Meh... I don't really care if this thread has turned into a discussion on bearings axles and differentials. I'm just here for the education, and to see what Greg will come up with to say next.

Now to get back on topic, and maybe I'm getting ahead of myself here because we haven't sorted the rear axle thing out yet, but my next issue to address will be front springs. I never noticed too much until I put the bigger tires on, but the front has settled some more after driving during the past couple of months. It is really low now, maybe a third of an inch lower than when we "finished" it in December. It's getting so low it's going to look like Doug's car if things keep up. I think it rubs on the inner fenders a bit on hard cornering. Since we rolled the front wheel well lips I might try an 1/8" spacer. I might also consider getting slightly longer springs because the ones we've got now are pretty compressed.

Ok, with that said, commence the conversation about Truetracs vs. Detroit Lockers. Oh, and I still want to hear from people running tapered bearings!

Matt

I was serious, I've been fighting this since day one. You would think a buddy ol pal would give a guy a call with inside info. I'm not sold on it being the true trac but I'm interested to know what DSE, Finch, Rupp, etc run since I've never heard any of them complain about knockback issues. If they have lockers or anyting else, I'm on board.

They just like to watch you suffer....


REAL LOCKERS -- SUCK FOR THE STREET. But so does leaking seals and pad knockers...

Just called DSE, they run True Trac's in both test cars. Hmmmmm

I know.. I talked to them yesterday..

I have a Truetrac unit I will be diassembling to day..

I personally
 

do not like a locker for what I am doing. If I had a drag car that I ran on the street...then yes. I find a locker to be very loud when it is unlocked around an corner and almost sounds like it is breaking on low speed parking. Also when you get on the power coming out of a corner and it locks the car will waggle...which I find a little unsettling at speed. This is all personal preference as I know others it does not bother.

The true tracs have very smooth operation and do not have the clutch problems of the conventional posi units. I love the one that I am running.

I think it was mentioned in another thread about the load being generated on the axles, especially with a high offset wheel (the ones with the big lips that look so cool)

On a side note, I am running the big sealed bearings from Moser and mine have not leaked. Yes I do have knockback. As I stated earlier, I am going to a floater.

DSE runs boosters on both cars I believe. Meaning they probably have no problem covering it up with power brakes. 1 1/8 master

Let's get back to Matt's problem. He doesn't neccesarily have a knockback problem. He has a leak. I still feel the fluid gets through the bearing itself or a portion. Sealed bearings aren't meant to be submerged in oil. They should in theory be able to withstand it but I'm not so sure. I'm interested to see what Cris has cooking.

if your running sealed bearings then just buy some inner seals, that you install when the 3rd member is pulled.

You can get
 

an oil seal they use on circle track cars that installs near the center section to keep the oil from roping down the axle or running down the tube. Use that coupled with the seal that is suppose to be behind the bearing and you should be good.

Have you checked the housing for straightness in a jig?

Well actually... Right now I have a knockback issue and not a leak. It's pretty bad I even notice it on the street.

Ok, about the sealed bearing, according to Kyle, it will leak oil if you autocross it just because so much load is put on that area. With that amount of stress, something is going to deform a bit and let oil through. I do find it interesting though that it continues to leak afterwards under normal driving. Maybe the housing wasn't straightened after it was welded, but I doubt it.

Matt

One thing to remember is not everyone is forth coming with their problems. I shouldn't assume people don't have the problem. I can't imagine that folks wouldn't want to share their problems with the world.:D I can't believe DSE silicones in their axles between events. No way I would put up with that crap! Matt, what master cyinder and is there any booster or hydraboost?

Can we clarify what "knockback" actually is or feels like?

I've got manual brakes, a Wilwood 7/8" bore master cylinder to be precise.

Todd, I'm a bit surprised they just use silicone too. I guess for them it is the best solution for a street car. Since they race what they sell, and they predominantly sell to people who will almost never drive on the track, their setup makes sense. There would be no point in running a full floater on their cars and then selling the Torino Bearing 9" setup to the public. I do wish they sold a setup that was overkill though, I know I would buy it.

