GTD Front A-Arms

Howard Jones · 11-12-07, 03:30 PM

Here's what I've been doing the last couple of weeks.

The problem we have with the front of the GTD chassis is nothing is adjustable, really. You can shim some things and move the others around in slots but neither really solves the problems. I began my GTD suspension journey at the rear with trying to address the huge camber change under bump problem and I believe I have made at least my car a lot better at the rear. This has caused me to really begin to feel the lack of camber for one and nearly no caster for the other at the front of my car. I have removed all the shims in an effort to increase camber somewhat and found that with all I can do the RF is .25 degree neg and the LF is about a 1/8th of a degree POSITIVE! To make matters worse the most caster I can get on either side is about a degree and a half neg.

All of this pointed to new upper A-Arms and mounting points. As you can see the camber is adjustable. I made them 1/2" shorter and with the 1/4" I gain with the mounts, this should give me about a max camber of -3 degrees with the rod ends all the way into the bung . The mounts are offset to the rear and with the increased adjust-ability by spacing the rod end in the mounts, I believe I should be able to set the caster to a range of -1 to about -6 degrees.

I have also eliminated the slots. I have been having problems with the settings changing due to curbing the car at the track. The slots just don't work and I believe I will have solved that problem by drilling fixed mounting holes in the U-shaped mounts instead of slots.

The bottom picture is the jig I had to make off of the original GTD A-Arm. What I did was copy the original part and move the 3 holes the upper ball joints bolts to inboard 1/2".

I should add that the material is 4130, was preheated before welding with the proper filler rod and then normalized as a complete assembly. I got the bungs from The Chassis Shop, the flat stock and tubing (.085 X 1) from Aircraft Spruce, and the rod ends from Jeg,s.

I did all the fitting and had a very good friend at work do the welding. It's amazing what you can do with a hacksaw and a 1/2 round file and a 3/8 drill motor. But then you gotta be "The cheap Italian" !!! to do it like this.

Mark Clapp · 11-12-07, 03:50 PM

Howard, great looking arms, very stout. They will be like a new set of t_ts on Betty!

Frank Catt · 11-12-07, 04:43 PM

Hi Howard, nice work with limited tooling, well done. Have you considered putting a web along the back of the outer plate ( near the three holes ) to prevent any stress on the linear weld between the plate and the tubes ? The plate is quite wide, and any twisting action in movement may stress that weld, how ever good it is. Better still is to consider a spherical bearing on the outer end and bring the arms together more, then you can dump the old cortina swivels. Just a thought ( as you say " my two cents worth " ) Frank

Malcolm · 11-13-07, 04:54 AM

Damm! I agree with Frank again and think that the flat plate could bend/fail under load. Bottom arm takes much more pounding than top arm but still I would hate to hear of an issue after installation. Surprised to hear you had so little adjustment range initially but this should really transform things for you on set up. Good stuff. Let us know if it improves the driving too!

Howard Jones · 11-13-07, 03:43 PM

I think I agree with you both on adding the webbing at the rear of the flat ball joint plate. Back to the hack saw!

Chris_K · 11-13-07, 10:46 PM

Thread drift alert:

Howard, I see a "Foward, Tighten, Rearward..." scribbled in the 2x4 of your workbench. Let me guess, is that for your knockons/offs?

Howard Jones · 11-15-07, 04:44 PM

Ya, that's what that is. I have that written just about everywhere. inside cover of tool box, track log book, etc.

I ordered some material for additional webbing as recomended above. I will post pictures of revised A-Arms when I get them welded up.

By the way, thanks guys for the input, We are all our brothers keepers here on this forum. We all owe it to each other to speak up when we see something like this. Everyone is doing the best they can to build/develop their cars but no one will catch everything all the time.

I had considered the same thing as I built them but I just didn't follow up and do it. Anyway your input just made me rethink what I had already knew to be the way to go.

This just goes to show how much this forum really helps people like me.

By the way Frank, are those A-Arms of yours for sale? If so, how much? And will the top balljoint or whatever that is you are using work with the standard GTD upright?

Thanks again!!!!

Bill D · 11-15-07, 04:53 PM

Great job Howard. It's great to see people take the bull by the horns and design a better product.

Malcolm · 11-15-07, 06:41 PM

Those A arms in the picture are I beleive Southern GT A arms. Available off the shelf if I am right.

Howard Jones · 11-16-07, 03:07 PM

Very nice pair. The question is can they be used with the Ganada uprights ? On another note, I would love to change out all of the suspension parts with something like what I see on the Southern GT, all four a-arms, uprights, trailing arms, the works but I just can't justify the cost. I do believe there might be a market for those front upper a arms if they could be used on a "standard" GTD.

Some one once said on this forum that the GTD is a good car if you change all the parts. Hummmmmm.................

Howard Jones · 11-19-07, 10:04 PM

OK, Here's the fix. I used 4130 1/8 X 1" strip I got from Aircraft Spruce. They are still in the primer here thus the ugly brown. I still need to turn down some spacers before I can put them on the car. I will post some more pictures after I get them installed.

Again thanks guys!

Malcolm · 11-20-07, 04:44 AM

Thats got to help a lot! I have successfully mixed GTD and Southern GT arms and uprights etc together to good effect. Contact Mick and see what he can do for you.

Howard Jones · 12-09-07, 03:27 PM

So here's how it worked out. The first picture is of the original GTD A arm. Then the next few are of the new ones installed. Lastly the two of them side by side.

I was able to get as much as -4 degrees of camber right off the go. Set afterwards to about -1. I intend to set the front to about -.5 at the alignment shop. Also as you can see I can get at least 3/4" more caster. I will need to set this at the alignment shop but I would like to see what about 3.5 degrees of caster feels like. Toe for now is as straight ahead as I can do with a steel tape. I would like to set this at 1/8" total toe in at the alignment shop.

I don't like how far the rodends are out of the bungs so when I do this the next time I am going to put 1/4" shims behind the mounts. This ought to put the treads far enough into the bugs to be safe.

So all that's left is to work on bump steer. Maybe after the first of the year.

Ron Earp · 12-09-07, 03:36 PM

Howard, question - what is the arm distance on one of those? That is, the dimension from heim joint to heim joint? Just curious and I assume it is the same on all GTDs.

My wife wants to know when you'll be making another album. She enjoyed the earlier ones I suppose!

EGLITOM · 12-09-07, 03:40 PM

Howard,

great job, i´m always amazed how much work all people here are putting in, in order to improve there cars. Very professional.

TOM

Howard Jones · 12-09-07, 04:56 PM

Ron......11 3/4" center to center

Ron Earp · 12-09-07, 05:09 PM

Quote:

Originally Posted by Howard Jones

Ron......11 3/4" center to center

And that would be the same on the "normal" ones without heim joints too, right? Should be, just be center to center of the bushing housing.

R

Howard Jones · 12-09-07, 06:04 PM

Yes Ron, center to center on both.... And if I was THAT Howard Jones I wouldn't be making A arms in my garage with a hack saw.

MikeP · 12-09-07, 07:41 PM

Hi Howard,
I was just reading about your plan to shim out the mounting points for the arms. This would seem to be a very bad idea as you will move the inner pivot out of the plane of the supension pivots and track rod ends. Unless you are very careful about rack position you could end up with horrendous bump steer. On my car this was done and the bump steer was very bad. A much better solution to the issue of the threaded portion of the heim joint being too far out of the threaded tube is to make the tube longer. A pain in the ass I know as it invoves yet more cutting and welding but ultimately better than incurable bump steer.
Cheers
Mike