Help! Handling problem with the A

My dad & I have just recently got our model A coupe on the road and we are having a handling issue that has us scratching our heads. I have not dealt with a straight axle car before so I am open to any and all suggestions. This speed wobble (for lack of a better term) starts at right about 55 MPH & steadies back out at just under 65 MPH. As you can imagine this is kind of annoying because staying below the wobble causes the rest of the traffic to almost run us over & to run above it is risking a ticket.

The spec's: 1930 all steel full fendered coupe. 350/350 (yeah I know real original but it is what we had) 2X3 tube frame. Four bars front & back, Magnum dropped "I" beam axle, GM metric disc brake calipers on magnum adapters, GM A body rotors (if memory serves me correctly) & a panhard bar. P&J hydraulic shocks. Cross steer with a flaming river Vega style steering box. 8 inch rear out of a late 70's maverick with stock drum brakes. All of the parts & pieces in the suspension & brakes and the assorted hardware are new with the exception of the diff itself. New wheel Vintiques steelies with BF Goodrich silvertown wide whites.

What we have done so far to try to fix it:

Checked ALL bolts/nuts etc in the suspension, all OK

Checked the front wheel bearings for looseness or broken parts, all OK

Did the alignment on the front end, a little better but not much. We have tried 1/8 & 1/16 toed in & out and are currently at 0 toe in/out

Checked & readjusted the angle of the axle, no change. We had it set at 6.5º and I have just changed it to 9º but have not driven it yet due to weather issues, hope to test drive tomorrow.

Checked the kingpins/spindles for any wear or play, all OK

Checked all tie rods for tightness/wear/play, all OK

Rebalance the tires/wheels, no change

Switched tires from side to side, no change

Changed to a different set of wheels/tires, no change

Checked the wheelbase side to side & for square, all OK

Checked the pitman arm on the steering box for any play between the splines on the box & the splines in the arm, all OK

Adjusted the steering box lash for almost no play, no change

Changed out the steering box entirely, no change (stole the one off of my Tudor for this test, also a flaming river Vega box)

Balance the driveshaft, no change

Ran the car up to 75-80 MPH on stands & had only a very minor vibration.

We have been chasing this shake/wobble for more than a month, if anybody can suggest anything we can try I am more than willing to give it a shot, I am pretty much out of ideas. I have put up a short clip of driving it when it starts to shake. Kind of a crappy clip but you should get the idea, I was trying to film with one hand & drive with the other. The shaking is pretty violent & I would like to get this solved before something breaks. Thanks.

http://www.youtube.com/watch?v=t_PQpxMONKc

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Sounds like you have checked it all. The 9 degrees on the axle most likely will smooth it out, but you will prolly will have to reset your toe in from 0 Good luck ...ghost

 

Yout 6.5 degrees was that set at ride height to the road, or to the frame? ghost

 

Are you talking about "Death Wobble"? Are the front wheels flopping around?
Have you checked the kingpins? any slop there will cause it as well as slop in the tie rod ends on the tie rod. Also seach here for death wobble. Good luck

 

Ditto.....

 

Other things to check if the above suggestions are not the problem: driveshaft out of balance, motor mounts bad, some sort of harmonic occurring (some Detroit cars would hang a weight off the tranny mount to dampen a harmonic vibration).

When the vibration starts, does it change if you shift to N and kill the motor? Does it change if you are turning right or left?

Check out of square with the rear end or something loose back there. Also rebalance the rear wheels. Maybe the problem is telegraphing itself up front from somewhere else.

Spin the wheels with them in the aor and check for out of round. Are the wheels properly seated/centered on the hubs?

 

Balance the tires?

 

since its cross steer, put a panhard bar in it and a steering dampner from so-cal speed shop.

 

steering dampner will solve your problem, helped me

 

I know you said you tried different tires but are you sure that both sets are round. I had a real bad vibration at the same speed with some Coker/Firestone ribbed dirt track tires on my roadster and it was frightening at around 60! especially if you put the brakes on!! I had the tires shaved and trued and it all went away. Sounds like your tires are bias plys so you might check to make sure that they are round.

I did have a problem with low speed "death wobble" and found out that I was running to much toe in. Went from 3/16 to less than 1/16 and it went away. This type of wobble will usually go away with speed as the wheels start turning in to gyros they will stabilize themselves, but at 60 mph I would really look at out of round.

