Please help solve the mystery...

[baldytheanimator]

I've been having an intermittent problem with my E-type for the past six months. I'm wondering if the forum can help identify it...

...I drive a 1969 Series II FHC...

The problem is a sound that appears on occasion. About once every five times I take her out and cruise at highway speed for over 20-30 minutes, a rhythmic sound will start to build up...a vibration/rubbing sound. It starts softly--tukkatukkatukkatukkatukka--but can grow to be quite loud over the course of 10 minutes or so--TUKKATUKKATUKKA--to the point that I pull my car off the expressway and cautiously limp home. It's almost is the same sound as when you're driving with a flat tire.

Here's some other clues:
--The sound first started appearing a good way into long drives...from LA to Vegas or Phoenix, or winding trips up in the mountains. Let the car rest and cool off for an hour or two and the sound would disappear.
--The sound gets faster/slower with the speed of the car.
--The sound rattles a bit harder for an instant then disappears when I depress the brakes. It comes back once I let up.
--The sound is accompanied by some vibration in the steering wheel/pedals.
--The sound fades when I take corners/bends, but returns once the steering wheel points straight ahead again.

In the past six months:
--Since the sound seemed to originate from the RF wheel, I had that wheel/rotor assembly inspected at an alignment shop on the road. No rubbing found.
--Had the tire taken off/inspected also. Nothing here.
--Had the car put up on a lift and the brake/rotors looked at for any funny rubbing. My mechanic said my brake system was so clean and straight, it looked brand new.
--Had the right front bearing re-seated.

Yet, when I least expect it, the sound comes back.

I simply cannot get the car to make the sound for a mechanic. I've spent the last four days trying to generate the symptom so I can take it to my shop and let them drive it, but no luck. Then, on the weekend, when I've got a girl in the car for a Sunday picnic--whaddya know--of course it appears!

I'm at the point where I'm considering replacing all four bearings...or turning all the rotors on the car. But I fear the sound will just return after my expense...

Help! Any ideas?

I need a beer...

baldytheanimator

 

[Steve]

Hmmmm, a good description of the problem, you took out a lot of the possibilities. I am sure that there will be several thories on the cause of this problem, but my gut feeling is that the tyre is the problem. You said that you have had it removed from the wheel and checked, but I have heard of tyres being "visually" okay but be found to have problems. Have you had another wheel and tyre combination put on to the right front? Did the noise persist?

Anyway, my theory is a seperation of the tread from the carcass of the tyre. When the tyre is cold you will not notice it, because the rubber is still hard, but once it gets good and hot, the rubber is able to expand and the sound that you hear is the "loose" section slapping the pavement. Braking and turning will make it go away, because uyou are stretching the rubber and placing stresses on it, which will make it behave, but once on the straight sections, the rubber is free to move out under centrifugal force once again. Change the wheel, don't drive it with this tyre on again. I am sure that if you take it to someone who can cut the tyre open you will find what I described. I have heard of this happening to tyres before.

 

[William]

I think Steve's on to something...tyres can have all sorts of defects that don't show up unless you dissect the thing. And, as the tyres get warmer with use, funny things can start to happen (my Miata always feels a bit funky first thing in the morning, cause the tyres are all cold, but after a couple of miles all's well). Best to swap that wheel out before the tyre blows or something...stick the spare on (if you have one) as a temporary measure. Also, if you have wire wheels (don't most E's?), a bad tyre could cause some damage, I would think.
-William

 

[William]

Oh, man, get those tires swapped out quick! I would imagine that tires from 1989 are starting to get a bit hard!
-William

 

[Dave Russell]

I had pretty much the same symptoms. The tire shop removed & checked the tires, couldn't find a problem. I insisted that there was a problem so the tire guy had me drive down the street while he ran along side watching the tires. Sure enough, he could detect a tread separation. Couple of months later it happened again on another tire. The tires were about four years old & still had plenty of tread. Time for new tires all around. Later the manufacturer recalled a bunch of the tires as a result of a class action law suit. (they were not Firestone)
D

 

[baldytheanimator]

Ah, yes--you've given me an "a-ha" moment...

One of my tires did fail about six months ago...the RR. I opened the garage door in the morning to find it flat, and had it repaired that day.

