Shortening a propshaft by 10mm?

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Coupe Racing
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Re: Shortening a propshaft by 10mm?

Post by Coupe Racing » Sat May 02, 2015 11:48 am

If the diff was rebuilt maybe the pinion flange was swapped due to wear where the seal fits


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Re: Shortening a propshaft by 10mm?

Post by bedders » Sat May 02, 2015 8:11 pm

If you need it shortening I can thoroughly recommend Dunning & Fairbank in leeds. They built me a new propshaft for a mk2 Jaguar for £115 + carriage + vat
They will refurbish also.


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Re: Shortening a propshaft by 10mm?

Post by rjeng » Sat May 02, 2015 8:34 pm

Hi folks, many thanks indeed to all of you for your suggestions. In answer to the further questions posed:

Ozscim identified an engine position reference of 87mm, by comparison, my engine is located 3mm further back at 90mm (which is in the wrong direction!)

I understand Windy’s suggestion to slot the inclined front chassis brackets – this would be a horizontal slot in the forward direction (to bring the engine closer to cross-member) and parallel to the chassis rails (might it weaken the mounting points ?). However, to do this I would need the engine out for access, and unfortunately it is not possible to do this at present.

The engine, gearbox + O/D, back axle and rear suspension have all been working well together for some time, but have all been rebuilt (i.e. replacement gaskets – thicknesses ?) rather than having been replaced. The significant work has been to the axle, with replacement of the pinion bearing (and re-shimming) and the inclusion of LSD components (all carried out by a motorsport axle specialist). I can confirm that the propshaft spline sleeve is not obstructed. This expansion problem became evident on re-commissioning the car.

Having looked closely at the engine mounting bolts, I suspect that I might win a couple of mm, and similarly I could save a few mm off the drive flanges: unfortunately I don’t think that is going to be sufficient.



In practice, there is only 2mm of drive train length adjustment i.e. for the propshaft splined sleeve to slide further down the O/D output shaft spline into the end of the O/D unit. I am guessing I need 10mm of length reduction, but I don’t know for certain – how much of the propshaft splined sleeve would one expect to be visible on the average SE6a ?
The company you mention, Peter, will shorten the propshaft for circa. £40 next day – which sounds impressive service.

My dilemma now is: how much to shorten it by ?[/color]
What damage I have been doing to the O/D over last 1,400 miles is another matter …
Attachments
20150502 Propshaft Spline Gap copy.jpg
20150502 Propshaft Spline Gap copy.jpg (82.96 KiB) Viewed 1176 times
20150502 Propshaft Spline Sleeve copy.jpg
20150502 Propshaft Spline Sleeve copy.jpg (61.48 KiB) Viewed 1176 times
20150502 Propshaft Overall copy.jpg
20150502 Propshaft Overall copy.jpg (50.08 KiB) Viewed 1176 times


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Re: Shortening a propshaft by 10mm?

Post by peter freeman » Sat May 02, 2015 8:48 pm

I would disconnect the prop at the rear and see how much it extends then pick the mid point and shorten it by that much - you cannot be far out that way ( I think ).



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Re: Shortening a propshaft by 10mm?

Post by Roger Pennington » Sat May 02, 2015 8:56 pm

rjeng wrote: I understand Windy’s suggestion to slot the inclined front chassis brackets – this would be a horizontal slot in the forward direction (to bring the engine closer to cross-member) and parallel to the chassis rails (might it weaken the mounting points ?). However, to do this I would need the engine out for access, and unfortunately it is not possible to do this at present.
For the reasons I mentioned earlier, I don't believe that's a viable option - you'd need to *move* the chassis brackets.


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Re: Shortening a propshaft by 10mm?

