Propshaft U-joint Angles

[peter_m7uk]

Evening Hoodies,

 

I recently ordered a propshaft from GBS and it set me thinking about the angles of the U-joints.

I measured the angles of the box and diff and their relative positions and got the following:

 

The gearbox output shaft and diff input shaft centre lines are at 1.35 degrees to each other.

The diff input shaft is 37.5mm higher than the gearbox output shaft, at a distance of 632mm

apart, giving an angle of 4.1 degrees (distance between joints is 525mm).

This gives a working angle of 4.1 degrees on the gearbox and 5.45 degrees on the diff.

 

I then read this link on propshaft angles, which states that the working angles should be within 1/2 degree (not 1.35!) on high speed propshafts and the maximum working angle should be 4 degrees (I have 4.1 and 5.45).

 

Clearly, I am out of spec by their standards. How much does anyone think I should be concerned?? I don't think there's

an awful lot I can do to adjust these angles, but is the prop going to vibrate itself to bits, or is that web link being too critical??

 

Cheers,

Pete

[Guest Nigel Novice]

Angles didn't seem to bother us old boys much when racing and we had live rear axles to contend with, non of this IRS I'll have you know

[agent_zed]

just have a look at lorries and vans and you'll see their prop shafts are at a hell of an angle, so i wouldnt worry too much. Just remember to grease regualrly. hth

[peter_m7uk]

Angles didn't seem to bother us old boys much when racing and we had live rear axles to contend with, non of this IRS I'll have you know

 

Nigel,

 

They may have been a bit more heavily engineered than the Lightweight! I would have thought constant vibration in an ali chassis is not great news.

 

Pete

[peter_m7uk]

just have a look at lorries and vans and you'll see their prop shafts are at a hell of an angle, so i wouldnt worry too much. Just remember to grease regualrly. hth

 

Hi Zed,

 

This is true, but lorry and van propshafts are going considerably slower than Seven kit cars, with their large wheels and slow-revving diesel engines. I don't think big angles at each end are a problem as much as the difference between the two angles. Looking at this and this suggests that, for each turn of the gearbox end of the prop, the diff end will slow up and speed down twice. Doing a quick calc for 1.35 degrees (like my Lightweight) shows that at 3000rpm, for example, the diff end will go from 2999rpm to 3001 rpm twice per rev. No idea how this will actually feel or what effect it will have on the chassis!! Can't be the only person with a slightly misaligned prop though

 

Pete

[Peter Bell]

Pete, me thinks you worry too much, hopfully you have 2 UJs on your prop at 90° to each other so as one is slowing down, the other is speeding up.

[ibrooks]

Problem is that they won't do it evenly. The drivelines MUST be parallel or it'll shake your teeth out because the axle is constantly speeding up and slowing down. I'd be looking at adjusting the mountings of the engine&box or diff to get them inline.

 

Iain

[fry61]

If the drive-lines must be parallel what's the point of the U/J's---also if the bearings never move in their housings what about "brinelling" of the bearing housing?

[ibrooks]

The prop-shaft has U/J's to allow you to have drivelines that aren't IN-line. Left or right, up or down they need to be parallel or one end will speed up and slow down in relation to the other throughout each revolution.

 

Not sure what you mean about bearings moving in their housings.

 

With the Sierra setup it should be easy to get right as the diff is fixed in relation to the gearbox(to within the tolerance of the rubber mountings). With a live axle it's a bit more tricky because you need to make sure the axle's orientation doesn't change as it moves up and down - hence four parallel links and Watts linkages in the ultimate applications.

 

Iain

[peter_m7uk]

Problem is that they won't do it evenly. The drivelines MUST be parallel or it'll shake your teeth out because the axle is constantly speeding up and slowing down. I'd be looking at adjusting the mountings of the engine&box or diff to get them inline.

 

Iain

 

 

I suppose I should have expected a difference of opinions! Some think I'm worrying over nothing and Iain thinks it is important. I suppose what I'm looking for is practical experience here - Has anyone run a prop with a degree or two difference in the working angles and actually had big problems??? The theory suggests that a small difference could be significant, but I have no idea in practical terms.

 

The problem is that I don't have much room for adjustment. It's basically impossible to adjust the diff angle on the Lightweight, I can't lower the gearbox, so that just leaves raising the engine. However, I'm using the EFi manifold on a Pinto and have had to cut a hole in the bonnet already. I don't really have the option to raise the engine any higher!

 

I suppose what I'm saying is that I don't really have an option to change the alignment, but how much does it really matter?

 

Pete

[fry61]

Sorry,confused in-line with parallel---I'll go & stand in the corner.

[Longboarder]

My impression is that it is of no practical importance. I would challenge anyone to accurately determine the relative angles of the diff pinion and gearbox output shafts in their cars in both horizontal and vertical planes. All you can do is line it all up as best you can by eye/string/spirit level/laser/prayer/magic and bolt it all up. You will never notice if you got it right or not.

Just remember to grease the joints well and watch out for the nipples. They snap off easy as pie!

 

Nigel

[ibrooks]

Practical experience would be me then.

 

Mate of mine built a recovery truck out of a MkII transit and lined it all up by eye. At 30Mph it really would shake your fillings out. The difference we measured between the drivelines was 8 degrees from memory. You're only running 1 and a bit but from having felt that thing before and after I really would make a serious effort to get them as close to parallel as you can measure. We used angle finders (cheap inclinometers) to make sure the flanges at each end were at the same angle to the vertical. Exactly how much better/how bad your amount of difference would make I'm not sure so you'll have to guesstimate for yourself how much work it's worth to get them closer to "right".

 

Would be nice to check a car that's on the road and been found to drive OK to see how close it is.

 

I must admit to not checking on the 2B having assumed that RHE would have jigged the necessary parts of the chassis to ensure it was right but it's definitely something I'm going to spend some time over on the 200 because I know it's been messed with.

 

Iain

[Guest peter2b2002]

seen those big foot cars ,big v8s ,huge tyres & props @ 30deg, my ex brother in law had a toyota pick up truck 4" chassis lift 8" suspension lift + big wheels on handled like a pig but no vibration from the drive train

peter2b

[Guest Ian & Carole]

If any one can remember when Ford produced the Mk 1 RS2000,, to overcome the issue with servo and exhaust falling out with each other, they simply put a

2 1/2 inch longer engine mount on the drivers side and the tuther one was 2 1/2 inches shorter.

 

Engine sat in the bay like it was going for a walk down the left hand chassis rail

 

Never had a problem with this and look how well they did in competition.