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Old 11-10-2018, 12:56 AM   #1
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Alignment - Caster is Key?

I learned something new today. Had the alignment done today on the 329DS in advance of potentially installing a steering stabilizer. When I picked it up, the tech told me the Toe angles had to be corrected significantly and the Camber was OK.

Then he mentioned Caster. I had to ask what it was, and he explained that Caster is the steering angle; similar to the amount of angle in a bike fork. I'm a bike nut so I understood that part. Higher/longer angles in a bike fork are usually more stable at speed while shallower angles are quicker in reponse but can be twitchy.

The Caster angle in my rig at 5.7 degrees right, and 5.4 degrees left, was fractionally more positive than Ford high range spec by .3 degrees. I guess it's desirable to have the right Caster slightly higher due to road crown. He was almost apologetic that they didn't get it quite down to the spec due to the F53 design not accomodating the perfect adjustment cam he wanted to use. However, he then commented that the motorhome handled pretty good in both his before and after test drives; better than most (I don't think he was just buttering me up...). He thought the relatively high Caster angle had something to do with that. I think it handles OK too. Maybe Caster IS a key factor in handling. I'm just a motorhome newby, but I'm sure some more experienced people here have a better handle on this.

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Old 11-10-2018, 08:39 AM   #2
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My alignment shop had to adjust all 3. Toe, caster and camber. The caster was the hardest to adjust. After the caster was adjusted the steering wheel was finally centered and the motorhome drives great. No fatigue after driving 500 miles straight. No other improvements except CHF.
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Old 11-10-2018, 10:54 AM   #3
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Quote:
Originally Posted by wrapperman View Post
My alignment shop had to adjust all 3. Toe, caster and camber. The caster was the hardest to adjust. After the caster was adjusted the steering wheel was finally centered and the motorhome drives great. No fatigue after driving 500 miles straight. No other improvements except CHF.
Yeah, my combined toe was off by 1/4". The tech said that would have caused a lot of tire wear without truing. If I understood him right, the higher caster could potentially wear the tires slightly faster too because it causes higher camber in turns, but RV owners want stability and care more about tire age than wear from mileage so its a tradeoff. He recommended rotating the 2 front tires after a few thousand miles or it might start pulling from wear.
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Old 11-10-2018, 12:22 PM   #4
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+Caster for Stability

Too little positive caster can result in the feeling of loose steering and wandering at highway speeds. Caster of +5 or more is good unless you are going to use your RV as a commuter around town.

POPULAR MECHANICS MAY 1973:
START QUOTE:
If too little caster exists, the car will wander and weave,
thus necessitating constant corrections in steering.
END QUOTE:
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Old 11-10-2018, 12:46 PM   #5
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Links to more +caster

https://www.ford-trucks.com/forums/1...of-caster.html

Wandering at highway speeds

Reply Post by 2kGeorgieBoy
Re: Wandering at highway speeds
Reply #36 on: March 14, 2018, 09:07:02 PM

START QUOTE:
Jeff..Although we have a 2000 Georgie Boy 31' Maverick "C" on a Ford E450 chassis, I can fully agree on the caster effects, at least for us. When we got the unit in Jan 2014, the dealer had us take into a truck shop for an alignment. It turned out OK....A trip to Moab shortly there after brought out the problems. I then started reading the threads and comments here about the caster settings....esp., from Harvard. I checked the data from the first alignment and found that it was set at about 3 1/2 degrees positive...about in the middle of Ford's recommended range. Shortly before a cross country trip to Maryland in fall of 2016, I returned to the shop where the first alignment was done. I talked to the service manager and he knew of the problems with the E450's and was happy to increase the caster as I asked. The alignment tech was also familiar with it and ended up with settings close to 5.5 degrees positive. WHAT A DIFFERENCE! The unit tracked straight down the road, passing semis no longer caused a white knuckle hold on the wheel, and overall it was just a lot more enjoyable. It did however increase steering effort a little but not anything to worry about. But, be sure that the shop you go to is willing to "think outside of the box". Our first alignment was "plain vanilla", right in the middle like it was always done. Second time out, they were very willing to increase settings beyond what normally would be done, and still stay with in Ford's guidelines (0-7 degrees, I believe). I realize that our E450 chassis is an entirely different animal than yours, but I was trying to add support to the caster increase thinking and how it helped us......if you go down that road.
END QUOTE:


E350/E450 Handling Problems are caused by too little + CASTER
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Old 11-10-2018, 06:38 PM   #6
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I always add more + caster. Adds stability. Helps steering return to center.
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Old 11-10-2018, 07:06 PM   #7
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Quote:
Originally Posted by Harvard View Post
Too little positive caster can result in the feeling of loose steering and wandering at highway speeds. Caster of +5 or more is good unless you are going to use your RV as a commuter around town.

POPULAR MECHANICS MAY 1973:
START QUOTE:
If too little caster exists, the car will wander and weave,
thus necessitating constant corrections in steering.
END QUOTE:
I love Popular Mechanics. Good quote. Fond memories of mom dropping us kids off at the town library and I'd bee line to the magazines for Car and Driver, Motortrend, and Popular Mechanics. PM is the only one I don't subscribe to now but I might have to again.
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Old 11-10-2018, 07:09 PM   #8
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Quote:
Originally Posted by Harvard View Post
https://www.ford-trucks.com/forums/1...of-caster.html

Wandering at highway speeds

Reply Post by 2kGeorgieBoy
Re: Wandering at highway speeds
Reply #36 on: March 14, 2018, 09:07:02 PM

START QUOTE:
Jeff..Although we have a 2000 Georgie Boy 31' Maverick "C" on a Ford E450 chassis, I can fully agree on the caster effects, at least for us. When we got the unit in Jan 2014, the dealer had us take into a truck shop for an alignment. It turned out OK....A trip to Moab shortly there after brought out the problems. I then started reading the threads and comments here about the caster settings....esp., from Harvard. I checked the data from the first alignment and found that it was set at about 3 1/2 degrees positive...about in the middle of Ford's recommended range. Shortly before a cross country trip to Maryland in fall of 2016, I returned to the shop where the first alignment was done. I talked to the service manager and he knew of the problems with the E450's and was happy to increase the caster as I asked. The alignment tech was also familiar with it and ended up with settings close to 5.5 degrees positive. WHAT A DIFFERENCE! The unit tracked straight down the road, passing semis no longer caused a white knuckle hold on the wheel, and overall it was just a lot more enjoyable. It did however increase steering effort a little but not anything to worry about. But, be sure that the shop you go to is willing to "think outside of the box". Our first alignment was "plain vanilla", right in the middle like it was always done. Second time out, they were very willing to increase settings beyond what normally would be done, and still stay with in Ford's guidelines (0-7 degrees, I believe). I realize that our E450 chassis is an entirely different animal than yours, but I was trying to add support to the caster increase thinking and how it helped us......if you go down that road.
END QUOTE:


E350/E450 Handling Problems are caused by too little + CASTER
Thanks for the reference. I'm duplicating a little. This forum has an incredible amount of good info thanks to all the members willing to share.
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Old 11-13-2018, 05:20 PM   #9
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Wrapperman, I'm with you. Front end alignment and CHF in 2012. None of the fancy stuff! Rides straight down the road!!
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