Knocking / banging noise when taking off from standstill

[APM]

Hello All

Can anyone advise on where to start looking for the below ?

I have a 1999 TJ 4.0 auto and when taking off from standstill, there is a knocking / banging noise coming from underneath the car.
Its like the shaft is banging on the underfloor.
Only happens when taking off from standstill.

I have had a look under the car, but first wrangler I have owned (best change of car ever) and I don't know what to look for.

You advise would be much appreciated.

Thanks

 

[Winks42]

This happens when I go into 4 wheel drive. I think my U joints are going in my front drive shaft but it doesnt sound like its hitting the floor board but just a clunk. Is there a lot of play in the driveshaft?

 

[mrblaine]

Hello All

Can anyone advise on where to start looking for the below ?

I have a 1999 TJ 4.0 auto and when taking off from standstill, there is a knocking / banging noise coming from underneath the car.
Its like the shaft is banging on the underfloor.
Only happens when taking off from standstill.

I have had a look under the car, but first wrangler I have owned (best change of car ever) and I don't know what to look for.

You advise would be much appreciated.

Thanks

The two most common causes for that are the transfer case linkage mount letting the end of the bell crank lever smack the side of the trans tunnel and the rear pinion hopping due to incorrect driveline angle.

Have someone watch the rear axle when you take off from a stop and see if it is hopping up and down.

 

[APM]

The two most common causes for that are the transfer case linkage mount letting the end of the bell crank lever smack the side of the trans tunnel and the rear pinion hopping due to incorrect driveline angle.

Have someone watch the rear axle when you take off from a stop and see if it is hopping up and down.

Like it
Thanks for pointing me in the right direction.
Much appreciated !!!

 

[APM]

The two most common causes for that are the transfer case linkage mount letting the end of the bell crank lever smack the side of the trans tunnel and the rear pinion hopping due to incorrect driveline angle.

Have someone watch the rear axle when you take off from a stop and see if it is hopping up and down.

Thanks gor reply
Not much movement in the shaft

This happens when I go into 4 wheel drive. I think my U joints are going in my front drive shaft but it doesnt sound like its hitting the floor board but just a clunk. Is there a lot of play in the driveshaft?

Thanks for the reply
Checked the shaft and there is not too much movement.

 

[fizzlebottom]

Based only on my past experience, here's what I'd check on top of what @mrblaine mentioned:

• Confirm all control arm bolts, sway bar end link bolts, and track bar bolts are tightened properly. Also check condition of the bushings.
• Check for worn tie rod ends on both your tie rod and drag link. All four of my ends were worn out, causing a knocking at weird times. Replaced them and this knock disappeared.
• Make sure your rear end pinion nut isn't coming loose, thus allowing the pinion gear to kiss the ring gear. If you don't have a leaky seal then you're probably fine. My Dana 35 blew up because of this lovely scenario.

 

[mrblaine]

Based only on my past experience, here's what I'd check on top of what @mrblaine mentioned:

• Confirm all control arm bolts, sway bar end link bolts, and track bar bolts are tightened properly. Also check condition of the bushings.
• Check for worn tie rod ends on both your tie rod and drag link. All four of my ends were worn out, causing a knocking at weird times. Replaced them and this knock disappeared.
• Make sure your rear end pinion nut isn't coming loose, thus allowing the pinion gear to kiss the ring gear. If you don't have a leaky seal then you're probably fine. My Dana 35 blew up because of this lovely scenario.

Those are not inappropriate but they are not commonly associated with the bump, bang, and clang taking off from a dead stop.

Loose control arm bolts will typically exhibit a pop or back once on take off, again when hitting the brakes.
Trackbar will exhibit pop on turns. Bushings will not make noise if they are mostly shot unless they are just totally destroyed allowing the ends of the arm to contact the mount.

Worn steering bits exhibit loose and generally vague steering. Not typically associated with a noise or clunk from a dead stop.

 

[APM]

I have come across something else.
When I put in 4H, the knocking noise near enough goes away when pulling off from standstill and when going over bumps.
Its still there some times but only ever so often.

Someone has suggested a transmission mount ?

The knocking does seem to be coming from the underneath centre of the car, around the auto box area.

Checked the prop shaft and no movement.
The pinion seals are slightly leaking so in process of replacing them.

Have ordered a transmission mount.....
Worth a try

 

[fizzlebottom]

That sounds like the transfer case linkage then.

 

[APM]

Spot on
Just tried slightly lifting the transfer lever on take off and knocking goes away.
Repair kit on its way to fix.
Thanks for the help !!!

 

[fizzlebottom]

What repair kit are you referring to? Did you buy a shifter cable kit?

 

[APM]

I have this kit on the way :

https://rover.ebay.com/rover/1/710-...0001&campid=5337789113&icep_item=254776104306

 

[APM]

Might take longer than expected as the UK borders have been closed for import and export for a bit...

Also fits TJ
5014148AA