How To: Restoration of Ford M8 armoured car US Ordnance number 7373

[Big D]

Hi all,

I’ve been tied up with a few other projects so have only just been able to get back to working on the M8 again.

The problem brake wheel cylinders are on the agenda again. As you might recall I picked one of the wheels which was particularly leaky and removed the wheel and drum assembly and took the brake shoes off. I got a magnifying glass out and lay there for a bit and just watched the base of the wheel cylinder to see where the fluid was coming from. Just with line pressure I could see fluid seeping out between the piston and the sleeve.

I figured then that it was time for a change so I ordered two of the Raybestos type MK37 kits from Ross Prince in Australia. Again, I was sure these would cure my wheel cylinder woes and I fitted them to two of the wheels. I cranked up the pressure bleeder to 5 pounds and had started to bleed the system but got distracted by a few other things. When I came back half an hour later I noticed fluid pooling around one of the wheels. Dammit! I pulled the wheel and drum off that wheel and sure enough, fluid is obviously working its way out again. Fluid is also coming out on the other wheel I worked on, so clearly these new kits have not fixed the problem.

I am back to pointing the finger at the wheel cylinders and I figure there are only two possible causes. Either the brake guy did not seal the sleeves in the cylinders or the sleeves are slightly too big in diameter. I’m not sure that it can be anything else….Anyway, I have packaged up two of the wheel cylinders along with each of the cylinder kits I have tried; standard pistons with NOS donut cups; standard pistons with new manufactured donut caps; the Raybestos MK-37 kit with new pistons etc. These are all on their way back to the brake guy now who will try them on his bench and see if he can identify where the fluid is coming out.

I liked Jeff’s idea about the hydrovac setup so much that I fabricated something like that myself. Like Jeff, I made up a small bracket that bolts to the side of the air-cleaner bracket. I also used a spare check valve from a White Scout Car that I had and ran that between the manifold and the hydrovac with some 3/8” solid tube. I will finalise this once I get the brakes sorted, but the picture should give you the idea.

I still have a small problem with the thermostat housing seeping a bit of coolant where it meets with the cylinder head. It is not much – maybe ¼ - ½ teaspoon - but just enough to be annoying. I find the design a bit frustrating that one of the studs is inside the housing and you can’t easily tighten both nuts on the sides of the thermostat housing down without disassembling the housing.

I picked up a nice Plum marked axe and have tidied this up and painted it to go with the shovel and pick that I have also freshened up.
Thanks to Charles, I now have the plate I was missing off the long electrical box in the engine mounting cross member in the engine bay. That finishes that part off nicely.

The .30cal spare parts box I got from Charles now has a coat of paint on it and I’ll add some decals to it shortly.

I got some exhaust tubing folded up and fitted that to the exhaust system. I don’t think I quite got the angle of the tubing perfect as it came out from under the hull but it looks pretty good.

I am still working on getting the ammeter going. I have three here which don’t seem to work so if anyone has a spare shunt type 100A ammeter I’d be interested.

That’s all for this week….

[Big D]

More photos.

[Mike K]

hi Darryl

My neighbour has had problems with modern replacement imperial size brake rubber cups ( Made in Spain ) . The old original cups had a wider sealing lip compared to the modern replacements which are a bit of a bodge. PBR cups were pretty good but they are not easy to find these days. A good brake place is TRADE Brakes http://www.tradebrake.com.au/ they are very good with older vehicles and even have the old style lining rivets. Don't know what size your cylinders are but old stock PBR stuff turns up on EBAY sometimes. https://www.ebay.com.au/itm/3-PBR-Cy...kAAOSwk~pegcS3

[Big D]

Hi Mike,

Thanks for the reply. I thought after writing that last update that the new cups I had made, were actually made to fit the sleeve bores so they must be a match to that diameter. That sort of rules out the idea that the bores are fractionally too big as those cups were matched to them. As you say, maybe they don't seal as well as the ones with the older material. I'm not sure. It seems strange. The brakes aren't rocket science so I am a bit baffled by the whole thing.

[Mike K]

Measure the pistons with a micrometer maybe and the bores ?

[Andrew Rowe]

Hi Big D, can you post a pic of the ammeter you are after, may have something laying about, Cheers Andrew.

[Big D]

Hi Mike

Yes, I have sent the cylinders to the brake guy and he will do that. I don't trust my calipers.

Hi Andrew

It looks like this but it is a special Ammeter designed to work across a shunt. I can give you a part number if that helps.