T34 prototype suspension travel

[Adrian Harris]

I thought this might be a useful tip for keeping our models running well.

While running at the South West Model Show, the T34 prototype seems to be "limping". This was caused by a build up of grass in the sprocket, causing the track to jump once per revolution.

With an eye to improving the running, I wondered what it would be like to film the tank running over an obstacle, to see how the suspension behaves.

This was the result:



Interesting, but a bit quick to see what's actually happening, so I used Microsoft Movie Maker to slow it down to quarter speed:



Now it's pretty easy to see that the rear two wheels don't have any suspension travel at all. A similar test on the RHS showed that there are problems there as well.

Time to get it stripped down and lubricated methinks.

Adrian.

[Ian Rodney]

Hi Adrian,

Thanks for showing us your quick and slow T34 suspension travel films, interesting to see the last two wheels did not have any suspension travel at all.
I shall bear that in mind to see that there is plenty of lubrication when I get my own T34 up and running.

Thanks for the tip to keep our models running well.

Cheers
Ian

[Adrian Harris]

Thanks Ian.

New track pins and springs have been ordered from Gill, so I hope to get it stripped down this weekend to see where the trouble lies.

Adrian.

[Ian Rodney]

Hi Adrian,

That's fine, it will be interesting to hear about your findings on your suspension, springs, pins etc.
To see what to expect on my own T34 in future!

Ian

[Adrian Harris]

A little later than I expected but running over Dennis's bridge at the show on Monday proved that there was very little travel in any of the suspension.

Now the track pins have arrived, I've broken the track on the left hand side and found that the CSK bolts which hold the internal suspension bars to the hull sides have come loose, and are rubbing on the suspension arms:

I'll need to move the arms out of the way, add some loctite to the bolts and get them tightened up properly.

Once that is done I'll be able to see how well the suspension works.

I don't think this will be a cure-all but it can't help but improve the situation

Adrian.

[Adrian Harris]

I've stripped down one side and found where the problem really lies:

The pivot pins were completely stuck in their bushes, to the extent that I needed to use a vice to push them out.

Once extracted, they cleaned up nicely though:

Adrian.

[Adrian Harris]

I was worried the CSK screws mentioned above might have damaged the inside faces of the swing arms, but the marks were quite minimal, apart from the front arm:

After a quick rub down with some emery cloth, they cleaned up quite nicely:

They also now move nice and freely within the bushes.

Adrian.

[Iacopo Di Giampietro]

Nice work of "restoration"!

[Adrian Harris]

Grazie

Buying a second-hand tank is always an adventure

Adrian.

[Adrian Harris]

Once I'd got all the suspension parts removed, I could see that the countersinking of the holes was too shallow, so the head protruded slightly even when fully tightened:

Bolt as found

Countersunk hole as found

Adrian.

[Adrian Harris]

I've removed the whole hull side and increased the depth of the countersink, so that the bolts are now fully recessed into the hull sides:

Hole after deepening

Bolt after hole deepening

This has the added benefit of increasing the amount of thread usage, as these are only 12mm deep CSK bolts, and deepening the holes would allow for a couple of mil extra to be engaged.

The holes in the hull suspension bars are approximately 25mm deep, so I have decided to fully tap them and use longer bolts to secure the sides, thus lessening the risk of the bolts working their way loose again.

Adrian.

[Adrian Harris]

Having refitted the sprockets with their new rollers, I decided to strip the right hand side suspension to see how well it was working.

Unsurprisingly, it is in exactly the same state as I found the left hand side - the pivot pins were mostly stuck fast in the bushes, and the CSK screws were rubbing on the suspension arms.

I know I can fix these issues relatively easily, but I'd be interested to know what people think about lubricating the pivot pins to try and keep them moving freely in the medium to long term.

As it's a steel pin turning in a brass bush, would something like white grease be suitable, as it's water proof, and the pivot pin is quite well protected inside and outside of the tank.

Adrian.

[Stephen White]

Hi, Adrian. You might use a dry molybdenum lube such as Oxylube

https://www.rocol.com/products/inorganic-dry-moly-spray

Rocol is the real deal but there are cheaper options on the web.

Axminster do a PTFE based alternative:

http://www.axminster.co.uk/axcaliber-dr ... ant-503468

All the best.

Stephen

[Derek Attree]

Hi Adrian
I added ptfe lube paste that comes in a small tub from a model shop on my comet build
as its the same set up as the T34 I was worried about brass to steel contact if it got wet.
I see your corrosion is with a green tint which would indicate a reation with the brass.

Hope this helps

Derek

[Adrian Harris]

Thanks for the recommendations

I've found a spray can of Rocol PTFE in storage in the workshop. I've no idea how old it is so I'll give a it a try on a couple and see how well it copes.

Adrian.