help advise needed pls...clunking noise series 3 v12 auto

[edward1]

when i engage D or R on auto box I get massive clonking from drive train somewhere. i have spent a fortune on parts ie replace gear box mounting, new shocks / springs, radius arms, whilst irs down replaced brake and hand brake pads. still clonking badly....also replaced hand brake cable as old one appeared streched, but new cable seems same length, but fitted hand brake still not holding car at all, i am resigned to having to remove exhaust, drop irs all over again. can anyone suggest where this clonking is coming from!!!!!!!!!!!! many thks

[AussieEtype]

Double check the oil level in the gearbox - if it is a bit low there can be a slight delay in engaging gear and when it does it can clunk.

Garry

[johnmack]

high, I checked the oil in gearbox it was low and my slow running was to high should be 600rpm on the v12 auto i think, these two things stopped the clonks on mine good luck with yours regards johnmack

[mgcjag]

Hi Edward.....have you looked at the universal joints on the propshaft Steve

[PeterCrespin]

When you took the IRS out did you check the four special bolts holding the diff to the cage? I assume so, but just because they are wired doesn't mean they are still rock-solid tight and they can fret.

Did you check the oil level and type and the free play in the diff itself? A vague spec is that with the input shaft held stationary, there should be no more than about a half inch of rotation on the output shft at a 1-foot radius. I.e. hold a ruler or 30cm bit of wood or wire onto the output flange and see how far the tip moves too and fro under free play conditions. If the backlash is excessive it will clonk no matter how tight the rest of your gear train is.

If the car still clunks with correct idle speed and oil levels, you could try a stethoscope test to locate exactly where the noise is coming from. Easy on a lift, but be careful if the back of the car is jacked up on stands and someone is underneath with a long screwdriver. I guess with a long enough piece of rod you could do it from alongside the car underneath by holding it to the gearbox casing, the propshaft ends, diff casing and half shaft joints in turn. By listening with a rod or stethoscope it should be obvious which one is the source of the clunk (although the driveline UJs are simple to check in the usual way).

Pete

[vee12eman]

Hi,

I can't help with the clonking autobox, but the poor handbrake may be explained by these posts - look at page 3 for the problem with new handbrake cables. It is possible to modify the normally available cable to the same standard as the JEC cable - that's how I cured my poor handbrake.

http://etypeuk.com/forum/viewtopic.php? ... ke&start=0

Regards,

[snowdmc]

wasnt there something in the etype magazine this month about worn handbrake self adjusting splines being worn, so the hand brake doesn't self adjust and take up the slack

[kingzetts]

Could be. My car squeaked through the MOT recently with borderline handbrake efficiency. On investigation, I was running out of cable travel because there is a maximum distance the compensator can move before the two attachment points for the cable (the fixed outer and the flexible inner) meet up and no more movement is possible. This suggested excess pad-to-disc clearances.

On further investigation, while the offside handbrake pads were "just" clearing the disc when off, the pad-to-disc clearance on the nearside was noticeably bigger. The n/s handbrake had recently been apart in the course of fitting a new disc and new handbrake pads, the self-adjustment was definitely working because I self-adjusted it off the car before refitting the IRS and the pad-to-disc clearances tightened up as expected.

What I did was to remove the access cover in the boot, remove the split pin in the link bolt which forms part of the self-adjustment mechanism, and found I could turn that bolt 1&1/2 turns before the pads were tight to the disc. I put the split pin back in 1/2 turn back from locked and now the handbrake seems to work much better without binding.

So I can only conclude that although the self-adjuster is working, it is not delivering sufficiently fine clearances. I guess the self-adjusting pawl must be worn or damaged so that it either has a dud tooth, or needs more than the intended amount of free movement in the levers to move forward a tooth. Next time I'll change the toothed pawls and ratchet parts rather than reuse the old ones.

[PeterCrespin]

As for the original clonking question, I forgot to mention wheel/hub spline wear as another possible source if the car doesn't have bolt-on wheels. The spinners do self-tighten but there's a limit to how much torque reversal they can prevent so I'm guessing if every other cause was investigated then sharply-pointed splies with fretting wear over the central section could be the cuplrit. Even new hubs inside old worn wheels (or vice versa) could still cause a noise i suppose.