Drivetrain knocking getting louder on braking

Clutch, Gearbox, Overdrive, Propshaft, Differential, Drive Shafts, Hubs.
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Llessur
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Drivetrain knocking getting louder on braking

#1 Post by Llessur » Sun Dec 30, 2018 7:00 am

Have finally taken my 2500S project out for its first test drive - goes quite well but there is a dull rhythmic knocking sound when driving. It seems to match the road, rather than engine speed but becomes noticeably louder on braking.

Any ideas as to what this could be or any way of eliminating components? I'm presuming it's either the prop or driveshaft(s). The gearbox mount is a brand new Mackay one so should be good.
Adelaide, South Australia (ex-Brighton, UK)
1977 2500S - White
1975 2500 - Murky silver parts car

My blog: https://triumph2500blog.wordpress.com/

tony
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Re: Drivetrain knocking getting louder on braking

#2 Post by tony » Mon Dec 31, 2018 12:56 am

Sounds like universal joints to me. That or loose drive shaft bolts.
Tony.
1976 2500 TC.

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Dave B
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Re: Drivetrain knocking getting louder on braking

#3 Post by Dave B » Tue Jan 01, 2019 3:45 am

This may sound unlikely, but my Vauxhall Insignia had exactly the same symptoms as your 2500 when I first bought it. The dealer did a couple of jobs on it before I took delivery, including new rear brake pads. Unfortunately they forgot to tighten the rear wheel nuts up afterwards!
Worth a look, I suppose.
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Re: Drivetrain knocking getting louder on braking

#4 Post by johnnydog » Tue Jan 01, 2019 1:42 pm

Another point to check is the centre exhaust section where it passes under the prop shaft. Some exhaust fitments (usually the mild steel variety) pass very close to the prop and need a 'tweak' at the rear with a crow bar to give a bit more clearance. This gives a metallic clang and the frequency is obviously speed related.
I'd also check where it passes through the subframe as it is very close and needs to be dead central and free from up and down movement. The bracket is designed to allow for 'for and aft' movement from expansion, not up and down movement.
But as said, the UJ's and their bolts security are probably the other area to check.
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Clifford Pope
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Re: Drivetrain knocking getting louder on braking

#5 Post by Clifford Pope » Thu Jan 03, 2019 12:53 pm

The prop shaft can also touch the horseshoe thing where the handbrake cable divides. The clearance is greater if you mount the propshaft with the sliding end at the back.

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Re: Drivetrain knocking getting louder on braking

#6 Post by Mike Stevens » Thu Jan 03, 2019 10:51 pm

Please check your wheel nuts! I guess you have the standard (alloy) wheel nuts on the 'S' type wheels? In my experience they can come loose, giving a regular knocking noise.

When I ran an 'S', I used to keep the wheel nut spanner next to the handbrake - just in case!

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Llessur
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Re: Drivetrain knocking getting louder on braking

#7 Post by Llessur » Fri Jan 04, 2019 12:01 am

Cheers for the replies and suggestions all - very easy yet somewhat embarrassing fix of slightly loose wheel nuts on one wheel :oops:

I'm usually pretty hot on doing up my wheel nuts so I'm wondering if this is a case of the wheel not quite being flush against the hub when lowered from the jack, causing the nuts to loosen once the car has rolled.

I've had a look at the wheel and it doesn't seem to have suffered any damage to the mounting holes. I'll keep a good eye on it and swap it over for one of my spares if needed. Good job I only did a couple of hundred metres around the block.

Any tips for keeping the alloy wheel nuts secure if, as Mike Stevens says, they are prone to coming loose through general use?
Adelaide, South Australia (ex-Brighton, UK)
1977 2500S - White
1975 2500 - Murky silver parts car

My blog: https://triumph2500blog.wordpress.com/

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Re: Drivetrain knocking getting louder on braking

#8 Post by johnnydog » Fri Jan 04, 2019 12:29 am

I am glad the fix was an easy one and Dave was spot on with his diagnosis!
However, I have had several 'S' models since 1985 all with the original alloys and wheel nuts, and I have never experienced a wheel nut coming loose.
They are easily overtightened and stripped being alloy, especially if tightened with an air impact wrench. Unlike steel wheels with a tapered nut face that mates to a slightly raised surface which acts like a 'spring washer' under tension to reduce the likelihood of the nut coming loose, alloy nuts have a flat face to the rim which does not allow for the 'spring washer' tension. As a result if not tightened correctly, they can easily work loose.
I tension mine by feel gained from experience and they haven't been a problem. I would check that the thread is not damaged from being overtightened from being previously tightened with an air 'buzz' gun.
There are also chromed or black steel nuts available for the 'S' alloys which are not as prone to stripping if overtightened.
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1967 Mk1 2000 in Gunmetal Grey
1969 Mk1 2000 in Royal Blue
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1973 Mk2 2.5 PI in Sienna Brown
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Re: Drivetrain knocking getting louder on braking

#9 Post by Llessur » Fri Jan 04, 2019 1:01 am

Is there a torque rating for doing them up?
Adelaide, South Australia (ex-Brighton, UK)
1977 2500S - White
1975 2500 - Murky silver parts car

My blog: https://triumph2500blog.wordpress.com/

tony
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Re: Drivetrain knocking getting louder on braking

#10 Post by tony » Fri Jan 04, 2019 3:12 am

I'm like Johnny Dog. I tighten mine until I feel a "click' in my head and then stop. Never had a problem with mine coming loose. It's all about 'feel'. :shock: :shock:
Tony.
1976 2500 TC.

Lots of bits

1999 BMW Z3.
2003 BMW 525i Touring.
Hopefully not needing too many bits.




.
Hopefully don't need bits !

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