SECTION 13
12. REPLACING HUB SEALS
Notice: This procedure is a description of the steps I took to remove and replace the hub seals on my coach. The following is not intended to replace or be used in lieu of procedures or instructions from Prevost Car Inc. and they have not been approved by Prevost Car Inc. Anybody that follows these steps assumes full responsibility for the work and any consequences as a result of that work.
12.1 Description
One of the more common issues with a Prevost is the leaking of hub seals. This problem is identified usually by the presence of oil in the back of the wheels or if the coach has been sitting for a while on the ground next to the wheels.
Apart from requiring replenishment of the oil in the steer or tag axles, or of oil in the differential, a leaking hub seal could ruin the brake pads or brake linings leading to poor braking and an expensive brake repair.
The replacement shown is for a bus with drum brakes, and the steps will be different for a bus with disc brakes, but the concept is the same.
12.2 Scope of work and tools
Replacing a hub seal requires removal of a wheel and tire, brake drum or caliper assembly, wheel hub, and requires two jacks or supports. While the tasks are not complex, the hub, and drum, especially on the drive axle are heavy and if a rolling floor jack or some similar means of lifting and moving the heavy components is not available, the job may require more than one person.
Some of the tools required will include a socket wrench of sufficient size to loosen and tighten the large hub nut. On my coach a 4” was required for the drive axle, and a 2 ½ was required for the tag or steer axle. I bought these at a local truck parts supply store and they were relatively inexpensive. I bought the 3/4” drive ratchet wrench in a kit through Northern Supply (558385, $100), and it will be used for other tasks on the coach so it is a good investment.
The screws holding the drum to the hub were difficult to remove. I fashioned a tool to use with my impact wrench to loosen them, but Sears has a drag link kit to be used with a ½” socket wrench (0934299, $20).
Removal of the seal was done with a seal puller, but it could be done with a pry bar. Once removed in this way the old hub seal will be destroyed.
I remove my wheels with a 1” impact wrench, but I also have a 12 to 1 gear reducer when I have no source of shop air. Whatever you use to remove the wheels, be aware when they are reinstalled they must be torqued to the correct values for your type of wheels, usually 500 to 550 foot pounds.
Other tools required were fairy common and include a socket set to remove the hub cover, a scraper to clean the gasket surfaces, a funnel with a long tube to make refilling easy, and in addition to the new hub gasket I used gasket seal.
I tend to take advantage of the fact I have something disassembled to clean and inspect everything I can in the area of the repair. I would estimate each hub seal replacement can be done in less than 2 hours, but if you have trouble removing the brake drum screws or spend time doing other tasks it could take longer. Each axle has a hub seal at each end for a total of six on the coach.
12.3 Disassembly
Remove the wheel. The brake drums (or discs) have to be removed next, so adjust the slack adjuster to loosen the brakes so the drum can be removed. Information on adjusting slack adjusters can be found in the brake section. The picture shows the drum in place. After the brakes are relaxed, remove the flat head screws to slide the drum off. Do not try to loosen of remove the flat head screws unless you have a tool that fits precisely. They can be corroded in place and if you ruin the slot (they can be slotted or Phillips) your only option will be to drill them and remove them with a bolt extractor.
It should be noted that you do not have to remove the brake drum or discs. I have written the procedure with the drum removal because of the combined weight of the components, especially the rear axle components. If you have a means of supporting and moving the drum and hub they may be removed as an assembly. In fact, the wheels may remain in place also, but be aware the weights, especially the dual wheel rear assembly are far greater than the average individual can handle without specialized equipment.
The following picture shows the brake drum removed. Notice in the photo that a jack is used to support the axle and a second jack is used to support the coach at the support point on the chassis.
Remove the cover exposing the hub spindle and nut. Note the photo below. Thegear oil will spill once the hub cover is loosened. Catch the oil in a pan or tray.
Loosen and remove the nut and pull the hub assembly from the spindle. The pieces of gasket still adhering to the hub will have to be scraped off before a new gasket or seal is applied.
The picture above is of a drive axle with the hub removed.
If the axle you are working on is the drive axle there is no hub cover to be removed. You have to pull the axle shaft to access the nut. That sounds scary, but it is easy. Around the end of the axle are a series of bolts. Remove all of them. There are two ways to slide the axle shaft out. The easy way is to hit the end of the axle with a big sledge hammer. (Don’t laugh, that is what the tow truck driver is going to do if you have to have your bus towed). The axle will pop out slightly and you can pull it the rest of the way. The other way is to thread three of the bolts you just removed into the three unused threaded holes that were in the end of the axle. As you tighten the bolts the axle will slowly slide out to the point at which it will freely slide completely out. I like to bang on the end of the axle with a sledge hammer. It is more dramatic.
At the rear of the spindle will be a greasy mess that must be cleaned so the new hub will seal properly.
Remove the old hub seal from the rear of the hub.
Note that when removing the old hub seal there is a potential to get dirt and debris in the bearings. Use caution, but if any dirt does get into the bearings the bearings need to be removed and cleaned.
Insert the new Hub seal in place.
It is very easy to damage the new hub seal, so its insertion should either be by the use of a tool specially designed for insertion, or by placing a flat board on top of the entire seal and gently tapping it uniformly in place with a hammer.
If the metal portion of the seal is dented or bent in any way, the seal will not work properly.
12.4Assembly
Reassemble by reversing the process listed above.
Tighten the nut snugly, but not so tight the bearings bind. Make certain the “lock” is in place so the nut will not back off. Failure to do this could result in the loss of the wheel and the entire hub assembly. The Prevost manual recommends tightening the nut until the wheel binds and then backing off the nut ¼ to 1/3 turn to assure .001/.007” end play and to insure the wheel turns freely.
A new gasket should be used when replacing the cover. When refilling with oil use the oil specified in the Prevost manual (Multigrade gear oil, MIL-L-2105-D, 75W90 for northern climates and 80W140 for southern climates). As the oil is very thick and tends to flow slowly the refilling process takes time because the oil has to slowly seep through the bearings. Be patient.
The drive axle is filled through the plug in the differential, and normal coach movement admits oil into the bearing area. Side to side slopes of the road allow the flow of lubricating oil into the bearings, but you cannot rely on this to occur naturally before damaging the bearings. Before driving the coach you must insure lubricating oil is in the bearing area. That can be accomplished by raising one side of the axle to allow oil to flow into the bearings or by pouring some oil into this area.
Readjust the slack adjusters so the brakes are ready for road service. The procedure for adjusting slack adjusters is outlined in the brake section.
When filled replace the rubber plug in the cover, reinstall the wheel, and give yourself a pat on the back for a job well done.
Because this repair involves the potential for hub and wheel loss and possible brake failure it should be done with extreme care. If in doubt get professional assistance.
The procedure shown was for a drum brake coach with manual slack adjusters. The procedure for a disc brake coach and a coach with automatic slack adjusters will vary slightly. Removal of the brake calipers will be required, in addition to disc removal with the hub.
Jon W. Wehrenberg12/17/05