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757driver · 08-31-2018, 06:59 PM

With the case of my front axle being very heavy I have sought solutions to the problem over the last few years. During my 2 year PDI it was brought up to Entegra but for the most part the problem was swept under the rug. It was brought up to Spartan but they referred back to Entegra and said they were overloading the front of their chassis with the house they were putting on top. I upgraded my batteries last year to lithium and moved the location to the rear center of the basement but the front axle was still heavier than I would like (left front 8350 lbs, right front 8770 lbs for a total of 17120 lbs).

A glimmer of light was illuminated last year at Homecomming by big Mike from Spartan in that he mentioned that there was an adjustment (pressure regulator) on the tag axle to control the weight that it carried and thus the weight (or lack there of) that was transferred to the front axle. Attempts were made to adjust this pressure regulator but all was in vane. It seems several years ago this user adjustable setting was removed from the tag axle because (in a quote from Spartan) “motorhome manufacturers were abusing the setting to remove weight from the front axle and severely underweighting the tag axle.”

That pressure regulator that is attached to the tag axle dump valve is to control the amount of air that is released from the tag axle when in reverse or by holding the tag dump. According to Spartan this should be set at 25psi so that not all the tag axle pressure is released when it is activated.

My only solution to reducing weight from the tag and thus the front axle (think teeter totter) was to install a separate pressure regulator. The entire process turned out to be very simple except for having to install zip ties one handed while reaching up in the frame.

I mounted the pressure regulator on the back wall of the wet bay and removed the factory line that runs to the tag axle dump valve and ran a new 1/4” line (7’) to the inlet of the regulator. From the outlet of the regulator I ran a 1/4” line (10’) to the tag axle dump valve.

During initial testing I set the pressure on the new regulator to max pressure to see what pressure the tag axle was at to start with. During reading of old forum posts as they pertained to tag axle air bag pressures it appeared that with older (about 2008 and previous) Freightliner and Spartan chassis manufacturers and owners were setting tag axle air bag pressures at 40- 55 psi to have a properly balanced coach. My tag axle pressure was 90 psi!!! According to Spartan this is a preset value that is regulated from what pressure is in the drive axle air bags. My tag axle at a recent weighing at Spartan was carrying 11000 lbs while the drive axle with twice as many of the same tires was carrying 15540 lbs. A little lopsided to say the least. The tag should as a general rule carry 1/2 the weight the drive axle carries. I am not sure how Spartan regulates the tag axle pressure but perhaps on some coaches it was not installed or has failed allowing for an increase in air bag pressure at the tag.

I have set the tag axle pressure at 50 psi to start and am anxious to take it to a local CAT scale to see how much of a weight reduction I have on the front axle. Initial looks of the clearance above the drive tires as compared to the tag axle tires have the two much closer to being the same while at ride height compared to premodification where the clearance above the tag tires was much higher than the drive tires.

brobox · 08-31-2018, 07:49 PM

Super interesting post Don, thanks. Let us know the weight change.

fla tom · 08-31-2018, 07:50 PM

Please please post more explicit parts list and install procedure..I need this mod thanks in advance.

gizmo123316 · 08-31-2018, 07:54 PM

I totally understand your viewpoint Don. I used to own an '08 Beaver and had the ability to adjust the tag axle air pressure, but just left it the way it was when I got it. I think the pressure was around 80 lbs. Don't know if the front was heavy or not, never did get it weighed. Now that I have four corner weights, maybe some air pressure adjustments would be appropriate in order to lighten the load on the front axle so that I can lower the tire pressures a few pounds for a smother ride. I think I'll make the adjustable pressure gauge one of my future projects.

757driver · 08-31-2018, 07:56 PM

Quote:

Originally Posted by brobox

Super interesting post Don, thanks. Let us know the weight change.

Chuck,

Will do.

Gasman 2 · 08-31-2018, 08:48 PM

Good post Don,
Appears to me Spartan and Entegra needs to put their heads together and get the weight balance to where it should be rather than pointing fingers at each other.
I questioned a Spartan tech about taking so weigh off the tag his response was: "oh no can't do that could lock up the tag brakes on hardbbraking and cause ABS issues. I guess they don't want the brake system do what it's designed to do.
Go figure.

Johnontheroad · 08-31-2018, 08:49 PM

My ‘09 Camelot had a adjustment for tag axle pressure. Here is the effect of the different pressure had on not only tag weights but drive wheels and front axle weights. Ended up using 45# pressure for the tag adjustment.

Edit: I have tried to paste the spread sheet here but no luck. Email me and I will send you the complete spreadsheet.

John

757driver · 08-31-2018, 08:53 PM

Quote:

Originally Posted by fla tom

Please please post more explicit parts list and install procedure..I need this mod thanks in advance.

