What would you do?

Lynn · 05-26-07, 09:38 AM

PROBLEM - When the front end was aligned, we were able to get it into spec, BUT the 3/4 rod end is threaded completely into the A-Arm excepting one thread. While I know the rod end cannot turn itself out, the slight amount of tolerance in the thread engagement will become larger over time. Even now, when circumstances are just right, I can hear a pop noise from the rod end shank as it loads/unloads. This is very unnerving to say the least. The bottom A-Arm has a fixed position ball joint, so I really can't easily manipulate the position of the bottom attach point of the upright.

So what would you do? Both short term and long term solutions appreciated!

Thanks,
Lynn

chuck smith · 05-26-07, 09:59 AM

I cannot understand why it would make a popping sound if it is seated well . Removing the heim and getting a shorter one or shortening that one would allow it to seat all the way in and still keep the alignment specs, that would be the simplest way.

Scott Calabro · 05-26-07, 10:09 AM

Lynn,
Is the lower control arm ball joint worn out ON THAT SIDE ? and is the opposite side of the suspension suffering from the same issue?
S

chuck smith · 05-26-07, 10:42 AM

thinking further I suppose you could not shorten the heim and keep specs . How about a non threaded spacer to fill in the small gap this should firm it up

Lynn · 05-26-07, 11:07 AM

Scott, No, ball joints have no wear; mileage on car is less than 500mi. Yes, both sides have the same issue and the track width is per GT40 spec. It is as if the leading tube of the A-Arm was cut to proper length, but the width of the shoulder on the threaded tube end was not subtracted so that the entire assembly ended up at the proper length.

Chuck, the threaded shank of a rod end does not bottom out or "seat" into/against anything. The threaded tube end is bored completely through and, as it is, the rod end could be threaded deeper into tube end. However, any change in position of the rod end would take the alignment out of spec. Ordinarily, a jam nut is used to remove the play in the thread engagement (this is where the popping noise is coming from) and fix the position of the uprights upper attach point. The only rod end dimension that, if changed, would help is the distance from the spherical bearing's bore center to the top useable thread on the shank. I have checked several different brands of rod ends and this dimension appears to be standardized. Any removal of material from the rod end collar to provide room for more threads and, thus, a jam nut, would reduce the tensile load along the shank centerline that the rod end could carry.

I have tried a two piece locking collar that I profiled to engage the rod ends collar. It did help a bit, but the two screws which hold the two "C" shaped pieces together quicly strectched. The collar also interferes with the stud onto which the rod end is attached at the limits of the upward movement of the suspension and this is highly undesireable.

chuck smith · 05-26-07, 11:11 AM

that is why I am thinking a thin collar that is not threaded would provide support in that area, a spacer so to speak..

Scott McDill · 05-26-07, 11:15 AM

As I understand Lynn's post, He is looking for more range of adjustment in the rod end. And possibly the ability to use a jam nut in order to prevent the threads from wearing. I don't think it is supposed to be "seated" since that would completely eliminate any future adjustment. Finding a different rod end with threads closer to the bore center would be very difficult and not desirable since most are made to sae specs in order to be easily interchangeable. If this is the stock control arm arm, I would expect it would have been designed with sufficient tolerance to allow for more adjustment. Since this is primarily a camber adjustment why not just adjust both of the rod ends out on the same side, and install the jam nuts. This will move the upright/hub/wheel further out, and result in need for adjustment in the tie rod also to maintain proper toe. Bump steer would also need to be checked. If the wheel/tire can't be moved further out due to clearance problems, the only other option would be to shorten the controll arm.

Pat Buckley · 05-26-07, 11:32 AM

Short of having new A-arms made up, I think Scott hit it on the head.

chuck smith · 05-26-07, 12:17 PM

would the camber specs not be wrong if you did that procedure?

