Why can't they set my caster to spec? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Tom · 06-18-2010, 09:55 PM

I had my alingment done today. Spec for caster is 2.8-4.8*, They set left to 5.0* and right to 5.7* Cross caster was in spec at .7*. Why would the two sides be off like this?

LONGHAIR · 06-19-2010, 08:38 AM

What kind of truck? how much lowering? with what method?.....we are not mind readers

The difference from side to side is to compensate for the crown of the road, but why they left it with so much is hard to say. Did they say that this was as close as they could get?

Tom · 06-19-2010, 02:07 PM

Sorry I relized it as soon as I wasen't near a computer. Its on my 98 gmc 1/2ton. It is lowerd with 2" belltech spindles and 3" western chassie springs. I didn't get a chance to talk to them [had brother do it while I was working] but the before and after specs are both above the max factory spec and the previous alingment was a different shop so Im assuming its the best they can do.

cdowns · 06-19-2010, 05:18 PM

you need special longer bolts to attach the upper aframe crosshaft and spacers when using those shorty springs

some slignment shops have them

Tom · 06-21-2010, 12:19 AM

Can't find anyone around here who knows what Im talking about. Anywhere I can order these pieces online so I can install them myself?

DKN · 06-21-2010, 12:48 PM

The suspension gained caster as soon as the rear was no longer higher than the front. You may be out of adjustment range.

Caster is an imaginery line from the center of the pivots between the upper and lower balljoints measured to verticle. So lowering the back several degrees to make the truck sit level increased the caster by several degrees. If the front springs are any shorter than new OE length then you would have increased caster again. This because of the anti-dive geometry, it increases caster as the suspension is compressed.

All this extra caster will do is make the truck want to drive straight. it will take more effort to turn. If you can turn OK then I would not worry about how hi or low the number is.

Danny Nix
CPP

aggie91 · 06-21-2010, 02:47 PM

Quote:

Originally Posted by DKN

...All this extra caster will do is make the truck want to drive straight. it will take more effort to turn. If you can turn OK then I would not worry about how hi or low the number is.

Danny Nix
CPP

That is the same thing I was thinking when I read thru this thread...

LONGHAIR · 06-21-2010, 07:38 PM

Quote:

Originally Posted by DKN

All this extra caster will do is make the truck want to drive straight. it will take more effort to turn. If you can turn OK then I would not worry about how hi or low the number is.
Danny Nix
CPP

That is true mostly.....an extreme amount of caster causes "camber gain". Meaning that the wheel "tilts" more as it is turned. This puts more pressure on the edges of the tread. This accelerates tire wear and higher in-put effort as well.

Tom · 06-21-2010, 09:52 PM

Quote:

Originally Posted by DKN

All this extra caster will do is make the truck want to drive straight. it will take more effort to turn. If you can turn OK then I would not worry about how hi or low the number is.

I love learnin stuff

I've been trying to get rid of a pull to the right and vibration, 2 alingments and 2 sets of tires hasen't done it so I was thinking perhaps the caster was the cause. I won't worry about it from now on. Thanks

ksbrktracer · 06-22-2010, 01:01 PM

One thing I am curious about and saw no mention of is did they knock out the plugs in the upper control arm mounts for the upper control arm eccentric bolts. This gives it alot more adjustability. My crew cab 1-ton converted to 1/2 ton with belltech spindles and springs is dead in spec and has excellent tire wear and drives excellent ,it is down about 5" in the front. As for your vibration that may be a case of diagnosis by elimination, lowered trucks I have seen vibrations (shudder) caused by pinion angle, loose u-joints , tight u-joints ( have to remove driveshaft to find this one) etc....just throwin some ideas out there...!!!!!!!!

06-18-2010, 09:55 PM	#1
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,748	Why can't they set my caster to spec? I had my alingment done today. Spec for caster is 2.8-4.8, They set left to 5.0 and right to 5.7* Cross caster was in spec at .7*. Why would the two sides be off like this? __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

06-19-2010, 02:07 PM	#3
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,748	Re: Why can't they set my caster to spec? Sorry I relized it as soon as I wasen't near a computer. Its on my 98 gmc 1/2ton. It is lowerd with 2" belltech spindles and 3" western chassie springs. I didn't get a chance to talk to them [had brother do it while I was working] but the before and after specs are both above the max factory spec and the previous alingment was a different shop so Im assuming its the best they can do. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

06-19-2010, 05:18 PM	#4
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Why can't they set my caster to spec? you need special longer bolts to attach the upper aframe crosshaft and spacers when using those shorty springs some slignment shops have them __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

06-21-2010, 12:19 AM	#5
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,748	Re: Why can't they set my caster to spec? Can't find anyone around here who knows what Im talking about. Anywhere I can order these pieces online so I can install them myself? __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

06-21-2010, 12:48 PM	#6
DKN Active Member Join Date: Feb 2008 Location: Los Angles CA Posts: 136	Re: Why can't they set my caster to spec? The suspension gained caster as soon as the rear was no longer higher than the front. You may be out of adjustment range. Caster is an imaginery line from the center of the pivots between the upper and lower balljoints measured to verticle. So lowering the back several degrees to make the truck sit level increased the caster by several degrees. If the front springs are any shorter than new OE length then you would have increased caster again. This because of the anti-dive geometry, it increases caster as the suspension is compressed. All this extra caster will do is make the truck want to drive straight. it will take more effort to turn. If you can turn OK then I would not worry about how hi or low the number is. Danny Nix CPP

06-22-2010, 01:01 PM	#10
ksbrktracer TNT-MOTORSPORTS Join Date: Mar 2008 Location: TULSA OKLAHOMA Posts: 2,692	Re: Why can't they set my caster to spec? One thing I am curious about and saw no mention of is did they knock out the plugs in the upper control arm mounts for the upper control arm eccentric bolts. This gives it alot more adjustability. My crew cab 1-ton converted to 1/2 ton with belltech spindles and springs is dead in spec and has excellent tire wear and drives excellent ,it is down about 5" in the front. As for your vibration that may be a case of diagnosis by elimination, lowered trucks I have seen vibrations (shudder) caused by pinion angle, loose u-joints , tight u-joints ( have to remove driveshaft to find this one) etc....just throwin some ideas out there...!!!!!!!!



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