Knock on rear end (sounds painfull)

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chrisfell
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#21 Re: Knock on rear end (sounds painfull)

Post by chrisfell » Tue Jul 31, 2018 5:35 am

I had a knocking at the rear under certain conditions. It was the drive shaft boot, which needed to be reseated. I also had a knock caused by a loose drive shaft boot when I first had the car. PO, a business, hadn’t tightened the clamp enough and the boot worked its way up the drive shaft to tap on the damper springs.
Chris '67 S1 2+2

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mikey1
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#22 Re: Knock on rear end (sounds painfull)

Post by mikey1 » Wed Aug 29, 2018 4:33 pm

I had exactly the same problem after completely, or so I thought, rebuilding the rear end, including the diff. My car also passed the MOT. It turned out to be the one thing I hadn't replaced, the bolt securing the rear radius arm bush ( the one which passes through the bush). It was considerably waisted in the middle but I thought this was the way it had been designed! Comparison with a new one showed me my error and replacement completely solved the problem. I would check this before taking everything apart. I diagnosed it with the help of my ex-mechanic and very trusting friend who held onto the radius arm as I rocked the car back and forth in first and reverse, when the clonk could be distinctly felt. Strangely the other side bolt was just as worn but there was no clonk.

Mike Williamson
Mike Williamson, series 2 ots,

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PhilP
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#23 Re: Knock on rear end (sounds painfull)

Post by PhilP » Thu Aug 30, 2018 5:01 pm

Thanks for the replies, I’m waiting for a slot at series one Etype for Ken to have a look but I’m off work tomorrow so I’ll have a look and post a picture of what I find.

Phil
1968 series 1.5 fhc

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PhilP
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#24 Re: Knock on rear end (sounds painfull)

Post by PhilP » Fri Aug 31, 2018 9:02 am

Just removed the radius arm bolt to have a look and they are both set screws ? I’ve had a look on a parts supplier to try and see what they should be but the radius arms are on but not the bolts. Could this be my problem as a bolt should fit through the bush better than a set screw. I have checked for movement on these bushes before and not noticed any.


Phil
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1968 series 1.5 fhc

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

Post by mgcjag » Fri Aug 31, 2018 9:39 am

Hi Phil.....i think that looks like the correct bolt......the bolt holds the cup in the bush on to the mounting so there should be no sideways movement once its clamped up tight...if the bush isnt tight on the mounting this could be the source of the noise..Steve
Steve
1969 S2 2+2 & Building a C type replica

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PhilP
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#26 Re: Knock on rear end (sounds painfull)

Post by PhilP » Fri Aug 31, 2018 11:03 am

Thanks Steve

I’ll take it fully off and have a good look. I’ve never done this as all the rear end had been rebuilt when I bought it and everything still looks like new. Nice day for it the suns shinning and no work just need a coffee now.

Phil
1968 series 1.5 fhc

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ralphr1780
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#27 Re: Knock on rear end (sounds painfull)

Post by ralphr1780 » Fri Aug 31, 2018 11:43 am

Phil, this is the correct bolt. It has to be tightened really tight or else you will have a movement giving a clear audible clonk and also a knock which you can feel. Had the same after driving a while newly fitted radius arms, it seems they need to bed-in a bit and retightened.
Ralph
'69 OTS + '62 OTS - Belgium

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288gto
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#28 Re: Knock on rear end (sounds painfull)

Post by 288gto » Fri Aug 31, 2018 12:22 pm

A long shot but just check the length of the bolt.

It now seems common practice by the large suppliers to quote “ now superseded by” and supply something vaguely similar to the original item.

IF there is movement at the radius arm cup I would also check the bolt isn’t too long and bottoming out inside the cup preventing it fully tightening.
If there has been a lot of paint and underseal applied to the cup this can also lead to it loosening as it wears off.


Simon
Simon
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PhilP
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#29 Re: Knock on rear end (sounds painfull)

Post by PhilP » Fri Aug 31, 2018 8:20 pm

Thanks for all your replies I have now removed the radius arm from the front mount and everything looks fine. I have made sure everything is tight. I also checked the bolt holding the small end of the radius arm and this was loose in fact very loose on both sides of the car I managed to get another 3 to 4 mm of thread showing past the end of the nut. Have I over tightened these or have they worked loose I’m sure I have checked these in the past?


