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shock absorber replacement
How do I tell if my 1991 XL needs shock replacement. Mileage is 140,000. If so which shock? Can’t miss something I never had. Thanx guys.
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18 Replies
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I have bought OEM shocks from Prevost. At 140,000 if the shocks are original it is probable you are going to see a significant change in how the coach rides with new shocks.
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Had my shocks changed (Prevost Ft Worth) because one was leaking on my 1991 57,000 mile coach (they were original equipment) a couple years ago and it seemed to take the sway out of it. They also adjusted ride height valves and after handled like a dream compared to what it drove before.
I think they are Monroe, well, they are Yellow.
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I changed all 8 shocks around 155k ($800 installed at Les Schwab). Made a big difference on secondary curvy roads taken at speed. Much less hobby-horsing- sometimes felt like I was on a boat before. Bus tracks much better now. Highway ride remained the same. I was hoping new shocks would prevent the wheels from thumping into pot holes. Not so.
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“I was hoping new shocks would prevent the wheels from thumping into pot holes. Not so”
Are there bushings that need to be replaced?
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Hi ThreeGreens,
What manufacturer’s shocks did you install? I had Koni’s on my steer axle but I swapped them for stock Prevost shocks which I believe are Sachs. After my initial inquirely, Prevost(TN) fessed up that they think the Koni’s are too stiff, even on the softest setting. I like the ride of the stock shocks but I did give up some of the razor-sharp handling, a worthwhile tradeoff in my opinion.
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I think there are many benefits to the Koni shocks, especially on the front axle. Koni has 5 adjustment positions you can choose from. As they come out of the box…. Factory set at soft position. With the aid of my ramps I tried each position and road tested. After this I went back to soft setting and really like that ride.
If you say firmer ride I agree. Judging the overall performance of the Koni I’ll agree somewhat with Prevost comments. Keeping in mind the front ends of our buses are heavy weights. I think we need a better shock in this position to help save the front end parts. Also, keep tires from rippling the outside edges of the tires.
When I traveled with the Prevost OEM shocks I had more movement up and down. Koni seems to reduce the continued travel limiting to one single flex set at the soft position.
AL
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Hey Al, what are your parameters for the “H” your searching for ?
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Since the purpose of the shocks is to limit rate of the travel of the suspension when hitting a bump so the bus will not bottom out or experience a great amount of rebound any shock that accomplishes that is what is required.
I think Prevost has done a pretty good job of reaching a compromise between controlling the up and down motion while providing a nice ride. I think a “stiff” shock for me personally will detract from the soft ride quality I want. I hope the racers on here will jump in because I sense some attribute handling in the corners with the shocks and that simply is not true. Our ability to maintain a relatively flat stance through the corners is controlled by the sway bars. The only time a shock resists leaning in a corner is if there is a very sudden and large movement of the steering wheel such as an emergency evasive maneuver and that resistance to leaning is only temporary.
If there is a harshness to crossing a pothole or expansion joint use softer shocks which will help, but I found the 365 tires (compared to the 315) might be a factor but that might be an illusion because of the increase in noise level.
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Jon is correct in this matter.
Shock absorbers is a misnomer. The correct term is “dampers”. The job of dampers is to attenuate the inherent oscillations of the suspension assembly. These oscillations occur constantly as we drive but are most pronounced when crossing sharp bumps or dips. Tire imbalance is another oscillation that the dampers have to tolerate but that is off the subject of handling for this purpose. Any harshness or softness of ride is due to the rate of damping of these oscillations.
Sway bars (more correctly “anti-sway” bars actually are what minimizes the tendency of the bus to roll when placed in a situation where centrifugal force is induced by a turning motion. Thus the anti-sway bars are a variable spring resistance to roll that play no part in ride softness or harshness when traveling in a straight line.
The air bags (“air springs”) resist roll but are llimited in this function by the rate at which they can change pressures and react to roll due to built in rate damping devices.
As far a Koni’s adjustability; if the most desirable ride is found to be at the softest position, it’s damping range is incorrect for the application. Properly fitted, the ideal ride will tend to be at the middle of the setting range.
My personal finding is that the stock shock from Prevost is a screaming deal and I can change them every 30-50,000 mile for a heck of a long time and save the cost of Koni’s.
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It does seem pretty certain to me that new shocks helped in handling curves quite a bit. When I first bought my bus a road marked at 55 or 60 MPH that had a curve in it would scare me to death. It felt like I was going to tip over. I even experienced the feeling on interstate curves. I do not drive fast at all but curves had me really slowing down. I am not even talking about a 90 degree turn. Even a long slow curve seemed dangerous.
When I mentioned this to a bus friend he suggested shocks. I replaced the shocks at Prevost Nashville and that tipping over sensation was completely gone. Maybe the old shocks were just so bad that new shocks made this difference. Maybe it was all in my head.
Davy
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Bill Jenson has said that the OEM shock is a 30,000 mile part,I have the Koni shocks and I expect them to last for the life of the coach which might be a savings over the long haul.I have my Koni shocks in the stiffest position and that suites me,as Jon said that might be the racer in me.The Koni shocks are so much better than the OEM ones that a employee of mine that has driven my bus on occasion said that the Koni will get you into trouble because it drives so well and THEN you are in a corner TOO fast.
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Davy,
The shocks are not going to make that scary curve treat the coach any differently. If you want the coach to avoid excessive leans in a curve slow down, or increase the diameter of the (anti) sway bar, or increase the size of the flow path for air into the air bags. Period.
As stated previously if you throw the coach into a curve with a hard and large application of steering the shocks will provide a temporary and short lived resistance to leaning, but that will never be evident in any case except extreme steering unputs.
Jack’s post is correct. If the oem shocks have outlived their usefullness it will be evident in how the coach reacts to certain road irregularities. Some dips will cause a coach with bad shocks to bottom out. Other bumps will cause the coach to seem like it is leaping back in the air after the coach has bottomed out. Good shocks will stop those issues.
If the coach is overweight or near the axle weight limits good shocks become very important to ride quality.
1999 XLV X-6872, liberty #440 -
I’d bet Prevost specs their shocks for passenger buses where ride is #2 right behind safety. Unless shells have different shocks than seated coaches, I’d suggest they aren’t the best speced shock for our application. I put Konis on the front and love the ride. In fairness to Prevost, I never experienced the ride of new Prevost shocks on the front which may have been just as good. The good news for those that like the ride of Konis, they will never have to buy shocks again.
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I once removed the steer axle shocks on my old bus and drove around the block. I wouldn’t advise anyone to do this but what an eye opener! I learned very quickly what failed shocks feel like on a bus. Besides having trouble staying in my seat I also gained an appreciation for the tire oscillations that occur. This happens at around 10Hz and is actually the tire sidewall resonating. Modern day shocks are true marvels. If you feel anything like a 10Hz vibration coming through the floor it’s time for new shocks! 🙂
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So the feeling you got David was “shocking”?
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