Engine compartment slightly twisted. How much is too much?

[Casgar 21]

I'm slowly but steady getting ready to replace the entire floor on my 69 fastback. The car is up on 5 jacks, 4 on each spot weld flange in every corner of the floor and 1 in the center of the radiator frame support. The floor has some very minor twist in it, ~1 mm difference between front right to left rear after I got it as level as possible. Not enought to care about.

After I got the floor level I decide to measure the shock towers and realise I can put almost a whole finger under one side of the water level to get it flat. I then measure from a level floor to the lower flange on the frame rail in front of the shock towers and I get ~8 mm (~0.35 inches) difference compared to the floor. I also measure at the back from a level floor up to the gas tank flange, ~1 mm difference. The rear end and leaf springs is only mounted in the front.

What do you guys think, is it within factory tolerances or should it be adressed? And if it needs to be adressed, how?

 

[newstang 388]

11 minutes ago, Casgar said:

I'm slowly but steady getting ready to replace the entire floor on my 69 fastback. The car is up on 5 jacks, 4 on each spot weld flange in every corner of the floor and 1 in the center of the radiator frame support. The floor has some very minor twist in it, ~1 mm difference between front right to left rear after I got it as level as possible. Not enought to care about.

After I got the floor level I decide to measure the shock towers and realise I can put almost a whole finger under one side of the water level to get it flat. I then measure from a level floor to the lower flange on the frame rail in front of the shock towers and I get ~8 mm (~0.35 inches) difference compared to the floor. I also measure at the back from a level floor up to the gas tank flange, ~1 mm difference. The rear end and leaf springs is only mounted in the front.

What do you guys think, is it within factory tolerances or should it be adressed? And if it needs to be adressed, how?

 

woah! we only speak inches here :-)

 

[newstang 388]

im not sure if it helps, but these are dims i made from my car,

also the usual dimension sheet from a 70

[barnett468 418]

Yeah, wow. ok, xlnt work, hopefully ridgerunner and others here will have some good ideas for you, but your question is actually a bit complicated and the issue can be addressed different ways with different results, but hopefully this will help you some.

Nobody has the production tolerances for the dimensions you are asking about, however, 8 mm will not be noticed in your application. It is more relevant in a 200 mph indy car etc.

I'm guessing you checked several points for center line as well.

A better point to measure to see if the suspension is level is the height of the front leaf spring mounts and the height of the upper control arm mounts, because they did not use the cars floor as the guide to build the car around, and a "frame" can be "square" but the cars floor may not be square to the frame, and it is more important to have the suspension square to itself front to rear than to the floor.

There are adjustable rear leaf spring mounts that use a "cam" to vary the height with. These have at least 1/2" of adjustment to them, so instead of trying to relocate part of the frame/shock towers etc, you could use these instead to compensate for the difference. If you use lowering springs on the front, you could also try to use those to level the car with by cutting one more than the other, but this is really impractical for such a small difference for several reasons, and it would simply be far easier to do with different height rear leaf spring mounts.

One thing to keep in mind is the height of the top of the fender aprons. These should also be "square" to the rest of the car as well, or more importantly, the same distance in height from side to side using the lower edge of the rockers as your level. If they are not, you may end up having to put shims between the fender and top of the apron if one side is lower than the other etc. You may have to do this anyway for several reason, but the less shims the better.

In addition, one "upgrade" I would do is to weld a thick washer around the upper rear shock mount hoes because this is a weak area on these cars and can crack, especially after 100k miles of use and/or if stiffer than factory shocks are used etc.

 

 

[Casgar 21]

Thanks for the tips. I'm going to take some more measuremetns this weekend.

On 10/2/2019 at 5:32 PM, barnett468 said:

I'm guessing you checked several points for center line as well.

I'm not sure I understand what you mean here.

[barnett468 418]

Looking at the frame and your drawing from the top you can use the front leaf spring mounts and upper or lower front suspension mounting points, then use a plumb bob to mark all four of their positions on the floor, then draw a line from side to side thru both the front and rear suspension points, then  from the center of one of those lines lines draw a line to the other end of the car that is 90 degrees to that starting line. This 90 degree line should intersect the other suspension line in the middle of it. If it does not, then the car is dog tracking.

