Technical Out of Balance "Feel" - out of ideas, got any?

I've got two '32 Fords and I have the same issue with both of them - what feels like an out of balance tire from about 62-66 mph. They're both set up the same as follows:
4" forged dropped axle
Hairpins
So-Cal "shorty" shocks
Reversed eye spring with buttons
Panhard bar
So-Cal steering stabilizer
Vega box
So-Cal spindles and disc brakes
Toe set at 3/16"
Caster set at 7 degrees
15X4.5 wheels with 145X15 Michelin XZX tires at 32 psi
Both sets of front tires have had the balance checked three times and balanced perfectly with little weight added.
I'm open to any ideas. Whatcha got?

 

What company made the steering box? How much torque on the pitman nut?

 

I don’t know who made the boxes. They both came from So-Ca but years apart. Neither one has any noticeable play. As for the torque on the pitman arm nut, I don’t recall. I can probably put a torque wrench on them to find out. They both have lock washers on them and are definitely tight.

 

Play with your front tire pressure, 32 psi is a little much.

 

We had the nut on the pitman arm bottom out so the pitman arm still had a little play. A large dia washer solved that.

 

I’ve had as little as 28 psi in them - no difference. I’m back at 32 psi. because they’re small and carrying a sbc.

 

Both pitman arms are definitely tight.

 

When you say "feel": vibration / shake in steering wheel; vibration in the seat; excess road shock???

 

I can feel it through the wheel, and seat. Road surface doesn’t seem to affect it.

 

check the wheelbase on both sides. it should be the same

 

I would feel more confident in the following if it was just the steering wheel. You might not feel play in the steering but the center pre-load adjustment could still be off and maybe the stabilizer is masking part of it. I would disconnect the steering box from the draglink and also disconnect the input connection. You should be able to find a 12 point socket that will fit the input spline. Then center the box and go through the process of setting the specified center pre-load with an inch-pound torque wrench.

 

I was reading somewhere that a seat vibration can be detected to a issue from the rear of the vehicle. Possible drive train issue.

 

I’m sure they are but I’ll check them anyway.

 

Avatar 5w looks like shit. You'd best send it to me.

Agreed on looking beyond the front end. Engine mount, trans mount, tailshaft bush, universal joints, rear end link bushes, rear wheel balance, rear wheel bearings. Those big rear meats chew bearings. First had experience here. 2 similarly set up 32's here, but no 5w!

Chris

 

I’ll try checking that kind of stuff, but everything you listed is new (2k miles) on the coupe. The roadster has @20k miles on it but I haven’t found anything worn on it. Weird thing is they both feel the same at the same speeds. Both 350 sbc’s but the coupe has a Tremec 5 speed and a Winters QC and the roadster has a Super T10 4 speed and a 9”.

 

Any Check on U joint angles?

 

Get it up to speed, right in the middle of the vibration, let off on gas and kick it in neutral, does that change anything? If it goes away kick back in gear and back to speed. Does vibration return? If so kick it in neutral again, does it go away again? If so it's drivetrain/engine related not tire.

....

 

I’ll try that

I hadn’t thought of that. I might try it but it only happens in a narrow speed range so it might be hard to catch it. Weird thing is that it’s the same on both cars.

 

I’m voting driveline on this one just because I had a very similar experience. Pinion angle is what fixed it.

 

Out of round , slipped belts , belt separation on front and/or rear tires , especially if the cars sit alot will cause this

 

By trying it in and out of gear and engine idling IF it changes nothing then it rules out engine/drivetrain and just leaves suspension/tires.

Went thru this on one of those 12 passenger box vans. A vibration just like you described. Several shops had looked at it and given up so they brought it to us.

We noticed in neutral and idle it went away. So we knew it was drivetrain. Long story short, after drive shaft balancing etc. We removed the seats and I crawled around on the floor at speed and mid vibration until I pinpointed it one spot. Brought into the shop and crawled under to that spot. Lo and behold a heat shield on the floor right above the muffler, removed it and vibration was gone. Re-installed and it was back, took it off and it was gone again. Thru shield away.

 

I had a set of Speedway ll" GM rotors (5 on 4.5") on the front of mine that had that out of balance shake at 50-55 mph. I tried everything I could think of and couldn't find the problem. After 7 years, I discovered the lug bold centerline was out of round by .035". They were drilled wrong!

I ended up putting some Mopar rotors (5 on 4.5") on and they were perfect, and the shake was gone!

I got them from Johnny Law Motors: https://www.johnnylawmotors.com/cat...ake-rotor-with-5x4-5-ford-bolt-pattern-1-pair

 

Where did you buy your tires?

 

How did you discover that?

 

bias ply tires? might be out of round.

 

2000 miles? About the time it takes for a poor quality th350 style trans mount to fail. Don't ask me how I know! Hard to spot too as it doesn't have to collapse much for the outer steel casing to bottom out on the mounting plate, giving metal to metal. Any misalignment between the chassis mount and trans mount just accelerates the process. I'm looking to fit an alignment wedge. Trans down 3 degrees, chassis mount level with chassis which has about 3 degrees of rake, so 6 degrees of misalignment, in my case.

Chris