Projects My "You didn't build that" 27 T Roadster build thread

Even though your front radius rod and drag link appear parallel they are not. Take a line from chassis pivot of the L/H radius rod to the center of the king pin boss on the axle, that is its pivot line as its the center of the wheel that counts. they are far from being parallel and will travel in a much different arcs to each other when the axle moves up over a bump and with the drag link being longer its arc is flatter than the other arc. This can be worked out with string, chalk and a tape measure....or wedge a front tire against the curb (with a rag to not mark the tire) and bounce hard up and down on the front of the chassis ( rags so to not mark the super paint) and see if the steering wheel moves back and forth. JW

 

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Wheeliedave, you Quoted my post, what was your point? JW

 

I'm guessing he was trying to emphasize that your way of checking it is good!

 

Thanks, Dick.... i like compliments. JW

 

First, thanks for the phone call and input Jeremy! We'll get this sorted, won't we? Hey, next time you call (if after my work hours) press 5 for emergency service so it rings my cell phone! Also, I'll PM you my cell.

Back at it this afternoon, confused as ever. Changing one thing at a time and taking notes.

Changed tire pressure to 25 lbs, no change.

Pulled panhard bar off, no change.

Checked oil level in shocks, both low. Filled with 30W per specs found on the interwebs, no change.

Double checked toe and caster. 8°-ish caster, 7/32" toe in. Yeah, didn't bother going for the extra 1/32" yet.

Steering arm is tapered so rever mounting the steering linkage (at this point) is a huge project.

I said last week I was going to buy a steering stabilizer but I didn't do it. After discussing the problem at length with Lenny at So Cal I wanted to try to fix the problem instead of masking it.

Here's what I've noticed:
1. The car seems to drive perfectly fine at any speed up to 50 (fastest I've gone).
2. Steers well, tracks well, responds well to steering input.
3. It SEEMS that when I hit a bump at any speed between 30 and 50 WITH THE FRONT LEFT TIRE ONLY that the issue begins.

Going to swap left and right front tires in a minute and see what happens.

Also, going to a local alignment shop Monday. Talking to the guy he made a suggestion that I think someone in here mentioned before - bounce on the front end and see if the steering wheel moves. If so, something is binding. Well it does and it's probably somewhat amplified by the removable steering wheel mount. Holding the wheel lightly stops the movement to the point where the steering wheel moves about as much as a tire out of balance.

Bob stopped by today and we talked about a million things. We went through step by step and checked thing of the list.

I think the last thing we are looking at is making a spacer to drop into the mount between the spring perch and the split wishbone, effectively giving more of an angle to the spring shackles.



Going to throw a few other pics in just for argument's sake. Thanks everyone for the help with this!












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I like the idea of the spacers to give more angle to the shackles Eric. It seems that the shackles are sitting stretched out fairly flat in the one picture.

I’m not sure if that will cause the problem but it’s good that Bob is helping you out.
It will be interesting to see how this plays out and what the solution is.

I’m definitely following along as I have from the beginning.

Good luck with it.
Larry

 

How about --- I screwed up ? I' not really sure what I did !


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Parallel to the split bones is not what it's supposed to be. With the drag link/pitman arm on the same plane as the bones is correct.

 

So draw us a picture to illustrate what is right.

 

Eric, you need to flip the steering arm so the rod end is on the top (hope the brake hose isn't an issue). this will get the arcs of travel closer to each other and WILL reduce the bump steer. You can do it without removing the rod end, just loosen the jam nuts and lengthen the drag link till it lines up again, i know it will make a difference. I didn't notice the spring mounts were adjustable, Bobs idea is good. WE WILL GET IT SORTED !! JW

 

After re reading what you wrote above, you said it only does it with the L/H front wheel hits a bump, that confirms it is the drag link that is at fault as if the R/H side moves upward it does not move in an arc with the drag link. You may need a new top arm that lifts the drag link higher than just flipping it. That will increase its angle and intern making the two arcs that much closer together.
Eric, if you send me the measurements we talked about i will work out exactly what it needs to be to fix it. JW

 

Had a little time to work on the car again today. Jeremy, I still didn't get the measurements for you but will shortly. And after doing the math I totally see what you're talking about and I think you're correct. I'll relocate the steering arm this week.

In the meantime I knew I had to get the proper angle on the shackles. I grabbed some washers for a quick test of theory.



I notched them and took the burrs off.



Loosened the spring perch and slid the spacers in.



And achieved the angle needed.



Haven't driven it yet to see if it's made a difference. Still have tools all over the driveway. Will report back shortly.

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Okay, lengths attached in photo.



At center/neutral steering position steering tie rod end is directly over the spring perch NOT KING PIN as I wrote in the photo.

Tie rod end at Pitman arm is directly wetical to pivot at center/neutral steering.

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Made a quick 4 mile loop tonight, chased down by a guy on a Harley that wanted to check it out, LOL.

