Installing axle, 4-link etc- How accurate?

db · Post by db » Mon Jul 14, 08 9:51 am

How accurate do i need to be with the mounts?
I've plumbed from the original chassis points as the added frame sections and axle were out by as much as 1/4", (to be fair i think it was just cobbled together to make it mobile)

I've a chassis and an axle centreline marked on the wonky sloping tarmac now but my lines are 1/8" thick! Is it worth my getting a sheet of ply on the ground so i can mark it more exact?

Dave-R · Post by **Dave-R** » Mon Jul 14, 08 10:25 am

I freely admit I know little about this but to my limited knowledge the rule of thumb is the straighter you make the chassis, the straighter the car will run and with less effort.

Dave-R · Post by **Dave-R** » Mon Jul 14, 08 10:31 am

Thinking more about this I would add it is probably more important to get all the wheels pointing in exactly the same direction without any variation as the suspension moves. If you can ajust the axle to get that then you are probably OK.

the dodge · Post by **the dodge** » Mon Jul 14, 08 10:37 am

looks like youve got the right person on the job thou!

Anonymous · Post by **Anonymous** » Mon Jul 14, 08 10:38 am

Lovely piece of equipment.

Blue · Post by **Blue** » Mon Jul 14, 08 10:50 am

Needs to be as close to dead on as you can get it. How are you going to fit the 4 link? Are you making new rear chassis rails?

Dave-R · Post by **Dave-R** » Mon Jul 14, 08 11:04 am

I seem to remember reading something about BMW writing off any car whose chassis is more than 3mm off in any direction. But they would do that though wouldn't they.

Ivor · Post by **Ivor** » Mon Jul 14, 08 12:36 pm

Paul, Blue's absolutely right, it has to be as close to cock as possible, to ensure the car runs straight and true.

Do you have a friendly local bodyshop that has an old Blackhawk P188 they can hire you for the weekend?

It doesn't require a level floor to give you accurate dimensions for you to jig and weld to as it aligns itself with the manufacturer's reference points, which you can find in the service manual.

db · Post by db » Mon Jul 14, 08 4:16 pm

I'll get a sheet of ply and pin it under the chassis stands (so theres no chance of movement)
I plan to plumbline (tricky when it's breezy!) from a few points on the original chassis to get an accurate centreline and i'll measure back from the steering rack to confirm my rear axle centreline.
I'm leaving the chassis rails as they are Blue and i'll make bracketry as necessary to mate up to the 4-link mount points and to even out any inaccuracies in the original work (if i can get 'em off neatly i'll re-use the ladderbar front mounts, they're nice and sturdy)
The coilover kit and the anti roll kit both come with a cut-to-length crossmember so i should have no trouble locating those.
I think the key to the whole job will be getting those 1st outer front plates absolutely cock-on, everything else will come right from that.
I suspect there'll be a lot of tack, measure, tweak, measure, re-tack, measure, cut off, tack, measure, stomp off for a brew, swear a lot, cut off again, fling into a corner of the workshop, sulk, leave it a day or two, try again....

db · Post by db » Mon Jul 21, 08 10:55 am

I know what you mean Terry but the amount of extra work involved has put me off.
The rollcage and the tubs are lined up perfectly with the frame and although it ain't the prettiest or the most precise, there's nothing wrong with it. It's solid, it fits well, the welding is professional and if there is any misalignment, i can correct it when i attach the new stuff.
(and don't worry, the red paint ain't staying!)