BAC Forum
General Boards => General Discussion => Topic started by: Robert McCormack on May 04, 2016, 07:42:00 PM
-
Just returned from first outing after major upgrades to my 96 Patriot. The one thing that really needs improvement is the ride quality. I put a new set of Koni shocks for the Magunum 8 bag chassis I got from Hendersons but they are terrible, totally unacceptable. Teeth rattling jarring on bumps, pot holes and coarse seams of typical California highways and too much proposing.
I looking for other's experience on better matched shocks to this chassis for a decent ride. I run light, around 26,000 total with about 2,000 unused capacity at each end of the coach. Toyo tires set at 95 psi.
So what are others using ??
Bob McCormack
-
Bob, have you checked the ride height? If the height is not adjusted properly it can cause a rough ride and porpoising.
-
Yes, that was set correctly at the time the shocks were changed. Spent a lot of time getting the specifications for the bag height since it was not correctly set when I bought the rig. The air gauge seems to settle at 110psi.
I can't complain about the handling overall but the harshness of the ride seems to indicated the amount of force it takes to initially move the shock seems better suited to a much heaver motorhome. The porpoising is only excessive when hitting really big dips and bumps.
-
This I don't understand. Henderson's put Koni's on our coach last fall and the ride generally improved a bit over the factory Bilsteins, but overall the new Toyos that went on immediately prior rode a little stiffer than the factory Goodyears. Porpoising and stark bump reactions are pretty much history.
I don't know which exact Patriot coach model you have, as it's not in your Forum profile or signature, but 110psi was a bit much for our Monterey out of the factory. RVSEP weight testing found lower pressures more appropriate, and although fuel mileage may suffer almost imperceptibly, that made for a better ride. The pressure obviously can't go too low, but there should be a safe recommended minimum that can be determined.
The bigger improvement was in handling, but Henderson's addressed that with other amendments well beyond just shocks. Robert Henderson is very good about customer service and listening, so I'd give him a chance to hear your complaint.
Joel
-
I've got a 96 Patriot Camdon but still running Bilsteins, I'm a bit heavier and I run my toyos at 100. I've had some issues with porpoising usually in Louisiana where the roads seem to be tuned to the wheelbase of a 40ft coach ::). I actually busted a shock lower mount on my trip back from Florida last month.
-
Let me clarify things. The 110 psi is the pressure the pump is maintaining in the air bags. The tires are set at 95 psi. I just had the rig weighed at the Escapee park and found it's almost 4000 lbs below the maximum chassis listed weight of 30,000gvw for a 37 ft chassis. 2000 lbs of that is at the front, even though the Patriot has the generator in the front middle. I'm just one person and I don't have a lot of "stuff" so I'm running light compared to most folks.
It's possible the total weight is too low for the shocks to work correctly. What we call the "head pressure" in racing shocks is the force necessary to initially move the shock. Bumps are dampened by this "high speed" head pressure valving in the shock to take sudden forces such as bumps etc. This as opposed to the "low speed" valving which effects both chassis roll and up and down movement which happen more gradually. The coach handles fine, it's just the bumps, seams and pot holes are unbearable.
Of course if the roads here in California were not so horrible it might be ok but I can't go anywhere without first traveling over them.
-
Hey Robert, we had the same problem in our 98 Pat. Now I am noticing some of it in our Marquis but this air guage works better. When the air is over 110 there is no problem but as it gets closer to 100 it is bad and 90 pounds is just rediculous. The air ride starts bottoming at 105 and 55 mph on bridges etc.
I have found that the air needs to recover between bumps and recovery is getting slower. A weak compressor, air leaks and faulty pressure valves are some causes. Shocks can be part of the issue but Bilstines or Konies should do the trick with Konies being a bit better. No shock will do well if the air is disappearing too fast to recover properly from frequent bumps and holes.
My 2 cents
-
That's useful to know. I've never seen it below 110 and have on occasion seen it hit 115. However that might mean the gauge is not fast reacting. Any one try the little air restrictors such as "Safe Steer" sold by Henderson. They have different internal settings available to custom tune the flow speed. Source Engineering also sells a similar device but many only work on their custom setups for the specific chassis they work with.
