| Author |
Message |
    
John Friederich
| | Posted on Sunday, February 02, 2003 - 04:56 pm: | 
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Is there any alignment adjustment that can help recover the total loss of steering self centering I got after installing the OME HD springs (I got about 2")?
I noticed the wife was having a hell of a time keeping it going in a straight line today on the highway coming back from a ride in the mountains. Same feeling for me.
What exactly is the part of steering geometry that imparts self-centering, and why did I lose it after the lift? Thanks.
Oh, a 2001 D2.
John F
Las Vegas, NV |
muskyman
| | Posted on Sunday, February 02, 2003 - 04:59 pm: |
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castor is what centers the wheel, a lift decreases castor lessening the centering effect
GBR has castor correction service that is very affordable |
muskyman
| | Posted on Sunday, February 02, 2003 - 05:01 pm: |
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just noticed you have D2 I dont think they do the castor correction on the D2 sorry |
Jess Brandt (Disco285)
| | Posted on Sunday, February 02, 2003 - 10:32 pm: |
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if you are saggin' really bad....would the car suffer from the same thing? |
muskyman
| | Posted on Sunday, February 02, 2003 - 11:00 pm: |
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no if you have stock springs that where sagging you would gain caster.
Castor is the inclination of the kingpin(swivel in LR lingo) angle
when the top of the kingpin is behind the bottom it is said to have positive castor
top in front of the bottom is negative castor
the more castor a vehicle has (within reason) the more stable it will be at speed and the more return to center it will exhibit
to much castor will cause heavy steering and intime overload the steering gear and pump causing failure
to little caster will promote whippy or light steering.
a good amount on offroad trucks is +5degrees |
John Friederich
| | Posted on Sunday, February 02, 2003 - 11:00 pm: |
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So, muskyman -
Is there no castor adjustment, or is there just a built in 2 percent or so of castor according to parts design and factory height?
Is there no way around this on a D2? Thanks...
John F |
muskyman
| | Posted on Sunday, February 02, 2003 - 11:07 pm: |
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there are a number of ways to effect/correct it
the problem you run is that if you just rotate the axle such as dropping the radius arm brackets on the frame you also effect pinion angle.
so to really do it correctly you need to cut and rotate the ends of the axle tubes.
I havent spent any time modifing a D2 so I cant tell you the best formula for that particular vehicle. but it can be done for sure. |
Steve
| | Posted on Monday, February 03, 2003 - 12:31 am: |
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On heavy duty trucks a slight increase in toein will aid self centering where a spring change effects stearing. I suspect that might also be the case with a Disco. The rotation of the axle caused by a lift, as stated above, effects caster and it also effects toein. So I'd have the toein checked and maybe adjusted.
IMHO
Steve |
Lance (Ely)
| | Posted on Monday, February 03, 2003 - 07:07 am: |
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The most familiar experience of caster that most of us have is with pivoting casters. Especially the casters on the front of shopping carts. If you look at a healthy one you'll notice that the wheel axle trails the mounting pivot. You push the wagon and exert a higher force on one side of the handle and the caster falls into line and on you go to the cereal aisle. But what if one of the lot attendants got a little wild and banged the cart through a pothole in an oddball way so that the pivot and axle are now in-line. Now when you go to head for the cereal aisle, a wheel flutters back and forth, seemingly unwilling to follow. You're now a bit peeved and since you just started shopping you unload and grab another cart... And the story goes on from here leading through geometric jungles and double-cardan corridors and finally to custom crescendoes where after tidy sums are spent one ends up with a car that is almost as good as the one they started with. "Liftit Emptor." |
Brian Friend (Brianfriend)
| | Posted on Monday, February 03, 2003 - 10:35 am: |
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That was a very good analogy. Gave me a good chuckle. |
Greg Davis (Gregdavis)
| | Posted on Monday, February 03, 2003 - 11:06 am: |
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John, one way to overcome this loss of castor is to install a True Trac limited slip differential. Because it is a "limited slip" unit, it is constantly trying to self-center. I have about 4.5" of lift on my D2, and when I installed my True Trac, it returned to almost normal. No more "wandering". Really tightened the front end up. But like Thom (MuskyMan) said, the only other option is to have the knuckles cut from the axle tubes and rewelded to gain your castor back. Eventually, you'll get used to it, but for someone that doesn't drive it regularly, it's a handful. My wife refused to drive mine before the True Trac install. |
Todd Juneau (Toddxd)
| | Posted on Monday, February 03, 2003 - 12:00 pm: |
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John,
You will most liekly get used to it if you drive the D2 regularly. I just installed the OME HD's with 235x85's on my D1. At first, I thought I was going to wander right off the road. Now I am used to it and I don't even notice it!
