Wilwood Pad Knockback

[another69]

I know this is an older thread, but has anyone figured out a way to get rid of the axle play that causes knock back? I would think it would be possible, especially with tapered rear bearings. Then you would be able to stay with fixed calipers and getting rid of play is usually a good thing.

[67rally]

I know this is an older thread, but has anyone figured out a way to get rid of the axle play that causes knock back? I would think it would be possible, especially with tapered rear bearings. Then you would be able to stay with fixed calipers and getting rid of play is usually a good thing.

I started this thread because I stilll have knockback even after swapping in a brand new rear with tapered bearings. The tapered bearings resolved the knockback in daily driving, but it was still very noticeable on the AutoX.

I installed a set of Wilwood D154 floating calipers this weekend, but need a new fitting for the calipers before I can plumb them in. My Wilwood Dynapros used an M10x1.0 fitting and these use an M10x1.5. I ASSumed I was going to be able to re-use the fittings, but no go. It'll have to wait till next weekend. The real test will be once I AutoX it again, since I won't be able to replicate the knockback on the street.

[another69]

I know you still had knock back with the tapered bearings, I was just curious if it was possible to tighten up the clearance on the tapered rear bearing (mine are the same as yours) to get rid of the play. It's a tapered bearing, so I don't see why it can't be done.

[gator68428]

Any updates?

[67rally]

Any updates?

The floating D154 calipers really took care of the problem. I did 3 track days at Palmer Motorsports Park last year with no issues other than a little heat fade by the end of the last sessions. I haven't done any more AutoX, I'm just having more fun on a road course for now.

Over the Winter, I switched to a bigger front brake setup (14" Aero6) with Hydroboost so braking should be much improved over last year as well.

[gator68428]

I see, makes sense. I just looked up what "4 piston Wilwood DynaPros" were and now see that they were fixed calipers. Makes sense that going to a floating caliper helped with knockback.

I have single piston floating calipers in the rear and C6Z Kore3 kit up front and overall braking is great, but I do hear some shifting out back (can hear the pads rubbing some under regular street driving under side loads out back--seems to have gotten worse after recent track days and autoXing). I'm running stock internals GM 10 bolt 8.5" posi rear end. I'm going to upgrade to c-clip eliminators. I noticed Strange has a complete kit including axles that configurable. Going to look into it.
https://www.strangeengineering.net/p...stud-kit.html/

[RSX302]

I have a Ford 9" and I tried a few things to resolve with no luck. I even made my dynalite calipers floating (0.05" on shoulder bolts)and for sure thought that would cure. nada!!

Only thing that worked for me (besides full floater) was going from manual to power. Replaced master with a larger 1 1/8 " with power assist. Gone!!

[GoodysGotaCuda]

I have a Ford 9" and I tried a few things to resolve with no luck. I even made my dynalite calipers floating (0.05" on shoulder bolts)and for sure thought that would cure. nada!!

Only thing that worked for me (besides full floater) was going from manual to power. Replaced master with a larger 1 1/8 " with power assist. Gone!!

Similar issue on my car, I'm surprised to read that lightly floating the dynalite calipers didn't do it. Do you have any pictures of those shoulder bolts?

In the end I want to go to power brakes, but I'd sure like to get rid of the knockback in the meantime. I have a 10psi residual valve on the shelf, I just cant figure out if it's worth installing and dragging brakes everywhere.

[RobNoLimit]

I would not use a 10 lb. RCV with discs. A 2 lb. may help a little. I will mention something that I do on a regular basis with aftermarket brakes. That is, Turn the rotors. You have a hat, and maybe an adapter ring, and a rotor all bolted together. Even when they are all new, once you torque then all up, they may not be true anymore. Take the assembled rotors (with hubs for fronts and/or floaters) and have them turned. You may be surprised that there is .005 to .020 of run out on a brand new rotor. You may be surprised at the result.

[Slick68]

I would not use a 10 lb. RCV with discs. A 2 lb. may help a little. I will mention something that I do on a regular basis with aftermarket brakes. That is, Turn the rotors. You have a hat, and maybe an adapter ring, and a rotor all bolted together. Even when they are all new, once you torque then all up, they may not be true anymore. Take the assembled rotors (with hubs for fronts and/or floaters) and have them turned. You may be surprised that there is .005 to .020 of run out on a brand new rotor. You may be surprised at the result.

