Shortening a propshaft by 10mm?

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rjeng
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Shortening a propshaft by 10mm?

Post by rjeng » Fri May 01, 2015 9:14 pm

Hi, has anyone every had to have a propshaft shortened ? - mine is now 5 -10mm too long.

My SE6a has a one piece prop, with a H/S type u/j flange at the diff end, and a H/S u/j at the overdrive end (u/js have negligible play). The sliding spline onto the O/D output shaft is fully engaged at the end of its travel - OK driving with a cool car, but when everything has got hot and expands, there are some horrible whirring and clonking noises at slow speeds which disappear as things cool down. I am guessing that the O/D output shaft is getting compressed and end-loaded, which I guess might be doing all sorts of damage. Inserting a wedge between the diff and prop u/j flanges only produces a couple of mm of movement as the splined sleeve cannot slide further into the O/D.

When I look at the position of the O/D unit on the slots in the chassis cross-member, it is fully back (i.e. I must have a long engine) and I see no position / length adjustment on the engine mountings. The diff has recently been professionally re-built, so it is conceivable that the input flange protrudes fractionally further than it use to.

Any suggestions / ideas will be gratefully received !


Roger
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Re: Shortening a propshaft by 10mm?

Post by windy » Fri May 01, 2015 9:41 pm

That sounds an unusual problem. The easy fix would be to slot the holes in the engine mounts if you only need to move 5-10mm forward?



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Roger Pennington
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Re: Shortening a propshaft by 10mm?

Post by Roger Pennington » Fri May 01, 2015 10:02 pm

I'm trying to visualise it, but I don't think slotting the engine mounts would work? There's only one hole you could slot, but that's already slotted up and down?

It certainly is an unusual problem. :?


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Re: Shortening a propshaft by 10mm?

Post by piman » Fri May 01, 2015 10:44 pm

Hello Rjeng,

it's not difficult to have a propshaft shortened but the question is why, it seems rather unusual?

Alec


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Re: Shortening a propshaft by 10mm?

Post by scimmy_man » Fri May 01, 2015 10:50 pm

loosen all the engine mount bolts, it may be the brackets are on the wrong end of the holes adjustment.


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Re: Shortening a propshaft by 10mm?

Post by windy » Fri May 01, 2015 10:51 pm

Roger Pennington wrote:I'm trying to visualise it, but I don't think slotting the engine mounts would work? There's only one hole you could slot, but that's already slotted up and down?

It certainly is an unusual problem. :?
I can visualise it, but its hard to explain without drawing it....
Something along the lines of slotting the front hole on the actual engine mount backwards a bit & the rear hole on the plate that it mounts on forwards a bit. That way he wouldnt break out of the bolt hole edges.



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Roger Pennington
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Re: Shortening a propshaft by 10mm?

Post by Roger Pennington » Sat May 02, 2015 12:52 am

Trouble is the lower (chassis) holes are already slotted, to move the mounts up and down, not fore and aft. The base of the mount is welded onto the chassis (this has the vertical slot). Then the actual mount is a bobbin with a single thread sticking out on each side. The top thread of this screws into a cast mount with a single threaded hole, and this casting has 3 holes which allow it to be bolted into the block So I don't really see where you're going to be slotting?

This diagram illustrates it, except that it doesn't show the chassis part of the mount, which is where the lower thread goes through (indicated by the arrow), and which is where there is already a vertical slot (and I don't believe you can slot a hole in two dimensions?). I think it's going to be difficult to do it any other way than cutting off the chassis mounts and rewelding them further forward.

I can't help feeling the problem lies elsewhere?
Engine mounts.jpg
Engine mounts.jpg (278.27 KiB) Viewed 1406 times


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Re: Shortening a propshaft by 10mm?

Post by scimjim » Sat May 02, 2015 2:13 am

Is it a trailing arm problem? With everything else standard reliant (I'm assuming the prop is standard), there's no way the prop can be too short.


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Re: Shortening a propshaft by 10mm?

Post by ozscim » Sat May 02, 2015 4:37 am

Interesting problem!

Have taken a photo of the measurement between the timing cover and the cross member on my car, it is 87mm, give or take a mm.

My car is an auto, but I would have thought that the engine position would be the same for a manual.
20150502_111937.jpg
20150502_111937.jpg (187.7 KiB) Viewed 1388 times
Would be interesting to know if your measurement is close to this?

Hope this helps,

Cheers Neil.



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Re: Shortening a propshaft by 10mm?

Post by Coupe Racing » Sat May 02, 2015 5:36 am

Could be an incorrectly re manufactured / remade prop

Think the type of noise needs considering


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Re: Shortening a propshaft by 10mm?

Post by kennatt » Sat May 02, 2015 7:51 am

You say the diff was professionally rebuilt,if so that's obviously the problem.get back intouch with the rebuilders.If nothing else has been done to the drive train and it was ok before then it has to be a result of the refitting or rebuild of the diff. not had a diff out of a scimitar,but is there any shims etc to locate the flange.



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Re: Shortening a propshaft by 10mm?

Post by scimjim » Sat May 02, 2015 8:10 am

Has it always done this or just started after the diff rebuild? I can't find the prop lengths but I wonder if the auto is a bit longer?


Jim King

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Re: Shortening a propshaft by 10mm?

Post by windy » Sat May 02, 2015 8:28 am

Roger Pennington wrote:Trouble is the lower (chassis) holes are already slotted, to move the mounts up and down, not fore and aft. The base of the mount is welded onto the chassis (this has the vertical slot). Then the actual mount is a bobbin with a single thread sticking out on each side. The top thread of this screws into a cast mount with a single threaded hole, and this casting has 3 holes which allow it to be bolted into the block So I don't really see where you're going to be slotting?

This diagram illustrates it, except that it doesn't show the chassis part of the mount, which is where the lower thread goes through (indicated by the arrow), and which is where there is already a vertical slot (and I don't believe you can slot a hole in two dimensions?). I think it's going to be difficult to do it any other way than cutting off the chassis mounts and rewelding them further forward.

I can't help feeling the problem lies elsewhere?
Engine mounts.jpg
Didn't realise they changed the mounts from the old "2 bolt fixing on the bottom" design :oops:

When the prop was off for the diff rebuild is it possible that some foreign object dropped into the splined sleeve on the prop, so limiting how far it can slide into the overdrive?



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Re: Shortening a propshaft by 10mm?

Post by peter freeman » Sat May 02, 2015 9:39 am

My "spare" shaft which I think I took off my 6A when I fitted the V8 is 1mtr long ( compressed ) - how does that compare with the length of your shaft. If you want/need it shortening there is a prop shaft place at the south end of the Team Valley - at least there was in 1989 when I fitted the V8.



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Re: Shortening a propshaft by 10mm?

Post by PeterSE6a » Sat May 02, 2015 11:25 am

Sorry might be a daft idea but is there any scope from machining any "spare " material from the diff flange as 5/10mm does not sound much to take out in the overall length.


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