need some help with rear suspension:

dave harris · 07-26-07, 11:20 AM

I have just installed the rear 1/2 shafts and, with the suspension at "full droop" (chassis is on jack stands, suspension is down as far as it will go) the right side (when looking from rear of car) has an interference in the 1/2 shaft joint at the transaxle when you turn the wheel. the interference is between the 1/2 shaft mount (flange that connnects to the transaxle with 4 bolts) and the universal joint end on the 1/2 shaft keeping the 1/2 shaft from turning. (clear as mud yet?).

the left side does not interfere this way. I can not detect a difference in angle (front to back) on the 1/2 shafts, or any angle (rotational) in the enginie mounting when viewing from the rear.

I've tried to "clearance" the 1/2 shaft mount a little in this area with a grinder, but i don't want to go any more until I hear back from the experts on the forum.

sorry for no pictures with the post - camera took a dump - will need to borrow one later this week and try to post if needed.

so - questions - is this typical (i hope not!) - or have i missed something simple?

thanks in advance for the assistance!
dave

Bill D · 07-26-07, 11:27 AM

I understand what you're saying. However, I think it's highly unlikely you'll ever have this situation in real life unless your car becomes airborne.

As you turn the wheel, can you "feel" any interference?

Bill D

Jac Mac · 07-26-07, 04:21 PM

The Flange with 4 bolts that attachs to the output shaft of the transaxle should have some slight reliefs machined/cast into it to allow the u-joint to clear at this point- Have you checked to see if left & right Flanges are identical in this area.
Are both halfshafts the same length and are the inner/outer u-joints aligned?
Are both rear coilovers the same extended length- perhaps this would allow one side to 'droop further.
Jac Mac

Dave Bilyk · 07-26-07, 06:23 PM

Dave,
I had this problem on my Dax. I have the Renault UN1 gearbox, and found that it fractured the roll pin that retains the half shaft to the gearbox output shaft. My solution was to increase the top and bottom suspension arm length by adjusting the heim joints. Since I still had sufficient thread engagement (> 2 diameters), almost equal arm length on both sides, and could not detect any other problems I was happy with that as a solution.

Dave

Peter D · 07-28-07, 02:17 AM

Dave, I had exactly that problem on one side of mine - one side of the yoke would just bind on the flange at full droop.

10 minutes with a die-grinder solved the problem - I just took about 1mm off the flange surface at the binding point, smoothed it all out & things are now ok.

BTW, another problem that I encountered with the old standard DRB sliding spline axles was that at full droop, the suspension was stopped by the extension limit of the splines, not the shocks (even with all spherical joints wound right in). The ends of the "male" parts of the splines were digging into the cork dust seal & chewing them out. The only solution I found was to get the last 3mm of the "male" splines machined off - it cost $150, but solved the problem.

Kind Regards,

Peter D.

Dave Bilyk · 07-29-07, 02:50 AM

Dave,
another thing that will affect this is the centring of the engine and transaxle. I guess that it would need to be centred in the chassis to within a couple of mm. If the transaxle is off say 5mm to one side, it might not be obvious to the eye, but could be enough to cause this issue.
So do any of you guys check engine/transaxle centring during the build?

Dave

dave harris · 07-29-07, 07:25 PM

THANKS FOR THE INPUTS EVERYONE.

I've tried to grind some off of the flange and will try some more later in the week and let everyone know.

the odd part for me is that it's only the right side - the left clears fine! So I will check to see if i may have the trans / engine angled on the mounts.

Peter, One more thing - when my suspension is at full droop, the upper rear trailing link bottoms on the rear chassis (angled portion of frame that goes up to the roll bar mount / top of shock mount etc). So, I'm not sure if the 1/2 shafts are all of the way extended or not.

Bill, while i agree with you about the "airborne" part on the street - both Sears Point (carrousel entry - remember the old bmw's!) and Thunder Hill (lover's leap on the rear section of track) have sections where we typically get very "light" at speed and just don't want to chance ripping that side off if it would happen.

thanks again for the inputs everyone!

dave

Peter D · 08-01-07, 08:03 AM

Dave, my trailing arms come very close to the angled chassis - 1mm on one side & 3mm on the other. Are you using the standard DRB-recommended AVO shocks like me ?

Dave B's suggestion of moving the uprights slightly outboard is a good one (if you have sufficient thread in the a-arms & top link). This might get you out of trouble with the trailing arms, & should also help a bit with the uni binding problem.

BUT, do be careful to check that you don't end up extending the drive-shafts too far. If this happens, I reckon that you then have 2 choices :

- get a few mm of the "male" splines machined off as I did to allow the shafts to extend a bit further

- make up some spacers to put between the g'box flanges & the drive-shaft flanges

I suspect that either of these solutions would exacerbate the uni-joint binding by allowing the suspension to drop that little bit further, so I would look to fixing the trailing arm problem first, then the uni-joint problem.

An alternative thought : perhaps all of the problems could be fixed in one hit by getting a shock-absorber expert to pull the shocks apart & shorten the travel at the full-droop end ? It might even be cheaper to just replace the shocks with ones that have an adjustable lower bump-stop ?
(I am guessing here, but I am sure that I have read about shocks that fully adjustable, both in terms of damping rates & bump stops).

Good luck mate,

Kind Regards,

Peter D.