Skip to main content ↑ ↓
Topic: Ride height question (Read 2474 times) previous topic - next topic

Ride height question

I had to move the coach to be able to pull the rear wheels off today. After moving and raising the bags to the max to make it easier to put the jacks under the rear end, I realized I had blocked access to get my trash out today for tomorrow pickup. When I started the coach back up I didn't want the extreme driveshaft angle when pulling forward again. After staring I waited for the bags to deflate to ride height. Nothing happened, put it in gear with my foot on the brake, still nothing. Then released the parking brake with the brake pedal still depressed, still nothing. If I would have moved it like that it would have been very bad for the u-joints. I then dumped all the air after which the coach rose to the correct ride height. Is this normal? If not where would I be looking for the problem?

Thanks, Chuck

Re: Ride height question

Reply #1 –
Chuck,

Our coach occasionally has a glitch when going to normal ride height. Very occasional so I don't worry about it.

When going down river washes to the beach in Baja, I will frequently drive with my fingers on the HWH keeping the coach as far off the ground as possible. Should keep both U joints in a parallel line and not as likely to cause damage as when one is a a different angle from the other. As long as the rear axle does not rotate but moves in a vertical plane, there should not be a problem.

When leaf spring cars are built for the drags, the rear end may be installed at a three degree difference so when power is applied, the rear end will rotate on the leaf spring bringing both U joints parallel to each other. Non parallel U joints will send power in pulses to the rear end and may cause damage to components. With air bags in front and behind the rear axle assembly, the bags keep the movement vertical so the housing never rotates.

Pierce

Re: Ride height question

Reply #2 –
Quote from: Pierce & Gaylie Stewart –
Chuck,

Our coach occasionally has a glitch when going to normal ride height. Very occasional so I don't worry about it.

When going down river washes to the beach in Baja, I will frequently drive with my fingers on the HWH keeping the coach as far off the ground as possible. Should keep both U joints in a parallel line and not as likely to cause damage as when one is a a different angle from the other. As long as the rear axle does not rotate but moves in a vertical plane, there should not be a problem.

Pierce
Raising the front doesn't change the driveshaft angle the engine goes up with the coach and the rear end always stays the same height. Not the same as a front engine vehicle. I had both ends raised to the max and the driveshaft was almost touching the frame. I will be duplicating the move later today or early tomorrow. Will post a pick of how severe the angle is.

Re: Ride height question

Reply #3 –
Chuck,

In a rear engined diesel pusher as the rear end is raised or lowered to change the apparent angle, the pinon and yoke U-joints still remain in a parallel line. The principal is the same whether front engined or a rear pusher. Yes, the drive shaft does have an angle to it and appears to be not in alignment with the transmission or third member but as long as the pinon and yoke centerlines are the same, it's OK unless the distance between the two parallel lines is too far apart. Here are two attachments of correct and incorrect driveshaft alignment. A short driving distance of greater than 3-5 degrees won't make any difference in wear. A picture is worth a thousand words.

Pierce

Re: Ride height question

Reply #4 –
From a far less technical standpoint - in the FT Manual / HWH manual, it says that you can drive with the airbags manually raised outside of travel mode, but that they suggest limiting speed to 5mph.

(Edit: For our 1999)

Re: Ride height question

Reply #5 –
Also, to answer your original question.:

Mine has done this before as well.  Raised the coach manually like Pierce described when going over what I felt was a large hump to enter a parking area so that we didn't risk scraping.  When I let go, it didn't lower.  But I was in a parking area maneuvering to let the coach rest for the night.  We were moving at slow speeds, so I didn't worry about it and continued my business.  Two minutes later when I was parked, the coach must have slowly worked it's way down to a normal ride height without me noticing.  I keep an eye out for similar behavior, but I haven't categorized it as "Attention Required"

Re: Ride height question

Reply #6 –
Quote from: Pierce & Gaylie Stewart –
Chuck,

In a rear engined diesel pusher as the rear end is raised or lowered to change the apparent angle, the pinon and yoke U-joints still remain in a parallel line. The principal is the same whether front engined or a rear pusher. Yes, the drive shaft does have an angle to it and appears to be not in alignment with the transmission or third member but as long as the pinon and yoke centerlines are the same, it's OK unless the distance between the two parallel lines is too far apart. Here are two attachments of correct and incorrect driveshaft alignment. A short driving distance of greater than 3-5 degrees won't make any difference in wear. A picture is worth a thousand words.

