Home » Public Forums » GMCnet » Dave Lenzi upper arms vs offset bushing install ( looking for info advice)
| Dave Lenzi upper arms vs offset bushing install [message #140533] |
Mon, 22 August 2011 19:43  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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I don't see these listed on his page but saw some talk of the engineered 5 deg upper arms. Wondering what they cost and the benefit vs just adding a rear offset bushing on my existing arms, assuming the OEM arms are still ok and the balljoints still tight.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Dave Lenzi upper arms vs offset bushing install [message #140554 is a reply to message #140533] |
Mon, 22 August 2011 20:20  |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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John,
I thought about installing a pair of Dave's offset upper control arms in Double Trouble after Tom Hampton, Lanny Young, and John
Sharpe all told me that they made a BIG difference in the way their GMC handled.
Driving John's GMC convinced me of it.
With offset bushings in the rear legs of the upper control arms the most caster Tom Hampton could get was 1.9° on both sides in
Double Trouble.
After John Sharpe and I installed a pair of Dave's offset upper control arms in Double Trouble the alignment shop was able to set
the following parameters:
Left:
Camber: 0.1 degrees
Caster: 5.2 degrees
Toe: 0.0 inches
Right
Camber: -0.2 degrees
Caster: 4.8 degrees
Toe: 0.0 inches
Double Trouble now drives like its on rails. Last year when a section of I-40 was closed due to flooding I had to detour to a two
lane highway out of Memphis. There was a constant stream of semis coming the other way. I hardly felt it when they would pass! I
have about 3/8" to 1/2" of slop in the steering wheel, however, every other component in the front suspension and steering meets
spec, has been rebuilt, or replaced. If I drive in the middle lane on the freeway I can let go of the steering wheel at 70mph and
Double Trouble goes dead straight ahead. If I'm in the left lane it drifts slowly to the left and in the right it drifts slowly to
the right.
The bad news is that they are $700 for the pair, however, making these requires PRECISION machining!
Here's a photograph of what they look like:
http://www.gmcmhphotos.com/photos/showgallery.php?cat=5861
Yes, I have a pair for The Blue Streak too!
Regards,
Rob M.
Sydney, Australia
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of John R. Lebetski
Sent: Tuesday, 23 August 2011 10:43 AM
To: gmclist@temp.gmcnet.org
Subject: [GMCnet] Dave Lenzi upper arms vs offset bushing install
I don't see these listed on his page but saw some talk of the engineered 5 deg upper arms. Wondering what they cost and the
benefit vs just adding a rear offset bushing on my existing arms, assuming the OEM arms are still ok and the balljoints still tight.
--
John Lebetski
Chicago, IL
77 Eleganza II
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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: Dave Lenzi upper arms vs offset bushing install [message #140634 is a reply to message #140533] |
Tue, 23 August 2011 11:56 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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I assume they come with the upper balljoints installed? Beautiful work on the closed boxing by the bushings. If you consider the shop time to press out the old bushings and the slight risk of damaging the arm factored in as well, then they are more cost effective. And if the handling is what you say, then they are worth even more. Mine have recent stock bushings and good balljoints so I can probably something for them as well to someone who might need them. Is there a point where there is too much caster which as I understand it increases stress loads? I suppose if I can get 4 on each side that should do it right?
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Dave Lenzi upper arms vs offset bushing install [message #140724 is a reply to message #140634] |
Tue, 23 August 2011 23:13 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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John,
Mine did not come with ball joints.
I didn't notice that you have a 1977 GMC; it has been my observation from reading messages on the GMCnet that GMC did "something"
that allowed later coaches to get more caster.
If I were you I would spend $40 on a pair of MOOG (P/N K-7104) offset upper bushing first and see how much caster you can get and
how it affects the handling of your GMC. Replacing the upper bushings isn't a very big job; with John Sharpe's help we replaced the
upper control arms in Double Trouble in a morning.
