New to me '51 M37 - having fun!

Discuss fixes, upgrades and modifications to your M37

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bazeven
Posts: 4
Joined: Wed Jun 28, 2017 7:00 pm
Location: South Dakota

New to me '51 M37 - having fun!

Post by bazeven »

I picked up a '51 M37 a few weeks back and am working on changing fluids and finding out what I've got! Love getting my hands dirty with old trucks. My truck idles and runs better with the fording knob pulled out. Any ideas why this would be? I've read that you shouldn't drive it this way, but when I push the fording knob in, the truck will idle good for 10 seconds and then sputter for 4-5 seconds, and then idle fine for 10 seconds, and this repeats. Difficult to drive too far when it sputters. I have full original 24v and have a 24v fuel pump and the mechanical fuel pump has been removed. Something with the vacuum? Or maybe something in the carb and the fording valves is getting stuck, but wanted to check first with the experts here. Thank you! bz
Cal_Gary
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Re: New to me '51 M37 - having fun!

Post by Cal_Gary »

Welcome aboard! Glad to have you with us! Could be vacuum related but I can't say for sure as mine doesn't have the fording plumbing on it. We have enough experts here who will certainly weigh in on this.

Please add your location (City, State) to your profile-makes it easier to steer you to the vendors and such if we know where you are.
Thanks!
Gary
Cal_Gary
1954 M37 W/W
MVPA Correspondent #28500
NAM VET
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Re: New to me '51 M37 - having fun!

Post by NAM VET »

You are me a year ago, when I first ventured into these vintage army vehicles. I knew next to nothing about my truck, but in the year since, I have gone back and read countless hundreds of threads, and thousands of posts on this and several other forums, and vastly increased my knowledge of my M 37, enough to take on the complete rebuild of my engine, and much of the electrical and brake work it has needed. Even last night, reading an old post about oil pressure, realized I need to make sure my pressure sender has a better ground than it probably does now. Like the above post says, I have established relationships with the vendors, big and small, of parts and advice and repair for my restoration. There is a vast wealth of experience available to you from the members on this forum. Every day I type some topic in the search box, and then read all I can about this or that subject, which has helped me avoid mistakes, or just find the best way to do something.

Learning how to post pictures of your problems and solutions will greatly help, too. Just transfer digital pictures you take to your computer, then upload them to some photo hosting site, I am quite happy with the free Photobucket site, then when you post some new question, or a reply to a thread, first click on the picture, then click on the link, on Photobucket, it is the bottom of the choices on the right, then click on URL above, and on my Mac, hold Command and V, and it will show up in your post. I always click "preview" below, to re-read my post and check my picture, and then click submit, and it will show up here.

And for all the help this site has provided me, it is time for me to send the moderators some $ again. So get out your tools and get the Tech manuals and climb aboard for the best ride you can possibly have.

welcome,

NAM VET, in Upstate SC
bazeven
Posts: 4
Joined: Wed Jun 28, 2017 7:00 pm
Location: South Dakota

Re: New to me '51 M37 - having fun!

Post by bazeven »

This is my 2nd M37 restoration. I can definitely post some pictures. When I pull the fording knob - both valves turn to the 90 degree position. With the fording knob pushed in, both valves are in the parallel position. In the parallel position (I would call this open), I get the alternating smooth idle, rough idle. Also with it open, when I rev the engine I get a puff of smoke out of the exhaust. With them in the 90 degree position (closed?) it run smooth and drives great. PCV valve stuck? Or does the PCV valve only operate when in the 90 degree position? I'm reading the manuals nightly too - just thought I'd see what others have to say. Thanks for the welcome!
bazeven
Posts: 4
Joined: Wed Jun 28, 2017 7:00 pm
Location: South Dakota

Re: New to me '51 M37 - having fun!

Post by bazeven »

Another quick update. When the valves are both parallel (open?) I notice that my add on inline fuel filter (right before the carb) looks likes it's starving for fuel. The fuel filter starts to empty and then runs rough and it refills and runs smooths again until the filter starts to empty. With the valve both closed (90 degrees) the fuel filter stays full. I have a 24v fuel pump back by the tank and the original fuel pump has been removed. Vacuum? Vent line to the tank? Troubleshooting tips?

Thank you!
ashyers
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Re: New to me '51 M37 - having fun!

Post by ashyers »

bazeven,
I'd check the PCV system over carefully and start looking for a vacuum leak. The valves are open when the arm is inline with the inlet/outlet. If the truck runs better with them closed that's pretty odd. When working properly the idle will slow a bit with the valves closed and the truck will not run quite right. If you keep them closed you'll start pushing oil past the seals.

I'm going to guess that you have a vacuum leak that the PCV system is covering up when you close it off. As far as checking the PCV system I'd do this:
1) Ensure the short tube that connects the PCV system to the intake below the carb is clear of carbon. They tend to plug up if things aren't maintained.
2) Check to see that the fittings in the system are tight.
3) Start looking for a vacuum leak.

As far as the fuel issue, you may have two things going on! The vent for the tank goes to the intake elbow ahead of the carb so it should not be effected by the fording valve position. That's a strange one! Once you get the idle behaving normally it should be easier to diagnose other issues.

Keep us posted on progress! I'm curious to find out what's up.

Andy
bazeven
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Joined: Wed Jun 28, 2017 7:00 pm
Location: South Dakota

Re: New to me '51 M37 - having fun!

Post by bazeven »

Thanks Ashyers. On the below image - the short tube you mention to clean - are you talking about V or J? Is P the actual PCV Valve?? After it's running smooth with the valves closed, I open the system by pushing in the T-Handle on the dash and the engine does idle up a bit and then starts to do the 10 seconds good idle, 4 seconds rough idle. The carb was replaced before I picked up the truck (the fuel tank was just lined and we have fresh fuel) so the air/fuel mix screw could be wrong too. 1/2 turn to 1 1/2 turns is what I read. Start at 3/4 turn, correct? I know the wipers vac line is not connected (due to no mechanical fuel pump) and I"ve seen a couple of other vac lines disconnected too, so will look everyting over tonight and report back. THANK YOU!

Image
ashyers
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Re: New to me '51 M37 - having fun!

Post by ashyers »

bazeven,
Tube "J" frequently plugs up, it gets pretty warm and if the engine has a bunch of blowby it gets cooked on the ID of the tube. I'd sort the vacuum lines before I worried about the carb settings!

Andy
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