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Propshaft UJ working angles on IRS Cars


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I recently read an article regarding UJs in propshaft applications that recommended that the working angles of each UJs should be between 1/2 and 3 degrees for longevity, and that the difference between the two angles at each end should not be more that half a degree to avoid vibration. My 6 has terrible vibration at motorway speeds so i thought it worthwhile to check them (inclinometer apps on mobile phones provide accuracy to 0.1 deg).

I found working angles at the gearbox- and diff UJs of 2.5 degs tail down and 5 degrees nose up respectively. In order to get the rear UJ angle down to 2-3 degrees to meet the guidance i have tried to lower the diff nose. Changing the front upper diff rubbers made the latter worse (became +6 degs) as the new ones proved thinner than the old ones, raising the diff nose instead. Im now looking for thicker upper rubbers, but i note that theres not a great deal of thread remaining on the front pins to achieve the drop required. I guess raising the diff rear would also work, but i can only see this being achieved through packing washers between the diff casing and the rear rubbers, which is a bit of a bodge.

 

Has anyone any experience or advice with this? Have you checked/adjusted your UJ angles to within the 3 degree/ 1/2 degree recommendations or am i seeking perfection where it never existed with in the first place?

 

Thanks,

 

Iain

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Well Hardy Spicer (who MIGHT know something about them ) recommended to me a max of 7 deg and 1/2 deg between ends on a TR7 V8 racecar, so I think on that basis yours as is would be ok.

 

Sounds like a balance issue to me, If you're bored try a jubilee clips on your propshaft and turn around maybe 20 deg a time after trying a road test to see if it reduces.

 

Mick Richards

Edited by Motorsport Mickey
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Ian,

Are the rear rubber mounted correct? You can install them above or below the flange of the diff cover.

Waldi

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Useful Spicer guide . . . . .

 

http://spicerparts.com/calculators/driveline-operating-angle-calculator

 

Don't overlook the tendency of knackered engine and/or gearbox mounts to influence the gearbox angle.

 

Remember to measure with driver and passenger in place . . . . .

 

Avoid cheap UJs which tend to vibrate of their own accord . . . .

 

Cheers

 

Alec

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Humming in the seats like somebody is acting below with a grinder

at 130 Km/h is mostly blaimed to the propshaft.

Problems in the driveshaft are more a rumble and similar

to fast hammering if I should explain.

 

I could destroy the joints in my V8 within a month.

Over a longer period I changed them every year,

never had to grease them because they are destroyed quicker.

When they die they give a rumble under load and get quieter

off throttle or the other way round.

 

Last possible culprit is the splined piece. It gets play and locks under

load in different position/angles. Sometimes they are okay and sometimes

they rumble.

 

Best way to avoid driveshaft trouble buy a CV jointed shaft and forget about

loosing wheels, too

 

Somebody is just selling a set from CCDC here at the forum

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Useful Spicer guide . . . . .

 

http://spicerparts.com/calculators/driveline-operating-angle-calculator

 

Don't overlook the tendency of knackered engine and/or gearbox mounts to influence the gearbox angle.

 

Remember to measure with driver and passenger in place . . . . .

 

Avoid cheap UJs which tend to vibrate of their own accord . . . .

 

Cheers

 

Alec

+1 and do not forget the wheels.

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Thanks all. The vibration (felt like it was under the seat) would occur above 70mph in OD top, and could sometimes be reduced by decelerating and quickly reapplying power. I am in the process of changing the worn driveshafts for the uprated rislan-coated type, and have now fitted the uprated GKN-type UJs throughout the drivetrain. I haven't road-tested since, but hope that these changes, together with replacement of a sloppy-fitting wire wheel spline, may have already reduced or removed the vibration regardless of the UJ angles, but i wanted to be sure I had removed all possible causes. To be honest, I would still prefer to get the prop UJs operating at the lower end of the working angle tolerance band anyway in order to get maximum life out of them so will give the gearbox and engine mounts a check too.

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Hi Iain,

I think you are looking too hard at the prop angles.

The relative position of the GB and diff is fixed so assuming the GB rear mount is OK and the diff rubber bushes are OK then the set up is as it left the factory.

Has the propshaft been balanced.?

 

Roger

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Hi Iain,

I think you are looking too hard at the prop angles.

The relative position of the GB and diff is fixed so assuming the GB rear mount is OK and the diff rubber bushes are OK then the set up is as it left the factory.

Has the propshaft been balanced.?

 

Roger

 

This.

 

Sounds like classic prop out of balance to me. Everyone else's box to diff angles will be much the same as the OP's but they don't have problems. Over-thinking that for sure.

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TBH I would have just gone for a new prop from Proptech Kidderminster as the problem with IRS cars is the sliding section gets a wear spot due to the fact that it does nothing unlike a prop on a live axle that does move in and out.

Stuart.

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Make sure the yokes are aligned on opposite ends of the shaft.

When I first got my 250 I replaced one of the joints on the shaft as it was knackered. I did this without separating the two halves of the shaft.

A couple of years later after much high speed vibration the same joint failed again.

 

This time I decided to separate the two halves of the shaft to make the job easier, but when getting ready to mark the shaft before I split it, I realised the shaft had been assembled one spline out.

 

Having replaced the knackered joint I reassembled the shaft with the yokes aligned properly and found the vibration had disappeared and the joints are still good 20 years and many tens of thousands of miles later

 

Neil

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