As I noted in my original message all Tom Hampton could get WITH offset bushings was 1.9°.
I'll bet dollars to donuts if you call Dave on (810) 653-3902 he'll tell you to try the offset bushings first!
Regards,
Rob M.
Sydney, Australia
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of John R. Lebetski
Sent: Wednesday, 24 August 2011 2:57 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Dave Lenzi upper arms vs offset bushing install
I assume they come with the upper balljoints installed? Beautiful work on the closed boxing by the bushings. If you consider the
shop time to press out the old bushings and the slight risk of damaging the arm factored in as well, then they are more cost
effective. And if the handling is what you say, then they are worth even more. Mine have recent stock bushings and good balljoints
so I can probably something for them as well to someone who might need them. Is there a point where there is too much caster which
as I understand it increases stress loads? I suppose if I can get 4 on each side that should do it right?
--
John Lebetski
Chicago, IL
77 Eleganza II
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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] Dave Lenzi upper arms vs offset bushing install [message #140798 is a reply to message #140771] |
Wed, 24 August 2011 15:30 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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In olden times (pre-power steering), "the word" was that too much caster
would cause shimmying (rapid, uncontrollable, left-right wobbling of the
wheels). Might have been a old wives tale, but I have had shopping carts
that the wheels would wobble like crazy -- maybe too much caster?
Ken H.
On Wed, Aug 24, 2011 at 10:13 AM, Rob Mueller <robmueller@iinet.net.au>wrote:
> Steve,
>
> Agreed!
>
> He told me that over 5° caused the relief valve in the power steering pump
> of his Vortec 8.1 to dump pressure.
>
> I asked if the pump on the Vortec 8.1 was the same as the 455 and he did
> not know.
>
> Trust me (and the other guys that run these arms) you don't need more than
> 5°!
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Dave Lenzi upper arms vs offset bushing install [message #140800 is a reply to message #140798] |
Wed, 24 August 2011 15:56 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
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| Ken Henderson wrote on Wed, 24 August 2011 15:30 |
In olden times (pre-power steering), "the word" was that too much caster
would cause shimmying (rapid, uncontrollable, left-right wobbling of the
wheels). Might have been a old wives tale, but I have had shopping carts
that the wheels would wobble like crazy -- maybe too much caster?
Ken H.
|
But don't shopping carts have negative caster??
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: [GMCnet] Dave Lenzi upper arms vs offset bushing install [message #140835 is a reply to message #140817] |
Wed, 24 August 2011 20:22 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Mac,
Reference:
Maintenance Manual: X-7525
Page: 3A-5 Front Suspension
Paragraph: Theory and Operation
There is a great description of FRONT-END GEOMETRY discussing CAMBER, CASTER, STEERING AXIS INCLINATION, TOE ADJUSTMENT, and TOE-OUT
on TURNS.
I didn't realize that Caster AND Steering Axis Inclination both lift the vehicle.
The GMC was different, it had positive caster; the OEM alignment specs can be found on page 3A-20; they are:
SET
Caster: +2°
Camber: - L.H.: +3/4°
- R.H.: +1/2°
Toe: -1/8" (toe out)
HOWEVER, I have a Shop Manual for a 1972 Cadillac and here's the specs for a 1972 Eldorado:
SET
Caster: -1° ± 1/2°
Camber: 0° ± 3/8°
Toe: 0" ± 1/16"
Therefore the statement the article made appears to be correct.
Regards,
Rob
-----Original Message-----
From: Mac Macdonald
If you look at the added explanation of caster, you should
notice that vehicles prior to 1975 or so used NEGATIVE
caster to make steering effort easier. It explains that with
bias ply tires, the tire distorts when in motion so that the
effective caster is turned positive at speed which stiffens
up the steering. Putting radial tires on such a vehicle gives
steering that is WAY too loose for comfort.
Modern radial tires on an "ancient" vehicle front end is
bound to cause difficulties!
