Virginia Military Vehicle Association
M20 Maintenance and Mechanical Assessment
Summary:
As of February 6, 2018, the M20 is in good running order. As with any vehicle of the WWII era, there is always maintenance to be done, but thanks to a hard-working and dedicated club, our beloved “20” battle ready! Previous repairs with the brakes and throttle are still working well. General maintenance has continually been checked and repaired as needed. And, all maintenance has been done on the trailer used to transport the M20, so we know she’s traveling safely.
Change Log:
· February 6, 2018
o Updated the format of the document to highlight changes made historically, and changes recommended. Also provided updates noted with dates.
· December 21, 2016
o Covers maintenance from April through the end of 2016, including further choke information, headlight wiring updates, brake and throttle maintenance, rust repair, and an update of required maintenance.
· April 16, 2016
o Rob White and Richard Crane replaced the thermostatic choke and taillight. Starting fluid should no longer be required.
· April 3, 2016
o Updated by Rob White to include work completed on March 26th
· March 20, 2016 Originally authored by Rob White
Maintenance Recommend
· Drivetrain Repair Needed
o The dust covers on the front axle are both torn and need replaced. Failure to replace these covers will allow water and dirt to get into the joint, causing premature failure. It is recommended that this be fixed as soon as possible. NOTE, I believe these covers are the same as an M35A2, which can be purchased from Mike’s Motor Pool or Eastern Surplus. There are two versions, one with a zipper and one without. The non-zipping design is correct to the vehicle, but requires the hubs to be removed, which isn’t a bad thing, as the wheel bearings are due for grease and adjustment. Alternatively, the zipper type can be installed without removing any mechanical components. Either would suffice.
· Charging System
o During the last few events of 2017, we noticed the battery was not holding a charge. Dabney tested the generator to discover that it was not charging. As we were leaving for the Charles City Parade, we could not take the time to research the issue further. To avoid future complications, we need to make this repair and consider purchasing a new, deep cycle battery. I recommend a blue top Optima available at most marine stores, as they can be full drained without loss of capacity.
· Choke repair needed
o In April, a new thermostat was put on the choke, which solved starting issues. There is a wire run from the crank side of the solenoid to the choke thermostat, forcing the choke shut during cranking. This works well on the first start, but caused starting issues on warm starts, so the wire was disconnected at the thermostat.
o To fix this issue, a switch needs added at the dash that manually puts power to the choke thermostat only when needed.
· Thermostat replacement
o It was very cold (about 25 degrees) the day of the Charles City Parade in 2017. The M20 started fine, but would not perform under load. On investigation, we determined that the engine was choking out, as the extremely cold air was pulled in. This was due to two reasons. First, the choke is run from the exhaust manifold. The exhaust was warm; therefore, the choke opened fully, but the engine itself was not yet to operating temperature. Second, and most critically, the engine would not go over 100 degrees. It is assumed that the thermostat is either stuck open or not installed. This can cause both issues with running too cold (as we saw here) and issues with running to hot (as the water flows to fast to be cooled by the radiator on hot days). To resolve this issue, it is recommended that the thermostat be repaired or replaced.
· Parking Brake Adjustment
o While still functional, the parking brake seems less taught than it should be. A small adjustment should do the trick.
· Headlight wiring update
o The lighting of the M20 has never been operational since the restoration. The rear lights are wired to the junction box, but not hooked up. The entire wiring harness for the headlights is missing. Vintage Wiring of Maine was contacted and provided a “wire harness”, but that did not include the conduit or wiring nuts needed at the dash, headlights, and siren. Further conversation with Mike at Vintage Wiring concluded that they do not have the diagrams for the headlight conduit. On 12/21/2016 Rob White contacted the tank museum in Danville, VA requesting pictures of the headlight wiring for their restored M20 that is on display at the museum. Once provided, we hope to recreate that wiring harness in partnership with Vintage Wiring. Once acquired, we will have a fully operational lighting system, which will make road travel much safer and allow for driving after dark.
o February 6, 2018
§ After many months of contacting Vintage Wiring of Maine with no measured progress, I stopped calling them. We have the wires, but not the conduit. Alternative sources are being evaluated.
