Getting the castor right on a front crossmember (pics)

Let me first say...I know just enough to be a danger to myself. Here's what the gauge showed when we decided we had what we needed (castor) before we welded it. Was told if you get 4 degrees (with the gauge set longutudinally (sp?) at the center of the front crossmember) you'd be good to go after the rake is added in to the mix.


So.....how far out am I? Any comments are appreciated.

 

Are you using a spring on top of the axle, with standard (non adjustable) spring perches?

 

Hmmmm. I set the frame to it's desired rake, with it's wheels, suspension and driveline mocked into position, then set the crossmember to get about 7 degrees of castor before welding it in. Thats just the way I do it though, which might not be 100% correct.

 

That's how I do it too.

 

If you screw up you can always heat the spring perches to get them the correct angle.
I had that problem early on,
kept blowing through those cheap plastic bushings.
TP

 

You were told wrong. When you add rake to the chassis, you will decrease caster. You want the chassis at ride height/rake BEFORE you set your front crossmember angle.

 

That's what I thought

I have been told it can just be corrected by notching the bones. Is this also correct? How much "wiggle" room is OK to get the king pin at 7 degrees if the crossmember is off just a bit?

Sorry for the hijack, but I'm at this same stage right now, and it seems relevant.

 

Boxcar, in your pictures, when you add rake, or lift the ass end , you will be moving the needle back to zero instead of closer to 7.

You'll have to do something different than what you have planned

Had you set it 10-12*, then add some 2-5* rake you'd be much closer.

Disregard the above if you are planning a nose high stance

 

A good solution to caster is a set of adjustable spring perches, cost under a 100. bucks and lets you set the degree after every thing is in place..........

 

Everyone is right, your crossmember is not set at enough of an angle to match the front axle caster. Typical rake is about 3 degrees, so if you subtract that from the 4 degrees you dialed in you will only have 1 degree at the crossmember. Your only fix now is the adjustable perches that have been mentioned.

I usually set the crossmember at about 10 degrees in relation to the frame. That way when you rake the car about 3 degrees you still have 7 at the crossmember.

Don

 

Correct me if I'm wrong but adjustable perches still require something to be done with the bones. Either adjustable mounts, pie cut and reweld, heat and bend, etc.

 

Yes sir I am...

 

A byproduct of experiance...one step fwd, two steps back

 

Might be the way I get out of the woods here. Dad will probally want to cut it out and reset with gauge at 10-12 degrees. I hate to start working around something not quite right.

Thanks for all the insight guys.....would you do it over or get the adjustable perch...It doesn't look that bad but seems to me that a guy would have to add a wedge of sorts to the top of the spring to get the right castor started from above rather than have it all happen at the perch.

 

I'm using hairpins.

 

Another good question...hope you get an answer.

 

Caster needs to be set at the kingpins. Adjustable perches will just keep your spring from binding and not require crossmember modifications.

 

The final adjustment for caster and camber can be done by the local front end tech on a good alignment machine. The axle can be twisted and bent into submission and as long as it's not chromed will be ok.

Dave.

 

Ok...now Im really confused.
Assumptions 1 & 2 are correct.
My crossmember has a caster of its own...4* ish and leaning back...SO I'd have called it nose up. Ultimately increasing my WB from 106 to a hipothetical 106 1/2 ish. I really wont know till later.

I'm away from the car now...my dad is with it. Had the conversation this morning of the issue. We're moving toward re-doing it...it's my fault, I went with some info and may have translated it wrong or ?? I was thinking my way ahead was to refit with the CM leaning back, placing the gauge at the center of the CM and look for 10*.....Is that right?

thanks for the help all!

 

No, you are reading the angle finder backwards, he actually has 4 degrees of crossmember leaning backwards. If he then rakes the frame nose down he will wipe out 3 of those degrees and have only 1 degree left.

If you are redoing it just lay the crossmember back 10 degrees with the frame level and when you rake it 3 degrees (or thereabouts) you will end up with a spring that won't bind on the shackles as bad.

Don

 

Don's Hot Rods....thanks....got it!

 

I'm asking. Don't mean to confuse this already settled situation.
Will any of this change when a load is placed on the spring?

Kinda in the same boat meself.

 

Sorry about that , I deleted that post.
Thanks don

 

Maybe I can get this up to the top and ask another question. Seem in line with this thread.

I understand that the 5-7 degree thing is in stone, tried and true. Got it.

Can someone explain why my stock model A has the kingpins at 1 1/2 degrees and it drives great? Just need to know the tech reason why it works at such a small amount.

Bryan

 

Every car is different. You could build two identical cars side by side and they could each like different amounts of caster and toe in. The numbers we post are just starting points and when the car hits the street you might have to fudge a little to get it perfect. I've had them at 4 degrees, 7 degrees, and even 10 degrees and each one ran right down the road.

Don

 

Any one in the Sunday AM crew care to chime in?

 

None here in my part of Ohio,rained last night though. I don't really want any snow thank you.

 

Heres a question. I'm doing the same thing but did it different/wrong. I set my frame rails at 0 and the crossmember at 0. I have not done anything in the rear of the from yet. So technically as long as I put 7 degrees or so of rake into the rear of the frame i would be good correct????

 

No, your castor will be 7 degrees in the wrong direction.

 

No. Because you are looking for "positive" caster. This means the top of the axle would be leaning back.
As the vehicle lifts in the rear via rake, it would make the top of the axle lean forward, creating "negative" caster.
So, as others have said, start with a level frame, 10* crossmember angle, 3" rake would net 7* caster.
BTW, Pete and Jakes recommends 5* positive caster. Others say 7*.
Good luck!