bogie wheel locking the brakes

[David Anderson]

Now after I tested all my brakes, my bogies are locking up on a hard application.  I heard them do this on wet pavement about a year ago, too.  Sounds like they are too light, but I measured the weight with my jack with a pressure gauge and I am showing about 3700 force lbs on each side.  According to Dan Lentz posting on the eagles board that is correct.  My ride height is 13.75" measured from the rails under the bays.   

I did not change the brake cans on the the bogies since they are only about 8 years old.  My rod stroke is 1 3/8".  Max stroke limit per eagle book is 1.75".

What is causing this? 

David

[buswarrior]

What size chambers are on it?

If bigger than spec, that'll do it, bigger chamber, stronger push, tire slides.

Have you changed tires recently?

Tags and bogies are a challenge to keep rolling sometimes...

Happy coaching!
Buswarrior

[luvrbus]

Does your Houston Metro Eagle have the 2 brake relays 1 for the bogie and 1 for the drive axle ?

[David Anderson]

Does your Houston Metro Eagle have the 2 brake relays 1 for the bogie and 1 for the drive axle ?

Don't know.  I will crawl under tomorrow and look.

[David Anderson]

Does your Houston Metro Eagle have the 2 brake relays 1 for the bogie and 1 for the drive axle ?

Yes it does.  Do you think I need to replace the R8 relay for the bogies?  The R8 relays for the drive and bogies are tied together in series as it is shown in the drawing attached. 
David

[David Anderson]

I checked the weight with my 12 ton jack that has a 10000psi gauge on it.  The psi on the gauge with the tire raised to barely touching the floor was 1750psi.

The piston diameter of the jack is 1.64" with a caliper gauge.

Formula is diameter squared times pi divided by 4 times psi weight

Check my math  (1.64 x 1.64 x 3.14)/4 x 1750 = 3696.88 force lbs on the bogie axle. 

My axle weight is within range.  If I adjust one spline it will go to about 4200 force pounds which is a bit heavy according to Dan Lentz from Eagle. 

[DoubleEagle]

Assuming the relays are okay, if you have manual slack adjusters, I would back them off a click or two from where they are normally adjusted. If they are automatic ones, then you might need to go up one spline. Moving weight around in the coach to put more weight on the bogie might help. It would seem desirable to get the right balance so that you don't create flat spots on the tires during brisk stops. Tire pressure levels might also affect the braking action.

[lovetofix]

If all else fails you could add a pressure regulator in line between the relay valve and the bogie brake cans. That is what My MC-9 has from the factory, it just puts a hard cap on the max pressure those brake cans can receive. It will not affect the braking at all until you give it enough peddle to hit the ceiling you set for it.

[buswarrior]

Hang on, is your measurement outside the jack? What is the potential error rate for being wrong with the diameter or the real air pressure?

Maybe go find the local scale and roll the bogie onto it and take the calculations out of it, get the real weight?

If your calculations have inflated the weight, that is critical, they need enough weight on them to prevent sliding.

I am big time lazy, don't go replacing stuff based on potentially flawed calculations! Cuz, it will still flat spot the tires after all that work!!!

Happy coaching!
Buswarrior

[DoubleEagle]

The calibration of your jack gauge could be off if the pressure gauge is not accurate even though your calculations are correct. It might be difficult to get a bogie weighed on just one side, depending on how the scale is set up, and it might be difficult to find a known weight to place on your jack. A good gauge like the Norco 78021 is calibrated for PSI readings and for weight in 12.5 or 22 ton sizes, and the gauge costs more than either size bottle jack (well over $200).

[chessie4905]

take it to scales. Calculations are fine, but in this case, scales give you the actual and then you'll  be able to check your math. Oh, and don't  use the one at your local stone quarry.

[windtrader]

take it to scales.

Any suggestion on options for getting a weight for each corner? When I got my bus, I went to one of those scales at truck stops and was able to get the front and rear weights which is fine for all practical matters. More out of curiosity would be to know how balanced the bus is starboard and port.


Who would do that sort of scale weighing and what sort of extra cost would one expect to pay for an all four weigh?

[chessie4905]

Cat scales at major truck stop. Google it.

[David Anderson]

I am showing   7300lbs on the two bogies with the jack gauge.
I am showing 10353lbs on the two fronts with the jack gauge.
   Total          17653

My coach is 36000 wet, but right now about 1000lbs short on water and fuel, so 35k lbs would be a good total.

35000-17653 = 17347 estimated weight on the drives.  Pretty darn balanced. 

I need to find out the number on my bogie cans.  They may be 24's instead of 16's.  That would be an easy fix.

Also, I may have to get a couple of air gauges and check pressure output from the drive and bogie relays with a brake application.

This all just another opportunity

[David Anderson]

I put a gauge on each R8 relay on the service output fittings for the drive brake and bogie brake and both read 60psi with a treadle brake application.  That eliminates an air relay issue. 

It sure appears I need to adjust the torsion spring 1 spline each and add 500 lbs of force.  Ugh. That will put it just above 4000 lbs each.  Dan Lentz doesn't recommend that weight. 

https://eagles-international.net/forums/viewtopic.php?f=15&t=46&sid=55f0efb759fa90b05f9ab7d757e10e30

Not sure what to do. 

David