Car Shakes at 50 mph, but not always

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expat

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This one is driving me crazy, I'm looking for some fresh ideas.

The car is my fully restored Triumph Spitfire, after restoration (25k miles) I fitted new Tires. The old tires were performance tires and wore quickly, but all was well and Tire wear was even.

The New tires where Yokohama Avid Touring (I'm not so much into competition these days)
Within a mile or so of having the Yoko's installed (Discount tire) I noticed the Shake at 50 mph.
At the time I put it down to the road surface.
I have about 2k on the tires now, and still get the shake about 50% of the time, sometimes worse than others.
The shake is not so much through the steering but through the front of the car (I see the hood shake and gear lever)

What I have done:
Rotated the wheels.
Checked Tires and wheels for Run Out
Had wheels re- balanced
Run the car up to speed on a lift
Replaced the drive shaft

Any ideas please.
 
I had a brand new tire that balanced just fine, but still felt "wrong". Took it to a place with a Road Force machine and they told me the tire had a hard spot in it. Took it back to the tire store and they exchanged it for free. Replacement tire was fine.
 
Possibly bad tires, could have an internal flaw in one or more tires. Might only show up when both tires are clocked in a certain manner, and makes things go into harmonics. Might try a road force balance.
 
1) Have you double checked the wheel alignment? I chased a similar shake (completely different car - 1970 GTO) for years and thousands of dollars (tires, rims, driveshaft, etc.) and it was a caster issue. Caster is a parameter that doesn't show up as uneven tire wear like toe or camber will. My GTO did not wear unevenly hence I never dreamed it was alignment causing the shake. I took it to a different shop and the amount the alignment was out from factory spec was atrocious. New alignment, no shake.

2) Is your clutch sound? Is the shake at all RPM related? If you go above 50, pop it into neutral and come down through the 50 shake zone do you get the shake? Similarly, if you rev the engine to the equivalent RPM at 50 while not travelling 50 do you get the shake? The reason I ask about the clutch is I chased an intermittent engine shake as well for a long time that came down to a clutch (actually pressure plate) issue.

In your case though, you have an event (tire brand change) that precedes this shake so make sure the tires are not defective i.e. excessive run out - which does not necessarily show up on a balancer. The tire can be balanced fine but oval in shape.
 
I've had new tires balanced three times b4 a tech who knew what they were doing re-did them right (Pepe's Boyz). You could have a bad tire too.
Yokos are usually round if nothing else though.

Its still likely a tire balance issue, but you may want to add a hydraulic steering stabilizer to the tie rod (horizontal shock absorber)anyhow.
Check jeep and lifted truck forums ...
 
Check your motor/tranny mounts. I've seen a bad mount cause a bad shake several times before, but typically on FWD cars.
 
ITs gotta be the tires- probably both front tires have a stiff spot or soft spot. Tires can be perfectly round and perfectly balanced, but if they have areas where the cord structure is more or less flexible than other areas, they can still feel like they're square. When they're in sync, you don't feel it but when they're out of sync it gets amplified.
 
Originally Posted By: Trav
Does this car have wires and knockoffs?


No.


I DO think it must be the tires, But I have rotated the wheels more than once without any change in the condition.

I might try and meet up with someone who has the same car, and ask if I can borrow their wheels/ tires.

I don't want to dump an almost new set of tires, but it seems right now, I would have a problem convincing DT that the tires are actually faulty.

Steering geometry is unlikely to be the cause. It is adjustable, and I have tried various set ups. Bushings are in good order and are mostly urethane.

As I said the shake is not really felt through the steering.
 