Mac
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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] Dave Lenzi upper arms vs offset bushing install [message #140839 is a reply to message #140835] |
Wed, 24 August 2011 21:05 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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And I have yet to understand RAKE and TRAIL on motorcycles!
Don't bother to explain. I'm too old now to give a damn anyway!
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~~ ~ ~ (TZE166V101966) ~ ~ ~~
~ ~ ~ ex-Palm Beach, 76 ~ ~ ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~ www.gmcmhphotos.com/okclb ~
> From: robmueller@iinet.net.au
> To: gmclist@temp.gmcnet.org
> Date: Thu, 25 Aug 2011 11:22:04 +1000
> Subject: Re: [GMCnet] Dave Lenzi upper arms vs offset bushing install
>
> Mac,
>
> Reference:
>
> Maintenance Manual: X-7525
> Page: 3A-5 Front Suspension
> Paragraph: Theory and Operation
>
> There is a great description of FRONT-END GEOMETRY discussing CAMBER, CASTER, STEERING AXIS INCLINATION, TOE ADJUSTMENT, and TOE-OUT
> on TURNS.
>
> I didn't realize that Caster AND Steering Axis Inclination both lift the vehicle.
>
> The GMC was different, it had positive caster; the OEM alignment specs can be found on page 3A-20; they are:
>
> SET
> Caster: +2°
> Camber: - L.H.: +3/4°
> - R.H.: +1/2°
> Toe: -1/8" (toe out)
>
> HOWEVER, I have a Shop Manual for a 1972 Cadillac and here's the specs for a 1972 Eldorado:
>
> SET
> Caster: -1° ± 1/2°
> Camber: 0° ± 3/8°
> Toe: 0" ± 1/16"
>
> Therefore the statement the article made appears to be correct.
>
> Regards,
> Rob
>
> -----Original Message-----
> From: Mac Macdonald
>
> If you look at the added explanation of caster, you should
> notice that vehicles prior to 1975 or so used NEGATIVE
> caster to make steering effort easier. It explains that with
> bias ply tires, the tire distorts when in motion so that the
> effective caster is turned positive at speed which stiffens
> up the steering. Putting radial tires on such a vehicle gives
> steering that is WAY too loose for comfort.
>
> Modern radial tires on an "ancient" vehicle front end is
> bound to cause difficulties!
>
> Mac
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| Re: [GMCnet] Dave Lenzi upper arms vs offset bushing install [message #140869 is a reply to message #140798] |
Thu, 25 August 2011 07:55 |
Steven Ferguson
Messages: 3447
Registered: May 2006
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Yeah but, shopping carts have negative caster.
On Wed, Aug 24, 2011 at 1:30 PM, Ken Henderson <hend4800@bellsouth.net>wrote:
> In olden times (pre-power steering), "the word" was that too much caster
> would cause shimmying (rapid, uncontrollable, left-right wobbling of the
> wheels). Might have been a old wives tale, but I have had shopping carts
> that the wheels would wobble like crazy -- maybe too much caster?
>
> Ken H.
>
> On Wed, Aug 24, 2011 at 10:13 AM, Rob Mueller <robmueller@iinet.net.au
> >wrote:
>
> > Steve,
> >
> > Agreed!
> >
> > He told me that over 5° caused the relief valve in the power steering
> pump
> > of his Vortec 8.1 to dump pressure.
> >
> > I asked if the pump on the Vortec 8.1 was the same as the 455 and he did
> > not know.
> >
> > Trust me (and the other guys that run these arms) you don't need more
> than
> > 5°!
> >
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Steve Ferguson
Sierra Vista, AZ
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| Re: [GMCnet] Dave Lenzi upper arms vs offset bushing install [message #140870 is a reply to message #140817] |
Thu, 25 August 2011 07:57 |
Steven Ferguson
Messages: 3447
Registered: May 2006
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Senior Member |
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And a lot of the cars had 17" steering wheels.