I never thought of that! I may have to try it, since I have similar issues.

[GoodysGotaCuda]

I would not use a 10 lb. RCV with discs. A 2 lb. may help a little. I will mention something that I do on a regular basis with aftermarket brakes. That is, Turn the rotors. You have a hat, and maybe an adapter ring, and a rotor all bolted together. Even when they are all new, once you torque then all up, they may not be true anymore. Take the assembled rotors (with hubs for fronts and/or floaters) and have them turned. You may be surprised that there is .005 to .020 of run out on a brand new rotor. You may be surprised at the result.

Drilled and slotted rotors are on my car. Not much turning can be done there. Looks like axle bearing preload seems to be a big player.

[RobNoLimit]

Drilled and slotted rotors are on my car. Not much turning can be done there. Looks like axle bearing preload seems to be a big player.

Not to over-simplify the question, but, Why not? You can turn D/S rotors just like solids. We're not talking about a lot. (we hope). But, if you measured the run out at say .015", the will effectively push the pads back a total of .030" (rigid mounted 4 piston caliper). It would be worth it just to chuck them up and check the run out.

[GoodysGotaCuda]

Not to over-simplify the question, but, Why not? You can turn D/S rotors just like solids. We're not talking about a lot. (we hope). But, if you measured the run out at say .015", the will effectively push the pads back a total of .030" (rigid mounted 4 piston caliper). It would be worth it just to chuck them up and check the run out.

I had the understanding that the abrupt holes in d/s rotors would quickly tear up the cutter.

That said, if I had a rotor runout problem it would be prevalent when driving in a straight line. I have zero issues with pad knockback when straight, it only occurs with hard turning.

Not to say there isn't anything there and that it couldn't amplify an existing problem, I believe whatever is done to mitigate the knockback will cover any rotor runout I may have right now.

[Hydratech®]

Chevrolet solved pad knockback issues WAY back in 1965 with the introduction of disc brakes on the C2 Vette's, yet everybody has either forgotten about it, died, or doesn't know this. Flash forward all the way to 2018 (!) and we're still talking about it like it's one of modern man's most mysterious mystery! Go figure... What did multimillion dollar General Motors engineering do to fix knockback problems with fixed calipers? (read that as stationary / solidly mounted calipers) Very simple - they simply installed springs inside of the calipers to keep the pads in contact with the brake rotors at all times! No matter what knock back occurred in extreme duty racing or even just simple nasty Detroit potholes in the road, the springs would instantly put the pads right back in place, completely eliminating the issue = problem solved. You would think this would cause drag, but nope! The exact same thing is accomplished by running a residual pressure valve on the brakes. We have coached thousands of customers over the course of 18 years regarding this, and it has resulted in an improvement / solution every single time. Not once has anybody ever come back stating any ill effects. In my own A/B/A (back to back, then back again) test sessions, laser temp gun tests on the brake rotors show no difference in rotor temps on a 30 mile straight highway run before and after RPV installation = no measurable drag (friction) is occurring. You can spin the wheels freely while up on a hoist while watching the pressure gauge holding 9-10 PSI on the calipers. I prefer the spring loaded caliper pistons versus the RPV, only because the immediately active mechanical effect of the springs is dead consistent (and also tunable through different spring rates), whereas the RPV's can be slightly~ less consistent in my testing (because the pads can knock back and blow off the residual pressure held by the RPV). After all of my years, it is amazing to me how the issue has been solved long before some readers where even born, yet everybody is still befuddled by it all of these years later.

BS you say? Contact Baer - their rear mega full floater kits include guess what - drum roll now please, yep, an RPV... Can I get a what what? and a who who?

Flash forward to the next gen C4 Vette's, and voila! The next improvement - full floating calipers, square cut seals (that hold the pistons in place much more rigidly) - again, problem solved through further engineering advancements.

