C3 1969 - Wheel Shake

[Blondie69]

Morning all,
Any ideas? C3 1969 has a violent shake. Random speed and I have not looked in deep just yet. It has been stationary for a while and driven very rarely. What should I look at first - tyres?? The front tyres do run on full lock so feel they may be too large but would that cause such a violent shack when moving. Complete beginner so any help appreciated

 

[Roscobbc]

Several things to look at Blondie.
If the car has 'old' tyres on it - so perhaps in excess of ten years old........they could be subject to damage from UV light and general degradation.
Some tyres can age harden and suffer from reduced grip even though seemingly in perfect condition).
Tread can de-laminate from tyre casing (inspect sidewalls and tread for micro-cracking.
If the car has been standing for a long period the tyres may be retrieveably 'flat spotted' (perhaps the cause of your issue)
Older casing damage to the tyre could result in tread separation when driving.....with the risk of a potential 'blow-out'.
Age of tyres can be determined by the following.
"The 'date of birth' is written on the tyre sidewall. Look out for a four-digit code. The first two figures represent the calendar week in which it was made (from 1 to 52) and the second two figures are the year of manufacture. So a code of 1316 would mean your tyre was made between 28th March and 3rd April 2016".
Otherwise look for missing balance weight on wheel that has the problem.
Inspection of steering and suspension components for excess wear..........or a combination of above items.
A knackered shock absorber can create shake (like you mention) as the wheel 'patters' up and down unrestrained by the shock absorber......it can be quite violent!

 

[Forrest Gump]

Check out North Hants Tyres if you’re looking for classic American style tyres with raised white letterIng on the sidewall. The Club gets a discount from them. They deliver the tyres to you, then get them fitted locally.

Tyres

www.northhantstyres.com

Assuming you have original 15” wheels, 225/70/R15 are a good fit. Some choose 215/70/R15, or 255/60/R15 but the width of these can rub on early C3s (maybe what you have fitted at the moment).

 

[Blondie69]

Thank you for your help. Checked the age of the tyres and they are 16 years old.... They look brand new. I've learnt a lot so far.
The front are 245 / 60 / 15 and the back 255 / 60 / 15. Yes I think front are slightly too big for full lock.
Thank you for letting me know about Northants Tyres and the discount. Will be another Christmas present for me !! .
Fingers crossed that's the answer - never want that shake to happen again. Scary stuff...

 

[Roscobbc]

My experience with older tyres and age degradation (in my case 20 year old B F Goodridge) on my C3 was firstly the squealing going around the slightest cornered smooth tarmac and that they seemingly never, ever appeared to wear out......the micro-cracking on the area where the side wall joins the tread was also a clue.
Supposedly if stored in 'ideal' conditions, so in UV free, dark temperature controlled conditions that perhaps a tyre manufacturer/distributor might have then they may be OK.
TBH, OK so tyres ain't exactly cheap but do have major safety implications - we've had a few instances in the CCCUK where members have had issues with major 'out of date' catastrophic tyre failure.

 

[Blondie69]

Yes definitely will be replacing the tyres. It's taken me too long to find this one and don't want to be silly and push the limits.
Do you think 225 would be okay on front but keep the back ( new all around ) as 255??.
It shouldn't effect the overall handling of the car, should it?
Many thanks

 

[Roscobbc]

Yes definitely will be replacing the tyres. It's taken me too long to find this one and don't want to be silly and push the limits.
Do you think 225 would be okay on front but keep the back ( new all around ) as 255??.
It shouldn't effect the overall handling of the car, should it?
Many thanks

Guessing if you use the 225/70/15 the ride height will be much as the 255/60/15 rears - perhaps others on here can comment.
Question
Were the tyres up front new when you replaced? - how long ago?

 

[Blondie69]

Guessing if you use the 225/70/15 the ride height will be much as the 255/60/15 rears - perhaps others on here can comment.
Question
Were the tyres up front new when you replaced? - how long ago?