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Tom W
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#30 Re: Knock on rear end (sounds painfull)

Post by Tom W » Fri Aug 31, 2018 9:04 pm

On the later cars where this bolt faces the other way and screws directly into the wishbone, there’s a lock tab that folds over the bolt head to stop it coming loose.
Tom
1970 S2 FHC

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JagWaugh
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#31 Re: Knock on rear end (sounds painfull)

Post by JagWaugh » Sat Sep 01, 2018 6:42 am

PhilP wrote:
Fri Aug 31, 2018 8:20 pm
I also checked the bolt holding the small end of the radius arm and this was loose in fact very loose on both sides of the car I managed to get another 3 to 4 mm of thread showing past the end of the nut. Have I over tightened these or have they worked loose I’m sure I have checked these in the past?
3-4mm on both sides suggests that the heads didn't get seated down in the cbores when you assembled it - they're nylocks, which don't generally work loose, definitely not in unison.

Check the hub carriers where the heads are/were, you may have some scratches.

If that wrench you show is the only leverage you used, then you probably haven't necked the bolts.

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Series1 Stu
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#32 Re: Knock on rear end (sounds painfull)

Post by Series1 Stu » Sat Sep 01, 2018 7:14 am

It sounds like someone has done the classic trick of forgetting to fully tighten the fasteners once it's all fully assembled. That rear radius arm bolt is a prime candidate for that. It could well have been the cause of the knock if the hub has been hitting the bolt head.

It might be a good idea to check the rest of the rear end fasteners.

Regards
Stuart

If you can't make it work, make it complicated!

'62 FHC - Work In (slow) Progress
'69 Daimler 420 Sovereign
'94 X300 XJR basket case

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288gto
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#33 Re: Knock on rear end (sounds painfull)

Post by 288gto » Sat Sep 01, 2018 8:08 am

With a rebuild taking several months (or in my case years!) it’s easily done forgetting to tighten bolts especially on the suspension where it is suggested they are tightened when the car is back on the ground or under load.
I have a notebook that I write everything that needs to be tightened in.
Another trick having tightened a fixing is to put a small dab of tipex on the nut where it meets the component to let you know you have finished that part and as a tell tale to any movement.

Hopefully you have cured the knock.

Simon
Simon
1969 S2 OTS

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PhilP
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#34 Re: Knock on rear end (sounds painfull)

Post by PhilP » Sat Sep 01, 2018 9:26 am

Thanks for the all the replies again

I didn’t do the rebuild but I am guilty of not checking it all properly. It was suggested that I check all the bolts by a forum member a while ago which I did but I must have missed these two. Most of the other fixings have got small paint marks on them but not these two so I will add some to these two to make sure they don’t work loose.
I’m going to take it out for a good run this afternoon and let’s hope there’s no more knocks and then I can leave you all in peace.
I’ll report back later :fingerscrossed:

Thanks again

Phil
1968 series 1.5 fhc

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mikey1
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#35 Re: Knock on rear end (sounds painfull)

Post by mikey1 » Sat Sep 01, 2018 5:36 pm

Phil, I hope you have solved the problem. If the rear radius arm bolt was loose I suspect that was the cause. As I said, in my case this bolt was tight but the shanked portion was very worn.

By the way,without wishing to start more discussion I have always thought that a setscrew was threaded all the way, as in the forward radius arm screw whereas a bolt has a non-threaded portion or shank, as in the rear radius arm bolt. The terms are often used interchangeably.

Mike
Mike Williamson, series 2 ots,

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

Post by PhilP » Sat Sep 01, 2018 5:56 pm

Just got back from a good spirited run and no knocks :dance: I can believe I didn’t find this earlier I’ve spend hours under the car checking everything.
One good thing that has come out of this for me is that it has given me a good knowledge of the irs.
Thanks to everybody who replied as this kept me looking and hopefully finally finding the problem.

:drinkingcheers:

Phil
1968 series 1.5 fhc

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Series1 Stu
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#37 Re: Knock on rear end (sounds painfull)

Post by Series1 Stu » Sun Sep 02, 2018 7:43 am

mikey1 wrote:
Sat Sep 01, 2018 5:36 pm
By the way,without wishing to start more discussion I have always thought that a setscrew was threaded all the way, as in the forward radius arm screw whereas a bolt has a non-threaded portion or shank, as in the rear radius arm bolt. The terms are often used interchangeably.

Mike
Yep. It's confusing alright. Some people call a grub screw a setscrew, which I think is probably the most correct use for the name as they are used to set things in place. I think that somehow the name got transferred to certain bolts because they are similarly fully threaded.

Regards
Stuart

If you can't make it work, make it complicated!

'62 FHC - Work In (slow) Progress
'69 Daimler 420 Sovereign
'94 X300 XJR basket case

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