As far as turning the rotors? Damn right! Especially if it is a multi part "hat" design. A carbide tip replacement in the lathe is pennies on the dollar to insure that your rotors are true. Setting the cutter tips at the optimum angle is also an art in and of itself. If the lathe used also has a follow up "multidirectional polish" function, then you have really hit the mark, as the brake pads will bed in vastly faster. I recall my days back in a previous life working with the GM Service Technology Group where it was argued that a brand new GM service replacement rotor shall not be turned before installation. Well, guess what? No matter what multimillion dollar mega certified down to ten thousandth's of an inch accuracy machine was used, drum roll again please, it was always a jaw dropper for the lab coat wearing GM engineers to see out of the box runout and T/V (thickness variation) in 25+ back to back rotors cut, literally with their own eyes and gasp! even their own hands - yeah, go ahead and push me out of the way and show me how it's supposed to be done... (it was actually quite funny to see a bunch of them arguing amongst themselves about how the rotors must not be chucking properly in the lathes, as these are the same rotors being installed on the assembly lines). They would then have the lathe machinations laser certified in disbelief and disgust. Never mind then doing further testing using "on car" brake lathes (which is the rarest yet most optimum method even discussed). Then the ensuing arguments that a "turned rotor" is then not legally considered brand new / within factory spec item (!)

And now there is the discussion of manual versus power brakes. What in the world does that possibly have to do with a cup of tea in China when discussing pad knock back gremlins? Everything... Whooo Whaaaat???? Why? How? Blasphemy you say? Yet again, it IS actually quite simple, but how? Power brakes allow for the use of a larger bore master cylinder sizing as compared to manual brakes. Yeah, and, ok, so what? The larger bore MC produces more volume per stroke, taking up any pad knockback vastly faster, most times even imperceivably - get it? Got it? Good !

I sincerely hope this information provided helps many out there find their "White Whale"

Hmmm – it looks like I just wrote my latest tech article after work on a Friday night!

Then again, what do I know - just some guy sitting out here in the hills and woods of Tennessee..., right?

[GoodysGotaCuda]

Chevrolet solved pad knockback issues WAY back in 1965 with the introduction of disc brakes on the C2 Vette's, yet everybody has either forgotten about it, died, or doesn't know this. Flash forward all the way to 2018 (!) and we're still talking about it like it's one of modern man's most mysterious mystery! Go figure... What did multimillion dollar General Motors engineering do to fix knockback problems with fixed calipers? (read that as stationary / solidly mounted calipers) Very simple - they simply installed springs inside of the calipers to keep the pads in contact with the brake rotors at all times! No matter what knock back occurred in extreme duty racing or even just simple nasty Detroit potholes in the road, the springs would instantly put the pads right back in place, completely eliminating the issue = problem solved. You would think this would cause drag, but nope!... like I just wrote my latest tech article after work on a Friday night![/I]

Then again, what do I know - just some guy sitting out here in the hills and woods of Tennessee..., right?

Great feedback. I am hesitant to use springs because I have to disassemble new calipers and I am not all that comfortable doing that.

It sounds like you use a 10lb residual, yes?
Rear only?
Front on each wheel?

[Hydratech®]

Installing springs in the calipers IS a PITA because you should have locator spring pockets machined into the caliper castings and pistons to make sure the springs stay exactly put. You wouldn't want a spring to start moving around inside of the caliper and then possibly chewing things up (as in the bores where the caliper pistons run)(despite the unlikeliness of actual damages). That's why the installation of an RPV is the fastest and simplest, but with the caveat of not being as effective...

RPV's can be installed simply anywhere you wish, with the generic choices of 2# and 10#, and the simplicity of also then removing them by installing a brake line union in their place if it is desired to remove them afterwards. This is the classic "Easy Button", but not as effective as going though the hassle of installing springs in the calipers, and then potentially redoing the spring rates with replacements to suit your individual needs - splitting hairs through countless hours of tuning. Again, the problem with RPV's is that pressure can be blown off past the valves, only recuperating when the next brake apply occurs.

Who said this was going to be easy?

[Ron Sutton]

No way to post this without sounding promotional. But here it is anyway.

Most cars, most pro-touring spindle & hub combos, rear ends with axle flanges & especially rear ends with c-clips have knock back issues. The cause is flex in the spindle, hub and/or flange axle under high loads from cornering. The more grip we build into our cars, the more the problem is amplified. Smaller rotors hide it to some degree. Larger OD rotors amplify it. The cars that don't have this issue run much stronger race style spindles & hubs with big bearings in the front & floater axles in the rear that use dual, large tapered bearings in the hubs.

