Exciting day - rebuild of 78 coupe

[kentvette]

Ross, I can't pretend to be an expert on poly vs rubber bushes, but I did do a lot of reading when I was considering the change of my trailing arms. I got the impression that in general, the oOEM bushes were favoured by most people (C3 owners), unless some serious other mods to power train etc were made. Poly bushes "stiffen up" the suspension anywhere they are used, so I guess there is something in your thought that they would "control" the arm more. And given your power train, poly might be good!

 

[Forrest Gump]

Inner sidewall of tyre (285/40/18 on a 18 x 9" rim - 5" backspace) when measured has about 3/8" clearance to frame. In use the tyre 'polishes' a small section of the inner frame where it rises up over the real axle assembly. It can't be much as there is no evidence of rubbing or abrasion on the tyre. My presumption is that its sideways flex of trailing arm, perhaps when cornering hard.......its both sides. But if trailing arm is supported closer to the end of the arm by strut rod and drive shaft (as JohnG notes) perhaps I also need to look elsewhere too?

Under acceleration the wheel will tend to toe-in more, so the combined play/movement in the wheel bearings and every bush - t/a pivot and strut rod, could allow the tyre to move closer to the frame? I would think if was solely the t/a pivot bush allowing the wheel to move 3/8” then you would be feeling some rear end steering effects when on and off the gas.

 

[Roscobbc]

Max tire size to rim width
So in my 1999 C5

Front rims are 10x18 inch, so I went with 275/35/18
Rear rims are 12x18 inch, so I went with 335/30/18
No bulge of sideways at all

Your tires are too wide for a 9-inch wide rim, so wheel spacer the cheapest fix
Examples :
1968 Corvette Wheel Spacers

View attachment 13825

I do not care for the 'stretched' tyre over wheelrim effect you seem see on so many cars with wheel/tyre upgrades - one of the 'downsides' of using large diameter, low profile wheels and tyres will the significant reduction in ride quality and increased tyre and suspension noise at lower speeds. Probably less of an issue with late model Vette where the suspension has been optimised for use with 18" and 19" wheels. Add-in our poorly maintained and badly potholed roads and the potential damage that can occur I decided to build-in a degree of 'old school' sideways yield in to the wheel and tyre combination. So front tyres are 255/45/18. With a 10" wide tread on an 8" wide rim it gives 1" over rim size each side of wheel. Rear is 285/40/18. So 11.5" tread on a 9" rim and 1 1/4" each side of wheel. Tyre diameter is aprox. 27" and close to OEM diameter rubber.

 

[johng]

Well as ever I've had some good news and some bad news.
Good news is that I've finished adjusting my suspension geometry front and rear and the rear strut rods are currently holding their settings. The LH side hasn't moved since I turned the cam washer around. The RH cam washer isn't dished (so my guess is that the LH side is only dished because it got bent at some point) and it did keep slipping. I've cut a load of thin grooves on the back of the washer and this has done the trick (so far). In fact I was able to torque up the nut without holding the bolt and it didn't slip.



The bad news is that I noticed today that my car has gone out in sympathy with Oneball's and I now have a 100mm crack in the top left of my windscreen

 

[Forrest Gump]

Argh you’re kidding, sorry to hear you’re screen has cracked too. Anything to do with you jacking the car up and down for the suspension adjustments do you think?
Good solution for the strut rods. Did you notice that small arrow symbol on the cam washer?

 

[Oneball]

Oh clucking bell. Do you think there’s a screw or something touching it?

Could be worse, you could have bought a brand new replacement screen that’s far from brand new.

 

[johng]

Might have been jacking the car. I never jack just 1 corner, either I jack front and rear on one side, or both sides at the front or the rear. Of course I do have to operate one jack then the other, so there's always a bit of unevenness.
Yes I'd seen that symbol, I believe that side has to go against the bracket. That's not how my LH side had been assembled originally.

