Hi all...
Happily had the brakes fixed on my Morris, but while doing it mechanic noticed that n/s/f trunnion needs work. He recommended getting a trunnion repair kit. What is it? Is it one of these from ESM:
The kit in the picture is top trunnion, but it's the lower that usually wears first. Note that if the kingpin thread is worn, these are still out of stock with all the major suppliers, but are meant to be coming in this month (but I wouldn't hold your breath)
Aye - you need to know if it's top or bottom that is worn. If bottom - it can drop out suddenly causing the wheel to buckle under the car! Good news is it usually happens at low speed - but of course it does leave you stranded - usually in a very awkward place. Replacing just the lower trunnion will take up 'half' the wear and would keep the car going for a while - but the best action is of course to fit a complete new assembly - if and when they are available again.
They were meant to be coming in last month. I emailed ESM a week or so ago asking what was happening and they said they had "no information" and would update the website when they were available again.
Alex Holden - http://www.alexholden.net/
If it doesn't work, you're not hitting it with a big enough hammer.
its easy to tell if the king pin thread is worn just look at at closely the tips of the thread should be flat if they look sharp and pointed then the pin is done for.
kennatt wrote:its easy to tell if the king pin thread is worn just look at at closely the tips of the thread should be flat if they look sharp and pointed then the pin is done for.
Top tip is that. Sometimes the wear is mostly in the trunnion and the KP can be saved. Fitting tele dampers is a good way to avoid the trunnion coming off the KP, as the damper acts as a suspension travel limiter into the bargain.
Fitting tele dampers is a good way to avoid the trunnion coming off the KP, as the damper acts as a suspension travel limiter into the bargain.
If tou have a teledamper between inner wing and the lower arm it WONT stop a catastrophic failure due to the trunnion.
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it will if the fully stretched damper is shorter than the length needed for trunnion to pull off the kingpin. It can only come off when 'drooping' with little or no load on the suspension - at other times the forces are holding it up and on the kingpin. However - an even better safety device is the larger 9" backplate of the Wolseley brake conversion - where the backplate envelopes the trunnion and it cannot come away from the kingpin - there just is not enough room. I suppose it would be simple enough to add a little 'catcher' ledge on the 8" backplate - to do the same job!
bmcecosse wrote:It can only come off when 'drooping' with little or no load on the suspension - at other times the forces are holding it up and on the kingpin.
No they aren't, the weight of the car hangs from the lower trunnion. I'm not convinced about the telescopic damper idea either - I would have thought that if the damper is at its maximum extension with the bottom trunnion as low as it can go, and the top trunnion is up against the bump stop as high as it can go, there will be plenty of room for the bottom trunnion to come off its thread.
Alex Holden - http://www.alexholden.net/
If it doesn't work, you're not hitting it with a big enough hammer.
The car is held up by the suspension! So the only way the trunnion can come off - is when the wheel is very lightly loaded ie cornering with that wheel on the inside etc. It's not possible for the tele damper to be fully extended AND the top trunnion hard against the bump stop - these two events are opposites as far as suspension loading is concerned. The 9" backplates are a better secuirty suystem though - absolutely no possibility of the parts coming completely apart then.
I'm convinced you're wrong about this. The end of the torsion bar pushes down on the bottom trunnion so the weight of the car is constantly trying to pull the trunnion off the swivel.
Alex Holden - http://www.alexholden.net/
If it doesn't work, you're not hitting it with a big enough hammer.
No - the weight of the car is pushing up on the trunnion - but is of course countered by the torsion bar - leaving an almost net zero force on the kingpin except when the suspension is in motion. It';s when it's moving downwards that it can pull off - the tele damper holds it on.
alex_holden wrote:I'm convinced you're wrong about this. The end of the torsion bar pushes down on the bottom trunnion so the weight of the car is constantly trying to pull the trunnion off the swivel.
The force of the torsion bar is trying to pull the trunnion off the KP, the weight of the car on it's wheels is the counter effect.
As for tele dampers preventing trunnion pulling off, as long as the tele damper doesn't have more than 10mm excess travel fully extended, compared to the suspension travel (120mm) then the trunnion cannot come off the KP unless the tele damper gets either ripped off it's mountings, or the end stop in the tele damper fails. A trunnion screws onto the KP by about 25mm or more.
I agree regular maintenance is essential in this area, but proper tele damper kits DO prevent suspension collapse where the lower trunnion is involved.
Seriously BMC take a breather and think about it. The car is hanging from the lower trunnions. With our graivity that would mean down. This is why it is so serious. Most other cars push down on the upper suspension leg.
You can call it 'hanging' if you like. It sits on it's wheels and force goes up and through the trunnion - but is resisted - just enough - by the torsion bar. If the torsion bar wasn't there - all the force would go through the trunnion and the top trunnion would sit up against the bump stop. The suspension only falls apart when the wheel is very lightly loaded - with the upper arm sitting on the rebound stop - then it come apart. I know - it happened to me about 40 years ago. And MT agrees with me - suitable tele dampers stop it happening!
Jack car up so all four wheels are clear of the ground. You will notice all wheels drop from their ride height due to suspension forces, which are there to counter the cars weight.
Looking at the front, you will see that the Armstrong damper arm, is hard against the lower rebound stop, this is due to the forces of the torsion bar, and the weight of the wheel and suspension parts.
Remove the torsion bar and the whole suspension is free to move up and down by hand, with only suspension weight being a factor.
Stick it all back together and lower car to the ground.
Via the Armstrong damper arm, part of the cars weight is pushing the top trunnion down onto the kingpin. Via the lower wishbone which is connected to the chassis, part of the cars weight is indeed pulling on the lower trunnion, as is the torsion bar lifting force. However, as the cars weight is on it's wheels, and for every force there is an opposite and equal reaction, the opposing gravity force results in near zero loading of the bottom trunnion. Remember the top trunnion is pushing on the kingpin, this force also pushes the kingpin INTO the lower trunnion.
The problem occurs when one side of the suspension goes 'light' either due to a pothole, or cornering forces. I've never heard of a trunnion pulling off at speed (thank God!)
