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Fixing Brake Pad Knockback with a Floating Axle System from Baer

Knocking Out Knockback

Aug 31, 2018
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Hot rodding has always found a way to adapt race car technology to our street rides. And, now that more of our street cars are hitting the track, it’s for more than just bragging rights at the local Dairy Queen. Bigger brakes, wider/stickier tires, and more capable suspensions help our cars turn harder, but sometimes that comes at a cost. With the increased side-loading, a new issue started to pop up: brake pad knockback. With a traditional non-floating axle there’s axle deflection. This bending and bowing of the axles occurs as lateral (cornering) forces rise. While you may look at a typical 31-spline axle and think there’s no way it can flex, it does due to the tremendous leverage effect of cornering at high speed. The problem is compounded by large wheels and rotors, which increases the leverage effect. The result is that the rotor pushes the pads into the pistons, forcing them back into the caliper, which in turn creates a space between the rotor and pads. Hit the brakes and the pedal goes to the floor until the calipers are pumped back up and make contact with the rotor. Repeated axle deflection also dramatically decreases bearing life, which causes pad knockback to get even worse and seals to leak, which can make a mess and diminish braking effectiveness.

027 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 2/29

One of the more popular rearends is the Ford 9-inch, which uses the bearing near the wheel flange and a plate to retain the axle and wheel assembly. Here, if the axle breaks it may or may not be retained. In a full-floating rearend, such as the system from Baer, the axles are splined on both ends instead of splined on one end with a wheel flange on the other. Because of this, the axle has nothing to do with supporting the wheel and only turns the wheel, by way of a drive plate, instead of turning it and supporting the car’s weight. So, if there’s an axle failure, the wheel stays put. Obviously, this is far safer since the wheel is supported by the much stronger axletube housing, and not the axle itself. Because of this, axle flex under high-g cornering is virtually eliminated. They are also easier to service, which is another big selling point for racers. Due to the design, a broken axle can be pulled and replaced without even having to remove the brakes, or in many cases even the wheel, from the car.

028 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 3/29

So why wouldn’t you run a full floater? The number one reason is cost. A floater is going to set you back more than a typical rearend. In all honesty, if you’re just cruising around town it falls into the overkill category. But, if hanging it all out around your favorite road course is in the plans, then a floater should really be factored into your build.

029 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 4/29
002 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 5/29

1. When our Roadster Shop (RS) Fast Track chassis showed up, it came equipped with this Strange Engineering housing that had the suspension brackets already welded in place. RS knew we were doing a floater kit, so they didn’t weld ends on the tubes and left them a bit long.

003 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 6/29

2. Welding brackets to a housing almost always causes the tubes to warp. It’s critical that the axles in a floater not be side-loaded, since that would cause accelerated wear. We were doing this install at Currie, who has a machine that straightens warped housings. The other alternative would be to offset machine the spindle to compensate for the warp. However you do it, the goal is to have the axle’s path from the drive plate to the posi be perfectly straight.

004 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 7/29

3. With our housing straight, it was time to do some math so that the new rear would be the same width as the rear that was in our Chevelle with the old chassis. Currie had built the previous rear, so they had all the dimensions, which made it easier. If you’re converting an existing rear to the full floater, 0.640-inch will need to be removed from the axletube in order to maintain the same wheel location.

005 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 8/29

4. Once we did our math, three times, and made our marks we went to the band saw and lopped off the ends of the axletubes.

006 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 9/29

5. The key pieces of the floater puzzle are the steel spindles (snouts). The floater snout has a flange machined into it to allow many systems using Big Ford ends (Torino) to bolt right to the snout. Once the snout is installed, the rest of the operation is a bolt-on deal.

007 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 10/29

6. After installing the spindle on their lathe, Currie milled down the end so that the OD of the spindle perfectly matched the ID of the Strange axletube.

008 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 11/29

7. We then chamfered the ends of the axletubes in preparation for welding. Having a solid weld is critical since the axletube, instead of the actual axle, will now support the weight of the car.

009 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 12/29

8. We were then able to test-fit the spindle into the axletube so we could start working on the clocking. While it doesn’t apply to our ’71 Chevelle, the Baer Tracker kit is fully compatible with ABS systems.

010 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 13/29

9. With the rear held so that the centersection mounting flange was level, we could then use a straightedge and a magnetic bubble level to properly clock the spindle in the rear. Currie also used a long steel rod as a jig to make sure everything stayed perfectly straight during welding.

011 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 14/29

10. Before tacking the spindle in place, we drilled several holes in the axletubes to accommodate rosette welds for additional strength.

012 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 15/29

11. With the ends tacked in place, the rear moved to one of Currie’s rotary welding tables. It’s a pretty sweet setup that rotates the entire housing so the welder can concentrate on making a spectacular weld instead of constantly moving the housing.

