 2009 Members Posted November 16, 2009 I agree. It is most likely something going on with the rear rotor, axle, etc. Let us know what you find out. I learn something new every day with brakes. Quote
johngeorge Posted November 17, 2009 Author Posted November 17, 2009 OK finally back from Cali.. Things that were learned: 1. Old front hubs - the nut was loose on both sides as it was reused. new nut and new hubs fixed problem (25hr race remember) 2. Rear end bearing play - pressed off bad bearing (Set 20 bearing), holding it in my hand pressing outer race/seal together like it is in the axle I was able to get the same play moving the inner race back/forth like it was in the car. Bought brand new bearing from Napa and pressed it on, put it back in the car. I used the same aluminum Wilwood bracket to hold the bearing to axle but added another metal plate on top to sandwich the Wilwood bracket to the axle housing hoping that if the aluminum has any type of flex the metal plate will hold it. Went out and ran 8 sessions over 2 days without any pad knockback or axle play. The problem is I dont know if its fixed, and if the rear axle will get worse over time. Quote
johngeorge Posted November 18, 2009 Author Posted November 18, 2009 Ed (car owner) said the old axles were bottoming out in the pumpkin and he had to get the axles fixed by extending the splines so that they would not bottom out. With the axles bottomed out the bearings were put under a pressure not designed, and when he put everything back the bearings were not changed thus causing the play we noticed. New bearings seem to have fixed this now that the axle does not bottom out. Quote
QUASAR Posted November 19, 2009 Posted November 19, 2009 Not sure what you (he) means by bottoming out. The splined end slides thru the diff side gear, and the outer end contacts the bearing. The axle shaft should never be touching the center section or tubes or there is a big problem. Do you mean the shaft ran out of spline length and bound up on the diff side gear? Knockback issues on my car have always been front wheel bearing related. And I just live with some slight rear axle movement (fixed axle/c-clip). I can't wait for the day I can run a robust front hub and full float rear. Quote
nape Posted November 19, 2009 Posted November 19, 2009 Do you mean the shaft ran out of spline length and bound up on the diff side gear? That's what it sounds like to me. With the splines bottomed out, it would axial load the wheel bearings. Quote
QUASAR Posted November 19, 2009 Posted November 19, 2009 That's what it sounds like to me. With the splines bottomed out, it would axial load the wheel bearings. That couldn't have been good for the diff gears either. Quote
AIMidwest27 Posted December 18, 2009 Posted December 18, 2009 Hi, my name is Ted...{hello Ted}... I also suffer from pad knockback ..{sob, sob}.. Recently I gave up and pulled the Wilwood 4 piston fixed calipers off my Ford 8.8 and went back to standard 1 piston floating caliper. What a BIG disappointment in braking. Then while cruising around the HRPWorld.com web site I ran across these: ------ PFC Universal 6 lb. Anti-Knock-Back Springs Can be used for other brake manufactures caliper pistons The PFC Anti-Knock-Back Springs are the best value and are made from Spring Material as opposed to piano wire used by other caliper manufacturers. Sold in 4 Packs 36.5mm & Up Piston Anti-Knock-Back Springs - 4 Pack PFC900.900.106.01 $6.99 36mm & Smaller Piston Anti-Knock-Back Springs - 4 Pack PFC900.900.106.02 $5.99 ----------------------------------- I've installed them [ pop the pistons out, install spring, reinstall piston ] in my Wilwood calipers and intend to give them a try. My question is: Has anyone had experience with these ? I really want my braking back. This one piston caliper stuff really sucks after your used to real bite. Quote
92MNstanger Posted December 18, 2009 Posted December 18, 2009 Hi, my name is Ted... My question is: Has anyone had experience with these ? I really want my braking back. This one piston caliper stuff really sucks after your used to real bite. I am not sure, who are you again? You have a mustang or something else? What? Your chatterbox is breaking up? Huh? Hello, Ted. What rear diff do you have that's moving around enough to push the pistons back into the calipers? Do you mean "you're"? Quote
jrsmotorsports Posted January 15, 2010 Posted January 15, 2010 wilwood had problems with the thickness and material of axle retainer, causing excess run out. i have heard way too many stories about wilwood knock back. i would make some steel axle retainers and call it a day. Quote
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