THUMP felt on acceleration

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danielbeek
Hard Yaka
Posts: 106
Joined: Thu May 26, 2011 7:17 pm

THUMP felt on acceleration

Postby danielbeek » Fri Feb 22, 2019 12:27 pm

Hi All,
Posted this on NPORA also, but maybe best to check locally given it's a Jap import...

Have a very long standing issue that I'd like to resolve - hope you can give me some pointers.
More often than not, when I take off from either stand-still, or simply having slowed for traffic lights (in 2WD), there's a delayed 'thump' felt coming from the driveline. Seems more noticeable when already moving, maybe due to not using clutch.
It's not audible as far as I can tell (over slightly noisy intake, exhaust, and tyres), but it's very clearly felt 'in the seat'.
It only happens once on acceleration, within a short delay of punching the gas pedal. ie car first starts moving, then it happens. I'm pretty certain it's not just lash in the gearbox/diff therefore.
If I slow down really gently, on the gears or just coasting, and then accelerate again, it's often not felt.
It almost feels like the clutch slips a turn, then bites aggressively... But clutch seems pretty good. Not slipping in 5th, up hill, etc... Doesn't hardly slip when dumped with revs.
I did wonder if sticking of the slip joint in the main driveshaft could cause this? ie torque from motor makes it adjust length slightly, but it's binding up.

Vehicle details:
R3M Urban - LBYD21 (thats a TD27T diesel model)
31" ATs
5 speed manual
H233 read diff with LSD (fitted from a higher spec vehicle years ago)
2" raised rear springs, and wound up torsion bars (no panhard drop bracket, or longer swaybar links)
Good HD shocks (issue predates replacement anyway)

Thanks for any suggestions!
1995 LBYD21, 31" ATs, 2" lift, 2.5" exhaust

zukmeista
Hard Yaka
Posts: 2379
Joined: Tue Aug 21, 2007 12:00 pm

Re: THUMP felt on acceleration

Postby zukmeista » Fri Feb 22, 2019 7:29 pm

Check all the bushes in the rear end

Fwb2700
Driver/Navigator
Posts: 39
Joined: Sun Sep 14, 2014 9:06 am

Re: THUMP felt on acceleration

Postby Fwb2700 » Sat Feb 23, 2019 7:05 am

Driveshaft universal maybe

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kbushnz
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Posts: 2482
Joined: Wed Sep 16, 2009 9:03 am
Location: Massey, Auckland

Re: THUMP felt on acceleration

Postby kbushnz » Sat Feb 23, 2019 7:36 am

Does it run a Dual mass flywheel. They can fail and cause movement in the clutch area... Personally never felt what one is like when it fails or is about to fail..
Cheers Calvin
KZJ78 Landcruiser Prado...

MihiT
Hard Yaka
Posts: 335
Joined: Sun Feb 08, 2015 12:33 pm
Location: RD8

Re: THUMP felt on acceleration

Postby MihiT » Sat Feb 23, 2019 2:44 pm

I know you discount backlash, but check it. Jack the back, 4th gear, have your apprentice turn it forward, then back. Look for slop in the uni's, loose hangers, if it's in diff then it'll have to be felt through the hub.
- 1990 LWB Safari flatdeck, TD42 -

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danielbeek
Hard Yaka
Posts: 106
Joined: Thu May 26, 2011 7:17 pm

Re: THUMP felt on acceleration

Postby danielbeek » Sun Feb 24, 2019 8:41 am

thanks heaps for all the suggestions guys, hopefully go through some of these next week.
1995 LBYD21, 31" ATs, 2" lift, 2.5" exhaust

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