013 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 16/29

12. And here’s the result of the welding. With the spindle completely welded around the perimeter and the rosettes welded in, there’s zero chance of failure. This also illustrates why it’s critical that the measurements are perfect since there’s no way to go back and fix a math miscalculation.

014 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 17/29

13. The Bear Tracker kit was one of the first floater systems to incorporate a parking brake. Its one-piece shoe design has 35-percent greater break-away-torque than a conventional two-piece shoe design. This really works to bridge the race technology of the floater to the street car market.

015 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 18/29

14. The backing plate was then bolted to the floater spindle using the four Grade 8 bolts supplied in the kit. We used a dab of red thread locker on the bolts for bit of added insurance.

016 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 19/29

15. With that done, we pressed the ARP 1/2-inch wheel studs into the bearing hubs. Currie has done so many of these that they have a jig setup that made it a snap to do.

017 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 20/29

16. The Baer rotors came pre-bolted to the parking brake drum so we simply had to bolt the assembly to the bearing hub, grease up the bearings, and slide them into the place. Two large bearings, spaced apart a bit, allow for maximum load capacity.

018 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 21/29

17. The bearing hub/rotor assembly was then slid over the spindle and locked in place using the supplied ring. For this, we needed a specific spindle socket with four tabs (Napa PN 3146).

019 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 22/29

18. Once properly tightened down, we lined up one of the notches in the locking ring with the one of the tabs and bent it down to ensure everything stayed tight.

020 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 23/29

19. Next up was installing the drive plates. These are built for Baer by Speedway Engineering and they utilize a 24-spline arrangement based off of NASCAR specs. This 24-spline plate is 0.050-inch larger than a standard 35-spline axle. Since this plate transmits a lot of power to the wheels, the added strength is critical. With the plate in place, we could take the measurements for our axles. The end of the axle needs to come right to the end of the drive plate.

021 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 24/29

20. We know of two companies that make axles for this kit that have the proper 24-spline setup on the wheel side of the axle: Speedway Engineering and Moser. We know the guys over at Moser make killer stuff so we had them make us up a pair of hardened axles with 24-spline on one end and 31-spline (to work with our Eaton Detroit Truetrac posi) on the opposite end.

022 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 25/29

21. On the inboard end of the axletube (toward the centersection) it’s a good idea to have an axle seal to keep fluid out of the tubes so that it doesn’t try to wash out the bearing grease on the outboard ends. We chose these pieces from Speedway Engineering based on the ID of our axletube. They were simply inserted in the tube and tapped in place.

023 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 26/29

22. With the seal in place we could install our Strange HD Pro Aluminum centersection. This case, with the integrated pinion support, increases gear life over an OEM cast- or nodular-iron unit due to its rigidity. In short, it has all the strength of iron in a lighter weight aluminum package. We did upgrade to a billet 1350 chrome-moly yoke, as much for looks as for added strength. Inside the centersection there’s a set of Motive 3.70 gears along with an Easton Detroit Truetrac posi, which is perfect for the autocross and road course work we have planned.

024 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 27/29

23. With the centersection installed, we simply slid the new Moser axles into place. Once the axle was in place we packed the end with grease and sealed it up with a billet aluminum O-ring-equipped cap.

025 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 28/29

24. Originally, we were going to run Baer’s 6S calipers, but given the two-ton-plus weight of our Chevelle we opted to try out their new XTR calipers. The 2618 aluminum alloy is uber strong and these monoblock forgings are incredibly stiff. This increase in stiffness allowed Baer to add a bridge system for quicker pad changes between the street and track sets. These also feature their new Boiling Point Barrier two-piece piston design that reduces pad heat transfer to the fluid, utilizing either aluminum pistons with crenelated steel caps or the optional TI pistons with crenelated titanium caps. Like all street-ready Baer calipers, these have dual dust and weatherseals.

026 Baer Floater Currie Strange Moser Rear Ford 9 Nine Inch 29/29

25. Given the heavy-duty track-ready nature of the new XTR calipers, we’re also going to switch from the drilled and slotted rotors to the more robust, track-ready, slotted rotors. The holes look cool, but when it comes to hard braking, mass is king and the solid rotors can suck up a lot more abuse. If your plan is autocross and light track work then the zinc-washed drilled rotors will serve you well.

Photos by Steven Rupp

Sources

Currie Enterprises
Corona, CA 92880
714-528-6957
http://www.currieenterprises.com
Eaton
Cleveland, OH 44114
800-386-1911
http://www.eaton.com
Baer Brakes
Phoenix, AZ
602-233-1411
www.baer.com
Strange Engineering
Morton Grove, IL 60053
847-663-1701
www.strangeengineering.net
Moser Engineering
Portland, IN 47371
260-726-6689
www.moserengineering.com
Roadster Shop
Mundelein, IL
847-949-7637
www.roadstershop.com
ARP
Ventura, CA 93003
805-650-0742
http://www.arp-bolts.com

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