Top Trunnion Poly Bushes - Maintenance Grease etc

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mollythemoggie
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Top Trunnion Poly Bushes - Maintenance Grease etc

Postby mollythemoggie » Thu Jan 05, 2012 11:44 pm

Hi All,
replaced my top trunnions 3 months ago at the time i used new poly bushes.. the other day was servicing the car and noticed on both sides they had just been obliterated and were in 2 pieces..

Talked to a fellow moggie owner and he said that I should have lubricated the outside of the bushes with moly grease not the inside of them as it is the only opportunity for them to get lubrication prior to fitting.. just wondering how often i should be re greasing those poly bushes and is it a matter of every xxx miles taking the bolt out.. putting new grease on the outside of the bush and away i go again?

Cheers,
Tom

mike.perry
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby mike.perry » Fri Jan 06, 2012 9:03 am

I greased my bushes when I fitted them years ago.
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IslipMinor
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby IslipMinor » Fri Jan 06, 2012 9:03 am

The suggested lubrication on initial fitting is more for ease of fitting and eliminating squeaks afterwards, than any need for actual lubrication. They are not supposed to turn on either the bolt or inside the trunnion. If they do that is how they will wear quickly.

What type of bush did you fit? The ones we fitted 14 years ago have never been lubricated and are still in perfect condition - they are 'Superflex'.
Richard



mollythemoggie
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby mollythemoggie » Fri Jan 06, 2012 9:55 am

Just the bushes I bought from esm

I fitted them and then wound up the top but where the lock washer was and then backed it off slightly and then greased the trunnion at the nipple.. Apart from that I originally applied no grease.. I'm just frustrated both died on me and am trying to work out what to do differently

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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby mike.perry » Fri Jan 06, 2012 10:30 am

Greasing the trunnions only greases the threads, not the bushes
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IslipMinor
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby IslipMinor » Fri Jan 06, 2012 10:52 am

wound up the top but where the lock washer was and then backed it off slightly
Tom,

Not sure what you mean by this? The pivot pin nut must be tight and secured with the lock/tab washer, otherwise the bushes can turn and wear very quickly.

The assembly order is that the bushes are fitted into the top trunnion, the lock wahser and nut screwed on so that everything is held in place, but not tightened. Next according to the BMC Manual 'Release the jack and allow the car to rest normally on its springs. Now tighten up the pivot pin retaining nut and lock it in position with its tab washer.' Nothing about putting the wheel back on first, which if you do you can't then get at the nut to tighten it up!!

The main thing is that the top pivot pin nut must be tightened with the suspension is as normal position as possible, which means jacking up the front under the bottom of the lower trunnion to load up the suspension, and then tighten/lock the top pin nut/washer.

The same principle applies to all the bushed suspension mountings.
Richard



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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby mollythemoggie » Fri Jan 06, 2012 11:35 am

Hi thanks all for the replies

I bought the bushes from esm the fitment I did on the set that failed after winding the top trunnion on and backing it off one turn

1. Put bushes and pin in without any grease
2. Jack up lower arm and slide in
3. Attach castle nut and secure pin
3. Tighten lock tab side completely and secure lock tab

Lower car and grease nipple for trunnion thread


I am just nervous that i stuffed something or missed a step and don't want to have to keep orderin more bushes from esm!!


The instructions from poly bush suggest no grease http://www.polybush.co.uk/instructions

But I know that failed for me last time!

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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby mike.perry » Fri Jan 06, 2012 12:04 pm

If you do not grease them they can squeak. A blob of grease cannot do any harm
Last edited by mike.perry on Fri Jan 06, 2012 12:48 pm, edited 1 time in total.
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mollythemoggie
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby mollythemoggie » Fri Jan 06, 2012 12:14 pm

Thanks mike!
I do just wonder why they failed so badly!

IslipMinor
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby IslipMinor » Fri Jan 06, 2012 12:30 pm

I used the 'washing up' liquid instruction 14 years ago on every suspension bush on the car and some have squeaked slightly ever since! But they have not worn, and are all from Superflex.