As for what knock back is, I think Greg might have posted a good link explaining it somewhere. Basically, under hard side loading, going around turns, there is enough stress on the bearings, and axle components that everything moves a bit causing deflection. What this does to the rotors could be compared to an outside wheel on an old car gaining positive camber around a turn. In other words the rotor flexes and is no longer perfectly parallel to the brake caliper, thus pushing the pads and pistons back. Then, when you need to brake and you step on the pedal, you get a really light feeling i.e. the pedal might fall halfway to the floor, or feel like it isn't bled properly. If you tap the brakes once and push the pistons back in place everything will feel normal again. I think, and correct me if I'm wrong, power boosters, like what DSE runs, will cut down on the amount of noticeable knock back feel, but doesn't address or cure the problem. On manual brakes like a bunch of us are running it is very noticeable. I've got a 7/8" Wilwood manual setup, and it does not inspire confidence before you tap the brakes up.

Here is a picture of one of our car's rear rotors. I think the reason I never noticed bad knockback sooner was because the rear calipers weren't evenly spaced and whenever I'd go around a hard turn, the rotors would grind against the retaining pins between the padlets on the C6 Z06 brakes. Because of this knockback was limited, and less apparent. The downside though, was that my rear brakes weren't ever working 100 percent.

You can see the ring caused by the deflection, where the rotors ground against the retaining pins:
http://i366.photobucket.com/albums/o...A/DSC_0651.jpg

Matt

What it is....

http://www.stoptech.com/tech_info/wp_knockback.shtml

knock back is generally only seen on radial mount calipers or lug mount. floating calipers like c5 etc will never get knockback because they float. radial mounts are generally run in race applications where larger/better bearings are used as well as full floaters in the rear.

That's exactly why I may still install a C5 caliper out back until someone comes up with a economical solution.

Matt, hope to have time to work on mine this weekend and will give you my thoughts on the 1" master cylinder with no residual pressure.:unibrow:

my 69 has 4 piston alcons up front with 9012 hawk pads and single piston c5 rears on a 13 inch rotor in the rear with hp plus pads. never got any brake fade, at any track, nhms,watkins glen,njmp,gingerman etc and the car is no slouch

So Todd, why is it that a power assisted setup knocks down this issue---greater initial hit on the first pump of the brake pedal? It's moving the pads further out (and away) from the calipers with the first hit?

Doug

Doug, I think the power booster reduces the apparent feel of knockback because it has a larger bore, meaning that less fluid is displaced as pads/pistons get pushed around.

Matt

Larger bore master cylinder means more fluid volume to the calipers with less pedal stroke. I got my 1" master back on tonight. All I need to do is bleed all four corners and go for a ride. Hang in there a few days.

What a larger bore master REALLY MEANS is that you'll MAKE LESS PRESSURE per pound of pressure exerted on the pedal (given equal pedal ratios)... and have a harder pedal feel vs. the 7/8" master.

Some people prefer a harder pedal. :D

The amount of movement at the pistons in the bore at the caliper would only back fluid up into the reservoir of the M/C, because it would arrive there (back flow) prior to having anything to do with the piston/stroke etc of the M/C. It's an open chamber without engagement of the stroke of the piston.

Can't fix the KB issue via the M/C. You're going to have to fix the flex / root causation.

Just a PS...

The very reason that under floor mounted M/C's REQUIRE residual valves to be installed is for the reason I stated above... the simple laws of gravity will allow the fluid to flow back into the M/C reservoir and overflow it without them!

10# valves for drum brakes

2# valves for discs

I still wonder if these valves wouldn't "help" (not cure) the KB issues on the discs you guys are using. If it's okay to drive around in a hot rod with under floor M/C using them (2#'s) it can't be an issue... Right? So maybe the 2# valves would make it a little better? Anyone?

It doesn't fix the knockback, it simply covers it up. There is a reason factory cars come with power brakes. It's not all pedal effort. A 2# residual valve didn't help mine. It's still in there. 10 pounds makes me nervous.

We have tried the 2 pound and 10 pound residual pressure valves on other cars with knock back issues and it did not work.

