| [GMCnet] Over steer [message #303791] |
Mon, 18 July 2016 19:07  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Senior Member |
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Hi Kieth,
Oversteer is not a common malady with our coaches. Check to see that all six wheels are running frame parallel. If they are, then you want 1 to 2 degrees of tire in at the top camber on the rear wheels to keep the back end in place during a turn. If you have tire out at the top camber, then the only way to get those 1 to 2 degrees is to shim the boggie mount or by twisting the boggie arm if only one is tire out at the top and the other is tire in at the top. That can happen by hitting a curb and it usually is found on the middle passenger side. The proper front spec for radial ply tires on our coaches is zero toe (tires frame parallel), zero camber (tire straight up and down) and as much caster as you can get (up to 5 degrees) so long as both sides are equal. Usually you will only be able to get around three or maybe four degrees. The factory spec of 2 degrees static was for bias ply tires and is too little static caster for radials which behave differently under speed. If you have stock single bag rear suspension there will be some wallow, but not excessive. If you have bag risers there will be a bit more wallow but still not excessive in normal driving. Check also the condition of the front sway bar bushings. If they are really loose or missing then the whole coach will feel loose in a corner.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
glwork@mac.com
http://jerrywork.com
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Message: 12
Date: Mon, 18 Jul 2016 14:51:15 -0500
From: Keith V
To: "gmclist@list.gmcnet.org"
Subject: [GMCnet] Over steer
Message-ID:
Content-Type: text/plain; charset="iso-8859-1"
So I am extremely picky about steering and suspension, too much time pretending to be a race car driver I guess.
My coach drives straight as an arrow, very nice and predictable.
That is until you go into a turn, like a cloverleaf, then it feels like the rear wants to come around on me. I feel like it should be better.
I've checked the ride height, it's within spec.
I've checked the front and rear alignment, also within spec.
Checked the bogie play, and it seems to be within spec, but spec seemed pretty loose to me
Shocks are good.
So for those of you that can feel such things, are these machines naturally loose?
Or do I have some rear suspension work to do?
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] Over steer [message #304287 is a reply to message #303791] |
Tue, 26 July 2016 16:10  |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Jerry,
While I agree with what you have noted below as to the front alignment specs I am going to respectfully disagree as to how much
caster can achieved at zero camber.
It is my experience that coaches up to and including 1975 you are lucky if you can get two degrees caster at zero camber. In fact
the best I could get with Double Trouble was two degrees WITH Moog offset bushings. After I installed a pair of Dave Lenzi's offset
upper control arms I got five degrees and the way the coach drove was amazing! From 1976 on something happened and it is possible to
get two degrees and a bit more without having offset bushings.
Also up to 1/8 inch toe out is acceptable because when you apply power to a FWD vehicle it tends to tow in. Zero camber is important
as radial tires like to run flat (parallel to) on the road surface.
Regards,
Rob M.
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Gerald Work
Sent: Tuesday, July 19, 2016 10:07 AM
To: GMC Motor Home Post
Subject: [GMCnet] Over steer
Hi Kieth,
Oversteer is not a common malady with our coaches. Check to see that all six wheels are running frame parallel. If they are, then
you want 1 to 2 degrees of tire in at the top camber on the rear wheels to keep the back end in place during a turn. If you have
tire out at the top camber, then the only way to get those 1 to 2 degrees is to shim the boggie mount or by twisting the boggie arm
if only one is tire out at the top and the other is tire in at the top. That can happen by hitting a curb and it usually is found
on the middle passenger side. The proper front spec for radial ply tires on our coaches is zero toe (tires frame parallel), zero
camber (tire straight up and down) and as much caster as you can get (up to 5 degrees) so long as both sides are equal. Usually you
will only be able to get around three or maybe four degrees. The factory spec of 2 degrees static was for bias ply tires and is too
little static caster for radials which behave differently under speed
. If you have stock single bag rear suspension there will be some wallow, but not excessive. If you have bag risers there will be
a bit more wallow but still not excessive in normal driving. Check also the condition of the front sway bar bushings. If they are
really loose or missing then the whole coach will feel loose in a corner.
Jerry
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Over steer [message #304288 is a reply to message #304287] |
Tue, 26 July 2016 16:23 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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Senior Member |
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The best we could do on my 75 is zero, one side was the problem the other side would go to 2 degrees.
Thats with offset upper bushings.
I like Dave Lenzi and his parts, but I'm really resisting buying more expensive parts at this time.
At least till I do a lot more camping in the thing
>
> Jerry,
>
> While I agree with what you have noted below as to the front alignment specs I am going to respectfully disagree as to how much
> caster can achieved at zero camber.
>
> It is my experience that coaches up to and including 1975 you are lucky if you can get two degrees caster at zero camber. In fact
> the best I could get with Double Trouble was two degrees WITH Moog offset bushings. After I installed a pair of Dave Lenzi's offset
> upper control arms I got five degrees and the way the coach drove was amazing! From 1976 on something happened and it is possible to
> get two degrees and a bit more without having offset bushings.
>
> Also up to 1/8 inch toe out is acceptable because when you apply power to a FWD vehicle it tends to tow in. Zero camber is important
> as radial tires like to run flat (parallel to) on the road surface.
>
> Regards,
> Rob M.
> USAussie - Downunder
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
>
> -----Original Message-----
> From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Gerald Work
> Sent: Tuesday, July 19, 2016 10:07 AM
> To: GMC Motor Home Post
> Subject: [GMCnet] Over steer
>
> Hi Kieth,
>
> Oversteer is not a common malady with our coaches. Check to see that all six wheels are running frame parallel. If they are, then
> you want 1 to 2 degrees of tire in at the top camber on the rear wheels to keep the back end in place during a turn. If you have
> tire out at the top camber, then the only way to get those 1 to 2 degrees is to shim the boggie mount or by twisting the boggie arm
> if only one is tire out at the top and the other is tire in at the top. That can happen by hitting a curb and it usually is found
> on the middle passenger side. The proper front spec for radial ply tires on our coaches is zero toe (tires frame parallel), zero
> camber (tire straight up and down) and as much caster as you can get (up to 5 degrees) so long as both sides are equal. Usually you
> will only be able to get around three or maybe four degrees. The factory spec of 2 degrees static was for bias ply tires and is too
> little static caster for radials which behave differently under speed
> . If you have stock single bag rear suspension there will be some wallow, but not excessive. If you have bag risers there will be
> a bit more wallow but still not excessive in normal driving. Check also the condition of the front sway bar bushings. If they are
> really loose or missing then the whole coach will feel loose in a corner.
>
> Jerry
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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