 

[Oneball]

I wouldn’t have thought Jacking the car would crack it unless there was something wrong to start with.

 

[johng]

I've certainly seen lots of warnings about jacking the car causing the body to twist, door openings getting bigger or smaller, etc

 

[Roscobbc]

That would indict potential birdcage issue allowing significant chassic chassic flex. My guess is that its just a fluke John. If you wnat to be double sure slip folded cardboard in the door gap between the door to rear fenders and door to front fenders in several places. Jack the car-up each side and by observing how tight/loose the cardboard is will hopefully indicate how much frame flex you are getting.

 

[Forrest Gump]

I wouldn’t have thought Jacking the car would crack it unless there was something wrong to start with.

……might just have helped along a pre-existing chip or flaw that was always going to crack sooner or later, but that’s not much consolation.
It can’t be very long ago when they fitted that screen, any chance you could get another one under guarantee for faulty product or fitting?

 

[johng]

I'm pretty sure they guarantee the screen against failure due to poor quality parts or workmanship. The trouble is how do I prove that's what caused it to crack? It could have been jacking the car, hitting a pothole (which I have) or a stone hitting it.

 

[johng]

That would indict potential birdcage issue allowing significant chassic chassic flex. My guess is that its just a fluke John. If you wnat to be double sure slip folded cardboard in the door gap between the door to rear fenders and door to front fenders in several places. Jack the car-up each side and by observing how tight/loose the cardboard is will hopefully indicate how much frame flex you are getting.

Not too keen on jacking it up at the moment Ross! Think I'll wait until the current dry weather has gone, so I can use the car a bit longer, then trying further jacking and then get the screen replaced.

 

[Oneball]

I'm pretty sure they guarantee the screen against failure due to poor quality parts or workmanship. The trouble is how do I prove that's what caused it to crack? It could have been jacking the car, hitting a pothole (which I have) or a stone hitting it.

Give them a ring and ask them to have a look at it, worst that can happy is they say it’s not their fault.

I genuinely believe that jacking it up won’t crack it. But could be a stone chip or my bet is that the screws for the side trim are touching it (assuming that’s where the crack is)

 

[Stingray]

The bad news is that I noticed today that my car has gone out in sympathy with Oneball's and I now have a 100mm crack in the top left of my windscreen

If it's a crack that grows from the edge of the screen it's a stress crack.

Convertibles and targas are particularly susceptible. One easy way to break the screen is by hanging your weight off the A-post to help getting in and out of the car. If you can't get the door open far enough to swing your legs out of the car it's better to roll out of the seat and push yourself up from the sill.

 

[Adtheman]

Oh clucking bell. Do you think there’s a screw or something touching it?

Could be worse, you could have bought a brand new replacement screen that’s far from brand new.

Im intrigued Tim how can you buy a brand new replacement screen thats not brand new. Oh please tell !!!

 

[antijam]

Im intrigued Tim how can you buy a brand new replacement screen thats not brand new. Oh please tell !!!

I suspect the 'brand new' relates to the screen as advertised and the 'not brand new' to it as received.

 

[Oneball]

What AJ said. Seller has said I can return it, just a lot of faff.

 

[teamzr1]

Give them a ring and ask them to have a look at it, worst that can happy is they say it’s not their fault.

I genuinely believe that jacking it up won’t crack it. But could be a stone chip or my bet is that the screws for the side trim are touching it (assuming that’s where the crack is)

Always been said that due to C3 frame flex is when jacking up the car is to unlatch the hood and 1 door partly open to reduce the stress cracks to body or glass.

But if the GM owners or service manual does not caution on this when jacking then the insurance should pay off

I got this directly from GM's archive, as I include in the attached PDF,
go through it and see if any warning of caution as to jacking C3 up and a page of that maintenance/service book Notice page 0B-12

 

[Adtheman]

What AJ said. Seller has said I can return it, just a lot of faff.

Its probably more annoying than anything else, some people have a cheek advertising things not as they appear.