Fwd Driveshaft alignment

[paulcrs]

Hi all. I'm doing an engine conversion in my FWD escort and want to push the new engine backwards in the bay to give better clearance on the rad and intercooler.

Does the gearbox outputs have to be straight in line with the hub centre lines or can they happily run at an angle? (Angle is in front to back more than up/down)

If so, what angles are acceptable? I will need custom shafts so I'm not worried about this as such.

I've also converted to fully adjustable (camber & caster) suspension so o be fair I'm not sure where my "centre line" will be for the wheels in their driving setup once built and aligned.

I remember looking at an old toca touring car at an open pit at Silverstone where the engine was almost touching the bulk head so I assume this can be/is done and one can still maintain reasonable power output.
Looking at about 280-300bhp

Thanks Paul

[Phil H]

There is a limit to how much angle they can cope with - if you add some to start with, you'll reduce what can be accommodated with during steering.

In short, if you add 10 degrees (example) of static angle, you'll need to reduce your maximum steering angle by the same otherwise you'll just pop the CVs out on full lock. Caveat - the outers will be able to cope with full steering lock but the inners might not be so accomodating as normally they only have to cope with suspension movement (plus a little more for safety). Chances are they're probably the same guts as it makes sense from a manufacturing standpoint.

Also - if you move the centrelines, the distance between the output from the gearbox and the hub will naturally increase, so longer shafts might be needed. I read stories of people with excessively lowered FWD cars popping shafts for exactly this reason.

[Dez]

Inner and outer CV joints on a typical FWD setup are entirely different designs, mostly because they perform entirely different functions.

An outer CV will typically be fixed depth, but not max out on operation angle until 45-50 degrees. This is obviously to allow you to steer.

Inners by comparison can only go to about 25-30 degrees. What makes them different to outers is they are not fixed position, then have ‘plunge’. Typically a couple of inches. This accounts for the change in shaft length due to suspension and steering articulation. If you think about how little the inner CV moves compared to the outer, you can see why they only need half as much angular travel.

This is a bit of a generalisation and obviously they’ll be exceptions to the rules, but I’d say at least 90% of FWD cars follow that model.

To answer your original question, it’s probably doable but it may harm you steering lock a few degrees. Wether that’s acceptable or not is down to various factors, including the wheelbase of the car, what it’s going to be used for, and your personal preference.

[Phil H]

Ah - when I've seen driveshafts they've looked to have CV "packs" at both ends and look similar from the outside - does it depend if they're "pot" type inners (thinking back to my Mini days), or is it despite appearances they are significantly different? It does follow one end stays where it is and the other one moves in and out though..

Dez has probably got it more right than me - I only tend to find out by discovery when things break!

[slater]

On a mini the inners and outers arnt so different. On other cars they can be totally different.

My worry would be misalignment adding up. If its lowered aswell it could put them in the dodgey zone. I know a few cars I've lowered excessively before haven't liked it too much.

[ChasR]

Oct 16, 2019 19:27:20 GMT slater said:

On a mini the inners and outers arnt so different. On other cars they can be totally different.

My worry would be misalignment adding up. If its lowered aswell it could put them in the dodgey zone. I know a few cars I've lowered excessively before haven't liked it too much.

I know of a Scooby converted Splitty Van that had no end of issues with driveshaft due to CV joint misalignments.

[stealthstylz]

I'd mock it up and see what angles everything is at. (doesn't have to be at the extremes - people seem to mock up for max compression/steering angle together but if you're at that point ever during use of the car it's probably about to go on its roof. Reality is you need to check at full lock/ride height and then whatever steering angle 120-ish degrees at the steering wheel gives and probably the suspension compressed to probably half of total compression. My Saxo does a pair of driveshafts every 30,000 miles but they're 18 quid each so it doesn't bother me. If you're getting expensive/custom shafts made it needs to be right really.