Knock on rear end (sounds painfull)

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PhilP
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#1 Knock on rear end (sounds painfull)

Post by PhilP » Sat Jul 28, 2018 10:16 am

Hi
I have got a knock on the rear of my car and know matter what I have tried I can't get to the bottom of it.
The knock only appears when I'm turning left out a junction and changing from 1st to 2nd and accelerating reasonably hard and only when the car has been driving for about 1/2 hr. I can stop the knock by changing from first to second gently and making sure the car is straight before I change. I've checked all the bushes and ujs and all seem to be fine. My next thought is the differential and the limited slip diff but my knowledge of these are limited. I can cruise at 80 all day and there is no whine from the diff at all. The car is also well used I do about 4000 miles a year.
Any advise would be greatfully accepted before I take it to a specialist.

Regards

Phil
1968 series 1.5 fhc

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mgcjag
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#2 Re: Knock on rear end (sounds painfull)

Post by mgcjag » Sat Jul 28, 2018 10:51 am

Hi Phil...suggest you recheck the rear drive shaft uj,s and wheel bearings..also are driveshaft to diff nuts tight...whilst there have a look at the irs mounts....and also the inner fulcrum shaft bracket to diff..and shocks..basically a real good look at the rear end.....if u cant check yourself then have a pre mot check....basically an mot without the paper work....you need the car up on a ramp to check this properly....Steve
Steve
1969 S2 2+2 & Building a C type replica

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#3 Re: Knock on rear end (sounds painfull)

Post by christopher storey » Sat Jul 28, 2018 11:12 am

And check that your spinners are tight ; also, have a look at the hubs to see that the splines still have squared off ends, and are not worn to a point

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#4 Re: Knock on rear end (sounds painfull)

Post by PhilP » Sat Jul 28, 2018 11:35 am

Thanks for the reply’s I’ll have a good look. It has passed 2 mots since the noice started the last one being last month, the examiner defiantly had a good look at the car. The one thing I can’t understand is why it only does it after 1/2 driving not before if something was loose I thought it might show up straight away. One thing I forgot to mention is that it is only one knock every time not several.
1968 series 1.5 fhc

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#5 Re: Knock on rear end (sounds painfull)

Post by PhilP » Sat Jul 28, 2018 11:51 am

I’ve just had a good look and checked everything, I know I’ve asked this question before and you were all good enough to give advice. I’m sure it must be the diff so I’m going to book it in to be looked at by a specialist. I’ve lived with it too long now.
Thanks again

Phil
1968 series 1.5 fhc

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#6 Re: Knock on rear end (sounds painfull)

Post by mgcjag » Sat Jul 28, 2018 12:00 pm

Hi Phil...you cant have had a good look and checked everything in the 15mins between your posts.....Steve
Steve
1969 S2 2+2 & Building a C type replica

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#7 Re: Knock on rear end (sounds painfull)

Post by PhilP » Sat Jul 28, 2018 3:50 pm

To be honest I’ve been looking at this for few months trying everything that has been sugested with no joy, I was hoping somebody was going to say they had the same problem and it was the diff before I book it in.
I was just trying to convince myself that it needed to go to a specialist before I take it in.

Phil
1968 series 1.5 fhc

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#8 Re: Knock on rear end (sounds painfull)

Post by mgcjag » Sat Jul 28, 2018 3:54 pm

Ok Phil...Good luck with that...please let us know what you find..all the best... Steve
Steve
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#9 Re: Knock on rear end (sounds painfull)

Post by PhilP » Sat Jul 28, 2018 4:04 pm

Thanks Steve
I’m going to see Ken Verity on Monday he’s local to me and I buy my parts from him so I know him reasonably well. The only problem is that I know he’s always busy, I’ll see if I can book it in towards the end of the year so I don’t miss too much valuable driving time he can have the car as long as he likes over the winter.

