Trunnion Thread??

Post by **dunketh** » Wed Jul 11, 2007 9:23 am

Fitted my new lower trunion/collar thingme last night so I could move the Minor off the local garage's forecourt where it died last week.

Anyway.. I noticed it was very hard to screw on.
In the end I needed a long bar through the hole where the pinch bolt goes just to turn it on.
After taking it off to check I found that the kingpin arm was 'changing' the thread in the collar. Not quite cutting a new one but as good as.

However, where it had cut this new thread you could unscrew and re-tighten the collar with no problems. It was solidly on there, perfectly straight with no wobble. It eventually tightened all the way up (with much gnashing of teeth and straining) and allowed the pinch bolt to go through in the right place.

Am I correct in assuming this is how they're meant to be fitted and the whole idea of the thread-cutting exercise is to make sure they're solidly on there and take account of wear in the upright?

If my assumption is right then great, what a clever idea.
If I'm wrong, well, s*d it. It fits, it does up, etc.. just a bit strange that's all...

Post by **alex_holden** » Wed Jul 11, 2007 9:35 am

Do you mean it was following the existing threads but altering the profile slightly? It sounds like they weren't cut very well. Make sure you thoroughly clean out any swarf that was generated when you forced it on, otherwise the small metal particles trapped in the grease may quickly grind down the threads.

Post by **dunketh** » Wed Jul 11, 2007 9:40 am

It was altering the profile a lot!

The thread on the kingpin was a lot flatter and wider (coarser?) than the one in the collar. Either that's through wear or they put the wrong thread in the collar - which doesn't seem likely..

Post by **bmcecosse** » Wed Jul 11, 2007 10:10 am

Sure you haven't screwed LH thread onto RH kingpin - or vice versa ?? They should screw on very easily - sounds like the thread on the old king-pin was completely knackered - get another one right away and be very wary of driving with that one on the car!!

Post by **Kevin** » Wed Jul 11, 2007 10:14 am

Have to agree mine went on by hand when I changed them, something doesnt seem right.

Post by **chickenjohn** » Wed Jul 11, 2007 10:21 am

Yes, get a complete king pin with both trunnions, sounds like the king pin thread is worn too. the repair got you home, as BMC said I wouldn't trust it any further.

Post by **Packedup** » Wed Jul 11, 2007 10:39 am

*mutters something about mentioning king pin threads a week or two ago* ;)

Though I can never remember if it's sharp pointy threads good, or sharp pointy threads bad...

Post by **dunketh** » Wed Jul 11, 2007 11:54 am

Collar was sharp and pointy, the kingpin quite flat.

Strange thing is, once the thread had been `modified` the collar and pin screwed together easily. You could tighten and un-tighten them as if the threads were perfectly matched. You also cant pull one off the other.

I haven't got the budget for new kingpins at the moment but, at the same time Id be stupid to ruin the other trunnion kits I have by force fitting them.

As usual it comes down to money.

I don't suppose anyone has any decent kingpins for sale - cheap?

Post by **kennatt** » Wed Jul 11, 2007 12:27 pm

they should just turn on by hand if you have had to use force there is something wrong with the threads, some trunnions from obscure makers arn't worth the money. One way or another you will have damaged the threads on the trunnion or post. I would not use the car, how much is a life worth.Having done many trunnions and posts(And having a wheel collapse on me Once )if you need a trunnion replacement ,for safety sake,I would change the whole suspension system.Kits are available and are not that expensive about £80 a side.If the post threads are sharp then it is U S The threads should be flat at the tips(Think that's the right way round) Be very careful if you need to use the car,belive me it can be very dramatic if it gives out on you.I was lucky when mine went',only doing about 10mph .

Post by **bigginger** » Wed Jul 11, 2007 12:37 pm

Yeah, they should be blunt with a flat top, and yeah, something isn't right - thet should go on easily. Can't see how you could have possibly got them on at all if you'd used the ones from the wrong side though.

Post by **bmcecosse** » Wed Jul 11, 2007 2:47 pm

The good thing is - they only ever seem to come apart at slow speed - when turning a sharpish corner. Although I suppose there is a chance of it happing if you fly over a brow with the front wheels off the ground. A bonus point of having front tele dampers on the car is that the trunnion cannot come away from the king pin - the length of the tele damper is too short to let it pull off!

