PROPSHAFT PHASING

cobraboy

Well-Known Member
#1
A question please.
Looking in the WM under the DATA for prop shafts the following info is given.

DATA

Manual gearbox models

Propeller shaft type Hardy-Spicer needle bearing

Tubular shaft 63,5 mm (2.500 in.) diameter

Overall free length (face to face) 1136,65 mm (44.750 in.)


Automatic transmission models

Propeller shaft type Hardy-Spicer needle bearing

Tubular shaft 63,5 mm (2.500 in.) diameter

Overall free length (face to face) 1003,3 mm (39.5 in.)

Yoke angular displacement (see illustration)

Up to final drive suffix 'A' 107 degrees

From final drive suffix 'B' onwards 144 degrees


My question is, do both manual and automatic propshafts have a yoke angular displacement or is it just the automatic propshaft ?

Thank you
 

harveyp6

Well-Known Member
#2
Both have the angular displacement, but manual cars will only be 144 degrees, it's the autos that have the two offsets, but it's only the very early cars that are 107 degrees.
 

jp928

Active Member
#4
While we are here....I have a 4 speed man, planning to go to LT77. Bought a prop shaft said to be an auto, difficult to locate arrow on main body, phasing looks < 90degrees? Also re the lengths above from the book - I make this shaft 940mm compressed, 980mm with slide fully extended - ?? Is that a problem? For bonus points, would there be any issues with using an SD1 shaft, if the length would fit? Iam told the length is 1040mm, but unsure of the extension/compression state of the joint plunge. Also, Haynes warns that the bolt hole spacing is different between front and rear flanges, so it can only be installed one way around. Since a P6 auto prop shaft will bolt up to an LT77 gearbox output, that would imply that the SD1 diff flange has odd bolt hole spacing...???
 
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colnerov

Well-Known Member
#9
Hi, Not really, it's accepted practice to use the auto shaft. If you're not happy about it find another longer shaft and have it shortened to what you think is an ideal length, after having measured the distance between the two flanges. Don't forget to allow for closing up of the shaft to fit it because of the register on the flange faces. In short, don't overthink it.;)

Colin
 

jp928

Active Member
#10
Will try it for fit when the LT77 goes in, just checking. Somebody here (Cobraboy, Quattro ?) mentioned needing a spacer as the slip joint was close to fully extended...?
 

harveyp6

Well-Known Member
#11
Somebody here (Cobraboy, Quattro ?) mentioned needing a spacer as the slip joint was close to fully extended...?
IIRC that was Cobraboy, but I never had to when I did mine. It may be that he had his gearbox rear flange positioned higher in the tunnel than I did, increasing the distance between the flanges, but even that I can't see being enough to warrant a spacer.
 

cobraboy

Well-Known Member
#12
Aye twas me.
I fitted a Britpart spacer, IIRC a 25mm one. The splines were at full stretch, I did raise the gearbox flange to equalise the angles on gearbox and diff flanges, not that it made much difference to the length.
Because the arrows never lined up properly on my prop shaft I suspect that the yoke at the diff end was replaced, in doing so I reckon the perpetrator shortened the shaft getting it off, thus the need for me to add a spacer, but I never did confirm what length a stock shaft was to check the theory.
 

jp928

Active Member
#13
Next time mine is in the air I will measure the current prop shaft on the 4 speed box to see if it matches the book. If I can use the spare shaft on the LT77 I will see if I can phase it at 144d. Havent counted the splines yet, but 8 or 9 wont give 144d, 10 will (4x36), but that wont give 107d - did the different propshafts have different spline counts?
 
#15
Next time mine is in the air I will measure the current prop shaft on the 4 speed box to see if it matches the book. If I can use the spare shaft on the LT77 I will see if I can phase it at 144d. Havent counted the splines yet, but 8 or 9 wont give 144d, 10 will (4x36), but that wont give 107d - did the different propshafts have different spline counts?
The phasing was achieved by offsetting the ends when the prop shaft was welded up, so the splines of the yoke aren't involved in phasing unless of course you assemble the shaft wrong.

Yours
Vern
 

GRTV8

Well-Known Member
#16
I had my prop shaft out recently for a gearbox job.
Lining up the two arrows on the splines meant the yoke were out of whack.
A test drive proved the arrows had to align.
Weird ,as all my farm implements worked best with the universal yokes opposite each other.
 

jp928

Active Member
#17
My slide has 16 splines, thats 22.5d each. Searched hard for any other possible arrows, nothing. Putting an angle finder on the diff end yoke at 0d, best reading I can get on other end is high 30s. The complement of 144 and 180 is 36, so I think I am OK. We will just have to wait and see. Would like to see a good explanation of why these offsets from 'true' are needed.
 

SydneyRoverP6B

Well-Known Member
Staff member
#18
My understanding is that in almost all cases, the yokes that join universal joints to a tailshaft are in phase, but the Rover engineers purposely designed the yokes and subsequently the universal joints to be out of phase, running most frequently at 144 degrees out of phase. Now I am not a mechanical engineer, but I am a civil/structural engineer so with my engineer's hat on, typically such changes are made to prevent vibrations that result from amplification of harmonics. The Fundamental and the second harmonic are typically the most damaging, so a means of attenuating their influence is required. Now why would this happen in a tailshaft? Universal joints are also known as Hooke's joints after their inventor English scientist and mathematican Robert Hooke (1635 - 1703). Their operation is far from intuitive especially if there is an angle subtended between the axis of the sliding joint and the tailshaft. The angular velocity measured in radians per second of the sliding joint will be linear, whilst the angular velocity of the tailshaft will be non-linear. How can that possibly be I hear you ask. I have attached a pdf which explains their operation mathematically. As a result of this non-linearity, the universal joint at the pinion extension case end of the tailshaft now a requires a phase shift to reconfigure the linearity allowing the pinion drive shaft to spin with linear angular velocity that equals the linear angular velocity of the sliding joint.

Ron.
 

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GRTV8

Well-Known Member
#19
My understanding is that in almost all cases, the yokes that join universal joints to a tailshaft are in phase, but the Rover engineers purposely designed the yokes and subsequently the universal joints to be out of phase, running most frequently at 144 degrees out of phase. Now I am not a mechanical engineer, but I am a civil/structural engineer so with my engineer's hat on, typically such changes are made to prevent vibrations that result from amplification of harmonics. The Fundamental and the second harmonic are typically the most damaging, so a means of attenuating their influence is required. Now why would this happen in a tailshaft? Universal joints are also known as Hooke's joints after their inventor English scientist and mathematican Robert Hooke (1635 - 1703). Their operation is far from intuitive especially if there is an angle subtended between the axis of the sliding joint and the tailshaft. The angular velocity measured in radians per second of the sliding joint will be linear, whilst the angular velocity of the tailshaft will be non-linear. How can that possibly be I hear you ask. I have attached a pdf which explains their operation mathematically. As a result of this non-linearity, the universal joint at the pinion extension case end of the tailshaft now a requires a phase shift to reconfigure the linearity allowing the pinion drive shaft to spin with linear angular velocity that equals the linear angular velocity of the sliding joint.

Ron.
I already knew that!!
 

harveyp6

Well-Known Member
#20
Would like to see a good explanation of why these offsets from 'true' are needed.
Because of the equal length of the driveshafts, the diff pinion flange centre isn't on the centreline of the car, and that combined with the long pinion shaft caused vibration issues, hence the big damper on the front of the pinion housing being fitted in addition to the offset prop UJs.

If you look at pictures you can see just how much the pinion is offset.

 
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