Post by Nigel Clark » Sun May 03, 2015 1:14 pm

I recently had a new propshaft made by Davemac Prop in Coventry www.davemacprops.com for my SE6A. Like yours, it's manual with overdrive. To ensure the correct length, they required a measurement of the distance from the front of the pinion flange on the axle to the face of the oil seal on the back of the overdrive. This has to be measured with the weight of the car supported on the axle, so the suspension is roughly at the mid-point of its travel. At either extreme of suspension movement, the distance is slightly longer due the arc the axle travels on the radius arms.

This measurement on my car is 1,063mm. I assume this is standard as my SE6A hasn't been modified - I doubt the engine and box have ever been removed during its life.

Davemac allowed 15mm of the prop collar into the back of the overdrive to protrude, so the length of my new prop measured from the U/J yoke shoulder at the overdrive end to the face of the pinion flange is 1,063-15 = 1,048mm. You have measured the same dimension on your prop at at 1.054mm, 6mm longer than mine. I hope these measurements help, my new prop works fine.

BTW, making and fitting the new prop is briefly featured in my Staff Car Saga in Practical Classics (latest issue, May 2015).

I hope this helps solve the mystery.


Nigel



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Re: Shortening a propshaft by 10mm?

Post by Coupe Racing » Sun May 03, 2015 1:29 pm

Have the trailing arm bushes been changed


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Re: Shortening a propshaft by 10mm?

Post by rjeng » Mon May 04, 2015 1:23 pm

Coupe' Racing wrote:Have the trailing arm bushes been changed
Yes the entire rear suspension has been completely rebuilt - same arms but all poly-bushed. Is this likely to significantly shorten the distance between the axle and the rear of the O/D ?


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Re: Shortening a propshaft by 10mm?

Post by windy » Mon May 04, 2015 6:09 pm

Just a thought but for reasons unknown to me part way through 6a production Reliant changed the rear trailing arms from all equal length to 2 different lengths, which makes me wonder, if you have the unequal ones, have you got the top & bottom arms in the correct positions?



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Re: Shortening a propshaft by 10mm?

Post by Coupe Racing » Mon May 04, 2015 6:21 pm

ok - bushes replaced

Are the upper and lower arms the same length ?
I cant recall

If not - then the angle of the diff will be altered !

OR - as previously mentioned - when the diff was professionally rebuilt - was the pinion flange changed due to wear ? Was it the correct one ?

I would only play with altering the engine mount positions if everything else is perfect


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Re: Shortening a propshaft by 10mm?

Post by rjeng » Mon May 04, 2015 8:40 pm

Coupe' Racing wrote:ok - bushes replaced

Are the upper and lower arms the same length ?
I cant recall

If not - then the angle of the diff will be altered !

OR - as previously mentioned - when the diff was professionally rebuilt - was the pinion flange changed due to wear ? Was it the correct one ?
Yes my original arms are all the same length, and the pinion flange is the original one (I know as I marked the flanges before I split them).
Having thought about all your responses (many thanks for these) and agonised with my ruler, I have decided to get 16mm removed from the length of the propshaft. Hopefully I will be able to road test the result next weekend !


Roger
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Re: Shortening a propshaft by 10mm?

Post by scimjim » Mon May 04, 2015 8:43 pm

Curious - I can't help thinking that shortening it is just hiding a problem elsewhere though?


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Shortening a propshaft by 10mm?

Post by surfer91919 » Fri Oct 02, 2020 6:22 pm

Anyone know what the conclusion of this issue was?
My prop is exactly the same length as this (1055 flange to shoulder, 1150 total) and I wonder if it's too long as I can only just slide the flange off the diff spigot with the car in the air and surely it'll only get tighter with the suspension compressed?



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Shortening a propshaft by 10mm?

Post by philhoward » Fri Oct 02, 2020 6:42 pm

Aren’t there different length trailing arms on a 6b? Eluded to be windy above.


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Shortening a propshaft by 10mm?

Post by surfer91919 » Fri Oct 02, 2020 6:51 pm

Mines a 6a and so is Rogers... Are you suggesting they've been fitted with 6b trailing arms?



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