Well, the good news is that I have an answer to my question. The bad news is it sounds like I probably should get a whole new set of tires. If the RF needs replacing, and the RR failed once, it probably means the whole set is getting a little tired. They may have good tread, but I'll bet this rubber's been sitting on this car for a good many years--probably at least since the PO's 1989 full restoration.

I've had rotor/bearing problems before on other cars, so I think that experience worked as a distraction from what was the real problem...

Thanks much!

 

[baldytheanimator]

Ah, yes--you've given me an "a-ha" moment...

One of my tires did fail about six months ago...the RR. I opened the garage door in the morning to find it flat, and had it repaired that day.

Well, the good news is that I have an answer to my question. The bad news is it sounds like I probably should get a whole new set of tires. If the RF needs replacing, and the RR failed once, it probably means the whole set is getting a little tired. They may have good tread, but I'll bet this rubber's been sitting on this car for a good many years--probably at least since the PO's 1989 full restoration.

I've had rotor/bearing problems before on other cars, so I think that experience worked as a distraction from what was the real problem...

Thanks much!

 

[baldytheanimator]

I almost got a whole new set back when the first tire gave me problems, but the guys at the local Jag club and my mech said I shouldn't be so panicky. But it sounds like my paranoia was justified...

...just met with my club again tonight and they agree with you fellas.

Now I've got another question--I could probably scare up a set of Michelin 185/15 ZXs at Price Club for $70 each...but a set of 185 XZXs would cost me a good $130 per. The difference? The XZXs are rated to 150mph...

I do plan on putting my baby to the test out in the desert --after all, why own the car if you don't? Every time I go to Vegas, I take her off the main highway and easily play around 120.

My question--is it worth the extra money for a 150 mph rating if you only plan on going over 120 maybe twice a year for short stints? There was disagreement at the club about this.

Hmm. I think my conscience knows the answer to question already

but I'm interested in your guys' thoughts on performance tires...

 

[baldytheanimator]

I almost got a whole new set back when the first tire gave me problems, but the guys at the local Jag club and my mech said I shouldn't be so panicky. But it sounds like my paranoia was justified...

...just met with my club again tonight and they agree with you fellas.

Now I've got another question--I could probably scare up a set of Michelin 185/15 ZXs at Price Club for $70 each...but a set of 185 XZXs would cost me a good $130 per. The difference? The XZXs are rated to 150mph...

I do plan on putting my baby to the test out in the desert --after all, why own the car if you don't? Every time I go to Vegas, I take her off the main highway and easily play around 120.

My question--is it worth the extra money for a 150 mph rating if you only plan on going over 120 maybe twice a year for short stints? There was disagreement at the club about this.

Hmm. I think my conscience knows the answer to question already

but I'm interested in your guys' thoughts on performance tires...

 

[Dave Russell]

There are several factors that go into a tire's speed rating. For a given rating;

The more lightly a tire is loaded in relation to its load (weight) rating the more speed that it can safely handle.

The higher the inflation pressure the more speed the tire can handle.(reduces flexing) Manufacturers sometimes recommend increasing pressure 10 psi for high speed driving.

Ambient & pavement temperature. The colder, the more speed that the tire can safely handle.

The speed limit for a tire is really a matter of how much heat the tire builds up. Most of this heat is generated by the tire flexing as it rotates against the pavement. Faster rated tires are built to flex less & to have less internal friction.

Lastly, the tire speed rating is the sustained speed that the tire can safely handle. The operative word is sustained since it takes time for the tire to reach dangerous temperatures. I believe that the tire speed rating is based on somewhere between .5 and two hours at the rated speed & conditions.

So; I personally would not be worried about running a 120 mph rated tire at 130 or 140 mph for 20 minutes or so. Especially if the tire was only carrying 70% of its rated load,or was inflated 10 psi over its rating,or if the pavement was cold, etc.

In the interest of legal liability I am not recommending this practice. It will have to be an imformed judgement call or gut feeling for each individual.
D
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by baldytheanimator:

My question--is it worth the extra money for a 150 mph rating if you only plan on going over 120 maybe twice a year for short stints? There was disagreement at the club about this.

Hmm. I think my conscience knows the answer to question already

but I'm interested in your guys' thoughts on performance tires...<hr></blockquote>