Farmall 70A - Brake Bellows Replacement

[klancf51]

I noticed transmission fluid on the floor under the right rear axle. The rubber seal (bellows) for the brake actuator rod was leaking.
The CNH bellows is part #47864249.

Removal

• Place the tractor in gear.
• Block the wheels, front and rear.
• Unlock the left and right brake pedals. If replacing left brake bellows, release the parking brake.
• Drain about 2.5 gallons of fluid.
• Remove the pin & disconnect the brake linkage.
• Remove the brake linkage.
• Remove the guard & spring.
• Remove the Seeger circlip and metal cup (external circlip and a tapered metal cup seal the bellows with the rod). It is difficult to view and access the circlip and when I opened it, it snapped in two.
• Using a putty knife and pry bar, remove the bellows from the trumpet housing. Be ready to collect fluid.

Tooling

The service manual states:
"Reassembly follows the disassembly procedure in reverse, ..."

"Use special tool number 84261390 to fit the brake rubber boot in the brake linkage groove and brake rubber brake boot with special tool number 84261391 in trumpet housing."

The main challenge is applying even force on the shoulder of the bellows to drive it into the bore in the trumpet housing.
There are 3 problems:

1. the bellows fits over the brake actuator rod and this rod extends from the trumpet housing and out of the bellows (i.e. the rod is in the way),
2. there is limited room to swing a hammer,
3. the shoulder of the bellows is narrow.

CNH special tool 84261391 looks like a bearing driver. In my seal & bearing driver kit, the best fit was a 1.965" bearing driver, but the shoulder of bellows is ~2.125" diameter. Also, the tapered part of this driver fits too tightly in the bellows and I was concerned it would keep the bellows from entering the bore, or worse, expand the metal in the bellows. So I fabricated a 2.125" x 1.72" x .020" washer to fit over the taper of the bearing driver. This allows metal to evenly contact the shoulder of the bellows and prevents the driver's taper from seating too far in the bellows. Additionally, the hole in the bearing driver is larger than the brake actuator rod, and fits over it, so that the bearing driver is concentrically seated in the bellows. To apply force evenly, I placed a Grade 8 1/2" flat washer and 1/2" Craftsman spark plug socket over the brake actuator rod. The rubber insert in the spark plug socket centers the socket on the brake actuator rod and protects it from the hammer blows. This driver setup is shown in the photos.

Installation

• Cover the threaded portion of the brake actuator rod with a shaft repair sleeve (tape, finger cut from nitrile glove, etc.) to prevent damage to the bellows.
• Slide the bellows over the brake actuator rod and into the bore.
• Remove the shaft repair sleeve.
• Using your fingers, press the center of the bellows (where it seals to the rod) firmly into the brake linkage groove - you will feel it seat (special tool 84261390 was not needed).
• By hand, start the bellows evenly into the bore.
• Seat the 2.125" washer and bearing driver in the bellows and slide the 1/2" flat washer and spark plug socket over the threaded portion of the brake actuator rod.
• Firmly grasp the socket and apply hammer blows to the socket to drive the bellows evenly and fully into the bore.
• Remove the tooling.
• Slide the tapered metal cup over the threaded portion of the brake actuator rod and seat it evenly and fully on the bellows.
• Slide the external Seeger circlip over the threaded portion of the brake actuator rod toward the tapered metal cup as far as possible by hand.
• Slide the 1/2" flat washer (tooling) over the threaded portion of the brake actuator rod and use it to push the external Seeger circlip into the groove in the brake actuator rod (you should feel it "click" into the groove). Remove the flat washer.
• Verify the Seeger circlip is properly seated by rotating it in the groove (it must turn and remain in the groove).
• Re-fill transmission with fluid.
• Check for leaks.
• Install the guard & spring.
• Install pin and brake linkage.
• Adjust the free play of the brake pedals (1.97" - 2.17").
• Lock the brake pedals together and set the parking brake.
• Unblock the wheels, front and rear.
• Road test to ensure that the brakes are balanced and will stop the tractor in a straight line. Further adjustment required to balance the braking should be carried out on the right brake.
• Check again for leaks.

Lessons Learned
It may seem that the brake bellows can be hammered into the bore or driven in with a large socket, bearing race, seal driver, etc. Any method which doesn't apply force evenly to the bellows shoulder is not recommended. CNH bellows #47864249 is not inexpensive.

The external Seeger circlip is CNH #47678664. It is a special type of external circlip used in sealing applications called an external inverted Seeger circlip. It is metric (14mm). When mine broke in two, it flew apart! Luckily, I was able to use a magnet to find half of it and identify it as the inverted type. Recommended source for this part is CNH dealer and recommend purchasing one with CNH bellows #47864249.

I considered using #5117518 (Sparex S.65374), a brake bellows that has been used on many tractors and widely available in the aftermarket. I even bought one. #5117518 and #47864249 appear to be identical, but they are different:

• #5117518 uses a garter spring to seal the bellows on the rod,
• #47864249 uses the tapered metal cup and inverted 14mm circlip to seal the bellows on the rod.
• CNH #47864249 supersedes #5117518.

The aftermarket #5117518 I got was not manufactured to the same quality as #47864249 (it had a rubber "flash" on the metal where it seats into the bore, whereas the CNH part was cleanly made). I'm not at all positive that #5117518 would seal the brake actuator rod using the garter spring alone, with the tapered metal cup/circlip alone, or with all in combination.

 

[TractorTech]

Actually, they can be driven in with a blunt rod on the rim to get started and then work around the outside until seated. The bellows with the rubber around the rim are harder to get started than the clean metal ones, but can be installed similarly.

Usually, the side of the brake seal being replaced can be jacked up or driven up on a stand to tilt the tractor and thus the oil away from the seal to allow replacement without losing any oil.