Help! Allison transmission control problem!

[michaeldterry]

I sent the following inquiry to Firestone a couple of days ago:

I've just had a new set of Firestone FS 400 tires installed on my 1996 Prevost XLV conversion bus (45 feet long) and am trying to determine the correct tire pressure at each axle end to insure safety and long wear. I'm confused about how to use the inflation tables and need guidance. I've had the bus weighed and have a weigh ticket that gives me the weight on each axle (steer, drive, tag). To match up with the inflation charts, do I divide the weigh ticket numbers by 2 for the steer axle, by 4 for the drive axle (duals), and by 2 for the tag axle to find the correct recommended psi on the chart? When I divide as stated above, I find that the individual derived tire position weight numbers for the drive axle are below the lowest number on the chart, which makes me think I'm doing something wrong. Please help! Thank you, Michael Terry

Today, I got the following reply:

Michael,
You are using the right method to determining the individual tire loads from the weight data.
As you already know, the tables represent a maximum load at several minimum inflation pressures.
The table does not extend below 80 psi because this represents a minimum inflation pressure no matter how lightly loaded you are.
However, for your Prevost I would recommend that you maintain 100 psi in your steer tires and 90psi in your drive and tag axle tires.

Michael Hayn
Engineering Manager
OE Truck/Bus Tire Accounts
Bridgestone Americas Tire Operations LLC
535 Marriott Drive
Nashville, TN 37214
615-937-3460 office
615-584-4711 cell
haynmichael@bfusa.com

What do you guys/gals think of what Mr. Hayn suggests?

[garyde]

Hi Michael. Yes. Although, I keep about 105 in my drives and 110 in my front
365's.

[hhoppe]

Mike: As an example my 45 Ft. Liberty weights are as follows:

Total Weight 47,450 Lbs.

Left Front 7500#------ Required Air Psi. 115 #
Right Front 7600# -----Required Air Psi. 115 #
Left Drivers 10,050#---Req.uired Air Psi. 100 #
Right Drivers 9100#----Required Air Psi. 100 #
Left Tag 6500 # -------Req.Air Psi. 90 #
Right Tag 6100 # ------Req.Air Psi. 90 #
Tags up Drivers # 15,700#
These weights were aquired using individual scales placed under each tire location courtesy of Weights & Measure personel S, Dakota State at one of our POG Ralley's in Spearfish, SD.
Best to use your own coach weights. Under Inflation causes heat and tire failure.
Safe Travels to you.

[Ray Davis]

That matches completely with what was suggested in previous posts. As I've mentioned, generally our drive wheels are lightly loaded (at least on a non-slide) coach given the load carrying capacity of the 4 wheels.

I ran 100 pounds in mine, even though mine, like yours, are off the bottom of the chart.

I run 115, 100, 95 in mine.

ray

[michaeldterry]

I found this info this morning by searching Prevost's Online tech manuals in the "Wheels, Hubs, & Tires" section:

13.1 Recommended Tire Inflation Pressure (Cold)
Inflation pressure should be checked when tires are cold. Driving, even for a short distance, will cause the tire to warm up and the air pressure to
increase. Check inflation pressure on all tires using an accurate tire gauge.

The maximum loading tire inflation pressure (cold) for 12 R 22.5 tires are as follows:
Front axle....................................115 psi (792 kPa)
Drive axle......................................90 psi (620 kPa)
Tag axle ........................................95 psi (655 kPa)
Note: It is recommended that all tires on coach be of the same type.
Note: Tires are considered cold when the vehicle has not been driven for at least three hours, or driven less than 1 mile (1,6 km).
Driving, even for a short distance, causes tires to heat up and air pressure to increase.
Note: Never bleed air from hot tires as tires will then be underinflated. Use an accurate tire gauge to check pressures. (Do not kick tires as an inflation check. This is an unreliable method).
Caution: In the case of a converted vehicle, weigh vehicle fully loaded and pressurize according to tire manufacturer's recommendations.
Caution: These tire pressures are established in accordance with the maximum allowable load on each axle. A lower pressure is recommended if the axle load is less than the above specifications.

