Re: (Fwd) Re: [MV] I have wondered about this myself...

Richard Notton (
Wed, 27 Jan 1999 20:38:26 -0000

-----Original Message-----
From: David C. Barbieri <>
To: <>
Date: 27 January 1999 13:40
Subject: (Fwd) Re: [MV] I have wondered about this myself...

>Forwarded message:
>Subject: Re: [MV] I have wondered about this myself...
>Date: Wed, 27 Jan 1999 07:11:28 CST
>Earlier, Richard wrote:
>>Most of the post-war UK fighting vehicles do not use "brake fluid" as
>> we know it but an ISO 15 hydraulic oil (OM 13)... the component parts
>>of these systems appear to use standard commercial items.
>It'd be pretty interesting to see what type of rubber/synthetic
>material the pistons/boots/cups are made of. I've had the
>[mis]fortune to witness the results of someone inadvertantly
>adding mineral-based oil (engine oil/ATF) to the brake system.
>Wheel cylinder cups and caliper o-rings became softened and
>swollen, causing the shoes/pads to drag. Incredible mess to
>repair; _all_ components had to be rebuilt or replaced, and the
>system had to be flushed repeatedly. (Gotta tell ya - one helping of
>this good fun is _more_ than enuff!)
That's interesting, perhaps its some other component of the oil that
causes the trouble, way back we had vegetable and mineral based brake
fluid but I think it is all now mineral, I recall being careful in the
60's to only use Girling fluid in Girling systems and Lockheed in
theirs. The UK Defence spec OM 13 is "Oil, Mineral type13", similarly
OMD 110 is "Oil, Mineral, Detergent type 110" or detergent SAE 30 and
OEP 220 is "Oil, Extreme Pressure type 220" which is EP 90.

The appearance of OM 13 is, I stress, very like ATF but I have no way of
analysing it, the commercial equivalent being BP Bartram HV 15 and near
equivalents Esso (Exxon) Nuto H 15, Shell Clavus 15 &/or Tellus R10,
Fina Cirkan 15; if you can find a rep for one of these companies maybe
he can give you the low-down on it, apparently for "domestic" use its
just a simple ISO 15 hydraulic oil.

The FV 623 needs 20 gals (US) of hydraulic oil so a cheap source was
needed as you have observed, most of this is contained in the crane,
winch and power steering circuit but the same stuff is specified for the
hydraulically operated, clutch, brakes, choke and accelerator fittings.

I don't think the PTO and smaller steering gear pumps would like the
decidedly non-oily "brake fluid" stuff, the seals in the conventional
circuits on this vehicle are just what you'd expect to see in any master
or slave cylinder of truck size and their moulded-in makers part numbers
are recognised by commercial suppliers so nothing special here. The
crane ram seals are, well, huge ram seals made of a resinous material on
a fibre base.

The vehicle has been running for the last two years with a commercial
ISO 15 hydraulic oil that I have serviced it with and cost a just little
more in 25L drums than detergent SAE 30 engine oil, over here this cost
is entirely similar to ATF in like quantities.

>Steve also chimed in, writing:
>> I have wondered about ATF myself. I have been told about heat. Well,
most auto
>> tranny's get pretty hot especially in the summer.
>Yup. Most ATF/engine oil begans to degrade at temps over 325
>degrees F; DOT 5 has a boiling point of 356 degrees F. The max temps
>are pretty close, and like Richard says, there _are_ components out
>there that will reliably work in this environment. Considering DOT 5
>brake fluid is only slightly less expensive than tungsten, it'd be
>great to use a readily-available, inexpensive hydraulic fluid like
20 gals of DOT 5 would cause a sharp intake of breath. . . . . . . .

>> Wonder if the 1st person to 'discover' this lived through the
Unless a quantity of air is admitted to a ram system I can't see how it
can diesel but no doubt the risk must exist.


(Southampton UK)

To unsubscribe from the mil-veh mailing list, send the single word
UNSUBSCRIBE in the body of a message to <>.