Open car cowl shake?

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David Jones
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Open car cowl shake?

#1 Post by David Jones »

Is it common? My 59 cabrio suffers an annoying shake from the front end around 60 mph but it is not consistent so I do not think it is wheel balance even though it is about the right speed. Now I have a 55 speedster that does the same thing. Anyone else have this happen?
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William Crowell

Re: Open car cowl shake?

#2 Post by William Crowell »

Just a thought, David: are your front strut reinforcement panels in good shape? Mine were rusty and I didn't even realize it. How's the paint doing where the front fenders meet the cowl? If the paint cracks there, that's usually the first sign.

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David Jones
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Re: Open car cowl shake?

#3 Post by David Jones »

Both cars have been resotred/repaired in that area. I am beginning to lean toward the bearings in the beam being worn allowing the trailing arms to move around.
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Bob Campbell
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Re: Open car cowl shake?

#4 Post by Bob Campbell »

David,

Check the condition of the tires and balance the wheels before you do anything else.

You asked,

Bob
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David Jones
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Re: Open car cowl shake?

#5 Post by David Jones »

Thanks Bob.
Did that and changed drums/checked bearings, king and link pins. Also checked tracking. What is the consensus on tracking. I know that a fraction of toe in is normal but when I ran radials on the F Vee a little bit of toe out worked better but I never had any shake either way on that and the front end was only bolted on like a VW.
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Frazer Carless
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Re: Open car cowl shake?

#6 Post by Frazer Carless »

I have a '61 T5 Cabriolet which does the same thing. With the top up, at 60mph I usually get a violent shake in the front, but sometimes it is barely noticable. I find with the top down, the shake starts a bit sooner, around 50m - 55mph! I have checked everything, wheels, tyres, king and link pins, tie rod ends, alignment, brake drums, rear axles, shock absorbers, steering damper etc. Like your car the shake is inconsistent which points to something moving in the suspension - the only thing I haven't changed is the suspension pivot bearings. I cannot detect any movement there and have seen cars with really bad wear there and all that has resulted is rattles and knocks, no shakes. The cost of the needle bearings is scaring me off just now but I guess at the end of the day I will have to change them if only to prove that point. If you solve this problem please let me know - I have been chasing it for 5 years!!!!!Frazer, (Melbourne, Australia)

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Re: Open car cowl shake?

#7 Post by George Walling »

David, I have a 55 Speedster that doesn't have the problem but I would re check tire balance and tire for out of round and check rims for true ness then check wheel bearings these are all cheap easy inspections before jumping into front end components. Hope this helps and good luck.
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Re: Open car cowl shake?

#8 Post by Charlie White »

I started to post this this morning, and they thought it probably didn't apply. BUT..................seeing the most recent posts, here goes a long shot. Yeas ago I had an SC Cabriolet which came with a factory removable hardtop. I also had the factory soft top. At one point, I decided to try out the soft top and installed it. To my great dismay, I encountered what I would call "chassis shake" that I had not experienced previously. Could not pinpoint where it was coming from or what was causing it. I checked all the suspect areas and found nothing. However, when I put the hardtop back on, the chassis shake stopped. I concluded from that, perhaps erroneously, that open cars have less chassis rigidity and when the hardtop was put back on, it strengthed the chassis, and the chassis shake stopped. Perhaps there is an element of this issue with your open cars.

CW
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Re: Open car cowl shake?

#9 Post by thomas kirkpatrick »

I had a very similiar problem with a 59 Austin Healy that drove me nuts. I could not figure it out until I asked a friend to drive the Healy on the high way while I drove a chase care. With the Healy in a center lane I could examine the car from all angles. Everthing appeared fine until at a certain speed I could see one of wheels to be literally start bouncing down the road. It was a lot cheaper than replacing parts not knowing the exact problem.

Tom

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Re: Open car cowl shake?

#10 Post by kurt hoelter »

same symptoms but no steering wheel shake. (open '60) put car on dyno and rear left tire was obviously doing the dancing. after many balances and rotations with no change, have found replacement drum to try. will get to it as soon as i fix my new fuel leak
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Re: Open car cowl shake?

#11 Post by Ivan Fuller »

I cant help thinking that "dancing" wheels can be symptom of worn shock absorbers. I know this was mentioned as being checked but checked for what - being loose, having worn bushes, actually removed and verified they are not worn out and function correctly? just a thought.

I would have expected tires with a flat spot or out of balance or bent rims would produce a consistent problem (dancing) that could be duplicated at certain speed.

Where as a worn shock will be variable depending on the road conditions as described.
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Re: Open car cowl shake?

#12 Post by Jim Fleming »

My Conv'D would "shake its head" in some rough road surface conditions like crossing railroad tracks. I tried a lot of things but installing a working steering damper really helped the most. This was mentioned in a previous post so I will second that comment.

For those of you who have learned to fly in a old warn out Cessna 150 like I did will remember the nose gear doing the same thing on landing. What worked on the 150 also works on the 356. When the shake starts begin some very gradual turns or swerves (within the lane) to "break the shake".
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Re: Open car cowl shake?

#13 Post by Ken Clark »

Could it be that the Beam Damper is ready to be replaced?

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Re: Open car cowl shake?

#14 Post by Bruce Baker »

David Jones wrote:Is it common? My 59 cabrio suffers an annoying shake from the front end around 60 mph but it is not consistent so I do not think it is wheel balance even though it is about the right speed. Now I have a 55 speedster that does the same thing. Anyone else have this happen?
Common problem for a very long time.
Last few fixes @ BBE:
Broken/slipped belt in an old radial tire.
Bad shock(s) that looked good (Koni) that had jounce but no rebound (mush!) (one car, on all 4 shocks!)
Bad tie rod end(s).
Loose link pin(s) on one side.
Clamp nut(s) loose on bearing thrust washer(s).

One recent Cabriolet had all of the above, but basic complaint was "shakes at about 60."
 

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Re: Open car cowl shake?

#15 Post by Greg Bryan »

There have been many good suggestions so far, but if possible, switch tires from a car that doesn't have a problem - if the problem goes away, you've narrowed down the problem to your tires - if it stays, you know it's something else - this is a very common dealership diagnostic technique where there are other cars around with the same equipment - called replacing with a 'known good unit' - actually a very effective way to diagnose problems.
Other things to check - tire/wheel concentricity. Jack the car up slightly until the tire is just clearing the ground and spin it. Observe the distance between the tire and ground - should be fairly even (within a few millimeters) all the way around - it won't be perfect - never is. If it's way off, you can see it. There is a special dial indicator with a rotating wheel to put directly on the tire as you spin it to do the job accurately, but not may shops have it.
Another problem is radial force variation in a tire (RFV). This is where one area of the tire sidewall is considerably stiffer than the rest of the sidewall. It can cause tire hop and the feeling of inbalance, even though the tire is perfectly balanced. A tire store with a Hunter 9700 tire balancer can check for RFV with a drum that comes in contact with the tire as it turns - RFV is measured in pounds. This condition is certainly more common in larger tires such as for a SUV. With both of these problems, you can balance the tire until you're blue in the face and it will still cause a shake at higher speeds.
Greg Bryan

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