Rex

 

I was going to blame it on Firestone! But can't. Have tires shaved, toe in an 1/8th, and try your new casting angle. Good luck! Also, drill out your bolts and pin them for safety!

 

Both the 6.5º & the 9º were set at ride height.

I forgot to put that on the list above, we checked the king pins & they are tight & smooth moving with no hint of play. New 40 ford repro spindles. all hardware is tight relating to the kingpins/spindles. Tie rod ends are also new & have no play in them.

We have had the driveshaft balanced. I also forgot to add to the list above that we ran it up to 75-80 MPH with the car on stands & there was only a slight vibration, nothing even close to what we are having out on the road. I will try & see what happens when I shift into N & kill the engine today. we did measure the diff for square & It is OK

There is a panhard already on it but no steering dampener, that may be the next thing that gets put on the car.

The tires are radials. the second set we tried were off of another car with no shake or vibration, so that is why we believed them to be OK (the second set). up to 55 MPH this car is a smooth as silk, then it starts to shake.

Thanks for all of the suggestions so far, I will try a couple of the new suggestions today & keep you updated. One other thing I forgot to put on the list above is the car has new P&J shocks on the front.

Later, Tone

 

Ok my .02
set Caster to 7.5 to 9 degrees
Set toe to 1/8 in
Set camber to 1/2 degree negative
Toe in will really affect straight axles
Good luck

 

2nd set of tires all around or 2nd set on the front?

If just on the front, any chance a rear tire is out of round or wheel is wobbling?



About the caster setting, was it done on a flat and level surface comparing caster against the floor and not against the flat area of the frame?



Does the car tend to 'dart' around when a steering command is input at highway speeds where the front end is not wobbling?

A dropped front end and running big & littles with insufficient caster tends to make the car dart around a bit.



Have you checked side to side runout on the wheel proper?

Vintique's wheels are probably straight in this regard.
My new steelies from Wheels of Steel in Visalia, California are very true.


If your wheels are off a small amount, you may want to borrow some mags - which run quite true due to being machined on a lather - and give that a try.


Fwiw - I ran a dial indicator against my 10" x 15" mags on the 32 roadster and found the left side to have .020 - .025 lateral runout and the right side was .030 - .035.

Probably due to using junkyard axles which could be tweaked a small amount and the axle flange doesn't run quite true.

Checked after Sweetie banged the pickup rear bumper into the rear tire - highboy - and I thought the wheel may have been bent.

Highway running is still quite smooth.


More than likely you've checked, but any chance you have a rivet head or similar under the front wheel mounting flange which would cock the wheel off a bit?

You may want to run a dial indicator on the front hub as well.
It's probably true running, but....

 

tie rod sleeve if stock put a new one in that the most comment problem in the old day make sure get a thick one.

 

here is the link to my post, when I had this problem, I was never able to fixed it, It hopped till the day I sold it. the only thing I never did was a steering dampner, http://www.jalopyjournal.com/forum/showthread.php?t=261512&highlight=high+speed+wheel+hop

 

this is very important, check that the wheel middle hole matchs the hub size so that the wheel is not just supported by the studs.
also does the angle on the wheel nuts match your wheel indents, in other words do the nuts sit properly in the wheel stud holes?

 

If the car has a vibration with the rear wheels up and spinning and the front wheels stopped on the ground, then there is a chance that your car is reacting to a harmonic vibration. Just changing 'something' can alter the frequency that the harmonic kicks in and your problem will be gone - if this is what it is. For example, run the car with a tie strap pulling the engine to one side so the mounts are loaded on that side and the motor/tranny can't oscillate on the motor mounts. See if anything changes. Try again, using a light chain on the mufflers. These types of tests are used to determine from whence a harmonic is originating. By doing these things you alter the frequency at which the wobble kicks in. You might eliminate the wobble or simply move it to a diffrent speed, but either way you are honing in on it.

Detroit irons out these types of problems as part of their development. With a home built car it is possible to inadvertantly stumble upon a situation where at a certain speed sympathetic vibrations arise.

I agree that these types of problems are less likely than a fundamental problem in your front end, but you have been so thorought that perhaps you should expand the scope of your investigation.

