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Currie 9-inch Swap into a 1955 Chevy Bel Air

Nine To (Tri) Five: Swapping a 12-Bolt for a Currie 9-Inch Rearend

Rob Fortier Apr 7, 2015
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Bow Tie purists may cringe at the thought of a “Ford” rearend under a Chevy product, but when you really get down to the brass tacks of it, today’s aftermarket 9-inch is about as much Ford as a modern-day Sprint Cup car sporting the blue oval.

Currie Enterprises has been producing their own brand of 9-inch rearends for decades. Matter of fact, it was the popular Chevy Vega V-8 conversions in the ’70s that got the company’s gears spinning in the non-off-road market to begin with … no pun intended. Despite offering Dana 60 and GM 12-bolt variations, the Currie 9-inch is their top selling rearend across various hot rod platforms, hands down. Hence there being no shock finding this particular variation differential beneath a GM vehicle today.

Based on the 9-inch’s popularity status, Classic Performance Products (CPP) has developed specific lines of disc brake and suspension kits for early Chevys, including the Tri-Five, with the non 10-bolt/12-bolt/OE applications. CPP also offers a leaf spring relocation kit, along with widened wheeltubs, that allow the vehicle to be lowered up to 2 inches while at the same time giving it the ability to run 10-inch wide wheels.

We came across a 1955 Bel Air that just happened to already have the relocation kit and widened wheeltubs; however, it had also been “victim” to an ill-narrowed Impala 12-bolt rearend. The use of reverse-offset wheels may have dictated that, but nonetheless, when it came time to install rear disc brakes it was a no-go. With the rearend narrowed too much (not to mention unevenly side-to-side), the calipers ultimately hit the framerails, even when re-clocked in a lower-mount position. What to do—other than stick with the old drum brakes, that is?

Well, since the owner did not want to be relegated to using the deep offset wheels—and “widening” a rearend is not possible—the solution was clear: order an appropriate-width rearend. A Currie 9-inch Crate Rearend (for a 1955-’57, to accommodate narrowed width/spring parameters) to be exact.

Chevy 9 Inch Rearend Swap Brake Complete 2/30

With its 100-percent Currie-fabbed housing (featuring Torino large-bearing ends and pre-welded spring pads), 31-spline axles, and 9+ third member with 3.50:1 ring-and-pinion, the Crate Rearend is literally ready to assemble, bolt in, and go—save for adding the performance disc brake package, that is. (Although this application dictated 1/2-inch wheel studs to match the front hubs. Normally, the axles are supplied with 7/16-inch lugs, in either 5x4.75 or 5x4.5.) A bulletproof rearend, perfectly suited to go beneath any vehicle—especially one with a Bow Tie emblem.

Follow along as we reassess the differential discrepancies on the Bel Air, righting the wrongs with CPP’s Crate 9-inch and adding a Ford-flange rear disc brake kit in the process.

(Note: As you will see in the following steps, it’s imperative that the E-brake mechanisms are correctly set for proper brake performance—preferably before the system is bled. The process is fairly straightforward. Without being performed, you risk premature pad wear at best; soft or no brake pedal at worst.)

Chevy 9 Inch Rearend Swap 12 Bolt 3/30

1. Here’s what our story centers around—an ill-centered, ill-narrowed Impala 12-bolt (differs from standard 12-bolts) stuffed beneath a nice little 1955 Bel Air. Our first realization we were dealing with an issue is when a set of CPP disc brakes were bolted up: they came in contact with the frame when the suspension was compressed. Not only that, but to accommodate the narrowness, deep offset wheels had to be used. Let’s fix all that, shall we?

Chevy 9 Inch Rearend Swap Spring Relocation Kit 4/30
Chevy 9 Inch Rearend Swap Relocated Leaf Spring 5/30

2. As mentioned, the ’55 had already been treated to a spring relocation kit, which along with allowing the use of up to 10-inch wide wheels, lowers the rear approximately 1 inch. CPP offers the complete kit, which includes weld-in frame pockets/plates, spring pads, tie plates, longer shackles, U-bolts, springs, and gas shocks.

Chevy 9 Inch Rearend Swap Cpp  Wide Wheelhousing 6/30

3. Naturally, when you relocate springs to accommodate wider wheels, you must address the wheelhousings above, as well. Rather than slice up and add metal to the existing ones, simply swap out for a set of wider wheeltubs, something else CPP conveniently offers.

Chevy 9 Inch Rearend Swap Pre Swap Measurements 7/30

4. Before pulling the 12-bolt out from underneath the car, we pulled a few quick measurements just to ensure a couple things: exact spring pad location (which was off) and exact required width, 57 inches—just over 3 inches less than the transplanted GM rear and 3 inches narrower than stock.

Chevy 9 Inch Rearend Swap Paint Prepped Before Install 8/30

5. A thorough prep and subsequent coats of satin black are all that’s required to ready the Crate 9-inch housing for installation into the ’55, as the spring pads are pre-welded on. (Note that the filler neck is a custom order option.)

Chevy 9 Inch Rearend Swap Axle Retainer Plate 9/30

6. For the forthcoming disc brake install, Currie’s axle retainers should be removed. The brackets can be bolted on with the retainers, but because Currie’s bearing stick-out is slightly more than an OE 9-inch, there’s a chance of bending the retainer, thus negating the ability to properly align the caliper bracket once it’s bolted tight.