Thanks again for all the advise and as soon as it’s resolved I’ll post what the problem was

Phil
1968 series 1.5 fhc

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#10 Re: Knock on rear end (sounds painfull)

Post by mgcjag » Sat Jul 28, 2018 4:20 pm

Phil....give Alan a call at http://www.ajsengineering.com/index.html he is a top diff man explain the problem..he will know if its diff related... Steve
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#11 Re: Knock on rear end (sounds painfull)

Post by PhilP » Sat Jul 28, 2018 4:39 pm

Thanks I’ll give him a call first
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#12 Re: Knock on rear end (sounds painfull)

Post by nefematic » Sun Jul 29, 2018 12:26 am

Phil,

have you recently had an oil change in the differential? The limited slip differential is sensitive to the correct oil being used. Wrong oil might cause the stated symptoms under your stated circumstances. Oil change and heartedly driving 8‘s to get the new oil well in would be my advice, before going mechanical. It may rectify your symptoms.

Martin
Martin Scherz
Late S2 1970 OTS US LHD

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#13 Re: Knock on rear end (sounds painfull)

Post by PhilP » Sun Jul 29, 2018 8:04 am

Thanks for the reply Martin
I replaced all the fluids on the car about 12 months ago including the diff with Triple QX 80w-90 LS which I was informed was the correct oil the problem has still persisted.

Thanks again

Phil
1968 series 1.5 fhc

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#14 Re: Knock on rear end (sounds painfull)

Post by Barry » Sun Jul 29, 2018 8:07 am

Check out the play in the differential as well as the other suggestions. I ended up having a diff rebuilt on a S1 3.8 because of a similar knock which occurred at bizarre times.

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#15 Re: Knock on rear end (sounds painfull)

Post by PhilP » Sun Jul 29, 2018 8:50 am

Thanks Barry

I’ve just got the car jacked up (again!) I keep promising myself I’ll leave it alone and take it to the experts but can’t resist one more look.
As I’m no mechanic how do I check the play in the diff with the wheels of the ground I can move the wheels about 5/10 mm before it turns the prop shaft in both direction.
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#16 Re: Knock on rear end (sounds painfull)

Post by johnetype » Sun Jul 29, 2018 10:01 am

It is difficult to quantify play in the diff this way with so many variables other than to say 5 to 10mm all the wheel sounds in the range of normal.

I suggest your knock could be related to the normal working of the limited slip diff. When the rear wheels turn unequal amounts, e.g. tight corners, that causes a peg to slide up a ramp inside the limited slip mechanism and lock the clutch plates. That action can make a noise and dependent on wear, oil temperature and exactly how quickly and hard the peg gets to the end stop could make the noise you're enjoying with spirited driving.

Diff experts such as Alan will be able to make a more informed comment than me and if your diff has done a high mileage maybe it's time for a rebuild. For me on my 50,000 mile differential, I can get noise/clicks etc. under similar circumstances.
John

1969 Series 2 FHC

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#17 Re: Knock on rear end (sounds painfull)

Post by PhilP » Sun Jul 29, 2018 10:42 am

Thanks John

I’m not sure how long it is since the diff was rebuilt I bought the car about 2 years ago, the irs has defiantly been rebuilt with new discs springs and shocks but I can’t guarantee the diff was rebuilt. It’s probably time to spend some money on the car as it’s given me two years of pure enjoyment and covered about 8000 miles for the cost of a few fluids and 6 spark plugs. My last car for the garage as my wife called it cost me £515 in road tax every year plus a main dealer service every year so I think the Etype deserves some money spending on it.

Thanks for all the comments

:drinkingcheers:
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#18 Re: Knock on rear end (sounds painfull)

Post by phil.dobson@mac.com » Sun Jul 29, 2018 11:52 am

if you have, or can beg borrow or steel one try a GoPro camera strapped at various places around the rear cage to see if you can narrow the noise down.
Best regards
Phil D

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#19 Re: Knock on rear end (sounds painfull)

Post by PhilP » Mon Jul 30, 2018 5:32 pm

Thanks Phil
Not something I had thought about but knowing my looked I’d loose the GoPro

Phil
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#20 Re: Knock on rear end (sounds painfull)

Post by Barry » Mon Jul 30, 2018 10:54 pm

To be honest Phil, I have no idea how to check the diff other than checking play as has already been written in this thread. I would go to your trusted E-type specialist, and get them to check it out. That’s what I would do. Sorry, can’t be more helpful.

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