Lotus Elan

Hissing sound from diff

PostPost by: JonB » Sat Mar 31, 2018 1:00 pm

Hi all

Went for a spin this morning and noticed a hissing sound coming from the rear of the car, when accelerating or with the foot off the throttle. Goes when the clutch is dipped. It's definitely coming from the rear. I have fitted a new pinion seal and torqued the nut up as advised. Changed the oil, it is running bog standard Comma EP90 GL4. I know it's not about to explode but it's an annoying sound.

What could it be?

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PostPost by: vincereynard » Sat Mar 31, 2018 1:12 pm

Are you sure you didn't come home with Wiggy in the boot?
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PostPost by: JonB » Sat Mar 31, 2018 1:28 pm

No mate. The car was level. :lol:
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PostPost by: rgh0 » Sun Apr 01, 2018 12:22 am

You should be running GL5 oil in the diff but that is probably not the cause of a hissing sound. If only under some load into the diff its probably not the new seal itself. The preload on the pinion bearings may have altered when you changed the seal which could be causing it.

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PostPost by: JonB » Sun Apr 01, 2018 9:39 am

I thought it might be the pinion bearing preload but I did tighten it to exactly the previous position, as marked on the shaft / nut prior to disassembly.

I thought GL5 was bad for the bronze bushings..?
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PostPost by: promotor » Sun Apr 01, 2018 12:11 pm

JonB wrote:I thought it might be the pinion bearing preload but I did tighten it to exactly the previous position, as marked on the shaft / nut prior to disassembly.

I thought GL5 was bad for the bronze bushings..?


It is a problem in terms of brass synchro rings in gearboxes loosing their effectiveness due to the metal being stripped from the synchro rings by the ingredients of the oil. You don't have that problem in an elan diff. If you had a transaxle where the gearbox and final drive shared oil you would likely want to use GL4.

Otherwise GL5 is better for higher offset hypoid gears such as those found in an English diff.

Did you use the old crush washer between the pinion bearings?
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PostPost by: JonB » Sun Apr 01, 2018 1:26 pm

Yes. I was advised to tighten it to the same position as before, by marking the nut and input shaft with a punch prior to disassembly. Could it have been over tightened?
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PostPost by: rgh0 » Sun Apr 01, 2018 10:48 pm

you may have gone a turn to far

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PostPost by: JonB » Mon Apr 02, 2018 7:07 am

Ok, thanks Rohan. We'll see if the Spyder chassis allows we to loosen it without taking the diff out.
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PostPost by: promotor » Mon Apr 02, 2018 11:02 am

JonB wrote:Ok, thanks Rohan. We'll see if the Spyder chassis allows we to loosen it without taking the diff out.


If you have gone one turn too far the chances that the crush washer has been crushed too far (once you've backed off the nut one turn) will be quite high.
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PostPost by: JonB » Mon Apr 02, 2018 12:09 pm

This is the procedure I used to tighten the pinion nut.

JonB wrote:Cleaned the nut and shaft threads as well as the splines on the input flange and shaft. Applied Wellseal to the splines and refitted the flange to the shaft, cleaning any excess. Applied Wellseal to the thread on the nut and wound it onto the shaft. "Turns" out (geddit??) that it's not necessary to count the nut revolutions, as you can feel the play in the flange reducing as you tighten the nut. Once there was no play that I could feel, I saw that the nut was half a turn away from its original position as shown by the markings, so I wound it up until they aligned. Checked the play, none, and the action of the diff seems OK.


I think it's unlikely I wound it on an extra turn, and so I would be thinking in terms of loosening it half a flat.

(And incidentally, this is why I tend to write detailed posts - because I can go back later and remind myself what I did.)
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PostPost by: rgh0 » Mon Apr 02, 2018 12:34 pm

Yes unlikely a turn to much but maybe you tightened it a turn to little. Hard to know when seating tapered roller bearings. Maybe you did it just right and the hiss is not due to the preload but something else - hard to diagnose from here unfortunately.

you could try a flat tighter or a flat looser and see which makes it better

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PostPost by: promotor » Mon Apr 02, 2018 12:48 pm

promotor wrote:
JonB wrote:Ok, thanks Rohan. We'll see if the Spyder chassis allows we to loosen it without taking the diff out.


If you have gone one turn too far the chances that the crush washer has been crushed too far (once you've backed off the nut one turn) will be quite high.


Is the flange shield catching the seal body or seal lip? That can make noise. It's more of a problem on the 86mm (early) flanges but can be a problem if the seal isn't seated properly on both 86mm and 92mm flanges.
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PostPost by: SENC » Mon Apr 02, 2018 10:47 pm

As I'm about to reinstall my diff after pinion seal replacement, I have some concerns I'll find a similar issue. To avoid getting there and having to disassemble the entire rear suspension again, would I have any risk in running the diff without wheel load to test for whining?
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PostPost by: JonB » Tue Apr 03, 2018 5:40 am

SENC wrote:As I'm about to reinstall my diff after pinion seal replacement, I have some concerns I'll find a similar issue. To avoid getting there and having to disassemble the entire rear suspension again, would I have any risk in running the diff without wheel load to test for whining?


If you have doughnuts they will be highly stressed by running them with the suspension in full droop. Same for CV joints (even on a +2 you'll be working them hard). Also, the sound I got only occurred when the diff was under load. To recreate the load, you might try to apply the handbrake.

If you run it without the wheels connected you won't get any loading, so the results might not be indicative.
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