I had a similar problem with on and off shaking(out of balance issue). Had the tires(Michelin LTX MS2) re-balanced and rotated, still had shaking at highway speeds. I was getting ready to go on a road trip and decided to inspect my brakes, once done with the brakes and after re-installing the tires I gave them a spin to make sure the calipers were releasing adequately, it was then I heard a funny noise INSIDE the tire. I took the vehicle(Toyota Sequoia) back to the tire shop and had them dismount the PS front tire, inside we discovered about 7-8 balls of rubber that were sized from about 5/16 to about the size of a BB. The tire tech told me he has seen this before inside the Michelin tires, probably a combination of not fully cleaning the inside of the tire with air and/or rag and using too much tire soap/lubricant to seat the tire to rim during the tire mounting process. Once the all tires were re-installed(we spun balanced them with the weights on them to be sure nothing was floating around inside the tires changing the balance) they were very smooth. I hope this gives another option for someone to look into if having balancing issues with their tires. Good luck, Todd
 
What does this have for a brake system? Any sort of conversion?
Its strange you moved the tires around and nothing changed, any chance of a grabbing brake when it gets warm?
 
Originally Posted By: Trav
What does this have for a brake system? Any sort of conversion?
Its strange you moved the tires around and nothing changed, any chance of a grabbing brake when it gets warm?


The Brakes are all stock Girling other than EBC Greenstuff Pads and Goodridge brakelines. There is no servo in the system. they seem to work well, pads do not rub when I spin the wheel, and the brakes feel normal (no pulling to one side) when I brake.

I will try left foot braking while the shake happening, to see if it has an effect.

The shake is very noticeable when you look at the gearlever. But not felt much through the steering wheel. The engine mounts are in good order and the design places the mounts on the engine front plate, and attaches to the suspension turret close to the suspension's upper wishbone ('A' Arm)

File photo for reference: http://www.carcentric.com/BWfrontsusp.jpg
 
Originally Posted By: Gokhan
Could it be some resonance? Do you have new shocks?


No.
 
Originally Posted By: expat
Originally Posted By: Gokhan
Could it be some resonance? Do you have new shocks?

No.

Shock absorbers are to damp the oscillations so that instead of continuous shaking you get a single bounce. Do a bounce test: Press each corner of the car down hard and release. If it bounces more than once, you have a bad shock absorber.

When you say "shake" to describe the oscillation, it doesn't describe anything. Describe the oscillation: Is it vertical, horizontal, or sideways? What is the period of the oscillation -- small fraction of a second (vibration) or about a second? What is the amplitude of the oscillation -- small fraction of an inch or an inch or more? Is it a uniform, sinusoidal-wave oscillation or some kind of irregular oscillation?
 
Originally Posted By: Gokhan
Originally Posted By: expat
Originally Posted By: Gokhan
Could it be some resonance? Do you have new shocks?

No.

Shock absorbers are to damp the oscillations so that instead of continuous shaking you get a single bounce. Do a bounce test: Press each corner of the car down hard and release. If it bounces more than once, you have a bad shock absorber.

When you say "shake" to describe the oscillation, it doesn't describe anything. Describe the oscillation: Is it vertical, horizontal, or sideways? What is the period of the oscillation -- small fraction of a second (vibration) or about a second? What is the amplitude of the oscillation -- small fraction of an inch or an inch or more? Is it a uniform, sinusoidal-wave oscillation or some kind of irregular oscillation?


The shocks are in good order.
I should also say this car has quite hard suspension for a lightweight car, add to that a 3/4" sway bar on a car with a 4' track. There is not a lot of oscillation for the shocks to Dampen.

I should better describe the "Shake" when it starts,
It comes in a about 50mph and feels a little like mild Washboard on the road surface.
It is very regular at about 4 beats per second, and more Up and Down than side to side, although the movement of the hood and gear lever are side to side, I believe this is because it's the easiest range of motion for these components.

I will try to get a video of the front of the car (taken by a Pace Car) while this is happening. Perhaps I will see a 'Hopping' motion of the wheel.
 
Could it be some engine or transmission problem? What happens when you drive at a different gear at the same 50 MPH speed?

If it's not the engine or transmission, it could also be some broken or loose part in the suspension.
 
Originally Posted By: expat
Replaced the drive shaft


Was it balanced before going on? Those things need balance weights like tires do.
 
Shaking through the gear lever makes me think you have some fuel and/or ignition issue making the engine shudder.
 
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