Transmission Problems and Overheating

[glcaines]

I now have problems with my M151A2. I decided to drive it to town, about 15 miles, to a friends shop and drain and refill both differentials and the transmission, since he had a lift. No problems driving to his place. However, when I went to leave, the transmission was bucking slightly in reverse and was grinding slightly when I shifted into 3rd. About 1 mile from my house another problem surfaced. The engine was overheating and I lost a lot of coolant. I had just checked the gauges about 10 minutes before and the temperature was where it should be. I'm a pilot and routinely check my gauges when driving any vehicle or flying a plane. There was also a grinding / scraping noise that appeared to be coming from the water pump. I now need to replace the water pump and thermostat. The engine had never overheated before even with a lot of driving. I'm assuming the thermostat failed, but it could also be the water pump. A friend of mine lost an impeller once. I waited until the engine was cooled down and added coolant and drove the rest of the way home. That's when my major problem surfaced. I no longer have reverse in my transmission. The transmission works fine in all 4 forward gears, but no reverse. When I put the shifter into reverse, there is no noise at all. Prior to this episode, the transmission shifted and worked flawlessly, including reverse. There is nothing in the troubleshooting section of the -20 TM to cover no reverse gear.
EDIT: Now I know what happened to the transmission. They guy helping me removed the pivot pin. Now I'm going to remove the transmission top.

[rickf]

Having the reverse shift pivot drop to the bottom of the transmission is not a big deal usually, but driving it while it is there could be a very big deal. These transmissions do not have a lot of spare room inside for extra parts to lounge around. You are going to have to get a magnet on a long wand and do some fishing and hope you get it back and it is in one piece. When you pull the water pump be sure to get a real good look inside the block to see if it is clean or full of rusty garbage. If it is full of garbage I would strongly suggest putting the thermostat housing back on without the thermostat when you get the new pump and then get a good brand radiator flush and follow the directions and flush it out real good. When it comes time to drain the flush out take the top hose off the radiator and start the engine and run fresh water in the radiator run the rpms up some. This will push a lot of water very fast through the engine and wash out as much as you are going to get out of there. After all of that you are still not done because while running the flush through it and probably while driving it all that crap was going into the radiator. So take out the radiator and turn it upside down and flush it with the garden hose on as full as you can get it to flush out the stuff that will be laying on top of the core tubes. After all of that you should not have any more cooling issues. And be sure to put a 180 thermostat in there! Do not use the 160 degree that they used from the factory. That is far to cold and not only will it run much better it will also cook out all that condensation that builds up in any engine as it cools. They used cold thermostats in the 40'-60's thinking that was the best way to keep the engine cool. Thermal dynamics says otherwise. The hotter the radiator the faster the heat transfer.

[Hambone]

You're not the first person to experience this and won't be the last, there was a bulletin put out about it back in the day.

drain plug.JPG

[m3a1]

A cautionary tale! Very good of you to share it with the group.

Maybe we ought to suggest that folks paint their pivot pin a slightly different color, or surround it with a small off-color square. Apparently the locker isn't enough to warn people Do Not Touch.

[rickf]

Later A2's used a completely different type of bolt.
All differential and transmissions and drains and fills and the oil pan drain use the same plug and the same wrench. If it requires a different wrench then it is the wrong plug.

[glcaines]

My A2 didn't have the locker. It has a round bolt with a hex socket. Unfortunately, I wasn't watching the guy that was helping me, which makes it my fault. I can see how he made the mistake, however. The correct plug is in a recessed location on the side of the transmission. The recess was packed with smoothed over grease and dirt and the spot looked like the side of the transmission. You couldn't see the plug at all, but the pivot pin plug was clearly visible with minimal grease or dirt on it. I pulled the top of the transmission off and retrieved the pivot. There was no visible damage to either the pivot or any gears. I have re-installed the pivot and the top of the transmission, but I haven't re-installed the starter yet, so the real test will be when I drive the A2. Since it was running fine in gears 1-4, I suspect everything will be OK. The whole task was actually fairly easy. The hardest part was getting the sheet metal removed to access the top of the transmission. I've ordered a new 180 deg thermostat but haven't ordered a new water pump yet. I'll do that tomorrow, along with three new belts. I'm also going to flush out the cooling system prior to installing the new water pump. Since I have the cover over the transmission still removed, I'm also replacing all of the deteriorated rubber boots before re-installing the sheet metal.

[rickf]

You did make sure the shift fork was engaged on the gear slider once you got the pivot pin in didn't you? I ask because I know someone that simply held the shift idler down there and slammed the pin in and bolted the top on and then couldn't figure out why it would not go into reverse.

[glcaines]

You did make sure the shift fork was engaged on the gear slider once you got the pivot pin in didn't you? I ask because I know someone that simply held the shift idler down there and slammed the pin in and bolted the top on and then couldn't figure out why it would not go into reverse.

No problem, I made sure it was in the groove. My new rubber pieces came in the mail yesterday so good timing on that. I'm going to paint the cover pieces today as well. This morning I'm going to put the starter back in. Then it's time to tackle the cooling issue. It's always something.

[rickf]

Antique vehicles are such a joy to own, they NEVER need any attention.

[glcaines]

Antique vehicles are such a joy to own, they NEVER need any attention.

Everything I own is old and so am I. I put the starter back in and took it for a 5 mile ride. The transmission works perfectly and no overheating, although it wasn't even completely warmed up. Now I need to install the cover over the transmission.

[rickf]

You got really lucky on that one!!!!