This is the link to Superflex - look to be more expensive than ESM though:

http://www.superflex.co.uk/products.php?cat=268

Do make sure that you jack up the suspension to get it as close as possible to its normal running position before tightening up the pivot pin nut and lock washer.
Richard



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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby mollythemoggie » Fri Jan 06, 2012 12:50 pm

Just ordered some superflex ones and will apply without grease to see how they go!

katy
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby katy » Fri Jan 06, 2012 3:40 pm

I’m confused, IslipMinor says that “The pivot pin nut must be tight and secured with the lock/tab washer, otherwise the bushes can turn and wear very quickly.”
Yet the BMC manual says that it is IMPORTANT that: "they must be given a .002” end float. If they are fully tightened the suspension will become solid” Then it gives instruction on how to adjust.
So which is correcet?
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby bmcecosse » Fri Jan 06, 2012 5:17 pm

2 thou endfloat?? I can't imagine how you will measure that....... The bushes that failed must surely be 'faulty' - I've had black poly bushes in my top trunnions for many many years. Any time I have them out - they look like new, and I always put a smear of moly grease on them - inside and out. The amount of angular suspension movement at the top trunnion means these bushes MUST move within the trunnion eye and/or on the pin in the damper arm.
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IslipMinor
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby IslipMinor » Fri Jan 06, 2012 5:44 pm

Katy,

The end float is for the earlier screw thread top trunnion horizontal pivot - there is a section later in the Manual that refers to the rubber bushed top trunnion pivot.
Richard



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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby IslipMinor » Fri Jan 06, 2012 5:52 pm

The amount of angular suspension movement at the top trunnion means these bushes MUST move within the trunnion eye and/or on the pin in the damper arm.
The more they move, the more they wear. The basic engineering design of a rubber bushed joint is that there is no relative movement between the bush and its housing or shaft - all movement is within the bush material itself. Just look at any more modern application using 'Metalastic' bushes - the rubber is very securely bonded to the inner and outer metal tubes and they are either pressed in or rigidly fixed into the respective moving parts.

If the bush needs to turn, then a bearing of some kind is required.
Richard



bmcecosse
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby bmcecosse » Fri Jan 06, 2012 5:57 pm

I totally agree with rubber or metalastic - but the poly material doesn't 'twist' internally like that, it's almost solid! But it is extremely hard wearing.
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby IslipMinor » Fri Jan 06, 2012 7:15 pm

I have emailed 'Poly Bush' to get a definitve answer!
Richard



katy
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby katy » Sat Jan 07, 2012 3:59 pm

On page K.7 of the BMC manual, 14th edition, it says, in bold type:

IMPORTANT.- Plain-type pivot bolts in the upper swivel pin link must be given .002 in. (.05mm) end-float. If they are fully tightened the suspension will become solid.

I found this to be true, because I had tightened the nut right up and wondered why there was no give in the front suspension. After I slacked the nut off the suspension was able to move.

Further down the page, the manual also says: In the case of bottom pivot bolts of the plain type, they must also have an end-float not exceeding .002 in. (.05mm).

Respectfully, Ken
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IslipMinor
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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby IslipMinor » Sat Jan 07, 2012 4:50 pm

Ken

There are 3 types of top horizontal pivot pin and 1 lower.

The first 2 types of top pivot pin were fitted to the early cars and are a greased 'bearing' type and have no rubber bushes fitted. They do have a rubber sleeve seal on each side, rather like the lower pin, and both need to have end float so that the suspension can move.

It is the 3rd top type that has the rubber bushes, or in the case of this thread polyurethane, and these are tightened up fully as there is no need for end float - the positioning and compression of the bushes is all controlled by the component tolerancing.

The lower greased plain pin is common to all Minors and needs end float, but this is normally provided by the component tolerances, as the bottom pin nuts are always fully tightened. There is a note in the manual to make sure there is the correct end-float, but has anyone ever needed to correct it?
Last edited by IslipMinor on Sun Jan 08, 2012 7:55 am, edited 2 times in total.
Richard



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Re: Top Trunnion Poly Bushes - Maintenance Grease etc

Postby bmcecosse » Sat Jan 07, 2012 6:27 pm

And - the suspension should only be finally tightened with the full load on the T bar. No need to put the wheel on - just stick a jack under the lower trunion and take the load up.
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