Front Ride Height Variation

Lin · October 31, 2012, 03:38:41 PM

Playing around with this leveling system has brought up some other things. First, I found the the front leveling valve was bad. It would raise the bus, but it would not lower it until it leaked down. Now actually, that would be good enough for me under normal circumstances since that is all I really cared about. This is attested to by the fact that I did not even know there was a problem until I tried to lower the front. So I have replaced the valve now and all seems well. Also while underneath, I noticed that one of the front airbags has some checking around its base, so I guess I must put that on my list but not this month.

One thing that seemed curious to me was that the passenger side height is slightly higher than the driver"s side-- less than an inch. I would have thought that since they are on the same valve, they would be the same. Would airbags from different manufacturers do something like this? The parking spot is not 100% level but reasonable close, and I would not think it should effect anything. I thought that possibly an imbalance in the inflation of the rear bags might cause it, but if anything, the driver's side is a drop higher in the rear.

RJ · October 31, 2012, 07:24:12 PM

Lin -

This has been covered many times over the years, both here and over on BNO. Lots more info in the archives if you're up to doing a search.

But the Cliff's Notes version of the Reader's Digest version is this:

Three leveling valves on most air suspended coaches, one in front, two on the rear. (RTS is reversed.) Front controls front ride height only. Rear controls not only vertical ride height, but also port/starboard list.

Thus, after setting the front ride height correctly, you then set the rear. If the coach lists, either to port or starboard, you have to adjust the rear valves.

Not a bad idea to take the coach for a short drive after adjusting the front, then come back and adjust the rear.

Proper settings are in the shop manual under suspension. On GMs, it's measured between the rubber bump stops and the axle. I suspect the 5A is similar.

FWIW & HTH. . .

Geoff · November 01, 2012, 07:15:45 AM

Having the right side slightly higher than the left side is good for road crown. My bus seems to have been designed like that, I figure, after replacing the leveling valves and adjusting both sides the same.

Low Class · November 01, 2012, 08:20:07 AM

The way I read his post, the ground is more uneven than he thinks (my guess) or his bus is twisted (unlikely).

Low Class · November 01, 2012, 03:05:47 PM

" one in front, two on the rear. (RTS is reversed.)"

Why is the RTS designed this way? It does not seem logical. The only reason I can imagine is that it has something to do with the kneeling feature(quicker to drop and raise one corner) if the RTS has this.

RJ · November 01, 2012, 06:55:56 PM

Quote from: Low Class on November 01, 2012, 03:05:47 PM
" one in front, two on the rear. (RTS is reversed.)"

Why is the RTS designed this way? It does not seem logical. The only reason I can imagine is that it has something to do with the kneeling feature(quicker to drop and raise one corner) if the RTS has this.

Name??? -

Partially correct. Original RTS came with independent front suspension, not a solid beam axle like most. Thus, a leveling valve for each side up front.

Later models were available with a solid front axle, but, TTBOMK, the leveling valve arrangement remained the same.

FWIW & HTH. . .

Geoff · November 01, 2012, 07:00:34 PM

Wow, an oportunity to talk about my favorite bus. The reason that RTS's have the two leveling valves on the front rather than the rear is that the earlier RTS's had independent front suspension (A-Arms like a pickup truck). So the RTS's with IFS had two leveling valves at the front and one at the rear. The later RTS's went to a straight axle front end and the leveling valves changed from 2 at the front to 2 at the rear and one up front.

I have driven both the IFS setup and the straight axle RTS and I like the IFS much better. It rides better and takes the bumps independently on the front wheels rather than transfering the bump to both sides of the front end. Several buses stole this idea from GM and designed their buses the same way in later years.

--Geoff

Low Class · November 01, 2012, 07:56:35 PM

thanks for the replys. design makes sense now.

Name??? -

Not sure what you are asking. I will guess at an answer.
The day I registered to the board, I had just read an article that said to be middle class we need to have an annual income of $50,000 to $150,000. That solidly put me in the low class category and that is my story. My name is Jim Keefauver from East Tn.

buswarrior · November 01, 2012, 08:35:25 PM

Excellent back story!

Be careful, ride height has a significant effect on suspension geometry.

Steering can be influenced by improper ride height.

One of the first things to check in a coach that steers/tracks badly.

happy coaching!
buswarrior

John316 · November 01, 2012, 08:41:41 PM

Quote from: Low Class on November 01, 2012, 07:56:35 PM
Name??? -

Not sure what you are asking. I will guess at an answer.

Jim,

It is nice when folks sign at least their first name. RJ is usually really good at replying to folks, and he is very knowledgeable, having been in the bus industry for years. He also does a great job of reminding folks to sign their first names....

FWIW

John

uncle ned · November 02, 2012, 08:13:57 AM

name

Jim "low class"

You need to realize that most of us here are retired. at least some of us are and that makes really low class as far as income.

If that is not enough the"busnutism" will make sure we never have much money left.

They "BUSES" eat it in large quanities

uncle ned

Oonrahnjay · November 02, 2012, 08:26:31 AM

<=== Retired. Low Class income. Bus note & broke.

Quote from: uncle ned on November 02, 2012, 08:13:57 AMJim "low class"
You need to realize that most of us here are retired. at least some of us are and that makes really low class as far as income.

DaveNCari · November 02, 2012, 09:12:26 AM

Even many folks that do "normal" alignments have no clue the effects of ride height on handling...

We measure ride heights on the Firestone Indy Lights and Izod Indycar Series cars to the THOUSANDTH of an inch.....and a really sensitive driver can feel as little as .003.....

Does anyone out there have any known good numbers for the PD4104 in terms of F&R ride height and camber/caster and toe?? Of course...with the solid axle there is not much to adjust I guess...

Dave

Lee Bradley · November 02, 2012, 10:36:29 AM

My Cityliner was setup with two valves on the front and one in the rear. I didn't like having the bus being torqued it's length so I moved the side to side operation to the rear which seems to be the standard.

RJ · November 02, 2012, 06:42:57 PM

Quote from: DaveNCari on November 02, 2012, 09:12:26 AM
Does anyone out there have any known good numbers for the PD4104 in terms of F&R ride height and camber/caster and toe?? Of course...with the solid axle there is not much to adjust I guess...

Dave -

All of those numbers you're looking for are in the Maintenance Manual.

A quick check: Parked level, the distance from the ground to the top of the bottom step should be between 14" > 15". An RV "bullseye" bubble level on the floor next to the shift lever should be centered. Adjust accordingly.

FWIW & HTH. . .