Crossmember Drop

[greatdaen]

I see the general approach to the front suspension mods is to put the lCA pivot way inboard and keep the UCA pivot outboard of the frame rail.

I know this makes the fabrication easier, but I wanted to just throw out an image of the suspension geometry. As you can see from the image below, the short UCA / long LCA causes the King Pin axis angle to traverse through a much more severe angle than the alternate long UCA / short LCA.

I suppose with this low of a ride, you never get going fast enough to need the control, but the name of the game in steering control is to keep as much of the tire patch on the ground as possible. And you do that by keeping the king pin axis as vertical as possible throughout the suspension travel.

The alternate approach would require the UCA pivots to be inboard of the frame and they would be competing for real estate with engine components. But it can be done - I have seen it.

This is just FYI/food for thought for the guy still in the planning stages - if all you want is looks - do the easy thing. If you want to have a suspension design that works as good as it looks, then....

-dch

[Bowtie67]

Some of you with the rack & pinion setups, do you have any good pictures of the routing of the stearing hookup from strearing column to the rack. I'd like to see a few before I start fabing my setup in. Also where the best place to pickup the stearing Ujoints from.

[Captkaos]

Originally posted by greatdaen
As you can see from the image below, the short UCA / long LCA causes the King Pin axis angle to traverse through a much more severe angle than the alternate long UCA / short LCA.

I suppose with this low of a ride, you never get going fast enough to need the control, but the name of the game in steering control is to keep as much of the tire patch on the ground as possible. And you do that by keeping the king pin axis as vertical as possible throughout the suspension travel.

The alternate approach would require the UCA pivots to be inboard of the frame and they would be competing for real estate with engine components. But it can be done - I have seen it.

This is just FYI/food for thought for the guy still in the planning stages - if all you want is looks - do the easy thing. If you want to have a suspension design that works as good as it looks, then....

-dch

There is alot more to suspension geometry than the arc of the front suspension as viewed from the front. You fail to realize that the spindle is leaned inward and is not on a vertical plane as you depicted. If you plotted out one that had an angle in it, you would see that the SLA keeps the wheel almost verticle as it rises, angling in under extreme jounce. The lower bumpstop limits this jounce and therefore eliminates the angle. Under rebound, the contact patch of the tire stays almost flat against the surface, and again, the upper bumpstop limits this travel. In addition, due to the affects of geometry and packaging it is impossible, and unfeasible to have a kingping vertical. This doesn't make the contact patch the greatest. Keeping the centerline of the tire/axis of the spindle hrizontal does this. You are also not taking in caster and camber changes cause by this setup. A SLA suspension is setup with the top control arm shorter than the bottom so the arc is shorter than the bottom arc so the spindle rises and falls almost vertically (negative camber taking over in extreme jounce) What you are suggesting it flipping the SLA setup upside down. Now when you go to full rebound the tire goes positive camber and your contact patch moves to the outside sidewall of the tire. Not a good situation. In addition, there is the problem with the frame being in the way for the upper control arm to follow and arc. The frame would limit rebound.

The way we are dropping the truck with the crossmember drop has no affect on the suspension components. It is only moving the centerline of the tires axis up and therefore lowering the vehicle.

[ncbiggj]

ok maybe Im wrong here but couldnt you Z the frame and not have to notch and change all kinds of stuff on the crossmember? But that would leave all the a arms in the stock spots and just bring it up 3 inches.. So if I am wrong please tell me because that is what we are getting ready to do to mine..

[Captkaos]

Look at the bottom of this thread where I replied, or search for "Z the frame"... BTW, yes you could Z it.

[ncbiggj]

Just seems like it would be alot easier then notching the crossmember and having all the issues of stuff hitting now.. I read this whole thread and damn you guys have got some good ideas and how to remedy stuff before the next person hits it..

[Captkaos]

Well z-ing the frame you will have the same issue only multiplied. You will be moving everything forward the firewall up. You will also be moving the front frame horns down. Now you have issues with the a/c box, distributor, brake booster, hood, frame to inner fenders (if you keep them), fan shroud, brake lines from the booster, steering shaft to a-arm... Z-ing Doesn't sound simpler to me. Cross drop (the Captkaos Customs way) just causes steering issues.