In the brakes I designed & sell HERE, we have ZERO knockback issues. In all of our brake packages that fit GM & Ford Muscles cars, C5/C6 Corvettes & most aftermarket Pro-Touring Spindles ... plus 9" Ford flange axles as well as 10/12 Bolt GM C-Clip axles ... we:
A. Reduced it a degree with more true rotor/hat/hub assemblies
B. Reduced it a degree with semi-floating rotors
C. Reduced it a degree with stronger front hubs with bigger outer bearings
D. Eliminated it completely with anti-knockback springs behind the pistons
* We do not run anti-knockback springs in our brakes for my RSRT GT spindles & hubs, nor the Speedway Engineering floaters, as they do not need any help.

The "ideal" solution is have much stronger race style spindles, hubs & big bearings in the front, with a race style floater rear end. This would eliminate the cause of knockback. But if you're keeping your stuff, curing the knockback with anti-knockback springs in the calipers is the best solution. Thinking that the micro small degree of drag on the rotor is a problem is inaccurate. Eliminating knockback ... and the need to double pump the brake pedal going to the corner on a race track or autocross course ... is paramount.

[Hydratech®]

Ron, I thank you kindly for coming in an validating / bolstering my discussion of curing knock back for all of these poor people driving themselves nuts! I also agree with every point that you have posted regarding your designs. Some that have the funds to come straight to you on a build definitely will, though there are countless amounts of enthusiasts across the globe that will need to fix what they already have. The problem is that I just can't picture them all disassembling and machining their calipers for spring pockets, then picking out the right springs, despite this being the answer for their long standing problems. Hmmm - maybe the aftermarket will pick up on this and start offering various anti knockback spring conversion kits? I'm not the man to do it...

What's really bizarre to me is that most everybody knows that loose (adjustable type tapered) front wheel bearings will cause all kinds of weird steering symptoms, with knockback, pulling, and low pedal problems *BUT* I can't tell you how many thousands of people we have worked with that have absolutely no idea what rear axle shaft end play brings to the table when converting from drums to discs in the rear! Drum brakes aren't particularly affected by axle shaft end play, but any end play is highly toxic to the operations of a rear disc brake system (which is where we find the vast majority of actual knock back discussions exist). Again, the hard way is the right way, and that is to go straight to the root cause inside of the differential and tune in the axle shaft end play with the correct shims and even possible axle shaft and / or spider gear replacement on C-clip style differentials. The Big 3 automakers got around the issue by running full floating rear disc brake calipers. Solid mounted calipers typically found in the aftermarket conversions are exceptionally sensitive to axle shaft end play. It is rare to find anybody that even understands what I'm saying, much less know exactly what to do to custom tune the axle shaft end play out of the equation. Some then look at C-clip eliminator kits, but then find that it interferes with their rear disc brake conversion kits. Sutton Technologies exists in a high end world where the ideal scenarios are, though most live somewhere else in the middle, unfortunately suffering from braking problems that are directly obvious to people such as you and I. I have often said that even though Home Depot will sell you a 200 amp breaker, you should not attempt to fool with it unless you know exactly what you are doing! If any of these discussions are "over your head", PLEASE ENLIST THE SERVICES OF AN APPROPRIATE TRUE PROFESSIONAL. We are not talking about door handles and hood ornaments here - we are talking about possible life or death brake failure issues, so please don't play with a fire you may not be able to safely handle...

The cure for your pad knock back issues has been now clearly identified and explained - now get busy!

[another69]

During recent re-assembly of my Strange 9" rear I decided to check axle endplay. I have the "Late big Ford" tapered A1013 bearings that are adjustable. I found .005" on one side, .014" on the other, which seemed excessive. After lots of frustration it finally hit me - the race contacts a steel ring next to the seal. This is what sets the bearing preload. I easily removed. 011" from one, .002" from the other. Now both sides are between .002" and .004". Timken spec is .001" to .005". Figured I would post in case anyone wants to tighten up their axles.

[Hydratech®]

https://wilwood.com/Search/PartNoSearch?q=300-2434

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