Frank Catt · 05-26-07, 12:31 PM

Lynn, there is only one way to do this, make new arms ! Do it safe rather than do it cheap, its a big accident otherwise

Scott Calabro · 05-26-07, 12:58 PM

Lynn,

I agree mostly with what is posted. This issue is probably because the chassis/control arms are not produced to exacting tolerances. I would chop off the inboard ends of both upper and lower arms and install rod ends in place of the poly bushings.

Before you do though check to see if the chassis is not twisted. I know it sounds crazy, but it could be it wasn't jigged correctly during mfg.

Just my .02

Glad to hear you are doing better !

S

Pat Buckley · 05-26-07, 12:59 PM

Quote:

Originally Posted by chuck 1

would the camber specs not be wrong if you did that procedure?

He would move the botom and the top out the same amount - zero sum.

Scott Calabro · 05-26-07, 01:33 PM

Not really Pat.

If he did it correctly (length), he would have a fully adjustable front suspension (except king pin inclination angle)

Lynn, google S&W race cars and check out the weld in threaded tube ends. These will make the solution simple.

Best,
S

Lynn · 05-26-07, 01:59 PM

Pat & Scott M - Can't move the bottom out to match the top. Notice the last sentence in the problem description: "The bottom A-Arm has a fixed position ball joint, so I really can't easily manipulate the position of the bottom attach point of the upright."

Scott C. - If new A-Arms are built, they will have rod ends on the inboard attach points. If the issue wasn't symmetrical side-to-side, a twist in the chassis would be more plausible. For the time being, I'll follow the Ocham's Razor rule and assume that there was a simple measuring error in the construction of the upper A-Arms.

BTW, as designed, the KPI is adjusted by a combination of the use of shims to move top & bottom A-Arms forward and aft, as well as, the in-out adjustment of the upper/outer rod end which also has a fore/aft component. Indeed, castor, camber and KPI are all affected any changes (including changes to the toe), so you really have to sneak up on proper alignment settings making tiny changes to one thing at a time.

Lynn · 05-26-07, 02:11 PM

Scott C,

Check out the prices for the weld in threaded tube ends here: Coleman Racing

Lynn

Joe T · 05-26-07, 02:52 PM

Well I suppose its a matter of how desperate you are to resolve in the short term.

You could cut a piece out of both tubes in the middle & thread an adjusting piece in, this would load the urethane bushes slightly and would depend on the compliance of them etc. Lots of race setups have these (my AC did).

You could also put a grub screw in the end to lock the rod end, I would put it near the top as it will damage the thread with repeated use.

If you know the rod end is in the right place, you could use threadlock on it, that should take out any movement and stop the thread wearing.

Russ Noble · 05-26-07, 04:27 PM

Not a big problem Lynn.

Franks advice is undoubtedly sound but in this case, IMHO, it's a bit like putting in a new motor to cure a fouled plug! I would just shorten the arm at the heim joint end to make room for a jam nut and also a wee bit more to provide for a little future adjustment.

You may be able to cut around the tube and remove and reuse the existing threaded sleeve reinstalled in a suitable position. Othewise just chop it back and so long as there is still sufficient length of thread left (rule of thumb is one and a half times the shank diameter), it will be OK. The amount you have to shorten it is not a lot.

If the modification involves also cutting a small part off the end of the other section of the arm where it joins in, that will not be problem just finish it off nicely with a welded cap. There will be more than enough weld holding this anyway and the top arm sees only relatively light loads.

Hope that helps,

Cheers

Big-Foot · 05-26-07, 09:32 PM

I would not run without a Jam nut - period.

I would carefully cut away the weld from the threaded b-u-n-g and the intersecting leg of the upper control arm.

I'd then shorten the primary leg a good 10-12mm.

Re-insert the threaded b-u-n-g and re-weld.

I would add a rosette weld where shown and I would gusset the legs of the control arm as shown.

Yes its re-work and a pain in the backside, but it;

1) Allows for the addition of a proper jam nut
2) gives you added adjustability
3) Will be more stabile as the gusset will minimize flexing under hard cornering
4) capitolizes on the work already done to the greatest degree

Well - You asked what I'd do - there it is...