Pressure on tag axle - Printable Version
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+--- Thread: Pressure on tag axle (/showthread.php?tid=257)
Pressure on tag axle - Brad Townsend - 10-08-2012
I run 25 lbs of pressure on my tag and was wondering what others are running. After putting on new tires i don't want to drag the tag which has been the case in the past. My brake adjustment could be an issue, I plan on making a stop at Camp Newell on the 29th of this month and will have them check the brakes etc.
RE: Pressure on tag axle - Fulltiming - 10-08-2012
I run 25-30 pounds on the tag without any issues. I have moved it up as high as 45 psi to decrease the load on the drive axle below 20,000 pounds but that transfered too much weight to the front end. In sharp low speed turns you will drag the tag axle unless you release the air pressure on the tag from the dash. That will cause the rear end to squat so be careful, especially towing a trailer.
Newell has adjusted my brakes every time I have been in for service and have done an all wheel alignment once. I have not had an issue with wear on the tag tires.
RE: Pressure on tag axle - RussWhite - 10-08-2012
I am under the impression that on my '99 the tag air is not adjustable. I tried dumping it a few times to see how that worked, and the rear is so low I decided not to do that again. I recently replaced my tires and the tags were definitely the most worn of the bunch. The wear was even, they were just worn out. They were all due for replacement based on age anyway, so it was not an issue. Russ
RE: Pressure on tag axle - Brad Townsend - 10-08-2012
Michael,
I thought that with less pressure on the tag that the tag would be prone to dragging.
RE: Pressure on tag axle - Fulltiming - 10-08-2012
Brad, you are correct. The tag will drag less on turns with less pressure on it. There are other issues that cause me to keep mine up in the 25-30 psi range and in those ranges I do not have any unusual tire wear. I do dump my tag when making very sharp low speed turns, although it takes so long to dump that it probably doesn't drop more than 10 psi before I have completed the turn and put air back on the tag again.
RE: Pressure on tag axle - Brad Townsend - 10-09-2012
I think I have mis-lead everyone. What I was meaning by dragging is the tires locking up when coming to a stop because there may not be enough pressure on the tag. When I first got the coach almost 6 years ago I took it to Newell for some minor work and someone had adjusted the axle pressure to around 8 lbs which I did not realize for quite some time as I was leaving long rubber marks at stop lights accompanied with blue clouds of smoke. I thought something was wrong with the brakes so took it to a repair place and they said the brakes were adjusted ok and knew nothing about the adjustment on the axles. I called Newell and was then told that 25 lbs was the correct pressure. The adjustment made a difference but I still was able to lock up the tag on a hard stop and not the drive wheels. Every time I would lock up the tag I would loose about 1/4 inch of rubber which would result in a flat spot about 6 inches wide which then would make a thumping sound for quite some time. What a difference with the new tires in the ride and much quiter. I just was wondering if everyone else was running 25 lbs of pressure and weather or not someone else experienced locking up the tag tires when coming to a hard stop. I also release the pressure when making a slow sharp turn. I am wondering if there may be an issue with the brakes and plan on having Newell look at them when we go there on the 29th. of this month.
RE: Pressure on tag axle - Fulltiming - 10-09-2012
At 25 psi on the tag axle, and 100 psi pressure in the tag tires, I have NEVER locked up the tag axle. Newell has adjusted my brakes every time I have gone in for service. Make sure you let them know that your tag is locking up!! That is not common.
RE: Pressure on tag axle - Brad Townsend - 10-09-2012
Newell will be looking at the brakes for sure.
RE: Pressure on tag axle - Gordon - 10-09-2012
Brad,
I suspect someone put the wrong brake chambers on your tag axle.
I'm not sure, but I think I have 12's on my tag which has a very short stroke. If you have 16's or 20's I think they have a 1/2" longer stroke which would account for you wheels locking up. I have either 20's or 24's on my front axle, so my tag chambers are noticably smaller than my steer chambers. The drive axle is the standard 3030's
OR
Now that I that I think about it there may be a compensating valve used on some tag or pusher axles.
My 2 cents
RE: Pressure on tag axle - RussWhite - 10-09-2012
Brad/Gordon,
Here's my pennies worth.....
So far I have not been in a situation where I applied maximum braking effort. I would be very unhappy if my tag wheels locked up and flat spotted. My ABS may prevent that, but as Gordon suggests you also need to be applying an appropriate braking force to the wheels. We have all seen the lightly loaded wheels on an empty flatbed lock up when the 18 wheeler is just trying to stop for a light or slowing traffic.
I have attached a little blurb on brake chambers. I think you will find that the numbers Gordon mentions represent the number of square inches of diaphragm surface. As you know the force produced is proportional to the air pressure applied and the area of the diaphragm. I really don't think the length of the shaft has any bearing on the force unless it is extended to its maximum length and then the force stops at that point. That is why the point where you adjust the brakes is based on the extension and length of the rod when the brakes are applied. In a modern air brake system, the self-adjusters take care of that until it is time for new shoes/pads. So, as Gordon suggests, should the wrong chambers have somehow been installed, braking forces on the tag could be excessive and result in lockup.