[ncbiggj]

Ok, tell me if I am wrong here, but the bottom of the crossmember hits before the frame does. What I want to do is make the crossmember hit at the same time that the frame does. What I was trying to accomplish by Zing the frame is bring that up. I see alot of the pics here and on your site that you are cutting out the center section. Is that raising the bottom section up or bring the top down? It looks like bringing the top down. I was thinking I could go in and cut some off the bottom of the crossmember and plate it all back in? would that work or no? Im learning on these older ones. I got my mazda Body dropped on 20's but it is a complete different set up.

Im not to worried about having to cut out the inner fenders or nayhting like that. I have tubbed the firewall before to get the tires to clear on my other truck. I have attached the pic of it..

[Captkaos]

Originally posted by ncbiggj
Ok, tell me if I am wrong here, but the bottom of the crossmember hits before the frame does....... Is that raising the bottom section up or bring the top down? It looks like bringing the top down. I was thinking I could go in and cut some off the bottom of the crossmember and plate it all back in? would that work or no?

No, that would be incorrect. The lower control arms hit before anything does. Z-ing will bring that up as you are cutting that section to Z. How you describe my process, bringing to top down or bottom up, depends on your perspective. With the bottom of the crossmember stationary I am bringing the top down, with the top stationary I am bringing the bottom up. In acutallity I am channelling a section out of the center of the crossmember. What you are describing about cutting the bottom wouldn't work unless you did something with the control arms. They hang below the bottom of the crossmember.

[loweredd]

Good pics Capt!!

It looks like when I "Z" mine in the coming weeks, I need to photo my ars off. I will be able to help out others with my beautiful pics.

[ncbiggj]

I will look tonight but I swear that the center hangs down lower on my 69..

[Captkaos]

Originally posted by loweredd
Good pics Capt!!

It looks like when I "Z" mine in the coming weeks, I need to photo my ars off. I will be able to help out others with my beautiful pics.

yes definitely get some pics loweredd. BTW, that picture was JUST my bag setup. No spindles, no notched Crossmember, just the bag setup without air.

[Hotrod70C10]

Originally posted by ncbiggj
I will look tonight but I swear that the center hangs down lower on my 69..

I'm not into all this crossmember hacking yet but, If yours is stock then the arms are lower than anything else.

[ncbiggj]

You are correct... Mine looked different because it is not lowered yet.. But I took some pics of it and looked at them compare to yours and you are correct.. The A Arms do hang lower then the crossmember..

[ghetocrewzer]

Grnddwn, On the left upper control arm did you have to notch it much w/ the crossmember drop. Mine already looks close just w/ the front lowered. Got it torn down to bag aand I really want to drop the crossmembe just wonder if I'll have to change the steering shaft angle also. Also are those 18's on the front of your truck or 20's, cause i'm running 20's and want my Suburban as low as yours in the front.

[Captkaos]

ghetocrewzer,
You must have not read the whole thing huh?
You WILL have steering/shaft issues that will need to be addressed with this Mod.

[loweredd]

Heck, I have steering shaft issues WITHOUT the crossmember mod.

[SCOTI]

I know this isn't actually part of the crossmember drop, but I just wanted to relay some info on one of the manufacturers mentioned within the thread. First, a little backround....

A neighbor of mine wants me to drop his 66 fleetside chevy. I gave him all sorts of articles to read & my list of recommendations. His budget dictated his choices for the most part (along w/ride quality), so I recommended Turners stepped a-arms (since he wouldn't have to spend more $$ for a disc brake upgrade).

He talked w/Bill & decided that's the way he would go. I warned him in advance about several board members complaints of lengthy waits for their parts but he felt it was worth the chance. He placed his order on 2-19/20 & received the stepped a-arms, new shafts/ball-joints, & 2" aluminum blocks/u-bolts on Fri 2-27. His only complaint was that he ordered a larger diameter sway-bar (& related parts) but it was back-ordered..... yet nobody told him, so he's kinda' bummed since he wanted to have me do everything @ once.

The quality looks great on the arms.