-
So, I just got done inspecting things underneath and have found a tear about 10 inches long where one of the I beams, that the axle actually bolts to, is welded front and rear cross tubes of the main square structure that the air bags sit on. This is on the curb side front which would seem to indicated the bags are collapsing and main structure is going solid against the main chassis. That cuses the force from the axle to try and pull the I-beam upward where it is welded to the cross tube.
Leads to some needed information. The above would indicate insufficient air pressure in the bags or too rapid air movement out of the bag, which is the same as a collapsed spring. The questions become :
How much air pressure in the bags is too much. The more pressure, the stiffer the "spring" becomes. Too stiff hard ride, too soft and suspension bottoms out. Can they run at 115 to 120 ?
Is the air pressure adjustable, say at a valve or such. I'm thinking just because the gauge says 110 doesn't mean that is being maintained when the suspension compresses.
Would this be a good application for an air movement restrictor such as the Safe Steer ?
-
Robert,
There seems to be some confusion here with the relationship between the air pressure in the air tanks (dash gauge readings) and the pressure in the suspension air bags. The pressure in the air bags is controlled by the height sensors and it is well below the tank pressure. You will probably benefit from air flow restrictors and ping tanks, but there are no suspension modifications that will smooth out the roads in California or stop proposing on Louisiana roads.
The 96 Patriot was the first Magnum chassis that was built, and it was not known as the best riding chassis ever built, but you may be looking for something in the ride of that coach that is not possible especially given your weight.
Gerald
-
Thanks Gerald
I've made an appointment with one of the top RV shops in the area at the recommendation of the folks at Henderson RV in Or. It seems highly likely the front suspension has been "bottoming out" and hitting the compression stops on the chassis. They are going to start out by checking the actual bag pressure and flow to each bag along with the accuracy of the gauge and go from there.
This isn't a case of comparing the RV to a car or even a heady duty truck, I've towed and driven 5ths with MDT's to 18 wheeler so I have some reference to go by. I've never experienced such jarring over bumps and strips etc. in any type of vehicle. This goes far beyond "not the best riding system" category since it actually caused damage. Clearly something isn't working as it should. The idea of adding ping tanks and some valves, such as Source Engineering has developed specifically for ping tank systems, has merit.
Should know by the end of next week so I'll follow up with a report.
-
When I was shopping for coaches, I test drove Country Coaches, Beavers, Alpines, and a Revolution and they all had the inability to isolate the coach from potholes. On a smooth road it was liking floating on a cloud but as soon as I hit a pothole, that jarring collision with the pothole would be transmitted through the coach. I believe that DP are not engineered or designed to isolate the driver from rough roads like car mfrs do. I have been on a few newer Prevost tour buses that were as bad if not worse.
Bottoming out, porposing and leaning are definitely a sign of a problem but the roughness experienced when hitting potholes is pretty much the norm (IMO). If someone has been able to find away around this, I would like to know.
-
Robert, if you had Henderson's mount the shocks and paid to have them run their before and after test program, such problems as you described should have been revealed and fixes suggested at the time. We were certainly happy with our experience doing that. We had several modifications made, for mostly safety and handling - some pre planned and others following the test ride.
Did it cost a bit? Yup. But Robert Henderson freely discussed technical and other topics with us, and his staff and techs spent quite a lot of unpaid time going over issues with us and chasing frustratingly illusive air leaks. They are one of the most honest, customer-friendly, chassis-knowledgable family and team I've ever run across, which is why I suggested you call Robert Henderson and bend his ear a bit, and I'm glad you apparently contacted them.
Thanks also to Gerald for added insight regarding Robert M.'s particular model year coach. It sounds like Robert's enroute to resolving his primary issue, and it's not his Koni's. Motion control valves (what I assume Gerald means by flow restrictors) were added to ours, although I've read some articles or reviews that question their real efficacy or value on late model rigs. What we can say for certain is that the sum total of modifications made a noticeably positive change in our coach, and that's what any of us strive for.