On Wed, Aug 24, 2011 at 5:04 PM, D C *Mac* Macdonald <k2gkk@hotmail.com>wrote:
>
> If you look at the added explanation of caster, you should
> notice that vehicles prior to 1975 or so used NEGATIVE
> caster to make steering effort easier. It explains that with
> bias ply tires, the tire distorts when in motion so that the
> effective caster is turned positive at speed which stiffens
> up the steering. Putting radial tires on such a vehicle gives
> steering that is WAY too loose for comfort.
>
> Modern radial tires on an "ancient" vehicle front end is
> bound to cause difficulties!
>
> ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
> ~~ ~ D C "Mac" Macdonald ~ ~~
> ~ ~ Amateur Radio - K2GKK ~ ~
> ~ ~ USAF and FAA, Retired ~ ~
> ~ ~ ~ Oklahoma City, OK ~ ~ ~
> ~~ ~ ~ "The Money Pit" ~ ~ ~~
> ~~ ~ ~ (TZE166V101966) ~ ~ ~~
> ~ ~ ~ ex-Palm Beach, 76 ~ ~ ~
> ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
>
> ~ www.gmcmhphotos.com/okclb ~
>
>
>
>
> > From: robmueller@iinet.net.au
> > To: gmclist@temp.gmcnet.org
> > Date: Thu, 25 Aug 2011 09:39:43 +1000
> > Subject: Re: [GMCnet] Dave Lenzi upper arms vs offset bushing install
> >
> > G'day,
> >
> > Googled Shopping Cart Wheel Caster and found:
> >
> > http://en.wikipedia.org/wiki/Caster
> >
> > As you can see in the photos the point of wheel contact is behind the
> pivot point.
> >
> > I also found:
> >
> > http://www.familycar.com/Alignment.htm
> >
> > It shows that GMC caster is the same as shopping cart caster.
> >
> > Regards,
> > Rob M.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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--
Steve Ferguson
Sierra Vista, AZ
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| Re: [GMCnet] Dave Lenzi upper arms vs offset bushing install [message #140975 is a reply to message #140869] |
Thu, 25 August 2011 20:01 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Nope. They just look like it. A precise definition of caster relates the
contact point of the wheel to the steering axis -- Positive caster is when
the steering axis intersects the ground ahead of the wheel.
On an automobile, the steering axis (king pin inclination) is angled back at
the top for positive caster, with the lower extension of that vector
intersecting the ground ahead of the wheel. On a Caster as used on a
shopping cart, the steering axis is vertical -- but it's well ahead of the
wheel's contact point on the ground so the caster is still positive.
In other words, in both cases, the line of force causing forward motion is
dragging the wheel behind, keeping it turned straight ahead.
Ken H.
On Thu, Aug 25, 2011 at 8:55 AM, Steven Ferguson <botiemad11@gmail.com>wrote:
> Yeah but, shopping carts have negative caster.
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Dave Lenzi upper arms vs offset bushing install [message #140985 is a reply to message #140975] |
Thu, 25 August 2011 20:50 |
|
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Ken,
Good explanation!
I was right! It is up to us Flyboys to keep them Swabbies straight technically! ;-)
Regards,
Rob M.
Sydney, Australia
-----Original Message-----
From: Ken Henderson
Nope. They just look like it. A precise definition of caster relates the
contact point of the wheel to the steering axis -- Positive caster is when
the steering axis intersects the ground ahead of the wheel.
On an automobile, the steering axis (king pin inclination) is angled back at
the top for positive caster, with the lower extension of that vector
intersecting the ground ahead of the wheel. On a Caster as used on a
shopping cart, the steering axis is vertical -- but it's well ahead of the
wheel's contact point on the ground so the caster is still positive.
In other words, in both cases, the line of force causing forward motion is
dragging the wheel behind, keeping it turned straight ahead.
Ken H.
On Thu, Aug 25, 2011 at 8:55 AM, Steven Ferguson <botiemad11@gmail.com>wrote:
> Yeah but, shopping carts have negative caster.
>
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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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