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Sierra driveshafts and correct track width?
craig1410 - 17/4/03 at 09:17 PM

Hi,
I'm building a de-dion backend for my McSorley 7+4 chassis and have got to the stage of being about to set the track width by virtue of where I weld my de-dion "ears" onto a large steel tube through which the driveshafts pass. The end of this tube has a mounting onto which the hub carriers mount. (I hope that is clear...)

Anyway, my question is:
Given that the driveshafts can lengthen and shorten by virtue of the design of the Lobro joints, to take account of varying suspension height, is there an optimum distance apart for the ends of the driveshafts when they are parallel to the ground?

Obviously I don't want them to bind on full "bump" or to pull the Lobro joints apart on full "rebound". Anyone got any tips or measurements which would help to get optimum positioning? Or, Does anyone know how far apart the inboard edges of the brake discs should be on a Sierra backend? I am using the disc brake backend with the 7.5 inch diff.

Thanks,
Craig.

ps. I'll post photo's if the above is unclear.

dmottaway - 17/4/03 at 09:45 PM

I am no familiar with the sierra rear-end but it seems to me that, with the driveshafts level, the carriers could be at the narrowest possible position. That is, any movement up or down (bump or rebound) only takes them away from the diff. therefore, move them apart just a bit to allow some flexibility but allow most movement to be away from the diff.

I hope this is right 'cause its my plan with my RX7 rear.

dave

craig1410 - 17/4/03 at 10:02 PM

Dave,
That's certainly how I'd do it in the absence of any firm information otherwise. However, I am concerned that the Lobro joints may have an optimum position and given that I'm using a torquey Rover V8 engine I don't want it to eat my driveshafts every 3000 miles or so...

Thanks for your input,
Craig.

stephen_gusterson - 17/4/03 at 10:05 PM

i set mine up so that the joints 'float' roughtly midway when the car is level on the ground.

There seems to be about 35 - 40mm at least movement in mine.


atb

steve

craig1410 - 17/4/03 at 10:14 PM

Steve,
When your car is at normal ride height, are your driveshafts level or lower at the ends?

I don't suppose you know the disc to disc distance on your car?

Cheers,
Craig.

Rorty - 18/4/03 at 03:40 AM

You need to work out the amount of plunge your CVs can accomodate, then install the shaft and CVs into their positions in the diff/upright.
With the shaft at 90 degrees to both the flanges (asuming rear camber is set to zero), grab the shaft, and push/pull it in and out, measuring the amount of plunge. If all's well, it should equal the plunge you measured initally.
If it doesn't match, then the axles will need to be lengthened/shortened accordingly.
The end result is that the balls in the CVs should lie the middle of the CV outers, while the shafts are level.

craig1410 - 18/4/03 at 11:05 AM

Rorty,
That sounds like a good way to go.

What you are saying is that the driveshafts should be in a "relaxed" position when the shafts are level and thus they are in the same position as they would be when off the car entirely?

The only concern this gives me is that as far as I can see it is only the gaitors which define this "relaxed" position and thus if my gaitors were not perfect in some way then wouldn't that change things?

I'm being very careful with this because when I weld the de-dion ears to the large tube I am welding 3mm steel to 5mm steel and it is going to be virtually impossible to separate them after they are seam welded. (At least I hope that they won't separate easily... ) I'll get this welded by a professional by the way because I think my 120A welder might struggle just a teensy bit!

Cheers,
Craig.

stephen_gusterson - 18/4/03 at 10:41 PM

i would agree with rorty and also your statement that the gators have something to do with it.


I just pulled and pushed the drive shaft in and out to check it has roughtly the same movement both ways.

Bear in mind that the shaft gets longer and shorter according to the arc scribed from the diff to the wheels.




Another thing to be careful of is that the shafts are NOT equal length. One of mine worked out fine, the other needed lenghtening using two shafts. The shaft is solid and hardened. im going to get mine sleeved as well as gas welded at the join. (been made as far as gas welded - still need a sleeve).

atb

steve

Rorty - 19/4/03 at 12:51 AM

craig 1410:

quote:

The only concern this gives me is that as far as I can see it is only the gaitors which define this "relaxed" position
Not so Craig, The width of the CV outer, and the inner knuckle and cage determine the amount of plunge (asuming the circlip is still in situ).
The CV boots are designed to cope with the amount of plunge, and so, give the impression that they govern the total amount of movement.
I strongly advise you to strip the shafts and CVs down to their bare esentials before doing the float test. That way you'll get a realistic, unhindered result.
I use a home made axle gauge (pic of it in my photo album here, I think, if not, it's on my site). You'll see I've ground off the shoulder at the base of the splines, you don't need to do this. I only do it for some of the axles I make for off-road use, where I don't run a shoulder or circlip. In my case, the plunge is often in excess of 80mm, so the axles need to be free floating.
With the amount of wheel travel in a Locost/Sierra, the CVs will more than cope with the amount of plunge, with a shoulder/2 circlips, as long as you set them up correctly to start with.

stephen_gusterson - 19/4/03 at 10:33 PM

the joints come apart easily when the boot is off.

clean em off by taking the inner cage out with the (6?) balls.

I did this so i could pack em with new graphite grease.


atb

steve