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

[Big D]

Hi all,

The Covid lockdown has slowed things down for me on the M8 but some progress has been made since we moved to Level 2 lockdown.

I fixed the joints around the water pump elbow and thermostat housing where coolant was seeping out. So far, so good, so hopefully that will cure my leaking problems. I refitted the lower engine panels around the engine. I couldn’t find an easy way to fit the panel on the exhaust side without removing the length of exhaust header which is bolted to the manifold. Has anyone else found this? I would have thought the panel would have been made so that it could be removed without disturbing the exhaust header pipe. The fitted panels certainly make the area around the engine bay look nice and neat.

I am not satisfied with the Hydrovac vacuum setup that I have so I will tidy that up a bit more over the next week. I have fitted the repaired voltmeter back into the instrument panel and that is working well.

I resolved my clutch issues by replacing the pressure plate. I’m not really sure how this did it, as the plates looked identical. However, I was did confirm that my original measurements were out by some 12mm so my original diagnosis of the problem wasn’t as bad as I had thought. I fitted the new pressure plate and gradually tightened it, while periodically sliding the transmission into and out of place and ensuring that there was still contact between the release bearing and the pressure plate fingers right through until I had fully tightened the pressure plate. I can only guess that the other pressure plate needed some adjustment. I am happy that it is resolved now though.

Once I was sure I had the clutch physically working I bled the clutch hydraulics using the pressure bleeder. This pressure bleeder does work well. What do you guys do for the bleed screw on the clutch slave cylinder? I have the original military type with the small ¼” ‘dust cap’ screw in the top of the bleed screw. I’ve found that during bleeding using the original bleeder, with the tapered thread, the fluid tends to come up the threads and spill out around the base of the bleeder before it works its way up the centre of the bleeder (with the dust cap off) and into the hose going into a jar.

I actually replaced the bleeder with a modern bleed screw with a bleeder nipple built into the top. It was the same thread (7/16-20) but what I didn’t realise is that the original bleeder has a tapered thread and the new one with the straight thread doesn’t seal properly.

How were these cylinders originally bled? Was it done the same way? Was it just a matter of them being loosened during the bleeding and allowing fluid to come out over the side of the cylinder? Is there a bleeder available with a tapered thread and a proper bleed nipple on the top?

The clutch now does work hydraulically and there is some satisfaction in seeing the slave cylinder operate while pushing the pedal! Thanks to Jonathan for his video of the clutch arm in operation as this showed the correct movement of the arm, and confirmed that I had everything set up correctly. The next time I am in the workshop I will run the engine with the drive-shafts disconnected and see if the clutch allows me to work my way through the gears in the gearbox which will tell me I have the clutch adjusted right. It looks good so far though.

I adjusted all the brakes and they have a good feel to them. However, I now have a problem with the wheel cylinders. The wheel cylinders were all stainless steel sleeved and I used NOS cups on the pistons which looked and felt good before I fitted them. After bleeding though, I noticed that four of the wheels were leaking hydraulic fluid though. I took two wheels off and the fluid appeared to have worked its way past both top and bottom cups on both wheel cylinders on both wheels, creating a small pool of hydraulic fluid at the bottom of the drum. One wheel was considerably worse than the other. I removed both cylinders on both wheels, pulled them apart and couldn’t see anything wrong with the cups or the bores.

My initial thought was that the original cups weren’t as effective with the modern brake fluid (Dot 4) and that perhaps the brake fluid back then had a higher viscosity. My other thought was that it was possible that the sleeves were made slightly too big for the original cups, but this was all done by my brake guy so it seemed unlikely. In the end, I took a wheel cylinder and pistons to a seal manufacturer and they made me a small number of new cups, enough to do two wheels.

When I got them back I found the new cups to be a very tight fit on the pistons and they looked to have a bit more material contacting the bore. I fitted these and bled the brakes, confident that it would solve my leaking problems. However, within a day of bleeding the brakes, the cylinders appear to be leaking again. I now wonder if the guy who fitted the sleeves didn’t seal the sleeve inside the cylinder properly and that the hydraulic fluid is working its way out between the sleeve and the cylinder. I plan to remove the drums again, remove the wheel cylinder caps and get a buddy to press the brake pedal gently to see if I can see where the fluid is coming out. I’m not sure how easy that will be to see but otherwise I figure the best bet is to return a couple of these cylinders to my brake guy so that he can bench test them.

Apart from the wheel cylinder problems, it is a good feeling knowing that all the hydraulics do actually work; throttle, clutch and brakes.

That is all for this week….

[Big D]

More photos.

[MikeV]

Nice looking Brakes

I have a question I am the other crew member helping Brian B. on the ONTAR museum M8 repair, have you honed or re-sleeved your brake Cylinders?

We have just reinstalled some new used cylinders which we honed and they are leaking. So we thought the only way to fix them now is to put a sleeve into them since they are pitting from the brake fluid, bare in mind our M8 sits around a lot on display and only gets run on a very few occasions.

[Lynn Eades]

Darryl, I have had re sleeved wheel cylinders leak from behind the sleeve- at the testing station, on the brake rollers. Customers vehicle. The finish in resleeved bores is usually very good compared to the cast iron and seldom gives trouble. Pictures of the tapered bleeder would help with understanding.

MikeV, this might be a case for stainless sleeves and synthetic brake fluid as ordinary (dot3, dot4) fluid is "hydroscopic" (attracts water) and will in a relatively short time cause trouble. A sealed system would help. That is a master cylinder with a diaphragm in the lid as opposed to a cap with a vent hole in it. (I realise this is not optional) It would be far better for all of your M8 to get a run each month. (brakes, seals, trans, engine etc)

[Big D]

Hi Mike,

These cylinders are all stainless steel sleeved. The fact that the vehicle wouldn't get a lot of use was the reason I went that way.

Hi Lynn,

That's a good point about the bleeders. I replaced the original WW2 bleeders with these ones and I can't recall whether I checked if they are tapered or straight. I guess it is possible they may not be sealing quite well enough and it is allowing fluid to leak from the bleeder seat into the area between the sleeve and the housing.

I'll take them off and photograph them. It would be interesting to fit the WW2 bleeders and see if that changes things.

[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.