Putting on a steering damper might eliminate the symptoms but it will not eliminate the cause.

I hope that you fond the problem in the front end as you have certainly tried about everything you can check.

 

One thing I haven't seen mentioned yet are shocks. What are you using for shocks?

 

What tires and wheels are you running and at what pressure? Tire pressure can have a great effect when it come to the DW. Remember that the unsprung weight ratio on light cars may could cause this condition as well. Each car seems to be unique with this condition but everyone seems to work it out. Tire pressure?????????????????

 

First post indicates P&J hydraulic shocks.


Darned good question though.

Last year a long running death wobble thread ended when the poster stated he had no shocks....

 

Just Dug nailed it, tire pressure. WHAT ARE YOU RUNNING? This is not a full bodied car, 25psi seems to be a good baseline for the stuff we play with. On my old T I ran 28 rear and 24 or so front. Coker will say otherwise but we all know how well their track record is DOH!

 

steering dampner is my vote.......have stopped many a wheel wobble with one. good luck let us all know................

 

I want to second (or third) the suggestion of adding a damper to the system. The steering damper went out on my daily (Jeep Cherokee) and it felt like the front wheels suddenly went square at highway speeds. Replaced it, and problem solved. Also, as already mentioned, check tire pressure. The t-bucket will adopt the "death wobble" if the front tires are slightly over-inflated. No, I don't have front shocks on the t-bucket, which undoubtedly makes it more sensitive, but it starts getting "bouncy" and then wobbles real bad. Lower tire pressure, and it settles right back down. Maybe the combination of the two is adding to your problems.

 

Throw a bare rim on each front hub and measure top to bottom runout. Not side-side. If it checks good prolly time to listen to the others about a damper. Seems like a crutch but if it works, go for it. Good luck.

 

Have you looked at the kingpin/ tapered locking pin? The one that goes through to hold everything together? Make sure it is tight and seated.

I guess you need to decide if it is a wobble or a bounce. Does the steering wheel vibrate or is it like the suspension is bouncing? I had some crazy stuff with the Fly when we first started taking it down the track.

You have talked about adding caster but what about reducing it? I think most Fords were factory around 5-6 degrees. 9-11 is dragster stuff.

 

The car has P&J hydraulic shocks on it. I checked them yesterday & I have to use moderate to high effort to make them extend & rebound. The whole car has less than 400 miles on it since being licensed. As I stated before all of the suspension components are new (+ 400 Miles) with the exception of the diff.

We are going to try some of these. It was also suggested that we try unbolting the drive shaft from the diff & turning it 180º & test. this is on the agenda as well.

The wheels are wheel vintiques & have a large hole in the center. I do not know what else I could do other than bolt the wheels on. Has anyone else had this issue?? the wheels are double bolt pattern wheels (4 1/2 & 4 3/4) We are bolted in the correct set of holes & bolted down & torqued properly.

I read this in one of the other threads & have yet to check it at different pressures. The tires are 255/70 R15's & 185/70 R15's BFG Silvertown wide white radials. Currently all 4 are at 30 PSI. I am going to experiment with different pressures to see what happens. I am trying to only change one thing at a time so I can tell what (if anything) made a difference.

I drove it today with the caster at 9º and it was slightly better according to my butt-o-meter. The wobble came on 4-5 MPH higher than before according to the GPS speed. I adjusted the angle to 11º & then it started to POUR so I will try it tomorrow. %^&*$* weather!!! If this makes no improvement, I will try tire pressure.

Here is the link to the build thread so you can see what we have. http://www.jalopyjournal.com/forum/showthread.php?t=348159

Here is a couple of fairly recent pics.

 

Dial that pressure back and you will be surprised. Use a gauge AND watch the sidewall for the proper "squat", light cars require different parameters. 30 is too much.

 

Nice looking coupe!!!
On tire pressure you can try this method
Find a concrete driveway and drive the model A over it and look at the dust pattern on the tire. Adjust the pressure up or down until you get the dust pattern to go right to the edge of the tread.
Also straight axles dont really like fat tires in front.
My roadster weighs 2300 lbs full of fuel
Front tires are 145R 15s and I run 28 lbs in them
Rear tires are 255 /70/15s and I run 16 lbs in them
Axle is 7 degrees
toe is 1/8th
Camber is 1/2 degree neg
Good Luck