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

[MikeV]

Drivers view from the grey hound yes that is a Sherman in the distance. And yes it Runs and Yes it fires Blanks.

[Big D]

Hi all,

I’ve been reminded by a couple of people that it has been some time since my last update. I’d been out of action after having an operation on my foot and having crutches and then a moon boot is not conducive to getting in and out of an M8. I can now get a shoe on my dodgy foot so I got back to work on the M8 in the last couple of weeks.

My last update was around the gear stick and the brakes. I fitted the other gear stick I had to the housing. I also raised the height of the housing a little bit as the rods were fouling a bit on the circular cut-outs in the intermediate floor. The height increase has worked. I also checked the front axle declutch system on the transfer case. That is working correctly so I am back now to experimenting with the rods to the levers. I don’t think I have the lengths of these right yet. The gear stick has quite a different angle to the other one and I think this will give me some more leg room.

After rebuilding all the wheel cylinders using those English and Spanish cups I can report that these are still working well. I’m not sure why the other ones leaked and my brake guy can’t figure it out either as the other ones were good quality. Touch wood, there are no leaks.

However, I was, and still am, having problems with a soft pedal since I changed to the Raybestos cups and pistons. I also found that the piston in the master cylinder was quite slow to return so I figured it was a good chance to strip the master cylinder and satisfy myself that all was well in there. I couldn’t find anything wrong in the master cylinder and so I reassembled it with some new rubber grease on the cups. One thing I did do when fitting the master cylinder to the hull bracket was to cut a slot in each of the mounting bolts. I’ve found that the two top bolts on the master cylinder are so close to the body of the master cylinder that you can’t get a socket or a spanner on them if you have to remove them from the mount. When I next have to remove the master cylinder, I can use a long screwdriver to remove those two top bolts.

While I had the brake master cylinder out I thought I might as well check the clutch master cylinder as well. I had noticed the odd drop of fluid at the back of this cylinder. It wasn’t such that it was leaving a pool of fluid on the floor, but just the odd drop near the top of the foot pedal. I stripped this and checked everything. Again, all looked good. I spoke to my brake guy who put the stainless steel sleeve in this for me and he was reluctant for me to change that donut cup on the end of the piston. As he said, it had done nothing and was new. I decided to reassemble it with some new rubber grease on the cups and set it up on the bench for a few hours and pressurised it with the pressure bleeder. The area at the back of the piston appeared just slightly wet but no drips developed so I decided to put it back in the vehicle and try it. I bled the master cylinder in situ and then connected everything up and pressure bled the system again. That all worked well and the clutch is fine again. There are no signs of any drips from the master cylinder yet. Touch wood again…

Back to the brakes and the soft pedal. Despite all sorts of attempts at bleeding the system with a pressure bleeder, the pedal is what I’d call ‘soft’ and gradually goes to the floor when it is depressed. The master cylinder is working fine. I removed the line to it, bled it in situ and connected a short line with a plugged end to the outlet. This gave me a hard pedal so I knew the master cylinder is working and the primary cup is doing its job. I've actually found that fitting the two master cylinders here and bleeding them in situ (rather than on a bench) does work quite well. You can easily manipulate the foot pedals and both master cylinders are right in front of you which makes bleeding them nice and easy.

In the meantime, I wasn’t happy with the right rear wheel as I had fluid seeping from the connections between the slave cylinders and the brake Tee at the top. The Tee and lines were both tidy but used and the tube nuts were not the greatest, so I wanted to replace both lines and the Tee connection. Some NOS parts that I had ordered arrived including some new brake lines, so I thought I’d fit those before going any further. Unfortunately the lines that arrived were all the longer ones for the left side of the vehicle, so I couldn’t use them, and had to clean up another couple of lines that I had here that had good tube nuts on them.

I now have a few of these NOS brake lines spare if anyone is looking for any!

While I was working on that rear wheel one of the guys from Action Engineering next door came through and knowing I had been having problems with the brakes asked why I wasn’t using a good vacuum pump to bleed the brakes. He returned with a fancy Snap On brand vacuum pump that runs off compressed air. I thought it was a good chance to use this system so I ran it over the entire braking system, bleeding at each nipple. As I’ve found in the past though, the difficulty with these vacuum pumps is that they seem to suck air in around the bleeder nipple , and despite applying some silicon grease around the bleeder nipples, you are never sure if the air that you see in the plastic tube is coming from the braking system or being sucked in around the bleeder nipple.

This bleeding had no effect on the brake pedal so then I tried isolating the various parts of the braking system. Using three sets of vise grips and some cardboard to protect the hoses, I clamped each of the rubber hoses that supply fluid to each axle. Viola! A very firm brake pedal. I then moved the vise grips to the far end of each hose to each axle. There was no change meaning the brake hoses were not expanding at all. This has proven to me that the problem is in the wheel cylinders.

What I had recently read about the difficulties in bleeding a system with these vertical wheel cylinders is now coming to fruition! There is obviously air getting trapped under the top cup in each wheel cylinder and no amount of pressure or vacuum bleeding wants to dislodge it.

I am still working on a solution but if anyone has come up with a novel way to get the last bit of air out of the wheel cylinders, I am all ears!

Damn brakes!

That is all...

[Big D]

More photos.

[T Creighton]

Hi Daryl,
You have overcome many problems along the way with your clever lines of thinking so I hesitate to offer this theory but it may be helpful (or not).

When the brake shoes are adjusted out to the drum, the cylinder cups will follow the shoe due to the spring between the two cups.
In a vertically mounted cylinder this could result in a cavity above the inlet port and below the uppermost cup that air could be trapped in from when the lines were first installed.
Being above the inlet port the air could remain trapped when bleeding the brakes.
If you were to slacken the shoe adjusters right back the shoe springs would draw the shoes back and move the cup down closer to the inlet to reduce the cavity and the risk of trapped air.
Then bleed the brakes.
Then re adjust the shoes out hard while holding some pressure on the pedal at the same time.
Then release the pedal and re adjust the shoes for clearance.
Best Regards, Terry.

[Big D]

Hi Terry

Great suggestion, thanks. Unfortunately we are one step ahead of you. My retired mechanic friend suggested exactly the same thing and I did that today prior to another round of bleeding. I neglected to put that in my update, sorry.

Any other ideas?

[maple_leaf_eh]

I just read through a number of recent posts, and smiled when you mentioned moving the M8 under its own power a few months ago. That is always a monumental occasion - like first flight in a repaired aircraft, or first shots downrange for a rebuilt rifle.

You are fortunate to have willing and equally clever businesses nearby who are helping you with parts and service. I could hear the voice of experience talking in the discussion of sleeved brake cylinders.

As for ergonomics, there is an acceptable modification in wartime Jeeps to notch the leftside wheel arch so the driver's seat can go back another 3-4". Otherwise, today's well fed enthusiasts wouldn't fit. Unfortunately the interior partitions of the M8 rule that out as an option. You might not have a choice except to change out the seat cushions for two thicknesses of folded wool blanket against a single thickness of curved seatback.

[Lynn Eades]

Darryl, have you disconnected the master cyl. and back bled it. Meaning using a pressure bleeder and pushing the fluid from the wheel cylinders back?