Joel
-
Hi Joel
I had a recommended shop in the SF Bay area do a lot of work which included installing the shocks I got from Henderson along with set the ride heights to the factory bag measurements. But the roads around here are not that bad. It was a trip down to San Diego, over to Arizona on Hwy10 then returning by Hwy 40 to Hwy 5 back to the bay area that exposed me to some really poor roads.
I didn't expect a car or even modern pickup type ride but the intensity of the jarring at even minor seams and tar strips was way beyond anything I have encountered. But anything bigger was like there was no suspension, it felt like it would eventually do damage and sure enough it did. A 1/4 thick steel plate got torn, there is no way anyone would every buy one of these coaches if they experienced this level so I have to go on the belief there is a fundamental problem.
Being a professional race engineer, if I have to I can put measuring instrumentation in place and find out exactly what is going on. We'll be looking at making sure all the bags are in good condition, there are no restrictions or leaks in the air lines and find out what ride height really works for the weight I'm running along with probably adding "ping tanks" and the associated control valves.
-
Robert,
FWIW, my advice is to get the chassis repaired and not spend $ and time chasing bag pressure, etc. As Gerald noted, the pressure is controlled by the level adjusters and is less than what you read on your dash gauges. Making a mod to lower the pressure more will possibly get you into a situation where you will again bottom out.
We lost a bag in west TX a number of years ago and decided a drive home to AZ. It was the worst ride of our lives on highway so I have an idea of what you are experiencing.
Good Luck.
Steve
-
I guess what I'm unable to get across is, as it is now it is unusable. The ride is so harsh it "broke" the suspension member, that is beyond a miserable ride, it's scary. It could be as simple as one bag that for some reason is under pressured thereby allowing one side to bottom out or some other issue. It's a situation that cannot be ignored.
I'll find out one way or another.
-
Robert,
If the bags air up to the spec'ed height (~9.5 -10.25") they would seem to be OK. However, with 8 bags, you might have one that is not fully inflated but appears to be due to the bag on the other side of the axle.
Steve
-
I promised an update once the root of the problem had been discovered. The answer lay with both the ride height setting and the shock mounting location of the early 4 bag system.
First for those not familiar with how an air suspension works a quick review. The air bags are the springs. Their "rate", the stiffness of the spring, is controlled by how much air pressure is maintained in the bag. The more pressure, the higher the "spring" rate.
Ride height is also controlled by how much pressure is held in the bag, with more pressure the more the bag extends and raises the ride height. So ride height and the "spring" rate of the bag is directly related to the amount of pressure in the bag. And the amount of weight of the coach being supported by the suspension will determine how much pressure is needed to achieve the desired ride height, more weight more pressure.
However the "compression" rate for air in the bag is not "linear" but progressive. The amount of force to compress the air in the bag goes up in an exponential manner, meaning that each additional inch of compression will require a higher force than the previous until the air in effect becomes solid. A crude example would be while 100 lbs of force might compress the bag 1 inch, 200 lbs of force would only compress the bag 1 3/4 inch, not 2 inches. And each additional 100 lbs compressing smaller and smaller movements.
The Damage :
The amount of force that I was encountering actually tore the vertical part of the "I" beam to which the front axle bolts. The crack was at the location where the "I" beam is welded to the "U" channel that runs from side to side with the air bags at each end. In short the bags were in essence going "solid", as if there was no suspension, allowing the upward force on the axle to try and rip the "I" beam off the "U" channel.
Bag Air Pressure Issue:
The issue to be determined was if the bags were completely compressed to the point the "inner movement stop" was hitting the upper bag mounting plate OR if the "spring" rate of the bag had gone up so high that it was in effect "solid", not able to compress the air any further.
In this case when I first got the coach it needed to have the ride height and level checked and correctly set. I search the web and this forum for any figures and the best I could find was setting the bags at 10 3/4 to 11 inches at ride height which was done prior to actually using the coach.
After the recent trip and the discovery of the problem I took the coach to Leale's RV in San Jose, CA at the the advice of the folks at Henderson's, from whom I had purchased the Koni shocks recommended for the 1996 4 bag suspension as found on the Beaver and Safari coaches of the mid 90's.