my $.02 |
Greg Davis (Gregdavis)
| | Posted on Monday, February 03, 2003 - 12:43 pm: |
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John, yes yo will get used to it if it's your daily driver. However, if your wife ever needs to take it out for an emergency or whatever, it could be an issue since it won't handle like anything she's acustomed to. Besides, that added traction of the limited slip is great in conjunction with the TC! 
In all seriousness though, the TT makes a world of difference in driving the vehicle. See if you can find someone locally that has done this, and you'll be amazed. |
mongo
| | Posted on Monday, February 03, 2003 - 12:51 pm: |
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Greg's right, it's night and day...The TT makes a HUGH difference.
Frank |
Joe W.
| | Posted on Monday, February 03, 2003 - 01:05 pm: |
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I have had the same issue with my RRC with about 2" of lift. Do the caster correction bushings help? If so, does anyone know where I could get a set?
Joe |
Bill Bettridge (Billb)
| | Posted on Monday, February 03, 2003 - 03:20 pm: |
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Joe - IMO (BTDT) forget the castor bushings - they limit front articulation, and wear very quickly (ie: replace within 25K). Though with a 2" lift, they will correct the wander problem.
Go the TT route - you'll never look back.
If you're set on getting the bushings GBR or EE can supply I'm sure |
Kirk Thibault (Kirkt)
| | Posted on Monday, February 03, 2003 - 08:33 pm: |
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If HD springs are installed up front on a vehicle with no winch/winch bumper (i.e., light weight), installation of these heavier objects on the front will also cause the lift to sag slightly. Theoretically this should also restore some of the castor...right? If you installed the HD springs and haven't put heavy stuff up front yet, but plan to, it's probably best to wait until you load up the front end before adjusting castor. Or, it's a good excuse to install a TT.... |
John Friederich
| | Posted on Monday, February 03, 2003 - 11:50 pm: |
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Damn it - You are not supposed to be trying to talk me into spending money on replacing a perfectly good part with one that is better. Where will this end? With a really great off-road vehicle?
TT up front will help the self-centering, eh? Wouldn't TT's in the rear help offroad traction more than up front?
I loved the 'Liftit Emptor' from Lance. Can I assume a TT install is beyond my mechanical skills if just installing the OME springs / shocks took all day?
It is not a daily driver, so I fear we'll never get used to it as it is now. We had the luxury of buying the Disco as a replacement for our '89 Dodge Raider, which in 13 years managed to accumulate 40,000 miles. All pretty hard miles, though.
Thanks for all of your help - the shopping cart explanation of castor was a little surreal, but great.
-John F |
Aleks
| | Posted on Tuesday, February 04, 2003 - 12:34 am: |
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Mebbe a bit off, not being able to look under a Disco (still, uhm, a Jeep owner, ...), but when I did a 3.5" lift on my XJ, I made 1/8" shims and lined the frame attachment point of the lower control arms, untill the new total lenght of the CA corresponded to a decent caster. Why can't this be done on a Disco? I've seen the lower CAs, they are held with a giant nut to the frame. Couldn't you extend it's lenght with some washers? Or wouldn't it help at all?
Cheers |
Way
| | Posted on Tuesday, February 04, 2003 - 01:00 am: |
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Have you tried checking the wheel alignment, a smal amount of toe-out may fix the problem. |
Lance (Ely)
| | Posted on Tuesday, February 04, 2003 - 08:16 am: |
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Aleks-
The Disco's front axle is located by three links unlike the five of the XJ. There are only two control arms and a track arm. All in all very similar in effect to a longarm XJ suspension where the upper arms mount to the beefed -up, elongated , re-bracketed lowers. In order to concentrate the associated forces, the XJ uniframe has to be reinforced with a subframe crossmember. |
John Friederich
| | Posted on Tuesday, February 04, 2003 - 08:27 am: |
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I've learned a lot about suspension geometry here. I will get an alignment and have toe-out checked. Thanks
John F |
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