So the results are in: still has death wobble but changing the shackle angles diminished it significantly. Instead of rapidly having +/- 15° until I got under 5 MPH it's now a slight +/- 1° until I slow to 35.

Major improvement but I won't be happy until its solved. Next order of business is to flip the steering arm on the spindle. Maybe tomorrow.

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Good results so far, i need the measurements of ground to center of spindle and rod end center on steering arm, also ground to center of radius rod pivot and drag link at pitman arm. I may have to come over early and help ya. JW

 

There is an extensive thread on the subject titled “Cowl Steering...Just Stop” started by Pete Eastwood. Title doesn’t accurately reflect that it really covers properly setting up any side steering config. With numerous contributions by many HAMBers it pictures and explains how to avoid or minimize bump steer.
https://www.jalopyjournal.com/forum/threads/cowl-steering-just-stop.1101046/

 

Here is a picture of my radius arm drag link set up. It's not perfect but close. I am going to make the pitman arm a little longer and it will be better but I don't seem to have any bump steer now. I did have some death wobble when I would hit a bump at speed but balancing the tires helped a lot. I've got about 9deg. caster and 1/8" tow in.

 

I'm not sure these things are contributing to your problem, but maybe you could think about them: Your shocks are so far back from the axle, that the little amount of travel the axle has is significantly less at the shock's attachment point. Say your axle jounces 2 inches, and your shock attaches 8 inches farther back down the wishbone. What amount of travel does the shock actually have? Maybe Armstrong didn't design their shocks to work accurately with only an inch of up/down. Maybe different viscosity fluid would make a difference?

And, that pitman arm looks really short. It might not make much difference for the death wobble, but maybe your ease of steering could be effected.

Also, I don't think you need a panhard bar with the shackles at such a shallow angle. If you add spacers behind those perches and get the angle closer to 45 degrees, the panhard might be a good idea though.

 

The upper example shows the idea. To keep the arc's as close as possible, and reduce bump steer, both the drag link and the radius arm need to have intersecting planes. The bottom illustration shows drag link and radius arm parallel, the arc's of travel are very different, which WILL result in bump steer.

 

You cheated, you didn't draw those pictures.
But yes you're right, I've seen those illustrations before.
I tried to get mine as close as I could to the top one, I guess I'll see how it works once I get out for a drive.

 

I would have, but my crayon's need to be sharpened.....

 

The top illustration is what i am working on with Eric, except his Pitman arm goes up. If we cant get the front of the steering arm up enough to get the arcs travelling together the radius rod pivots will need to come up with correction to the castor angle....... WE WILL FIX IT. Here's my setup, no bump steer and NZ has the roughest roads!! JW

 

If balancing is an issue, maybe dynabeads (I think that is the name in the in-tire balance beads) might help? I don’t have any personal experience with them but there are several threads on the H.A.M.B. about them.

 

One aspect that both those diagrams fail to show is the spindle center, this is where the axle arc is taken from......NOT the bones to axle point. JW

 

Thanks for pointing this out. I didn’t know this.

 

Watching for an update

 

Sorry to just pop in on this topic, but I think Alchemy is on the right track. The Armstrong shocks used on british cars are attached directly to the lower A-arm, or in the case of the MGB/Sprite, it is the upper A-arm.
The end of the axle is where you would have maximum travel, but your shocks are mounted so close to the centerline, the levers are not going to move but a couple of inches. Are those rebuilt shocks? Are they "handed" (i.e. a left shock and a right shock if they handle dampening and rebound differently?)
Try disconnecting the shocks to see if there is any difference in your bumpsteer. You may have a non-performant armstrong on the left side...
Good Luck, great car, cant wait to see how you fix the problem.

 

I had the chance to visit Eric and check the roadsters steering. I flipped the steering arm on the spindle so the rod end is on the top so it runs upward to the front. Its better but we still got the wobble on ''once'' ! A new steering arm with a 1 1/2- 2'' kick up may be required yet. On close inspection i found that the perch bolts are loose in the axle and believe this is a good part of the issue....... WE WILL FIX IT, Buddy !!
Of note on all spring over axle perch bolts is they are not long enough for use on radius rods after 1934 due to the extra material required on the canter lever spring mount. They should have full to near full purchase in the axle...... you will only get 2/3 or so. The fix i made on my T was to turn down two 5/8 unf nuts to the perch/axle size and lock them on tight. The perch bolts has a lot of load when braking and even more so with a dropped axles and even with over coming the effect of steering caster. JW

 

Just re reading what has been suggested and the talk of the amount of (or lack of ) travel of the front lever shocks on bumps is not of any issue to this, BUT..... if you were to rotate the shackle plates 180 degrees (the top is still the top)and then move the linkage to outside of the shocks arm it will have more movement. This is due to the point its now mounted to moves down when the radius rod moves up due to the hinged effect caused by the lengthening the spring has. It will let the shock do its job that much better.
I should be calling in again on the 12th (Monday) so we can do it then if you like. Its not a big job. JW