This is a follow up to the message posted below a few weeks ago. I had
the offset bushings installed and they increased the castor up to
2.5-3.0 deg. Unfortunately it didn't help the wig wag like I was sure it
would. Jim Bounds also thought this would fix it. Interestingly when I
drop the old girls ass in the back I still get rid of most of the wig
wag. Right now I am not sure what to do next. Just getting ready to take
a trip from Redding CA to Seattle and then to northern Idaho and back to
Redding. If anyone spots a yellow GMC with its tail down on that route,
its me.
Subject:
Wiggle Waggle & Castor Alignment
Date:
Mon, 14 Jun 1999 22:21:10 -0700
From:
Larry & Kaye Kepple
To:
GMC MAIL LIST
CC:
Gene FISHER
I have had my 73 GMC for about a year. It has always wandered. Its sort
of like a big fat boy on a water bed going around corners. Ruts and
pavement edges cause a sway and you tend to oversteer. I have replaced
all the steering components such as:
1. Hydraulic Steering Dampener.
2. Upper and Lower Control Arm Bushings
3. Ball Joints
4. Stabilizer Bushings
5. Steering Gear Box (first a rebuilt and then a new one from
Cinnabar)
6. CV joint in steering column
7. 6 wheel alignment including adjustment of rear camber
8. New tires and Alcoa Wheels
9. Previous owner had replced rear bogie pins and I have checked for
loosness
10. Idler arm and bushing
All of this work made for a very nice tight steering system but the
wander never changed much. Early on in my replacement work I discussed
the problem with Jim Bounds and with Wes Caughlin. Wes thought it was
the steering box per his recent article.Jim suggested I get anything
loose in the steering fixed and be sure and set the castor right. He
said to set it at +2.5 deg. which is upper end of limits recommended in
manual. I told the guy doing the 6 Wheel align. to set it that way early
in my replacement sequence. But recently when I went back for a check on
the alignment I found out that he only set it at 1 deg. because he said
that is all he could get without getting the camber out of limits. Then
after doing some checking he said that GMC makes an offset upper control
arm bushing that would allow them to probably get the 2.5 deg. However
that meant changing the upper control arm bushings which had already
been replaced and a new alignment.The cost will be $300 for the offset
bushing replacement plus another $100 for another front wheel alignment.
So I said I would think about it.
Then I got an idea and tried a little experiment. If I drop the rear
end at center of tandems 3" below the normal height I should pick up 1
deg. of castor. So I tried it. The old girl was really setting on her
ass and I thought this was a silly test especially since the air bag
pressure would be quite a bit lower than the 90 PSI I typically run to
get the correct factory ride height.
I was absolutely amazed at the difference. It made the steering and
stability much better and I believe you would get few complaints from
the handling. Believe me I wouldn't have done all this steering work had
it been this way. I raised it up and down twice to verify I wasn't
fooling myself. Each time I raised it the wander would come back and my
passengers were also amazed at the difference they felt in rear end
sway.
So now I am convinced it is the lack of castor. Jim Bounds said they
will wander all over with out the full positive castor and now I believe
it. But I thought I would ask for opinions before I spend the $400.
I am still interested in the 4 bag suspension, but I have always said
I am going to get the steering as right as it can be first before I make
that decision.
the offset bushings installed and they increased the castor up to
2.5-3.0 deg. Unfortunately it didn't help the wig wag like I was sure it
would. Jim Bounds also thought this would fix it. Interestingly when I
drop the old girls ass in the back I still get rid of most of the wig
wag. Right now I am not sure what to do next. Just getting ready to take
a trip from Redding CA to Seattle and then to northern Idaho and back to
Redding. If anyone spots a yellow GMC with its tail down on that route,
its me.
Subject:
Wiggle Waggle & Castor Alignment
Date:
Mon, 14 Jun 1999 22:21:10 -0700
From:
Larry & Kaye Kepple
To:
GMC MAIL LIST
CC:
Gene FISHER
I have had my 73 GMC for about a year. It has always wandered. Its sort
of like a big fat boy on a water bed going around corners. Ruts and
pavement edges cause a sway and you tend to oversteer. I have replaced
all the steering components such as:
1. Hydraulic Steering Dampener.
2. Upper and Lower Control Arm Bushings
3. Ball Joints
4. Stabilizer Bushings
5. Steering Gear Box (first a rebuilt and then a new one from
Cinnabar)
6. CV joint in steering column
7. 6 wheel alignment including adjustment of rear camber
8. New tires and Alcoa Wheels
9. Previous owner had replced rear bogie pins and I have checked for
loosness
10. Idler arm and bushing
All of this work made for a very nice tight steering system but the
wander never changed much. Early on in my replacement work I discussed
the problem with Jim Bounds and with Wes Caughlin. Wes thought it was
the steering box per his recent article.Jim suggested I get anything
loose in the steering fixed and be sure and set the castor right. He
said to set it at +2.5 deg. which is upper end of limits recommended in
manual. I told the guy doing the 6 Wheel align. to set it that way early
in my replacement sequence. But recently when I went back for a check on
the alignment I found out that he only set it at 1 deg. because he said
that is all he could get without getting the camber out of limits. Then
after doing some checking he said that GMC makes an offset upper control
arm bushing that would allow them to probably get the 2.5 deg. However
that meant changing the upper control arm bushings which had already
been replaced and a new alignment.The cost will be $300 for the offset
bushing replacement plus another $100 for another front wheel alignment.
So I said I would think about it.
Then I got an idea and tried a little experiment. If I drop the rear
end at center of tandems 3" below the normal height I should pick up 1
deg. of castor. So I tried it. The old girl was really setting on her
ass and I thought this was a silly test especially since the air bag
pressure would be quite a bit lower than the 90 PSI I typically run to
get the correct factory ride height.
I was absolutely amazed at the difference. It made the steering and
stability much better and I believe you would get few complaints from
the handling. Believe me I wouldn't have done all this steering work had
it been this way. I raised it up and down twice to verify I wasn't
fooling myself. Each time I raised it the wander would come back and my
passengers were also amazed at the difference they felt in rear end
sway.
So now I am convinced it is the lack of castor. Jim Bounds said they
will wander all over with out the full positive castor and now I believe
it. But I thought I would ask for opinions before I spend the $400.
I am still interested in the 4 bag suspension, but I have always said
I am going to get the steering as right as it can be first before I make
that decision.