Post by **kennatt** » Thu Jul 12, 2007 10:33 pm

now thats another good reason to fit teles on the front never thought about that but great safety tip

Post by **leyther8008** » Fri Jul 13, 2007 9:01 am

Steering loads are at their highest when doing slow speed manouvers I know it goes against logic, but most fail when doing slow turns in car parks anywhere theres a 'high grip' surface not usually on gravel drives or the like and its usually the outer wheel of the turn that fails due to side/down loads on the joint.

Post by **paulhumphries** » Fri Jul 13, 2007 9:20 am

What actually happens when they fail ?
Does the threaded section snap off or does it just come apart due to the threads being so worn.
I've heard of this from my early days of driving but have never seen a car with it occuring so don't know which aspect fails.
Does regular greasing on known good threads virtually guarantee (on a standard car driven normally) that it won't happen ?

Thanks.

Paul Humphries

Post by **bmcecosse** » Fri Jul 13, 2007 9:51 am

I would say regular greasing helps v considerably but eventually they will wear. In my experience it's the INNER wheel on the turn - because it's lightly loaded the king pin can pull upwards and away from the trunnion which remains fixed to the bottom arm assembly. The king-pin thread pulls straight out of the trunnion. I did replace mine when it happened (40 years ago now!) at the side of the road - just put them back to together - and tied a tow-rope round it all betwenn top arm and bottom arm to hold it together - and drove home on it!

Post by **paulhumphries** » Fri Jul 13, 2007 10:03 am

bmcecosse wrote:I would say regular greasing helps v considerably but eventually they will wear. In my experience it's the INNER wheel on the turn - because it's lightly loaded the king pin can pull upwards and away from the trunnion which remains fixed to the bottom arm assembly. The king-pin thread pulls straight out of the trunnion.

Thanks.
I was worried that the thread actually sheared off.
I suppose moral of story is BEFORE greasing jack up wheel and check for play which might give an early sign that wear is occuring.
I say before greasing because wear is going to be more obvious then rather than after a layer is gease is applied.
On my A35 there was play in kingpin which would probably have meant MOT failure but after greasing none present. Needless to say I've got new kingpins to be installed before putting back on the road after a long rest in the garage as I don't avocate tyring to fool the MOT inspector when you know a component is suspect.

Paul Humphries

Post by **dunketh** » Fri Jul 13, 2007 11:01 am

Given what you chaps have replied with I'm beginning to think the thread in my trunnion collar might have been slightly off.

It now twists on and off easily enough. The kingpin has a wide, flat topped thread whereas the collar had a wide sharp thread... very sharp infact.

My forcible winding seems to have taken the sharp edge off this thread so it now 'appears' to match the kingpin thread.
They seem to work perfectly together and looking through the pinch bolt hole you can see it all lines up - meaning the pinch bolt will stop them coming apart, as its meant to.

I'm doing the top of this side and the complete other side at the weekend and will compare threads - as these haven't yet failed I'm hoping there'll be more to compare!

I'd just like to know whether its a 'me' cockup and my pins really are bin fodder or if its a manufacturing cock a doodle diddley up and the thread is wrong in the collar. Given the collars a reasonably soft material and provided there's a meaty enough thread in there that matches the kingpin thread I can't see there being a problem in the long term.

Of course I will add new kingpins to my shopping list, I might as well do - every other ***ing component has thrown the towel in so far. I may as well end up with a mechanically 'new' car out of it all.

Also, fyi, mine failed while turning at slow speed. My steering at full lock.
It was the drivers side that failed while turning right having just bumped over a lowered curb onto a garage forecourt.

Post by **bmcecosse** » Fri Jul 13, 2007 11:49 am

Ah - so it was indeed the 'inside' wheel - and the bump down was what allowed it to 'fall out'. Sue the garage for the uneven forecourt - and consequent damage to your car!!
When you screw them together - and they are almost at the top of the thread - is there any 'rocking' or 'play' in the threads ? If so - scrap it - if not - I still think it's not perfect, and you continue to use it at your own risk!!

Post by **dunketh** » Fri Jul 13, 2007 1:00 pm

Ah - so it was indeed the 'inside' wheel - and the bump down was what allowed it to 'fall out'. Sue the garage for the uneven forecourt - and consequent damage to your car!!

Less said about the better - more likely they'll sue me for ploughing a trench in their forecourt.

There's no play in the threads at any stage of them being screwed together.
Its certainly not going to come apart, my only concern is that the possibly damaged threads will wear at an increased rate thus resulting in premature failure at some point in the future.

Post by **chickenjohn** » Fri Jul 13, 2007 1:11 pm

I would save up for a new/reconned King pin complete with trunnions. £80 and with regular greasing it will last decades.