My last 7 cars have had this problem....
Tri Trip
Red Witch
Thrasher
Mule
Camaro X
Jackass
Red Devil (The knock back is good on this car but it is still new)

I'm very close to going to a full floater to solve all this problems.

Knock Back
Oil leaking tube ends

But it induces some problems of ABS sensors, park brake system, wheels, cost and complexity

I have gotten used to left foot braking to pump up the brakes going down the straights. :rolleyes:

The standard tapered roller bearing Ford big bearing seems to have about .020" - .050" end play after track use. This is what causes knock back of opposed piston calipers (4 piston).

I'm going to work on a better design to help fix the problem.

Stielow

Have you tried shimming the race out to put more pre load on the bearing? I've got some .010 shims coming right now. I'm going to measure the rotating torque before and after if and when I install them.

Mark- The bearing issue has eveybody looking for a solution.. I got two things I am working on that might help..

Working on designing a housing end that will use angular contact call bearings & doubling them up with a beefed up bearing retainer.. In theory it should have about .001 to .002 end play...

Have a meeting next week with Kenny Sapper from Speedway Engineering.. Working on getting a Street/Race floater built.. The parking brake will be challenge.. rotor adapter is easy.. can even float the rotor..

I spoke with Kenny last week
 

about building me a floater as well. I am going to for go the parking brake as mine does not work worth a crap now.

Cris, would a single piston parking brake from Brembo help simplify the issue of putting one on a full floater?

Matt

Just a note on the inner axle seals. DO NOT USE THEM! I went through several manufacturers of them when I raced circle track. In every case oil would get past the seal and fill up the right axle tube and trap the oil there. This then starves the center section for lube. Luckily it never bit me, but several people lost several gear sets until this was figured out. They were used in our case not to solve a leak as we used full floaters. We needed to keep the lube from leaving the gear set and traveling up the tube and starving the bearings. In the end it actually magnified the problem over time. I will never use them again!

I put a single disc parking brake on my Ford 9" --- bolts onto the yoke -- has a hand brake style lever - it's own disc (tiny) -- it's a PARKING BRAKE not an "emergency brake".


http://www.tsmmfg.com/Pinion_Mounted_Parking_Brakes.htm


Mark -- Good info on the residual valves not working. I didn't think they would because that's not really their job... but thought maybe it might help.



Gonzo -- Can I tell ya sumthin.... :rofl:

I will keep you in mind when working on a floater.. whose parking brake do you have now??


As long it is a floating caliper.. In the long run it will be be the cheapest solution..

Wilwood parking brake
 

Not their fault as it is a good design. Using Lokar hand e brake. Not enough throw or leverage.

I discovered a miracle fix for all these axle leaking brake knockback issues!!!!


A set of 6.70 X 15 - 2 ply nylon tires like we used to run on the mid year Corvettes....

Never experienced any issues back in the day!


EEEEEEEEEHHHHHHHHHAAAAAAAAAAAAAAA :rofl: :rofl: :rofl:

GregWeld. I think that a set of 6.70 X 15 - 2 ply nylon tires will be effective in our car. :D I hope there will be no issues back then. :D

Well, I took the car out to the track last week with the group that went out to Adam's Motorsports park in Riverside. The track is pretty much just a big kart track, which isn't such a bad thing as it's quite technical and has got a good mix of turns. All of the changes we made to the car made a huge difference - I mean a night and day difference. The car might understeer a little turning in now, but it's not bad at all. Exiting corners is insanely easy the way it is set up too. I can almost plant the gas and take off, when it's almost straight I can let it go wide open, and the car will step out just enough to straighten out. Then it just goes. The only issue I had was bad pad knockback issues. I had to tap the brakes once to get reasonable feel back, and twice to get the pedal all the way back to the top. On my last lap I forgot to tap the brakes up after a long straight and the pedal fell almost to the floor, needless to say, I put the front two wheels off track.

