brake fluid

m37jarhead · Post by **m37jarhead** » Sun Jun 07, 2009 3:33 pm

I heard that some M 37's use DOT 3 brake fluid and
some use Dot 5 (silicone).
Which one is correct?
I know the fluids are not interchangeable but can one
be substituted for the other if all parts are purged?
Any advise appreciated.

Tom @ Snake River · Post by **Tom @ Snake River** » Sun Jun 07, 2009 6:09 pm

I highly doubt that any M-37's were converted to Dot 5 silicone by the miliary. If by chance that it was, it should be marked somewhere near the res. or on the lower seat panel. The earliest that I have seen the conversion is the late 70's.

k8icu · Post by **k8icu** » Sun Jun 07, 2009 6:36 pm

Ah the old Dot 3 vrs Dot 5 subject. I agree with Tom. I doubt if any M37 where converted by the military as most would have been out of the system. I know even our local NG unit did the conversion in the early 80s to M880s...which are the very younger brother to the M37s.... So it would have been surplused out with Dot 3. Now if someone changed it after it got into civilian hands is the question. You'll have to look at your fluid. If it is brown, has rust in it, or off color it is most likely Dot 3. If it is more purple and clean most likely it's Dot 5.

As to what you want to run that's up to you. If you change to Dot 5 it's best to flush the system out first before you change over. If say your in a restoration and all new stuff is going in then choose the one you want and go for it.

m37jarhead · Post by **m37jarhead** » Sun Jun 07, 2009 6:37 pm

Thanks Tom:
I'm thinking of purging my system and going to
silicone fluid for the obvious advantages.
I don't think the silicone is as harmful to the rubber
parts as the DOT 3 might be.
Anyone with thoughts on that...... I'd like to hear your
opinion.
Thks,
m37jarhead

KenInGA · Post by **KenInGA** » Sun Jun 07, 2009 9:01 pm

The system was designed to use DOT 3, and works and has worked perfectly well for about 56 years. I wouldn't recommend changing anything...

refit1701 · Post by **refit1701** » Mon Jun 08, 2009 1:47 am

Didn't Charles say that Dot 5 will destroy any natural rubber seals in the system and that you need to change to synthetic or modern seals? I have changed my entire system and have a gallon of Dot 5 waiting.

Lifer · Post by **Lifer** » Mon Jun 08, 2009 3:26 am

I learned the hard way, 20 years ago, that DOT5 brake fluid is not compatible with natural rubber components. At the same time, I discovered that DOT3 and DOT5 do not mix (poured some DOT5 into a jar with some DOT3 in it to save for fuiture use and ended up with a jelly-like glob).

MSeriesRebuild · Post by **MSeriesRebuild** » Mon Jun 08, 2009 3:32 pm

My recommendation is DOT3, used it in many systems, never an issue if you build the system right. Silicone is high $$, from my experience I really don't see that much benefit. I have seen the mess that results from mixing DOT3 & DOT5. However some say I'm crazy, doesn't matter, just pour it in. I've never figured out how to get jelly through the lines. I guess some have.

k8icu · Post by **k8icu** » Mon Jun 08, 2009 6:09 pm

I have to respectfully disagree with the gentleman from NC. If one is going to use a HMV on a daily or weekly basis then I would agree that Dot 3 is ok to use. But, if it is like most MV that get driven maybe once a month and sometime not at all for a few months I think Dot 5 is a better choice. With the Dot 5 you will not get the moisture issues of the fluid sitting and pitting and rusting the lines cylinders etc. I owned my M151 for 23 years and from the time we rebuilt it, year one, to the time I sold it it had dot 5 in it and I never had an issue with brake failer or even rusting or pitting in the system. And being in the north as I am MVs don't get run from late October through late March or early April. That's a long time to be sitting in an unheated garage that get's condensation in it from the heating and cooling cycles. I believe that if I had put Dot 3 in I would have had brake issues in those 23 years. I even had a few years where I didn't drive the jeep at all for 2 or 3 years for one reason or another and still no issues with the brake system.
That's my $.02 worth.

Lifer · Post by **Lifer** » Tue Jun 09, 2009 4:22 am

k8icu wrote: I even had a few years where I didn't drive the jeep at all for 2 or 3 years for one reason or another and still no issues with the brake system.
That's my $.02 worth.

I'm assuming, then, that you used all new components when rebuilding your system and replaced all rubber components (including flexible lines) with neoprene substitutes? DOT5 will eat your rubber lines up from the inside out over a period of time, which is not a good thing.

pfrederi · Post by **pfrederi** » Tue Jun 09, 2009 4:42 am

Its your truck and when it comes to brake fluid like lubricants everyone has an opinion.

One of the reasons the Army changed over to Silicone was that large numbers of Army vehicles are rarely used and spent most of their life sitting...(for you older members think POMCUS stocks in Europe). Even though the silicone was much more expensive for the government especially back in the 80s they still felt it worthwhile to replace DOT 3 and reduce brake system failures in many vehicles (especially stored or lightly used ones)

brake fluid

brake fluid

DOT 5