Parts consist of:

1) Pressure regulator 1/4” with gauge. $35.00
2) 90 degree press to fit swivel fittings 1/4” $11.00
2) Pieces of 1/4” DOT air line one 7’ and one 10’ $10.00
17) Feet of 1/4” wire loom $4.00
5) Zip ties

Total cost $60.00

This applies to a 2014 Anthem. The referenced locations on your coach may be slightly different. No warranty is expressed or implied with doing this modification. Do so at your own risk.

Raise the coach and secure. I built 8” high ramps to drive up into. Dump the air suspension by extending the jacks until the front and rear airbags release the pressure and then turn the jacks off. Check that the air bags are deflated.

On the inboard left frame rail (DS) in between the drive and tag wheel disconnect the airline from the tag dump valve that runs forward to the drive axle air bags. There is one other air line on the tag dump valve which runs to a T fitting with lines running to each tag air bag. To remove the air line push the collar in while pulling the air line out. Remove the zip ties that secure this air line as you move forward. Release the other end of this air line where it attaches to a manifold also on the DS just forward of the drive axle.

Mount the pressure regulator with the 90 degree swivel fittings attached (use pipe dope or Teflon tape) in the wet bay rear wall just above the door latch. Drill 2 appropriate sized holes through the wet bay into the front drive axle wheel well high up in the wet bay. Check where you are drilling first. Don’t drill too close to the out board edge or too high up or else you may run into metal frame work. The height above the pressure regulator allows for a gentle 90 degree radius bend to attach the air lines to the regulator.

Cover the air lines with the 1/4” wire loom. Run one airline (approximately 7’) from the pressure regulator input to the drive axle air bag manifold push to connect fitting. Cut the tube square with plastic tube cutters. Push the new line fully into the connection until it is firmly seated. Run one air line from the output of the pressure regulator to the input of the tag axle dump valve. Run both airlines at the front of the wheel well ceiling (where other wires are run) and go over top of the left frame rail and run them towards the rear. Watch the routing for pinch points. Secure the lines with zip ties. Caulk the holes you drilled in the wheel well.

Increase the setting on the pressure regulator to maximum. Start the coach and set high idle. Retract the jacks once air pressure builds to a value over 100 psi on the dash gauges. The suspension should now inflate (if not push all retract again). Watch the new gauge in the wet bay and see what the pressure increases to. Decrease the setting on the pressure regulator by a few turns and then dump the pressure by holding the tag dump switch for 10-15 seconds. Release the tag dump switch and watch what the pressure on the new pressure regulator builds to this time. Repeat as necessary until you get the pressure down to about 50 psi. Check the new fittings (4 of them) for air leaks. Weigh the coach and note the decrease in the weight on the front axle. Adjust the pressure regulator up or down as necessary to get the desired results. Reweigh as necessary. DO NOT unnecessarily decrease the tag axle pressure to lighten the tag and front axle. I would not want to go lower than about 40 psi on the tag axle. Any weight removed from the tag and front axles gets transferred to the drive axle. DO NOT overload the drive axle.

757driver · 08-31-2018, 09:06 PM

Quote:

Originally Posted by Gasman 2

Good post Don,
Appears to me Spartan and Entegra needs to put their heads together and get the weight balance to where it should be rather than pointing fingers at each other.
I questioned a Spartan tech about taking so weigh off the tag his response was: "oh no can't do that could lock up the tag brakes on hardbbraking and cause ABS issues. I guess they don't want the brake system do what it's designed to do.
Go figure.

Richard,

I think they have since 2016 for the most part when they moved the batteries from the front DS to the rear of the basement and moved the chassis air tanks to the rear between the tag and drive axles BUT having said that there are still problems such as David (DeeGee) with his 2018 Anthem.

I would agree that if the weight on the tag axle was reduced too far then braking efficiency could be reduced because the ABS would be working/cycling too soon. Older coaches that had 8000-9000 lb tag weights with (I am sure ABS braking) reported no problems with tag axle reduced braking or ABS issues.

As with anything push a good thing too far and it could turn into a bad thing.

757driver · 08-31-2018, 09:11 PM

Quote:

Originally Posted by Gasman 2

Good post Don,
Appears to me Spartan and Entegra needs to put their heads together and get the weight balance to where it should be rather than pointing fingers at each other.
I questioned a Spartan tech about taking so weigh off the tag his response was: "oh no can't do that could lock up the tag brakes on hardbbraking and cause ABS issues. I guess they don't want the brake system do what it's designed to do.
Go figure.

Richard,

It’s funny that you mention a Spartan tech conversation. On two separate occasions speaking with two very senior Spartan techs they both told me to get Entegra to install a proportioning valve to reduce the tag weight but that they would not do it.

fla tom · 08-31-2018, 09:35 PM

Don where did you order these parts? I don’t know wear to look.

757driver · 08-31-2018, 09:46 PM

Quote:

Originally Posted by fla tom

Don where did you order these parts? I don’t know wear to look.

I got the parts at my local Princess Auto here in Cambridge but I would thing that you should be able to find the parts on Amazon or at Fastenal. The pressure regulator is the same sort that would be used on a air compressor.