Rear End Bushing Question

[71tanker]

can anyone tell me what the name of this bushing is, and has anyone ever changed them?

[HK Trucking]

Trunnion Bushing. The rubber type.

Yes, I've changed them.

Jack up the truck, put blocks under the trunnion.

Remove the wheels from the rear axles on that side.

Put a jack under each spring box on the side that you're changing.

Since it appears that someone has put a home made retainer on the end of your trunnion shaft, that must be removed.

Cut off the U bolts that hold the spring to the saddle.

Remove the bottom half of the trunnion saddle.

Jack up the rears so that the upper half of the trunnion saddle separates from the trunnion bushing.

Remove the worn out rubber bushing from the trunnion shaft.

Be sure that the trunnion shaft is clean and no pieces of the old bushing are stuck to it.

Using some waterless hand cleaner as a lubricant, slide the new rubber bushing on to the shaft, center it in the middle of the area where the old bushing was.

Let the rears down so the upper saddle contacts the trunnion shaft.

Install the bottom saddle on the trunnion, install new U bolts, and tighten.

Replace the home made retainer on the end of the trunnion shaft.

If I remember correctly the torque spec for those U bolts is well in excess of 1,000 ft lbs. so if you don't have a torque multiplier that will achieve that torque, have the U bolts torqued at a shop with the proper equipment, this is very important. Insufficient torque on the U bolts can lead to broken spring centerbolts, and broken U bolts, and possible damage to the truck and personal injury.

[CML Service]

Just a couple things to add to what Herb said. The retainer looks like the early factory type. The 3/4" rod goes thru to the other side. If the truck isn't going to work hard consider trying to save the U-bolts. They cost arount $180 for the set. Use only new if it is a working truck. Then the bushings come in several different lenghts. Bring the saddle to a good spring shop and they should be able to suppy the correct ones. There are also two spacers inner and outer they need to be checked for wear as well as the saddle where they contact on hard turns. And lastly the spring needs to fit the saddle with little to no side clearance. Many of these wear points need to addressed in relation to how the truck will be used. Don't take shortcuts on a hard working truck or it may dissapoint you.

Chuck

[chris88]

For the U bolts we just get on em good with the 3/4 gun and hit down on them with a big hammer.

[CML Service]

The torque on the U-bolts is 1400 ft-lbs. and shouldn't be less on a hard working truck.

Chuck

[Rob]

The torque on the U-bolts is 1400 ft-lbs. and shouldn't be less on a hard working truck.

Chuck

My first "R" model truck had both lower saddle caps broken from lack of torque on the ubolts. They were aluminum. I use a 1" drive impact on the nut and finish, (by hand) with a torque multiplier. Tight, but even is the key. Also, definately check the wear pads, (welded to trunion tube) for very little side to side play. The trunion tube keeps the tandem centered, (side to side) under the truck and if worn will be very noticeble during turns when loaded and tire wear will be pronounced.

Rob

[mudslut28]

I get a headache when I ever seen the word trunion now..lol. We had an inch gun at word for those saddles. Sure did help although the lighter Mack suspensions sound quite a bit different from the 50k's and 60k's.

[71tanker]

yea its definatelly a hard working truck, and the axles do move from side to side thats why i figured they needed to be replaced, thanks for all the tips, hopefully it goes smoothly

[Kav]

Trunnion Bushing. The rubber type.

Yes, I've changed them.

Jack up the truck, put blocks under the trunnion.

Remove the wheels from the rear axles on that side.

Put a jack under each spring box on the side that you're changing.

Since it appears that someone has put a home made retainer on the end of your trunnion shaft, that must be removed.

Cut off the U bolts that hold the spring to the saddle.

Remove the bottom half of the trunnion saddle.

Jack up the rears so that the upper half of the trunnion saddle separates from the trunnion bushing.

Remove the worn out rubber bushing from the trunnion shaft.

Be sure that the trunnion shaft is clean and no pieces of the old bushing are stuck to it.

Using some waterless hand cleaner as a lubricant, slide the new rubber bushing on to the shaft, center it in the middle of the area where the old bushing was.

Let the rears down so the upper saddle contacts the trunnion shaft.

Install the bottom saddle on the trunnion, install new U bolts, and tighten.

Replace the home made retainer on the end of the trunnion shaft.

If I remember correctly the torque spec for those U bolts is well in excess of 1,000 ft lbs. so if you don't have a torque multiplier that will achieve that torque, have the U bolts torqued at a shop with the proper equipment, this is very important. Insufficient torque on the U bolts can lead to broken spring centerbolts, and broken U bolts, and possible damage to the truck and personal injury.

HK - That was a standard suspension trunnion set-up at one stage. I have a 1969 R model which has the same through bolt and cap on each end which was an original Mack fitment here in Australia. When you tightened up the U-bolts the rubber bush used to ooze out the same as in the picture. I broke a few of the through bolts when you did a real tight turn at slow speed- usually broke off at the end of the thread. The one I still have still has the original U-bolts and through bolt and plates. I fixed one through-bolt by making a one inch high tensile bolt and boring out the two end plates to fit. The dead axle on that model is a couple of inches shorter on each side than the later one which has the collar on the end with the bolt through it. Best regards - Michael.