Driveshafts & Geometry...

[jayw]

Good evening Class, here begins your Geometry Lesson for today...

I've seen it mentioned several times in the past and want someone to explain it to me:

'When lowering the car never go past the point at which the
driveshafts are at a right-angle to the strut (i.e driveshafts should
NOT point upwards at the outboard end)'

Now, i've brainstormed all i can about this and i can't figure any reason for it?

As far as i figure the angle of the shafts is not relative to any point of the geometry or outside the scope of what a CV joint was designed to do. And besides, when the strut is compressed under cornering load the shaft is then pointing up anyway.

I doubt i'm missing any simple 'slap in the face' principle of engineering so hopefully it's a lot more technical or just a fishy old wives tale...


Please complete your homework in Black pen and don't forget teachers apple in the morning... Class Dismissed!

[Kitch]

AFAIK, its the fact that its continually at an aggressive angle.

E.G if you corner hard and the joint points up to match the strut compressing, it will only do so for a number of seconds.

Whereas it'll be pointing up much more of the time than normal if the car is much lower and will wear faster. My girlfriends VTR is lowered about 50mm and its already killed one driveshaft. You don't get the rumbling around bends like normal....this sounded like a wheel bearing and happened as you drove in a straight line!

[Vanny]

Pretty much as Kitch, but its the CV's that fail rather than the driveshafts. at 90 degree angle there at maximum compresion between hub and diff which doesnt help them, and they'res a good chance of the CV's locking up and then cracking under high load, it will result in all kinds of fun breakages! (think about it, have you ever seen any car that has its drive shafts straight out?)

[jayw]

I hear what your saying, but as a CV joints position is infinitely variable (such is their purpose) i can't fathom how it's static angle makes a difference on the car?

The inner joints are spring loaded to account for the inward-outward movement and vanny you are right that they are most compressed when at 90deg to the strut. So, in pivoting upward from that point we're take compression off the joint again (if you follow...)

Surely they'd only lock up when we bent the joint/shaft too far off of straight, in which case thats impossible as the shaft movement up & down is no more increased? i.e driving on max height for ages would knacker the CV's due to the excessive angle of the shafts

Still confuddled...

[Toddman]

You will have to do some pretty outrageous lowering to cause problems.
The only way you can do damage is if the cv joint runs out of movement and then stress is placed on eithe rthe wheel bearings or diff seals and I doubt you cabn do this at rest.
You might manage too much movemment if the shaft slope up a lot at rest and then when cornering you exceed their limits but I seriously doubt you will do m,uch damage when driving on the road.

So basically Jay I am with you there really is not a real problem only theoretical ones.

The joints may of course wear quicker if constantly rotated at an angle rathe rthan in a centreline but my car is low nad has been for a good few years but the spheres are sorted to stop too much travel and the suspension does not hit the stops when on the road

Cheers
Luke

[AlanS]

Could it be that once you get past the horizontal, that the driveshafts then begin to support some of the weight of the car instead of the struts?


Alan S

[Anonymous]

Could it be that once you get past the horizontal, that the driveshafts then begin to support some of the weight of the car instead of the struts?


Alan S

The driveshafts never support weight of car, whatever angle they're at. The Idea of the driveshaft preferred working angle operating range is to give the joints an easy life as possible.
The design of the BX's suspension (ie long travel) means that the shaft's design is suitably robust and able to cope with pretty wild angles anyway, and I agree that lowering the BX's ride height will not bother the driveshafts or joints too much. Other steering goemetry, however, will alter but a small ride height reduction will present no problems.

[Anonymous]

ok excuse my ignorance but what is the best way to adjust ie lower the suspension to improve handling? what do i need and how is it done as id love a bit more confidence when taking corners at high speed?????

[Timmo]

Probably the easiest way is to move the height lever to a position that gives you the amount of lwerness you want without causing drivetrain issues and mark the gate, then move it out the way and cut a new slot in the gate (drill and file works!), that way you can have it in normal for everyday driving then drop her down a bit for 'enthusiastic ' driving!
Just remember to let the car rise to normal height before lowering otherwise its boneshakingly uncomfortable!

[Anonymous]

you may find lowering a car a long way altering the angle of the drive safts does cause cv's to fail at first, if you think that your car has probally already done 80,000 miles plus with the drive shaft running at 1 angle this will cause the c.v's and all othe componants on the suspension for that matter to have a "normal" operating range,
by lowering the car exesivly you alter the angle of the d/s camber of wheel ect causing bearings to run in different place from where they have for the last 80k or so moving the "operating range" so worn bearings are now running on unworn or less worn parts of c.v's or bearing races.
which is why when you lower a car 9 times out of ten you will end up replacing wheel bearings and in extreme cases c.v's
i personally have never lowered a car and not had to do at least 2 wheel bearings within about 6 months or so and in the case of the old nova which was about 80mm lowered all 4 bearings and both cv's
but once they were replaced it never caused me any more problems

[Daniel B]

Don't believe I have had any problems with mine in that department, and she has been lowered via the height correctors for around 7 years/40K now.

Dan

[Anonymous]

i dont know if bx's may be slightly different, i'm not sure ifbx's get the camber problems that cars with normal suspension (shocks and springs) get

[Timmo]

i htink becuase when the bx sinks to low the bearings etc will get may be a bit more used to it if you know what i mean as for hours on end the floor shafts pointing up! (well not quite on the floor but you gett he gist!) also due to the extra travel the susp gives you when on the move it may change things in terms of wear where as the normal lowered cars like the saxo's etc have a lot less travel!?! (especially when they are dropped on the bump stops which seems to be the fashion with the know nothing brigade!:D)