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How to Adjust Ride Height Valve?
Still performing first maintenance and late today checked the ride height and discovered the rear is slightly off and I would like to get it right on the money per Prevost’s spec for my H3.
Can someone please tell me if this type of ride height valve is adjusted by moving the rod within a boot(s) OR if it is adjusted by loosening the sole nut at the valve, then moving the arm? Thank you very much, Jeff
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10 Replies
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Adjustment is made with the rubber boots on the ends..
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Jeff, Before you try to get a ride height adjustment made exercise your coach using level low, up, down tilt left, tilt right, etc, and after every position return to the ride height and re-measure.
The arm on the ride height valves has a “dead spot” at ride height that shuts off air in and air out. But even if that dead spot is accurate within 1/2 of a degree of movement of the arm it will have a measurable affect on the ride height.
You can adjust the ride height until the cows come home, but the best you can hope is the ride height averages what is called for in the service manual. It is rarely going to be exact.
2000 Featherlite H3-45
2024 Jeep Grand Cherokee
Leesburg, FL -
Had my ride height adjusted at JoSam’s and front end aligned, in that order. Shop manager made the tech do the alignment over (at their cost). He said once the ride height is changed it changes the alignment.
Chuck
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Great info from all – sincere appreciation.
I did not mention the fact my steer axle ride height is at least an inch too high. (I did not mention it as I clearly see how to adjust the steer valve)
AND I TOO, and just a over a month ago had an alignment performed at Josam’s in Orlando as I was very nearby. I asked the tech to check ride height, but apparently that was not done.
The main reason I wanted a check of ride height is that I have felt that perhaps all air bags had too much air as the ride is pretty darn rough at bridge transitions and poor pavement. (Smooth as silk on good pavement – all air bags are +/- 3 years old and Koni shocks were installed all the way around this calendar year)
Now that I have for sure confirmed the front is too high by at least an inch, I wonder how lowering the front air bags will adversely impact the alignment. I live just north of Houston so a return trip to Josam’s is not practical. Thoughts? THANK YOU
***EDIT – Guess I should have waited to reply until after I exercise the air bags as Jon describes… Maybe that will make the difference… Will advise
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Ride height changes dramatically effect alignment, especially on vehicles where both the front and the rear ride height are adjustable. Adjusting one end effects the other end so it is not a simple twist and go operation. There is enough hysteresis in the suspension that the coach needs to be driven (or exercised as Jon indicates) to get it to settle into where it is going to be going down the road before re-measuring ride height once it has been changed at one end or the other. Only when ride height is correct can alignment be performed.
In the front wheel drive GMC motorhome community this is especially a problem. There, the rear ride height is determined by air pressure in the bags much like our Prevost, and the front ride height is adjusted by twisting torsion bars. With those coaches if the rear ride height is off, the front will be very hard to get right due to the weight transfer that takes place.
I built alignment kits for that community because I found that even experienced alignment shops would routinely drive a GMC onto their alignment rack, take an alignment reading and then jack up the front end to make it easier to reach the alignment cams which were located on the upper a arms. They would let the coach back down and then use a chain or bar to jiggle the front end and re-measure the alignment. Satisfied, they would punch the button to print out what they felt was the perfect alignment specs and drive the coach off the rack. The unsuspecting customer would drive the coach home only to discover that the front end settled down on the way altering caster, camber and toe in the process.
To get it done right the owner had to get ride height correct front and rear, which required blocking the coach at proper rear ride height, then setting front ride height to spec, then driving the coach two to ten miles and checking it again until it was correct after that drive. Then they could either go to an alignment shop, or use one of my kits to set the alignment insisting that the tech NOT jack up the front end in the process.
I doubt if our front and rear air bag suspensions are quite as touchy, but likely some of the same forces and hysteresis are at play.
The other exacerbater with GMC motorhomes is the spec on ride height is +- 1/4″ while the spec on the ride height controller is +- 3/8″. Go figure!
Jerry
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Each increase in height on any of our coaches is brought about by an increase in air pressure in the respective air bags.
But do not expect a 1″ reduction in height in the front is going to magically provide a smooth ride. First recognize that there is a significant change in how 315 tires handle things like expansion joints and bumps in the road compared to 365 tires. I hate the extra noise made by 365 tires hitting bumps as well as the increased harshness. The only thing you can do apart from adjusting the height to slightly reduce the air bag pressure is to make sure the 365 tires are not over inflated. The pressure I would expect to see required is around 100 for the tires but that is totally dependent on front axle weight.
The tag 365 tires ARE over inflated. The lowest pressure on the charts calls for 80 PSI, but if the required pressure is calculated using the formulas used by the tire industry the tags will likely have a 70 PSI inflation pressure. The reason such an oversize tire is used on the light weight tag axle is because that becomes your spare tire source.
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I should add that for my coach the pressure required to bring the front to ride height is about 100 PSI. That also happens to be the pressure limit printed on the rubber casing of the air bag. To increase the height another 3 to 4″ to the upper limit takes a little less than 120 PSI. It is unlikely the small difference in pressure required to lower the coach to the specified height will make much difference.
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If your interested, the “Prevost Service Manual” for your coach is available.
The procedure for setting ride height is on page 16-10 of the service manual. (PDF page 906)
Just another source of information.
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Thank you all once more for sharing your experience and links. Yesterday I exercised the suspension by moving up, down, and corners independently then re-measured the rear and decided to leave well enough alone! I never would have imagined that exercising the suspension was necessary.
2000 Featherlite H3-45
2024 Jeep Grand Cherokee
Leesburg, FL -
The only reason for exercising the coach up and down and side to side is to get an average. Because of the dead spot in the ride height valve, and because the height is going to vary depending on the direction you are coming from when you hit the dead spot the best you can hope for is when you average the highest and lowest measurements taken you end up with the specified height.
You will drive yourself absolutely nuts if you don’t do that.
Having said that, you can adjust to the correct height if you adjust the coach to the correct height, and insure the arm on the valve is in the center detent. If not adjust the rod connecting it to the chassis so it is in the detent. But them measuring to verify the setting you still have to go up and down and rely on the average.
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