[Ridge Runner 1,113]

First of all ,dont level from the floor . Check level from the rockers and frame rails ,the floors can be up and down in these cars . If your rockers and frame rails show level together you are good to go . Has any of the front clip sheet metal been replaced ,was the car leveled first ,this could have caused a twist if it wasnt leveled first

[Ridge Runner 1,113]

A simple way to check the center line would be to mark center on the bottom of the brace below the radiator support ,then find center at the rear between the shackle mounts in the rear frame rails and stretch a string ,then you can measure rocker pinch weld front and back to the string from each side ,do the frame rails the same ,this will let you know if something is cocked over to one side or the other

[Casgar 21]

3 hours ago, Ridge Runner said:

First of all ,dont level from the floor . Check level from the rockers and frame rails ,the floors can be up and down in these cars . If your rockers and frame rails show level together you are good to go . Has any of the front clip sheet metal been replaced ,was the car leveled first ,this could have caused a twist if it wasnt leveled first

My fault. I meant I leveled the rockers in the front and rear of the door.

I did some more measuring on the front and rear frame rails. The rear just ahead of the front spring mount is within ~1 mm, the front under the firewall about the same, but the rear end of the front frame rail on the driver side is about 3-4 mm lower (~1/8") than the passenger side one. The front end of the driver frame rail is also 8 mm (~3/8") higher than the passenger rail.

The car has been in a crash in the front right corner some point in time because the radiator support and battery tray seems to be hammered back in shape somewhat. Doesn't seem to be any direct damage to the frame rail though. The passenger side shock tower also have some strange damage, apart from the usual crack. It looks like the rear bolt for the upper control arm is pulled outwards 3/8" together with the tower and that they have tried (and failed) to heat and hammer it in place too.

Some more information that I've been withholding is that the driver floor is totally rotten on both sides of the frame rail, but the passenger side seems fine. Can years of use with a bad floor make the whole driver side frame rail twist up in the front and down under the floor with the center point at the firewall? There is a crease in the upper cowl too. Looks like the plate connecting the fender to the cowl have tried to push down or twist the cowl. This is also more apparent on the driver side than the passenger side and seems to point towards some twist in the driver side rail mostly.

[barnett468 418]

3 hours ago, Casgar said:

1. The passenger side shock tower also have some strange damage, apart from the usual crack. It looks like the rear bolt for the upper control arm is pulled outwards 3/8" together with the tower and that they have tried (and failed) to heat and hammer it in place too.

2. There is a crease in the upper cowl too. Looks like the plate connecting the fender to the cowl have tried to push down or twist the cowl. This is also more apparent on the driver side than the passenger side and seems to point towards some twist in the driver side rail mostly.

1. The front frame is probably pushed over to the side some them.

2. Holy crap!

[Vicfreg 772]

Sounds like you have a real challenge on your hands

My '70 Vert was missing half the lower body reinforcement when I got it, was strapped to 6x6 inch lumber to keep it straight.  Mike (latoracing) got it straight.  You may want to PM him and ask him some specific questions.  He used a laser (pretty common these days in home improvement stores) to index the points on my frame.  He also built a frame table, which he will use for other projects, but that isn't really necessary.

Some pics from my archives..

 

[Casgar 21]

2 hours ago, barnett468 said:

1. The front frame is probably pushed over to the side some them.

2. Holy crap!

1. We'll see when I cross measure the frame. I lost the measurements that I did earlier, but if I remember correct there were hardly any differences.

2. I don't think it's really as bad as it sounds. I don't even know if it's related to the twist. I'll post some pictures later, but the thing is that I can't find anything that indicate that a possible twist of the front clip would cause that damage. I think you would see alot more obvious damage on the firewall if that was the case, which I don't. It's more like the cowl side of the plate on both sides is bent downwards to fit an already damaged cowl. From the look of it you could probably just remove the plate, push out the cowl from the inside and bend the plate to fit the fixed cowl.