How do you clear out a wishbone bush thread?

[David Lawrence]

Picked up the new diesel auto just over a week ago, and knew that it had a bit of a knock developing, and a bit of a lurch that we thought was engine mount.

Today i set to and cured the knock which was the left side track rod end, then replaced the left side wishbone bush which was on the verge of its centre separating from the housing, and this shuffling forwards and backwards was responsible for the lurch.

For once the wishbone replacement went easy, and soon had it back on and bolted down. I was pleased with how smooth it went and turned around to check the driver side.

I found that the back bolt was not fully in. It has about 6 threads showing above the top of the bush mount. Front bolt was fine.

I removed the back bolt to find it a bit chewed about half way down its thread so set to with a hacksaw to try and clear it, but no joy. No matter what that bolt screws in about 6 threads then jams.

To go in 6 threads seems a bit unlikely that it has been cross threaded. Also a bit odd that the bolt appears chewed in the middle and not at the end. Anyway, point is any ideas how to clear the threads in the subframe?

I did wonder about buying a shorter bolt as i would have thought 6 threads was plenty to hold it down.

[klarzy]

Picked up the new diesel auto just over a week ago, and knew that it had a bit of a knock developing, and a bit of a lurch that we thought was engine mount.

Today i set to and cured the knock which was the left side track rod end, then replaced the left side wishbone bush which was on the verge of its centre separating from the housing, and this shuffling forwards and backwards was responsible for the lurch.

For once the wishbone replacement went easy, and soon had it back on and bolted down. I was pleased with how smooth it went and turned around to check the driver side.

I found that the back bolt was not fully in. It has about 6 threads showing above the top of the bush mount. Front bolt was fine.

I removed the back bolt to find it a bit chewed about half way down its thread so set to with a hacksaw to try and clear it, but no joy. No matter what that bolt screws in about 6 threads then jams.

To go in 6 threads seems a bit unlikely that it has been cross threaded. Also a bit odd that the bolt appears chewed in the middle and not at the end. Anyway, point is any ideas how to clear the threads in the subframe?

I did wonder about buying a shorter bolt as i would have thought 6 threads was plenty to hold it down.

As a rule of thumb you want to have as many threads inside as the width of the bolt.. ie M8 ISO bolt with 1mm pitch wants 8 threads, het a die nut to clean the bolt, or another bolt..?

[trebor]

I had one cross threaded which would not go in all the way and tried retapping but to no avail, eventually i cut a few mm off the bolt so it did go in all the way but there was enough threads to hold it in firmly.

Another method is to dril the chassis and use a nut and bolt, others have done it that way if all else fails

[steve811]

If you have a spare bolt, use a grinder to cut two slots in the bolt at about 30 degrees to the centre line of the bolt, this will then give it a cutting edge at the threads, similar to a tap. put the bolt in with a bit of lube (light oil) and wind it in and out like a tap to cut a new thread. Similar to this:

http://www.instructables.com/id/Make-a-tap-from-a-bolt/

[David Lawrence]

If you have a spare bolt, use a grinder to cut two slots in the bolt at about 30 degrees to the centre line of the bolt, this will then give it a cutting edge at the threads, similar to a tap. put the bolt in with a bit of lube (light oil) and wind it in and out like a tap to cut a new thread. Similar to this:

http://www.instructables.com/id/Make-a-tap-from-a-bolt/

Now thats a good idea. Now to find a bolt, i see rimmers list is as nla. How can a bolt be nla?

[COLVERT]

Now thats a good idea. Now to find a bolt, i see rimmers list is as nla. How can a bolt be nla?

You can get a bolt at somewhere like B&Q.----:eek:

( Take the old one with you to compare threads. )

[steve811]

Rimmers also don't list the thread type, be careful, if the thread is 14mm it could be either 1.5mm pitch or 1.75mm (fine pitch). Get it wrong and you could damage the thread beyond repair.

[Mike Noc]

Worth mentioning that if you always start a thread by hand you won't damage it.

If it feels tight then don't put a spanner to it. ;)

[klarzy]

Rimmers also don't list the thread type, be careful, if the thread is 14mm it could be either 1.5mm pitch or 1.75mm (fine pitch). Get it wrong and you could damage the thread beyond repair.

use a ruler and measure 10 threads for an idea... and make sure its a high tension bolt... a soft DIY bolt could snap under tension...

[trikey]

Do it properly, drop the subframe and retap the hole, unlikely but if that bush were to twist due to losing the bolt it would pull the bottom arm and cause the wheel move, not good if you were doing any speed.

[klarzy]

Do it properly, drop the subframe and retap the hole, unlikely but if that bush were to twist due to losing the bolt it would pull the bottom arm and cause the wheel move, not good if you were doing any speed.

its the bolt thread that's knacked bud (the male)

[trikey]

Ahh, I thought it was the threads in the subframe that was causing the fault...

[David Lawrence]

Do it properly, drop the subframe and retap the hole, unlikely but if that bush were to twist due to losing the bolt it would pull the bottom arm and cause the wheel move, not good if you were doing any speed.

I dont know how long the bolt has been this way, as i found it this way when replacing the other side one. I will remove the bolt again today so i can confirm what the thread pitch is.

[Mike Noc]

I changed a rear shock absorber last year and the lower bolt picked up as it came out. Unfortunately not only was the bolt damaged, but also the thread in the hub.

As luck would have it I found the correct size tap at the back of the garage that I'd bought for another job but was no good at the time as it was the wrong size. :D

[steve811]

I thought it was the subframe threads that were at fault too! Dropping the subframe is all very well, but to tap it he will need a bottoming tap, as it is a blind hole!

[David Lawrence]

If you have a spare bolt, use a grinder to cut two slots in the bolt at about 30 degrees to the centre line of the bolt, this will then give it a cutting edge at the threads, similar to a tap. put the bolt in with a bit of lube (light oil) and wind it in and out like a tap to cut a new thread. Similar to this:

http://www.instructables.com/id/Make-a-tap-from-a-bolt/

Thanks to Steve for suggesting this, it worked !

Bolts are now secured, and i can rest a little easier knowing my bush isnt going to fail me. No idea what was wrong. The bolts threads looked a little chewed but after cleaning them up were still tight, but gradually must have cleared out the threads in the sub frame, and little by little the bolt went further in each time, removing it numerous times to reapply oil and clean it up.

For anyone who needs to know, there are 20 threads in 40mm so presumably a 2mm pitch thread.

[steve811]

Yep, that's coarse pitch (2mm). Fine pitch is 1.5 (I got it wrong when I said 1.75). Some bolts (the ones that hold the rear suspension plates on for instance) are made with cut outs in the thread to clear out paint left during manufacture that gets in threads.