[Archived]

I presume not to pack the hub bearings in grease since they are immediately bathed in gear oil at first drive. Can someone confirm this?

Are the hub to rotor bolts one time use stretch bolts? I have not read that they are.

[Archived]

Dan,

Front and tag axle hub bearings are in oil for certain as soon as the hubs are filled to the proper level and the wheel is slowly rotated. Unlike the drive axle hubs you are certain these are lubricated as soon as everything is put back together and the oil is refilled.

One thing to be sure of is the oil level. Since the oil is so thick and does not easily flow it appears to be filled quickly as you put oil in it. But it takes time for the oil to flow between the rollers on the bearings so after a period of time what looked like a full hub may actually look empty. So it takes a little time filling the hubs, and also be sure to not over fill them. Finally, make sure the pin hole that is in most of the plugs is open because that is how the hubs breathe.

[Dick]

Anybody happen to know what size socket is needed for the adjustment nut and jam nut on the front hub? Would like to get it before starting the procedure. Thanks.

[Archived]

Going by memory…..2 1/2″, but that was on a drum brake coach.

[Raymond]

Just finished swapping in new front rotors, pads and inner seals. It was a physically challenging job. The rotor weighs 75 pounds, hub probably 50 pounds, caliper slack adjuster brake chamber assembly probably 50 pounds, could not use air tools on the hub to rotor nuts of which there are 10, 130 pounds torque. The hub jam nut was a 2 1/4 inch socket. The adjustment nut had no flats on the outer circumference, but two round holes on the face in which one can use right angle needle nose pliers to make the adjustment. Before I took the hardware off the axle, counted the number of threads showing through the jam nut, and used that count to prexactly reinstall. Took about 2.5 days. Working on the oil fill now, cold weather means slow flow.

The front rotors had cracks when we got it 9.5 years ago (60,000 miles), but we never had a problem. The challenge now is to try to drive in such a way as to not crack these. The tag rotors have never cracked, maybe because Prevost put 16/24 chambers there. Couple years ago I changed those to 30/30, and still no cracks. Now all three axles are on 30 service brake chambers.

I enjoyed doing this project, it is my way of playing golf.

[Archived]

Dan,

Great post. Can you explain “Prevost put 16/24 chambers there. Couple years ago I changed those to 30/30, and still no cracks. Now all three axles are on 30 service brake chambers. “?

What is the difference and why did you change them from original?

Thanks,

[Per]

Dan, Two concerns because I worry about stuff.

The hubs at all positions have a specified procedure in the Prevost shop manual available on line for tightening the hub nuts. One procedure I have read requires a specific torque and than to back off the nut a certain number of degrees, and the other procedure I remember called for a runout of a couple of thousandths. Whatever it is for your particular vintage it should be followed to the letter. Too loose or too tight creates problems that show up as a damaged bearing or a worn spindle. The damage takes time to be seen but in both cases it gets expensive.

As to changing to 30 brake chambers that alarms me because when our coaches are engineered the size of the brake chamber and in some cases relating to drum brakes the friction material is sized for a balanced brake application. If you put the same size shoes or chambers on a lightly loaded axle as a more heavily loaded axle (service brakes) the lightly loaded axle locks up sooner than the more heavily loaded axle. Under almost all driving and braking conditions this is not an issue, but when you have a panic stop you have an un balanced braking system and the ABS (if equipped) comes into play. As a racer you likely would not have ABS on a race car because a skilled driver can modulate the brakes and get better performance, but in street cars, trucks and buses the ABS is used to compensate. If your ABS kicks in on your tag which has a brake chamber with twice the normal brake force you have lost some braking force as it cycles.

A 16/24 for example is an odd size and from an economic perspective the temptation to go to a 30/30 is great, but I found I could buy a 16/24 piggy back combo and a 16 service chamber and swap parts to create a 16/24 almost as cheap as a 30/30 or 30/36.

[Corey]

John, the oem tag chambers on my vintage were 16/24. I’ve never known what the numbers mean except that the bigger the number, the more air volume the chamber uses, the more braking force is produced. The first number is the service brake and the second number is the parking brake. Since my tag and steer use the same rotors and pads, and since the steer is a 30 chamber, I wanted the tag to provide more braking contribution than the 16 was providing. The risk is, as Jon mentioned, the tag could lock up or kick in the ABS on low traction surfaces. But since the tag is positioned on the back and since it carries only about 8,000 pounds while the drive carries 27,000 pounds, I was comfortable with the risk. Though the braking performance is now better, I can never be happy with the stopping ability of our rigs.

Jon, the maintenance manual that came with ours says to tighten the hub adjustment nut to 100 pounds while turning the hub in both directions, then back off, then tighten again to 50 pounds, then back off 1/3 of a turn and done. Spec run out is 01″ – 10″. Since the adjustment nut had no flats to use any kind of wrench, did not use any torque specs. But did tighten it with right angle needle nose pliers until the hub would no longer turn, then backed it off about 1/3 turn. Did this a couple times. But the confirmation of adjustment was after installing the two indexed washers and jam nut, that I had prexactly the same amount of stub axle thread showing through the jam nut as before I started. The jam nut spec is 300 pounds and is what I did.

[Rudy]

All I can say is I will never screw with my braking system. With all the engineering that goes into it, with all the certification testing required, the engineers had to know what they were doing. If I wanted to get bold, before I made any changes, including one of such significant proportions as changing brake chamber size I would speak to the engineers.

I have zero concern about changing the parking or emergency brake to a different, especially larger, size with one exception. The service brake modifications are what I would be concerned about.

The parking brakes with larger chambers are going to hold better. That is a good thing. The exception to my feelings on that is if the emergency brakes deploy it is a spring brake, not controlled by ABS and if it locks a lightly loaded tag axle as a result you know a sliding tire has virtually no traction so you know emergency stopping distances are going to be compromised.