Posted: Sat Feb 11, 2017 11:41 pm Post subject: dash primer pump leaks with inline fuel pump
I installed a 24v inline fuel pump on my vehicle and had a couple issues I hope someone can enlighten me on. First off the truck runs much higher in rpms now with the 9 psi pump on it and I don't think its normal. I haven't installed the fuel regulator yet at the carb. So I'm not sure if that will taper the rpms back down or not. Some guys say you need a regulator with those electric pumps, and some say you don't.
The other issue is much more dangerous and scare. I bypassed the old fuel pump and ran a line straight to the carb. Well while she was running I noticed fuel dumping out of the dash fuel primer for cold weather start. Can I just replace the o rings inside the primer and club it up? Why is it leaking so bad now and not with the old pump? And last why is there a vent line going to the hand primer pump next to the fuel line? Is there brake fluid coming out of the MC up that line, or is there fuel going down that line into the MC? If I brake that line do I need to bleed the brakes? I know there is a lot of questions here, but I just have no idea about this hand primer and need to pick some experienced brains. Thanks guys for any Intel you throw back at me.
The primer has a suck line from the tank feed line and a pressure line to the injectors on the intake manifold. If you have anything connected to the master cylinder and the hand primer get it off of there.
If your electric pump is in the tank supply line before the "T" for the hand primer pump then you are pressurizing the hand primer pump to 9 PSI which it is not designed to handle.
If that electric pump is between "B" and the gas tank then the problem with the hand primer leak is new pump. It must be on the other side of B towards the carb.
Your master cyl vent line is suppose to go directly to the aircleaner.
Finally, you will need to add a deadman shutoff switch in the electric fuel pump circuit. Most folks use a simple oil pressure switch so if the engine isn't running the electric pump gets no power. You also need a bypass switch for that circuit when you are starting the engine. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Thanks for the information, that makes since, it would pressurize that primer line. I was thinking of just plugging the line off, but I hate to lose that option. The old pump still works, its just leaking quite a bit, and the other day when driving the truck started violently bucking back and forth as soon as I hit 22 mph. Its never done that before. When I would drop the speed it would stop. Then it finally got so weak on me I had to pull over and then the engine shut down on me. I waited 3 minutes and she started right up and drove fine for another 3 minutes, then started bucking again at 24mph. It figured maybe its not getting enough fuel pressure, or there's a clog somewhere where fuel is restricted. Plus what happens when these old pumps do leak or fail, all that fuel is dumping in the crankcase. That's a bit too scary for me..lol. so I think I'll have to make this sucker work and disconnect the primer. It probably needs rebuilt anyway. I don't know what's going on with the MC connecting to the primer. That's scary looking as well. Thanks again.
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Sun Feb 12, 2017 9:52 am Post subject:
Those pumps served the military for decades with proper maintenance, and private owners have hundreds in service today. The manuals are available here for free, and Then and Now sells the pump rebuild kits.
Do you have vacuum operated wipers?
If so, how do they operate with the AC fuel/vacuum pump out of service or is it still in place?
Joined: Feb 20, 2007 Posts: 606 Location: Illinois
Posted: Sun Feb 12, 2017 10:06 am Post subject:
I have a primer pump on my M38 but it had been disconnected. After taking it apart and doing a little research, I discovered the piston seals were made of leather - no wonder they had dried up and shriveled to nothing with age! I've asked on this forum and looked elsewhere but haven't found replacement seals that are made of more gas resistant materials. The problem with the primer pumps is that even when new, they were prone to leaks and were only needed in extremely cold (arctic) conditions. If the pump is leaking gas, it is also leaking air serving as a vacuum leak - not good. That might be the source of some of your problems. So, many were removed or disconnected. I am a private pilot and light aircraft are almost universally equipped with primer pumps mounted in the instrument panel to aid engine starting. But those are of a superior design and I've never encountered a leaky one. In short, the jeep primers are pretty useless and dangerous - a bad design to boot. I left mine in the dash for the sake of originality, but its not connected. _________________ 1951 M38
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Sun Feb 12, 2017 10:13 am Post subject:
Sky,
As I understand it when working they do aid in starting as they inject vaporized gas directly into the intake manifold, unlike the primer handle on the fuel pump itself.
One would think that with as many of these around there has to be a set of seals that would work in these pumps.
McMaster-Carr, Grainger...
What kind of material are the seals made from in the aircraft pumps? Are there difference sizes? Maybe you or Wes or another aircraft fan could look around in the industry and see if there are some we could use for these pumps.
How's this for a guess, does anyone thing this electric pump is forcing fuel threw the dash primer and I to the manifolds injector ports making the truck run at the high rpms its doing right now?
I'm not running wipers at this time so the vac system for those is not important yet. I was going to go with the 24v wipers anyway so they actually work better..lol.
Also sorry , it was late last night when I posted this and I started writing on the wrong forum site. This is not an issue I'm having with my 1952 m38a1. This is an issue with my 1955 Canadian M43. I thought I was on the power wagon site, although the issue is pretty much the same I guess.
Having worked on these aircraft since 1966 I can say the aircraft primers (later ones after WWII) had "O" rings and they usually have a check valve in their suck line and the squirt line. The military hand primer also has check valves in both line ports. The leather seals function fine as long as you keep them wet. Here's a post I added good info to 10 years ago:
The only way to safely continue use of the hand primer pump when you have an electric boost pump is to make sure the electric pump is down stream of the pickup "T" for the hand pump.
If you need a hand primer but wish to modernize then buy a modern hand primer pump.
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Sun Feb 12, 2017 12:41 pm Post subject:
Wes,
Thanks for the info. I was reading that ten year old post just a couple
of days ago.
Back to the seals. The pump would perform satisfactorily if one had OEM
seals in good shape. Still wondering if we could find a modern replacement.
Are the aircraft seals neoprene, nitrile, or some such? We could easily measure the shaft and bore and come up with a proper diameter ring or
square seal. Stack if necessary like the leather ones. The cups seem to
hold up ok.
The M43CDN has the tank a lon way back from the engine. Most guys add the electric pump inside the frame rail or the crossmember just forward of the tank. So yes the military hand primer cannot hold against 9 PSI and yes the end result will be gas running out of the plunger at the dash and extra gas getting shoved into the intake manifold.
The simplist work around with the M43CDN is to add a manual shutoff valve in the suck line of the hand primer. Leave it turned off except when you need the hand primer. When you need the hand primer you can open the valve, give her two long pumps and then close the valve and start her up. The new shutoff valve can go right behind the dash in the suck line making it easy to access. I have a M37 and that is what I would do if I had to use an electric pump.
Thank you, that's what I'll do. I'll put a shut off valve on there once I figure out the suck line fitting size. That way I can pump it a couple time in the cold before I turn the actual pump on. I will go ahead and try to rebuild the primer while I'm at it. Hopefully I can find some random gaskets that size. Also at closer look the MC is not connected to the primer. Its caped off but pressed up against the bottom of the primer. That was scary, and I know you guys must have been scratching your heads about that question...lol. thanks for all the replies. That is exactly where I placed the new pump too. The regulator will be here tomorrow.
I believe the suck line is 3/16" x .028" wall steel originally and the output line is 1/8" steel but there seems to be an error in the ORD 9 for the Dodge that shows both lines 3/16". Just look at your line to the intake manifold. The primer pump I have in my hand is using compression fittings.
As for seals the four leather packings on the plunger shaft are odd shaped ID 0.375 and OD 0.593 x 5/32" thick. The cup is leather and measures 3/32" thick at the edge, ID hole is 3/16", rear face diameter is 1/2" and outer face diameter relaxed is 5/8". _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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