72 cutlass, bought non-running, complete suspension/brake rebuild, driveline angles are correct, all tires at 32psi.
I've got a minor vibration only at speeds over 70mph. Not steering wheel chatter, more like it's from the rear. But the odd part, it takes about 15 minutes of driving before the vibration develops.
I've never had a vibration that wasn't there all the time. Is this just a tire issue?

 

Does it vibrate when your coasting at that speed? If it vibrates whether under throttle or coasting it's probably a tire or wheel issue, if it stops when coasting, possibly another issue.

 

It vibrates all the time at speed after it warms up, independent of engine speed. Clutch in, coasting, still vibrates.
I didn't have the driveshaft balanced, but the warming up time is what confuses me.

 

Swap front to rear tires and see if the vibration moves from rear to front. The warmup part makes me think it is tire related.
How old are the tires?

 

What kind of wheels do you have? My uni-lug Cragars will cause vibrations unless I mount and torque them perfectly.

d1

 

x2!!

 

Yeah, I'll try the front/rear swap.
Tires have very few miles on them, but the car sat for a year (no motor), but I have absolutely no idea how old they are. They're on original 14" rims. I do torque them correctly.

 

my last set of truck tires did this...bad belt was what I beleived caused it, they would need a warm up for it to happen, balancing them did not help, if it was really cold out (winter in NE) there were no issues, they were near end of life so I replaced them and no issues since (only one appeared bad, I determined that by moving them around)

 

Tires develope flat spots from sitting in 1 position over a long period of time. I bet thats what it is!

 

That's an old myth from the bias-ply days.

Besides, if it was a flat spot, it would improve as the tire warmed up.

- Eric

 

Absolutely not a myth. Why do you think all OEM manufacturers ship their vehicles with 40-50psi of tire pressure. They know that if they leave the vehicles sitting in one place for too long the nylon ply found in many modern tires will take on the shape of the buldge at the bottom of the tire and cause a vibration. It is very common for tires to develop flat spots on dealer lots when they PDI the car and then the vehicle sits for too long without being moved.

But you are correct that it would improve as the tire warmed up. However it would likely not go away. The only way I have ever been able to get rid of a flat spot is to drive with the tires at 50PSI until they get very hot and then leave them at that pressure until they cool.

 

Yep.
My neglected '86 gets out about once a year and I can feel the flat spots a little. They do disappear after a while though, longer in the cold. Tires are from the mid 90's so they are harder than normal, too.

 

There is a code that will tell you the age tire was manufactured. Usually on inside side of tire. Example 2201= 22 week of the year 2001. I found my great looking tires with great tread to be...are you ready, 11 years old!!
Please don't tell me you had them balanced by a local tire shop with HS sloths who can't wait to get home!!!
I use to have my tires balanced while still on the car but I can't find anyone out here in MN who does it. I had constant issues with my GTO and Malibu SS until tires were balnced on the car.

 

Just find a shop with a good road force balancer and they will be able to tell you if its out of round or has any hard spots.

 

Definately not a myth, and the flat spot will not completely disappear as the tire warms up!!!

 

Had the same thing on my car for a long time one day the front tire blew at 40 mph all the way across the face. I think it had a bad belt in it the whole time put a new tire on and it was fine after that. The old tire had lots of tread left but was over 10 yrs old it was a BFG TA

 

I'll vote belt failure since it's worse after warm up, espeically if they are old. At least they are not the blow out prone Uniroyals GM used back in the day.

 

When I bought my 72 convertible, it had BFG TA radial tires that looked brand new. When driving on 441 south toward Ft. Lauderdale/Miami, the car developed a slight vibration. Little by little it got worse, and then it became dangerous. I pulled off to check the tires, and I had a huge bulge in the tread where the belt was separated. Like navvet said, the age of the tires is critical. Mine were close to 10 years old, but looked almost brand new. The rubber dries out and the belts can begin to separate. It starts as a slight vibration that there is no visable evidence of and balancing won't correct.

Experts have varied opinions. Some say 5 years and others say somewhere between 5 and 10 years. It makes no difference how much tread the tires have. Articles have been written about some shops having 3, 4 and 5 year old tires on there shelves for sale. They are "new" tires, but they may be reaching the end of their safe life before they even hit the road. I'd check them before doing anything else.

Tire separation can be sudden and might have disasterous results. About 10 years ago, I was driving my 1970 Bonneville convertible back from Hershey, PA. Coming down a big mountain in NC on Interstate 81, I developed a slight vibration. I pulled off at an exit and checked all the tires. Pressures were fine, no visable bulges or other signs of problem, so I continued on. As I accelerated down the on ramp, a semi was in the left lane and another semi coming up in the right lane. I got to about 55mph and a belt let loose in a front tire. The steering wheel ripped out of my hands and I almost hit the right guardrail. I hit the brakes and almost got run over by the semi in the right lane. I'm sure he cussed me as the stupid idiot who slammed on the brakes right in front of him going down a steep mountain grade. It was too steep to pull off and change the tire. I had to limp to the next exit 7 miles away. 5 mph was uncomfortable and 10mph was about impossible. It took a long time to travel 7 miles at 5-10mph to the exit to change the tire. Those were high end Goodyear radials that looked new and had proper inflation. But they were between 5 and 10 years old.

 

I clearly remember them - the blowout we had on a 6 year old Uni made for a memorable photo on our Carlsbad vacation back in 1992... Tire shop guy knew exactly what brand it was from 15' away.