So....... it seems if Turners actually has things pre-fabbed, there's decent ship times. Possibly on other things that are done more on a per order basis you will have to wait though. I will also mention that this guy commented that Bill Turner was one of the nicest guys he'd ever talked w/over the phone.

[Captkaos]

I can attest to the fact that putting one of these together is no simple order. It takes a good number of hours to cut it, verify it is straight and the weld it back up making sure it is still straight. I know my process takes a good 4 hours of fab time (I am anal, and it might take longer than that) If you place that on top of the fact that a lot of people don't want to supply the core as it is cheaper, THEN you have to go out and find a core. That could take a up to a week! Multiply this times 10 people wanting at once, and well you start having delays. If you called me TODAY and wanted one, I would ask for at least a month because well I have no cores now and would have to find them. And trust me. It seems that everywere I go to find one ALL 73-87 owners want to wreck the truck from the front! (unless of course I need parts from the rear of a truck.... )

[bagged87chevy]

So Captkaos. Your saying that it is easier to do the crossmember drop as opposed to "Zing" the frame? I just want my truck to lay the body on 20's with 35's. Will the 1.5 inch crossdrop do that for me? I really don't understand how the crossdrop is any less complicated though. Won't you still have everything to deal with besides the distributer and fan shroud to contend with? Just with drop spindles and bags my truck is right against the ac box so I know thats gonna have to come out. And my brakes look like they could be an issue with the added 1.5 inches of drop. I am going to do one of these mods! I would really like to know which way to go though.

[phantom dually]

Scoti you are correct Bill Turner is possibly the the nicest guy I have ever dealt with. He just seems to be slow at getting back to me. Maybe he just dont like me!! Im glad to hear that he got someones parts out in a timely fashion.

[SCOTI]

Phantom, I e-mailed him @ the link on their web-site about pricing & shipping info 2-weeks before my neighbor ordered his parts...... & Bill still has yet to respond. So it's not just you.

Oh, it's time to update your sig......

[phantom dually]

Oh yeah the sig Thanks!!

[Izzy]

Originally posted by ncbiggj
Ok, tell me if I am wrong here, but the bottom of the crossmember hits before the frame does. What I want to do is make the crossmember hit at the same time that the frame does. What I was trying to accomplish by Zing the frame is bring that up. I see alot of the pics here and on your site that you are cutting out the center section. Is that raising the bottom section up or bring the top down? It looks like bringing the top down. I was thinking I could go in and cut some off the bottom of the crossmember and plate it all back in? would that work or no? Im learning on these older ones. I got my mazda Body dropped on 20's but it is a complete different set up.

Im not to worried about having to cut out the inner fenders or nayhting like that. I have tubbed the firewall before to get the tires to clear on my other truck. I have attached the pic of it..

Saw a pic of your mazda in the Novemberfest coverage in the newest ST.

[Captkaos]

Originally posted by bagged87chevy
So Captkaos. Your saying that it is easier to do the crossmember drop as opposed to "Zing" the frame? I just want my truck to lay the body on 20's with 35's. Will the 1.5 inch crossdrop do that for me?

Z-ing requires ensuring the front and rear of the frame to stay in the same posistion as related to stock so fenders will align, core support will connect, everything is welded on square to stay in alignment etc.. It moves the whole suspension system, frame section (bewtween the horns and the firewall) AND engine up.
Your radiator is now 3" lower than your fan, and your shroud is sitting on the fan. This will have to be addressed. The distributor is now 3" higher and will be interfering with the firewall. This will have to be addressed. Depending on the motor you install, you might have interference with the brake booster possibly. With any major drop there will be inner fender/heaterbox/AC interference so this is the same for both..... BUT NOW your drivetrain is out of alignment, it is angling down more. The transmission mount will need to be moved up accordingly to put it back into alignment, or you could lower your motor. Moving the trans mount will cause problems interfering with the floorpan possibly.

Notching the crossmember (my way) the engine doesn't move, only the location of the suspension pieces. You will still have to address the inner fenders and the heater/AC box, and steering issues, but... none of the other stuff.

As for laying the body on the ground, well, the frame will hit first as it is lower than the body. As for which way to go, that will have to be your decision. You can notch the front 2" if you wanted.