Pierce
This is the angle I was worried about. Yes the shafts are in the same plane, but very severe angle.

Re: Ride height question

Reply #8 –
Were you at correct ride height when you took those pictures???

Re: Ride height question

Reply #9 –
Quote from: wolfe10 –
Were you at correct ride height when you took those pictures???
No!
I had the coach raised to service the slack adjusters. The original post was that I didn't want to move it at that height and it didn't automatically lower when in gear and the brake off. I had to manually dump the air then it did raise the coach to correct ride height. I was asking what system is supposed to lower it automatically to prevent damage.

Re: Ride height question

Reply #10 –
Chuck,

Yes, excellent photos! While the angle IS quite a bit and you certainly would not want to drive on a trip with it like that, moving the coach won't do any kind of damage. The rectangular tubing has been relieved so at the limits of the air bag extension, the U-joint won't hit the tubing. When the coach is raised to maximum height and driven down river washes like I do, there is no chance of damage. The operating manual does NOT warn against driving with the bags at their maximum extension.

When we see 4WD trucks, jeeps, etc with lift kits, the drive shaft is operating at much higher angles than stock. They daily drive with the driveshafts at extreme angles. 15 degrees is considered maximum for street use as the angles can increase to 30 degrees in off road use. As the angle increases, the torque capacity of the U-joint is reduced and may fail with application of much power over 30 degrees. To cure this problem, some operators change to CV (constant velocity) joints where the maximum angle can be doubled.

Bottom line is with our coaches at maximum height, they are safe to be moved or raised to go over uneven terrain without a failure. 

Here is a quote from a 4WD parts store blog: "All suspension lift kits alter the driveshaft angle and can result in vibration, a short u-joint life, or even sudden and total failure if you don't correct it at the time a lift is installed. Basically, every degree of driveshaft angle above 10 degrees shortens the life of the universal joint and increases vibration. Consider a continuous operating angle of about 15 degrees the practical maximum at normal ride height. When the suspension flexes, about 30 degrees give or take depending on u-joint size, it's put in the area where it could bind and break. The torque capacity of a universal joint also decreases with angularity."

Here is a photo of a replacement drive shaft lengthened for use with a lift kit. This is the normal operating angle.

Pierce

Re: Ride height question

Reply #11 –
Could it be that Fortravel believes the coach will automatically lower itself that no warnings are mentioned?

Re: Ride height question

Reply #12 –
From the HWH manual:

"NOTE: The system monitors the transmission speed
switch. The system will not allow the suspension to
move to the MAX position, UP or DOWN when the
vehicle is moving faster than the setting of the speed
switch. This is usually between 5 MPH to 15 MPH.
If the suspension is set to the MAX position, when the
setting of the speed switch is exceeded, the system will
default to the MED position. This would be normal ride
height for the vehicle."

This would indicate to me that slow driving in max position is perfectly fine as long as the vehicle is somewhere between 5 and 15mph as set in the speed switch by the manufacturer.

Looks like this explains why your coach didn't come down to normal ride height when you started it. It either had to be lowered manually using the HWH controls or the 5 to 15mph speed exceeded.

Pierce

Re: Ride height question

Reply #13 –
That explains it. My system is probably fine, I can't get up to speed in my driveway.
Thanks for the info.
 Is that info in the big books that came with the coach or is it on HWH's website?

Re: Ride height question

Reply #14 –
Pierce, you are right about FT cutting enough clearance, but barely enough and you can tell the used a cutting torch to make the clearance.
 

Re: Ride height question

Reply #15 –
Here is the official HWH operator's manual but only for this HWH model: http://www.hwhcorp.com/ml55121.pdf Foreforum members should note that their systems may have a different control panel and may or may not require the buttons to be held down to keep the bags in max position. Use the operator's manual that is applicable to your model by searching their site.

Chuck,

Good eyes! They did a crude job of cutting the tubing for clearance. Ours is exactly the same. I would have expected a flat bar to be bent to the contour of the relief and then welded. The cutting torch job weakens the tubing and may allow cracks to develop. This is shade tree work that an expensive coach should not see! (not that I haven't done some myself)

Great series of posts and opinions. This is how we all take away new knowledge each time we read the forum.

Pierce