 

Then why don't the tires on my '68 get flat spots? It sits in the same spot for up to nine months at a time with 35 psi. BF Goodrich Radial T/A's. The first time I take it out for a spin each year the tires roll nice and smooth.

 

Exactly.

- Eric

 

So as I read it you didn't buy the tires and do not know the history. I bought a 20K mile Caddilac several years back from an unmarried woman. Couldn't get the new tires she had on it balanced and stop a vibration. I finally found someone who knew what was happening. The woman had used a can of Fix A Flat in one tire for some reason. The stuff was liquid and moved around all the time and settled in a different place each time I got to cruising speed. Took the tire off, cleaned everything up (it was a real mess in there). Problem solved.
Moral of the story, there are a lot of things that can be giving you problems. Getting agressive in finding the problem may give results. Good tire shops have a run out gauge to find out of round tires. They have gauge things on the spin balancers to check wheel run out. Of course finding a tire shop that cares to look closely at all the rolling stock and help find a problem is a real problem in itself. Keep looking, it will turn up.
Flat spots are real, even on the new radial tires.

 

One of my first jobs in the mid-60's was at a Chevy dealer, as a 'do-it-all' for the service department.
Besides chemical washing the new cars, [getting the 'white stuff' off] I also had the job of changing tires around, as some liked one brand over the other, etc.
The one thing I remember well, is that Uniroyals were the worse - if you stepped on one, at the edge, they folded right over - like they were the same material as the sidewall!
None of the other O.E. tires did that, and it was bad enough that I swore off them to this day!!

 

Most likely due to the construction of that particular tire. Just because your car tires don't get flat spots doesn't mean its a Myth.

All the major tire manufacturers sure believe in it.

http://www.yokohamatire.com/assets/docs/tsb_112102.pdf

http://www.dunloptires.com/care/storage.html

http://continentaltire.custhelp.com/...943/redirect/1

 

35 psi on a BFG is max air pressure for that particular tire. But I bet if you lowered it down to what would be normal for your car, 28-30, you will probably get it. Most of the cars that develope flat spots are sitting on our lot in the same spot, baking in the sun! Here in Texas the weather is really hard on tires and batteries!

Over the years, I've saved a few bucks personally, by siping my tires. Not many places left that do it! Can only be performed on good tires with no defects! You lose a few thousand mile of wear, but you get perfectly round tires!

 

Yeah, but why would I store it with only 28 psi? I put it away in October when the daytime temps are still in the 70-80 degree range, if I only had 28 psi in it then in Feb when the daytime temps are 12 degrees (no heated garage for me!) then my tires would be sitting there woefully underinflated. Therefore when I store I bring them up to max pressure.

I can see your point about Texas and other very hot places having problems with tires. I would think that flat spots would be the least of your problems with the heat you get.

 

My point exactly about temp and tires. in the fall thru spring, we can start out at 30 degrees and go all the way to 80 in the same day!! Texas is extremely hard on tires and batteries!!!

 

I sort of have the same vibration (but 55-63ish). Getting worse over the years too and I've owned it since '78. Then I had new SS/t's and FS SS Radials at each corner, and it still vibrated. Now original ssII's and Bfg's adorn it and STILL it shakes. Different driveshaft, engine (for other reasons), 2 transmissins, but to no avail. I did have my 3:91 posi in it but I had so much fun I forgot to check. Chilton has a neat chart denoting the possible causes;trans-driveshaft-rearend. This "process of elimination" is fun but seemingly endless. Must be the rear end?

 

No tread sepatation, a slightly bent wheel that was out of balance.

 

Glad you found it!!

 

I have been chasing a vibration in my 66 vert for a while. I did the "throttle/coasting" test yesterday and sure enough based on that, I have a tire/wheel issue. Tried the test on several hills and straight aways along with different speeds. I will start by looking for new rims as the current tires are in excellent condition. Question is 14 or 15 inch rims.
Thanks for the help.
Wayne

 

Before writing off the rims, take your car to a tire shop and check for rim runout and separated tire belts. If you plan on using your current 14" tires your stuck with a 14" wheel.

 

Unless you are looking for an excuse to buy new wheels, why not start by checking your current wheels for straightness and balance? And if you plan to use your current tires, haven't you already answered the 14 vs 15 question?

 

I have had the wheels balanced. Tires are in excellent condition as one has been replace because of a belt issue. That one has been relegated to a temporary spare. I only would consider 15 inch wheels because everyone is commenting on the demise of 14 inch tires. Anyhow I really believe it's the rims and not the tires. I would really like to change to steel 14 inch wheels and the wire/spinner caps. I think it's a nicer look for a Cutlass. I need to find some nice 14X7 rims.
Thanks
Wayne

 

Just because the wheels were balanced does not mean that they were checked for trueness or runout.

Of course, it sounds like you've already made up your mind to buy new wheels...

 

Start a parts wanted classified ad for your needs. There was someone selling the hubcaps recently in the classifieds.

I doubt they will do away with 14" tires completely, just the availability of some sizes.

 

I understand that balancing doesn't take care of the runout issues. The rims were not checked for runout that I know of. If I an get a nice set of 14X7 steel wheels with no or minimum runout issues, add a set of wire 14 inch 66 wire spinner caps, that will be a nice look with redlines I already have.
Which begs a question of what is the best setup for checking rims for runout. Is there a source for good steel wheels for my Cutlass. Thanks Wayne.