Chevy 9 Inch Rearend Swap Tie Plate Install 10/30
Chevy 9 Inch Rearend Swap Tie Plate Shock Stud 11/30

7. The bare/empty housing is loaded atop the leaf springs, secured using CPP tie (spring) plates with fresh U-bolts and bolt-on shock studs.

Chevy 9 Inch Rearend Swap True Trac Differential 12/30

8. Next, the TrueTrac differential is installed. It features a 9-inch nodular Sportsman case housing a 3.50:1 ring-and-pinion to accommodate a 700-R4 overdrive transmission.

Chevy 9 Inch Rearend Swap 31 Spline Axles 13/30

9. Axles are 31-spline with upgraded 1/2-inch wheel studs (to match the front hubs; 7/16-inch studs are standard).

Chevy 9 Inch Rearend Swap Axle Bearing Stick Out 14/30

10. With the Currie retainer plates removed, you can see the amount of axle bearing stick-out. (With drum brakes—or factory Ford discs—this is not a problem whatsoever; it’s the nature in which the CPP caliper bracket attaches that this becomes an issue.)

Chevy 9 Inch Rearend Swap Ford Flange Disc Brake Caliper Bracket 15/30

11. Speaking of which, the Ford-flange disc brake kit’s caliper bracket is a multi-component arrangement, with stackable spacers to perfectly align the caliper with the rotor for optimum performance.

Chevy 9 Inch Rearend Swap Bearing Retainer Bracket 16/30
Chevy 9 Inch Rearend Swap Bearing Retainer Bracket Install 17/30

12. The “new” bearing retainer is also the initial caliper bracket piece. It sandwiches against a supplied 1/8-inch shim meant to duplicate the OE drum brake backing plate.

Chevy 9 Inch Rearend Swap Bearing Retainer Bracket Shim 18/30
Chevy 9 Inch Rearend Swap Bearing Retainer Bracket Shim Install 19/30

13. Additional shims, more often than not, will be required to space the initial bracket sufficiently for caliper alignment (mainly affects aftermarket 9-inch rears). They are available separately from CPP (10271-KIT).

Chevy 9 Inch Rearend Swap End Play Check 20/30

14. The amount of endplay will determine the correct amount of spacers required. If you have a dial indicator, that will give you a more precise measurement, obviously, but it’s not absolutely necessary to use one.

Chevy 9 Inch Rearend Swap Caliper Bracket Spacer 21/30

15. The next round of spacer installation involves offsetting the caliper bracket. CPP recommends installing all eight (four upper, four lower) spacers and then removing as necessary per process of elimination, if necessary.

Chevy 9 Inch Rearend Swap Caliper Bracket Bolts 22/30
Chevy 9 Inch Rearend Swap Caliper Bracket Bolts Backside 23/30

16. The bolts retaining the caliper bracket need to be inserted from the axle flange side, pointing toward the differential; this prevents the rotor from interfering with the hardware.

Chevy 9 Inch Rearend Swap Rear Caliper Install 24/30

17. With the rotor installed (secured fairly tight with lug nuts), slip the caliper on with just the outer brake pad inserted.

Chevy 9 Inch Rearend Swap Rear Caliper Alignment 25/30

18. Your caliper alignment is determined by 1) if it fits over the rotor to begin with, and 2) if it does, how evenly spaced the pads are, as well as the amount of gap there is between the bracket and the caliper’s mounting ears.

Chevy 9 Inch Rearend Swap E Brake Mechanism Tension 26/30

19. It cannot be stressed enough how important correctly setting up the E-brake mechanism is for proper rear brake performance. By removing the lever, washer, and seal, you can adjust the piston to set the tension of the lever. To avoid running it in too far, install the lever nut on top of your 9/16-inch wrench.

Chevy 9 Inch Rearend Swap E Brake Mechanism Reset 27/30

20. Marking the lever’s alignment/orientation prior to adjusting will give you a good indication of where it needs to reset in order to have minimal play (no more than 1/8-inch) and butt up against the caliper stop under tension.

Chevy 9 Inch Rearend Swap E Brake Mechanism Complete 28/30

21. Once the E-brake is set, complete the assembly of the mechanism; install and adjust the cable, leaving a small amount of slack, and test-operate from inside the vehicle to ensure proper operation. Regular use of the E-brake is also crucial for overall performance and proper pad wear.

Chevy 9 Inch Rearend Swap Pre Bent Brake Lines 29/30

22. CPP’s pre-bent rear line kit was used, secured to the 9-inch via their band-clamp T-fitting kit and hard line to flex hose tab kit; the system was fully bled once all the fittings were tightened up. Notice, too, the rear wheel is installed here. Be sure to check fitment of disc brakes before they’re installed on the vehicle, not after. It was also verified that there would be no interference between the calipers and the frame beforehand.

Chevy 9 Inch Rearend Swap Fluid Fill 30/30

23. All Currie Crate 9-inch rearend kits are supplied with three quarts of 9+ 85W/140 racing gear oil. Normally, the fill would occur from the third member side, but in this case, the 9-inch was ordered with an optional rear-fill spout.

Sources

Currie Enterprises
Corona, CA 92880
714-528-6957
http://www.currieenterprises.com
Classic Performance Parts (CPP)
Placentia, CA 92870
800-522-5004
www.ClassicPerform.com

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