Centurion shock absorber question
 

Hi, no responses on HMVF so I'm trying here.
I'm still plugging away at getting our Mk 5/2 Centurion drivable at the Ontario Regiment Museum. I'm lubing the long-neglected suspension now, and have a question about the two shock absorbers at the top of each large suspension unit. They are supposed to be submerged in a reservoir of a light ISO 12 viscosity hydraulic oil and they draw from that reservoir in operation. When I removed the fill plugs I found all of them very low in oil, possibly dry, and one with a fill of grease, or at least grease had been slathered down in the fill hole. I was surprised at the lack of oil because none of them showed any signs of leakage. Other oil-filled assemblies like the final drives and gearbox still had clean oil in them up to the correct level.

Then a member here who had served in Chieftains expressed his surprise that's the Cent has shocks, because he said the Chieftain didn't.

Now I'm wondering if it was decided the Centurion shocks didn't do anything useful and were just given up on, in the sense that no further maintenance was done on them. And the Chieftain consequently didn't even bother with shocks. Seems strange to me, but I thought this forum might shed some light.

Malcolm

Hi Malcolm.

If maintaining oil in the shock reservoirs was stopped as an official change, perhaps a Service Bulletin, or equivalent, was issued on the subject, either by the Canadian Forces, the British, or both.

David

Australia changed from oil to grease: perhaps Canada did the same?

Were the plugs, plugs or those flat, slide-on type grease nipples (don't remember the name)

Mike

Alemite button head fittings?

Thanks, sounds about right, Rob:the grease gun had a head that slid onto the flat nipple from the side and clicked into place.

Mike

David, I have no access to these these bulletins. We don't have them at the museum, even though we got a lot of good documentation from the Canadian Forces archive department. Perhaps others have them?
Malcolm

Hi, Mike,
I found the pivot arms between the road wheel stub axles and the suspension units were converted to grease. These are hollow and were originally filled with oil to lubricate the bushings. The oil fill plugs were simply drilled and tapped for the weird (and in my opinion hopeless:) ) British grease fittings. Perhaps that's is what you are thinking of? Because the shocks need a thin oil to pump through small orifices to do any damping, rather than a grease.

The shock reservoirs just have a large fill plug.

I made the executive decision from a maintainabilty point of view to convert all the British grease fittings to standard grease fittings. It's an easy conversion as the British fittings use 1/8"-28TPI BSP threads which are so close to 1/8"-27 NPT they thread right in.

Malcolm

Might be worth a quick email to Bovington to see if they have any information in their archives, on the topic, Malcolm.

David

Actually the flat topped 'button head' nipples that accept a grease gun fitting that slides on from the side are an American design, originally made in the USA by Alemite, as Rob has said. They were used in plant applications (most wartime crawlers and scraper boxes for example) and came in two head sizes and many thread sizes. These were referred to as Small TAT and Big TAT I believe, but possibly only in the UK. They were adopted by the MOD as standard and are still available commercially here in the UK.

David

Oil in shocks--grease in axle arms
 

Hi Malcolm, yes, I think you are right: conversion to grease was the road wheels axle arms, not the shock absorbers: sorry to mislead you.

The 1973 Aust EMEI Data sheet for Centurion lists shock absorbers, each reservoir, as 4 gallons of 0-134 (OM-13) oil (sounds too much? Maybe 4 gallons covers all the shocks and that is a typo?) and axle arms as XG-274 grease.

OM-13 is listed as 'lubricating oil, general purpose, petroleum, light' with a viscosity of 13 @ 38 degrees C.

XG-274: I don't have a spec for, but XG-276 is a moly grease with extreme pressure additives, and XG-279 is a general purpose automotive and artillery grease. XG-279 sounds closer to the mark.

I also looked at the maintenance book, and the shocks, when serviced off the vehicle, are filled using a special jig that works the shock back and forth to pull the oil into it. They are then topped off and the plug inserted before assembling back into the suspension unit.

Regards

Mike

XG-274 is still a General Purpose Grease (I got a tin of it when I bought my Perentie Land Rover), manufactured by Shell as an Aviation grease. Specs are listed by Shell HERE.

David, thanks for the information. I stand corrected. I thought these fittings were obsolete but I see Amazon is still happy to sell me all types of them!

Mike, I suspect the 4 gallons per suspension unit is correct. Each unit is about 3 feet long, about 10" wide and the shock absorber section at the top is about 6" deep, which works out to be a volume of about 8 gallons. I'm reluctant to commit 16 gallons of oil to the 4 suspension units that have shocks without being sure that it's doing something useful. According to our expert here, the T-54 didn't have shocks either. So did they go out of fashion after the war?

What puzzles me is if you neglect the shocks because they are not effective, what happens when they'd seize up?
Malcolm

Tony,

I put a thank you up for the grease info yesterday, but it seems to have evaporated (must have hit the wrong key!)

So... thank you. All adds to what we know.

Malcolm, 4 gallons each: that's going to be expensive, but better to put at least some oil in each, I'd suggest. You are not going to war in it, so enough oil for the very limited use it will be subjected to, ie just enough to prevent seizing.

Mike

To my mind, there is a huge difference between a shock that is moving but not absorbing much shock and a unit that is behaving more or less as a solid steel rod (seized). As stated above, enough oil to stop it becoming solid would seem to be good.

I agree, I'll fill up the reservoirs. The spec'd OM-13 is a very thin hydraulic oil, with an ISO viscosity of 12-13 cS. These lighter oils are expensive, so I think I'll use the common ISO 32 hydraulic oil. I can get 20 litres for $50, so about $200 total. That's no problem. And we'll only be out $200 if it all leaks out. :)


Malcolm