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Old 12-11-2016, 10:50 PM   #1
Rd1
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Have Freightliner Steer tag axle or plan on buying one, watch how the tag steer works

If you have a Freightliner chassis with passive steer tag axle, or plan on purchasing one, you should review this TSB from Newmar. This highlights certain problems with the design/production of the steer tag axle on Freightliner chassis.

https://comnet2.newmarcorp.com/insta...s/BLTN458P.pdf




I have a 2017 LADP. The very day (august) I drove this out from the dealer, I noticed the coach was wondering about too much. I called both Newmar and Freitliner and asked the alignment to be checked. Unfortunately, I was not aware of the above TSB or existing problems with the FL tag axles. I listed my issues here on this forum some 3 months later and thats when a couple of helpful people pointed out to me the existing TSB and tag axle problems. Thank you.


So far we have had 5 attempts in dealing with the alignment issues and the problem persists.
After each and every attempt, I was assured by Freightliner, all is well and every thing is within spec!
I have had 8 tires replaced within 8000 mi. the tag sets were replaced twice. (FL must have very good deals from Michelin!).


The coach started having some vibration/shuddering from the rear end in about 4k-5k miles. FL claims it is normal. So I placed a camera behind the tag wheel to see what is going on.


There is a plunger actuated by air valve, one on each side. Once the plungers are extended, they are supposed to keep the tag wheels straight. The plungers extend, when the speed is over 20-25 mph, or when reverse gear is selected, or when the parking brakes are applied.


The plungers retract when speed drops below 20-25mph, or when parked and parking brakes are released and the coach starts moving forward.


The camera was placed behind the passenger side tag wheel. The test consistently highlighted a delay from the driver side retracting the plunger and then a few seconds later the passenger side retracting. Great majority of time, during this delay, the tags started turning to the left, while the coach was tracking straight. In a few cases, it remained straight. The steering of tag occurs likely due to road camber or loading on left rear.


There is also a delay during the time plungers extend. The driver side extends first, then some seconds later the passenger side extends. Perhaps, this is by design. I do not know. However, during plunger retracting, there is clear evidence the tags do steer to the left, even though the coach is tracking straight. I believe this is the reason for slow speed vibration/shuddering I notice. As the tires are dragged and bounce over the road. This will also cause some tire wear over time.


We made two 30 min recording before rain started. Due to clouds, the first recording is a bit difficult to see. The second run we added a flash light which helped.


Run-1, was driving on a state hwy coming to a red light. As the coach slows down to 20-25, you will hear the air release. Then, if you look at the lower left of the video, you will notice the toe link/control arm starts moving to the right and steering the tag to the left, indicating the driver side plunger has retracted. And seconds later the passenger side plunger retracts. Once the coach starts moving, you'll hear the air valve closing. Then the toe link/control arm moves to the left, steering the tag to the right, to center the tag, indicating the driver side has extended. Then seconds later the passenger side plunger extends.
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Old 12-11-2016, 10:58 PM   #2
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Run-2, added a flash light with the same passenger side view. Also placed a white line marker on the plunger to observe its movement. This recording started while at speed approaching a red light. In this view you can observe the steel plates on the tag wheel itself where the plungers make contact to keep the wheel straight. Once again, the air is released. The steel plate and tag wheel steers to the left , indicating the driver side has retracted. Seconds later the passenger side also retracts. In this case, the light turned green before coming to a full stop. As the coach speeds up, the tags straighten up (Driver side extended) and seconds later the passenger side is extended.


In this view, you will also notice the steel plate seems to have developed a grove where the plunger makes contact. This begs the question, what happens over time as the grove deepens? There will invariably be a gap developing which would potentially compromise the integrity of the tags wheels to remain straight and constant at speed.


More testing when time permits.
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Old 12-11-2016, 11:09 PM   #3
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I was looking forward to seeing the video but my iPad came up with could not be loaded, format not supported?
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Old 12-11-2016, 11:54 PM   #4
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John, here is the mp4, should work on ipod.
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Old 12-11-2016, 11:57 PM   #5
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Run-2 in mp4 format
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Old 12-12-2016, 01:07 AM   #6
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Hmmmmm.... I have ran steerable lift axles on 18 wheelers....... I wonder if you don't have enough caster on the axle or have enough weight on the tag??? could be either one... or sumpin else all together... such as needing to add a steering dampener or a tie rod....similar to what is available on the aftermarket for off roaders front axle??? just letting mind wander and wunder a bit is all...
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Old 12-12-2016, 08:37 AM   #7
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Following, although I hope/think we are not experiencing this (yet).

Surely RD1 is, was, or should have been an engineer. Really good info - thanks!
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Old 12-12-2016, 07:09 PM   #8
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Hmmmmm.... I have ran steerable lift axles on 18 wheelers....... I wonder if you don't have enough caster on the axle or hl...

I have had 5 visits to freightliner dealers for the alignment. one hopes they know what they are doing. experience shows otherwise, unless you know a place that does have qualified people.

Just looking at it, would "guess" 5-6 degrees of castor. should be more than enough to keep the wheels centered and minimize steer angle. The discrepancy in the plunger retracting and releasing is peculiar. Unless one of the diaphragms in the air valves is damaged. The plungers had a gap of 3/8 for the first 7500 miles or so, before it was corrected during the third attempt to fix the alignment. Makes you wonder why the first two freighliner dealer missed that setting!!!!

With that 3/8 gap, the tag wheels were free to steer back and forth at speed and wack the plungers. I have raised that issue with FCCC, however they say all is within specs!!! They are in denial. Perhaps more tire replacements might get their attention.
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Old 12-13-2016, 08:42 AM   #9
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Have you considered making an appointment at the factory Gaffney SC?
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Old 12-13-2016, 09:11 AM   #10
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Tried to schedule visit, they were booked, had one visit scheduled, they canceled because of some construction work. I am out west now.
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Old 12-13-2016, 09:19 AM   #11
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Maybe they will work with you and get your problems taken care of because your problem is very good advertising for Spartan. Good luck.
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Old 12-13-2016, 12:00 PM   #12
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Thank you for posting video. Was initially unable to open using Mac's Safari web browser, yet it did open using Firefox. GOOD LUCK and please keep us posted
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Old 12-13-2016, 04:05 PM   #13
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Interesting. So the two tag axle steers appear to be free castering, not connected together in anyway and lock straight with the air pin mechanism. So what happens if the driver side during a slow left turn hits a large rock or pothole, which displaces it in the opposite direction of what was going on before hitting the obstruction, while the passenger side hits another rock/pothole and heads off in the other direction? Wildly unlikely but could the front of both tires swivel in opposite directions thus simply dragging along?

Wonder if the Spartan chassis steer is also of the same design?
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Old 12-13-2016, 07:05 PM   #14
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...Wonder if the Spartan chassis steer is also of the same design?
Gosh. I hope not...but, anybody got a Spartan they want to volunteer to the OP for the case study and the greater good?
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