My tires are 315/80R22.5, so I guess the following would apply?:

RECOMMENDED TIRE INFLATION PRESSURE AT MAXIMUM LOAD (cold)

Tires 315/80R22.5
Front axle.............................................. .................................................. ............................100 psi (689 kPa)
Drive axle.............................................. .................................................. ..............................90 psi (620 kPa)
tag axle .................................................. .................................................. .............................80 psi (551 kPa)
Spare tire (if applicable)....................................... .................................................. ..............100 psi (689 kPa)

Caution: In the case of a converted vehicle, weigh it fully loaded and pressurize according to tire manufacturer's recommendations.

My guy at Apalachee RV reviewed all the information so far and recommends 120 psi in the steers and 110 psi on both the drives and the tags.

So many options, so many ways to screw this up!

[Ray Davis]

Where are you getting those numbers?

Your front weights were 15,200 if I remember correctly. In the Firestore tables, that's a minimum of 110 pounds. Where in the world are you getting 100 pounds for your steers?

Here is the values for your tires.

tirepressures.jpg

I don't see where you are getting 100 pounds for your steers, if you are weighing in at 15,200? I see 110 pounds.

And as the Firestone guy said, I personally wouldn't run 90 pounds on your drives, I would bump it to 100. That's just my personal opinion. Obviously, that's not required, but allows you some extra carrying capacity.

Ray

[GDeen]

Tire pressure is a case where more is definitely better from a safety perspective

[Jon Wehrenberg]

I'm zipping up my flame proof suit so feel free to respond.

Do you think if it is this hard to figure out how much air to put in your tires you should be driving one of these buses? Especially considering that is something that should have been on the to-do list for the first pre-trip inspection.

Seeing all these posts, especially with the diverse opinions leads me to believe that if I asked if everyone is doing the pre-trip brake inspections I would be getting the "deer in the headlights" look.

Come on guys.

[sawdust_128]

I'm zipping up my flame proof suit so feel free to respond.

Do you think if it is this hard to figure out how much air to put in your tires you should be driving one of these buses? Especially considering that is something that should have been on the to-do list for the first pre-trip inspection.

Seeing all these posts, especially with the diverse opinions leads me to believe that if I asked if everyone is doing the pre-trip brake inspections I would be getting the "deer in the headlights" look.

Come on guys.

O.K. there Sunshine. Who was it that pissed in your cornflakes today?

Deer in the headlights???? Not hardly!

[michaeldterry]

Where are you getting those numbers?

Ray - "where I got those numbers" was from Prevost's online technical manuals in the "Wheels, Hubs, & Tires" section. I wasn't saying that they were appropriate for my/our application - in fact, the reason I posted that info was to highlight the wide range of inflation/load numbers out there which add to the confusion of "what's right" for idiots like me!

At any rate, tomorrow I'm going to adjust the steers to 115 psi and the drives & tags to 100 psi. After reviewing all the diverse specs, suggestions, recommendations, and opinions - those are the numbers that make the most sense to me. I'm now realizing that I way over analyzed this and turned what should have been a simple process into a royal cluster f%#k!

I realize that I'm driving you guys crazy with idiot questions and for that I apologize. The problem is that, since my accident my lack of mobility/dexterity prevents me from digging in and figuring out stuff that I would have figured on my own in my former life. It often leaves me to "depend on the kindness of strangers" these days. The good news is - I do eventually learn and retain what I'm taught (or take damned good notes)!

Also, while at the bus tomorrow, I'm going to pull the shift pad module out of its frame and see if I can clean the pad contacts on the back to resolve my shifter issue. W.W. Williams has obtained a new shifter module from Alabama and will install it for me, but the parts are over $1,300 and with labor/time/etc the bill will be over $2,000. The other option is a "shifter repair kit" that they can get for about $100 from the Greer, SC location, but after labor, tax, tag, & freight - that option would be almost $800 and the tech said he can't guarantee that the repair kit would resolve my issue. (We wouldn't know until after they "installed" it and then I would have "bought" it and might still have an inoperable shifter) Soooo... before I "jump off the cliff" with one of the expensive options, I figure I've got nothing to lose by seeing if it's as simple as a dirty or corroded contact on the pad. We'll see....

Sorry guys....