I was thinking of replacing with 225 / 60 / 15 on the front. The tyres are original from import ( 2014) - not by me. I have only just purchased the car. Shake didn't happen on the test drive. But it has lovingly been stored but maybe not driven too much.
Thank you for your help. It's a learning journey that I am loving

 

[Forrest Gump]

A 225/60/r15 is too small in diameter (25.6“). It won’t do any harm, just visually won’t fill the wheel arch.
The factory fitted tyres were known as F70-15 (which you can still get but are very expensive), these are 27.1”. The tyre sizes I mentioned above are all close to that diameter ie. what was designed for the car.

You can fit wider tyres at the rear, though people tend keep them the same all round on a C3 if on original 15” wheels.

Reading your first post again, you said the shaking was random. If this was a tyre issue I would expect it to get worse as your speed increases, and your later post says, the car didn’t do it on your test run. This makes me think perhaps something else causing the shaking - engine or transmission/ driveline.

 

[Chuffer]

Thank you for your help. Checked the age of the tyres and they are 16 years old.... They look brand new. I've learnt a lot so far.
The front are 245 / 60 / 15 and the back 255 / 60 / 15. Yes I think front are slightly too big for full lock.
Thank you for letting me know about Northants Tyres and the discount. Will be another Christmas present for me !! .
Fingers crossed that's the answer - never want that shake to happen again. Scary stuff...

16 years old !! You are driving a potential death trap , trust me . I have personal experience of large carbuncle suddenly coming up on a rear tyre that was getting on in years but masses of tread left . Fortunately I was only travelling at slow speed when it happened . The scary thing was that only the week before I had covered about 100 miles mostly on duel carriageways at 70 / 80 mph . A salutory lesson !! I also witnessed a fellow club member have an aging front tyre blow out whilst following him on a 70 mph dual carriageway . He was very lucky .
I agree with Forestgump about North Hants Tyres . They are very good and helpful and used them twice for new tyres with raised white letters . Most recently was replacing the fronts which were ` only` 8 years old and the handling was completely transformed .

 

[CaptainK]

I'll add my 2 pence too. My FTO had been off the road for 5 years a short while back. On the road now and slowly being restored cosmetically. At the time of first putting back on the road all the tyres looked fine, and indeed passed an MOT all fine. But after first driving it after being off the road is was quite apparent that the front tyres weren't so great to drive on. Loss of grip in anything but perfect conditions, locking up of tyres and screeching down the road on hard braking etc etc. The tyres weren't that old, but I swapped them for new ones and it was like night and day.

 

[Roscobbc]

I had something similar - perhaps 15 years of so ago I bought a set of brand new Koni shockers for my '68. Didn't really need them at that time so I put them in stock.
A good few year years later I decided to install them and after a bit of use I couldn't figure why on certain major 'A' road surfaces one of the front wheels would at times develop a rythmic 'patter' for some reason. The reason why eluded me for some time. I eventually 'borrowed' a good KYB front shocker off Andy, our Essex regional rep which cured the 'patter' immediately. On further inspection of the Koni shocker - when compressing the pair of front Koni's one shock returned to fully open far quicker than the other, (although seemingly still having damping action) ......indicated perhaps the valving was faulty?

 

[teamzr1]

Thank you for your help. Checked the age of the tyres and they are 16 years old.... They look brand new. I've learnt a lot so far.
The front are 245 / 60 / 15 and the back 255 / 60 / 15. Yes I think front are slightly too big for full lock.
Thank you for letting me know about Northants Tyres and the discount. Will be another Christmas present for me !! .
Fingers crossed that's the answer - never want that shake to happen again. Scary stuff...

The GM specs for 1969 as you see are F70 x 15 so sidewalls are deep


Keep in mind the choice of wheel and tire size can affect the speedo output and may require a gear change from end of speedo cable to tranny

Attached below I have included the 170 pages from GM engineering for 1969 MY you should download, save and make use of as it
details everything about the design of your 69 Corvette