So, I've been talking to Cris G and his Wilwood friends, as well as Tobin at Kore 3 and have decided to try a somewhat affordable solution to lessen the apparent knockback. For now, I'm just going to go with a C6 Z51 rear brake setup and see how it works. It's a floating rear caliper, and I don't think I need the huge 4 piston setup on there now. It's not like I'm doing any serious, sustained roadracing, and even then I ran a Z51 'Vette at Bondurant, and never really noticed the brakes fading badly. If I'm not happy with that I'll swap to a 1" bore master and if the problem still persists I'll try the SET20 bearings that are shipping on Moser's axles now. I also decided to swap pads to the Hawk HP+ instead of the ceramics because the ceramics don't have much of an initial bite to them, especially when using manual brakes.

If none of this works, I think I'll be going Greg's route and getting a pair of 6.70 x 15s or maybe I can trade Doug for his rear drum brakes.

Matt

Hey, those are "Bear" one-off self energizing rear drum brakes on my car. Just need to paint those drums red. That's the one and only problem I don't have on the car, pad knock back.

You sure looked good out at Adams track---car sounded great also---

Doug

which ceramic pads were you running? did you ever run the stock padlets? what size master are you running on the rear now. i set mine up with 1" front and 7/8" rear for my manual c6z brakes. i hope i dont need another 1".

Right now I've got the Hawk Ceramics on the car, which I ordered along with my brakes two years ago, way before I picked out a master cylinder, so I never ran the stock padlets.. When it came time to get a master cylinder Dick at Best of Show recommended the Wilwood 7/8" tandem piece, after all, it worked great for Steve on Bad Penny.

I really don't know enough about brakes to tell how your setup will work. I also don't know what you intend to do with the car, what other components you have, or how you like the car to feel under braking. For me, at least on a track, I like to have firm pedal feel with a bit of initial bite, which I think acts as feedback to help tell me how much I can modulate the brakes. Currently my combo gives me a little bit of squish in the brakes, even after a tap, then as I hit the brakes hard the car does decelerate well, but does so in a real smooth manner, especially with the DSE sub which doesn't allow for much front end dive at all. The feel of stopping in my Camaro is different than any other car I've driven, because despite the fact that the brakes really grab, you're never really able easily feel how much pedal travel you have until you lock the fronts up, and you can't judge how hard you're braking by weight transfer because the car doesn't dip down or lift up noticeably. Long story short, I'd give Tobin a call. If you tell him what you're after, he will be able to name all of the components you might need to set up the system exactly the way you want it to feel.

Matt

Oh, and before I forget... Doug how is your car doing? have you had time to fix the rear coilovers? I'm pretty set on heading back up to Adam's Motorsports Park Tues. Aug 10th and was wondering if you would be up for another track outing. If you're not ready but want to go you're welcome to ride shotgun.

thanks for the info matt. i looked back through the thread for the answers, but as you know its pretty long. tobin set me up with the brakes and he recommended the 1" front and 7/8" rear for my triple master setup. i am running the tapered bearing, so i hope i wont have any issues. oh, and my intentions are to run with you local guys when this damn thing is done......

have you thought about the carbotech pads? expensive, but the z guys seem to love them.

Tim

RP valves won't help knock back at all.. Think about how little two pounds (or even 10 lbs) of force is.. almost nothing.

Sure, they will stop fluid from gravity flowing backwards but they arn't going to stop piston knockback at all.

And you're right, you can't stop knockback with a MC.

Knockback is a mechanical issue, not a hyd/fluid one. Physical forces are acting on the caliper and pushing the pistons (by way of the pads) back into the calipers. The first pump of your brake pedal resetst the pad to the rotor and the next "pump" works the brakes.

The basic truth is that our axle ends aren't designed to handle high side loading like we get in autocross or road racing. If your axle tube is off center or warped then the problem is compounded.

A floating rear caliper will help mask the problem of the bearing/axle tube. If you want a rear fixed caliper then you need to

1) make sure your rear housing is as straight as possible to take pressure off the bearing
2) service your bearing on a regular basis (when it gets play in it)
3) Move to a stronger system like a floater or such
4) Move to a stronger bearing than can handle the forces involved better

Once I had my rear housing done by Currie my KB issue was nearly solved. But I'm sure it will creep back with more laps and require a bearing service.