Only after several conversations with the folks at Leale's and the engineer at Henderson's did we discover that in fact the bag height was too high. Fortunately there was a long term employee at Henderson's who remembered the correct height was 10 inches. Once the bag heights were set correctly the ride improved dramatically. The correct bag height was especially important in light of the fact that my coach runs well under the rated weight capacity at both ends thereby needing less pressure to achieve the desired ride height and ride rate. In essence the air in the bags were going "solid" and transferring the forces directly to the suspension structure instead of "absorbing" the movement of the axle. The "springs" were way too stiff.
As to Shocks
Unfortunately the original design of the bag system was deficient in using just a pair of shocks mounted to the axle rather than as on the later systems putting a shock at each air bag location. The amount of the "unsprung" weight of the axle, "I" beams and "U" channels, along with the leverage due to their location is too great for a pair of shocks with the size pistons used.
One of the advantages to being in the racing business is our access to shock engineers. I had one of the engineers from the Heavy Duty Division at Koni check out the suspension. He confirmed there was inadequate shock for the amount of forces needed to be controlled, the size of the internal pistons in the shocks being too small. In the absence of the ability to place a shock at each bag location a much more "robust" size shock is needed to correctly control the forces. In his estimation the common complaint of excessive "porpoising" in class A coaches has a lot to do with with chronically under shocked designs.
We are in the process of doing a rough calculation of the "unsprung" weight of the suspension and then will configure a shock similar to those used on the big off road race support trucks used in the long distance desert races. These will be a re-buildable and adjustable twin tube design, a one time purchase good for life .
I'll follow up once we have completed this upgrade.
-
Thanks for the update, Robert, and glad you're finally resolving the problem.
Henderson's is indeed one of the, if not THE, best resources for chassis issues. I don't know where you got the specs of 10 3/4 to 11 inches of Ride Height... hopefully not on this forum. Most coach specs I've seen were tucked snugly around the 10 inch parameter, as Steve mentions.
This may also go to why Monaco electrically overrode the raise/lower feature of HWH air ride systems. Rather than have people neglectfully driving around at highway speeds raised or lowered far from Travel Mode, Monaco set the system to automatically return to there once your finger was off the button. Full Raise, for example, may get me over some high object or help get my hitch over a driveway entry feature, and full Lower under a limb, but those settings out on the road with potholes, speed bumps, etc., would play havoc with no effective suspension in play.
-Joel
-
Very interested in what you come up with Robert, I would love to slow down the porpoising in my 96 Pat.
Keep us in the loop on whats going on
Thanks
Bill
-
I would love to slow down the porpoising in my 96 Pat.
We had Henderson install its SafeSteer restrictors on our PT ~5 years ago and were very pleased with the reduction of porpoising they brought about.
-
I know there are some that question if there is any real benefit from those little valves, and granted we had more done at Henderson's than just having those installed last fall; but there was a noticeable reduction in the "porpoising" and associated side-to-side roll afterward on our coach too, Joel. I'm sure they're making good profit on those "Motion Control Units" of their own in-house Steer Safe brand - there doesn't seem to be much to them. The price varies with valve size needed - ours were about $180 a pair, one valve for each of 8 bags, plus a couple man-hours labor, for around $1k total.
But if you invent something and it is simple and it actually works and satisfies customers, you deserve compensation. If you ever have the good fortune to have a personal conversation with Robert Henderson, you understand and respect his chassis engineering expertise. Robert's one of those few men I've known (my father, my brother-in-law that was an GM Regional service rep, a somewhat ornery old-boy service tech at the Kearney, NB, Ford dealership, and - while growing up on the farm - a couple neighbors of the Ott family) that must've came into this world with that singularly elusive mechanic's gene on their chromosomes, possessing an innate understanding the rest of us can only graciously envy and dream of having.
Whether it came from the new Koni FSD shocks or something else like the seemingly innocuous valves, or a combination of chassis changes/adjustments, the overall result on our Monterey was worth it. I thought the existing HWH ride control system was supposed to be handling everything by micro-managing bag air flow at least on curves if not bumps. Yet even though we haven't put too many miles down since last fall to thoroughly test things, there was in those miles a discernably improved muting of rock and roll.
Hmmm... I guess Elvis has left the Beaver.
Joel