Maintenance Completed
· 2018 Pre-season (January, February, and March)
o Following the Charles City Parade, the M20 was moved to Dabney’s garage, where it was stored for the winter to receive maintenance, and to avoid transporting the M20 on salted roads or in bad weather. During this time, the following improvements were made:
§ An exhaust leak was repaired between the manifold and the exhaust pipe, which quieted the engine noise significantly.
§ A larger mirror was added to the driver’s side. The passenger side mirror was repaired, with greatly improves safety and reduces the risk of an accident.
§ Antifreeze was checked, and was not adequate. Dabney drained two gallons of fluid, replacing it with concentrate. This brought the freeze point to a good level, which was much needed, as this particular winter was very cold.
§ The “20” got a much needed bath, removing the trail mud from our various events.
§ At this same time, several club members enjoyed “helping” Dabney; meaning, we shot his amazing collection of firearms, enjoyed our 2nd amendment rights, and finished the day with a beer … or two.
· Throttle Repair
o For a long while, the throttle on the M20 was non-responsive; especially, when held in the same position during long drives. The driver was required to frequently pump the throttle to regain responsiveness, making road travel very difficult. This also caused excessive wear to the gearing, due to jarring from the pumping and clutching to keep the engine at an operational speed.
o While the throttle fluid was very low, no leaks were found; however, DOT3 or DOT4 fluid was used, which is not the correct fluid for this application. Note, DOT5 silicon fluid is needed to avoid corrosion and to provide heat resistance with the slave cylinder in close proximity to the engine.
o The system was flushed and power-bled using the recommended DOT5 fluid. The M20 was test driven on several occasions – no pumping, bleeding-off, or leaking was observed.
o The throttle performed flawlessly when driven from Rob’s to Field Days. There was one issue with the throttle on the return ride from Field Day’s to the VFW Post at the intersection of Ashcake road and route 33. Driver Richard Crane pumped the throttle, the engine responded and drove to the VFW without further incident.
o In preparation for the November Trucks and Tanks event, Rob checked the throttle on-site at the VFW. The throttle worked perfectly, even having not having been driven since Field Days. The fluid was topped off, but again, no problems or leaks were observed following a visual inspection.
· Brake Repair
o While the M20 was at Rob’s garage, a severe leak formed from the master cylinder forming a puddle under the front of the machine. It was first thought this was from the throttle, given the recent issues with it, but an obvious leak was found around the seal of the master cylinder. The master cylinder was removed and given to president Richard Crane, who was unable to find a rebuild kit. The part was returned to me, who disassembled the master cylinder hoping to find a seal that could be replaced with ‘over the counter’ parts. During disassembly, a brake in the plunger was discovered, making any repair to the internals impossible. However, measurements confirmed that the internals were identical to those of an M35A2 “deuce” master cylinder, which Rob had new in his inventory. The kit was installed, the master cylinder was cleaned and painted, and then reinstalled into the M20.
o Again, it was discovered that incorrect brake fluid was used. This was likely the cause of the failure, as corrosion had built up in the cylinder, which caused the plunger to crack, allowing for a breach in the seal. DOT5 fluid was added and the system was power bled through each of the wheel cylinders.
o The brakes worked very well at Field Days and the November event; however, there does seem to be air in the line due to the ‘first pump’ being squishy. Further bleeding is recommended.
· Rust Repair
o Due to the apparent long-term use of incorrect brake fluid, over-filling, and leaking, the paint in the floor of the M20 (around the peddles) corroded away, allowing the floor to rust. A rust pneumatic scaler was used to remove the rust; after which, the floor was sealed with primer and painted white.
