Crosman 1377 Repair - Would not hold air

[toddk63]

My old 1377, purchased sometime around 1983 or 1984, finally gave up the ghost and wouldn't hold a pump.  I read some threads here without much luck so I just decided to tear into it to see what I could find.  Now, not knowing what part of the gun needed to be dis-assembled, I took everything apart., including the trigger assembly.  The pump cup appeared to be in good shape.  The exhaust valve assembly had a deep scratch running down it. I do not know if I did this taking it out though, since I had to use some force to get it out the last part of the tube.  The outer O-Ring seemed a bit worn.  BTW, the valve assembly slid right down the tube with a light tap without any resistance.  I took apart the valve assembly, cleaned and oiled.  I tried to replace the inner o-ring but the only one I had was too fat and I could not get the assembly fully screwed back together, so I put the old one back. It seemed snug enough.  I did replace the outer o-ring.  Now when I put the valve back in the tube, it had some light to medium resistance due to the new outer o-ring.  Re-assembly was easy except for that dang tiny spring and ball for the safety.

OK, so now it pumps up and shoots.  7.9 gr. pellet, 10 pumps, 445 fps.  Does that sound normal?

[toddk63]

Update:  I noticed that the gun would still not pump if I pumped real slow.  I had to stroke it fast to get a good stiff pump.  The exhaust valve appears to be holding air once it is pumped.  Does this sound like a worn pump cup?  I oiled the cup real good with some ATF and it improved the situation, but I could still get an occasional loose pump if I pumped real slow.  Now 10 pumps is shooting the 7.9 gr. pellet at 500 fps.  Improving!

[spark22]

Or get the good stuff pelgun oil.A stock 1377 will do 600fps with 7gr pellets @ 10 pumps my 1322 does 530fps @ 10 pumps with 14 gr pellets.Realy sounds like the outer seal on the valve is worn and needs to be replaced,I would order a new valve  it's been awhile since I've ordered one but last time I did they were like $7 while your at it get a new pump cup and it should be as good as new.

[toddk63]

Great thanks,.  I went to Crosmans website but can find nothing about ordering parts.  Where do you get parts?

Todd K.

[Brutuz]

Grab the phone and give them a call.

[Bentong]

You need to order with parts number with Crosman which can be found here >> http://www.crosman.com/pdf/manuals/crosman/1377/C1377-EVP-1&2.pdf or if yours is a diff variant just go to Crosmans manual all the way to bottom >> http://www.crosman.com/airguns/service/manuals/crosman-pistols. From what you described, looks like your pump cup is worn out. If you are going to order from Crosman...might as well get a valve assembly for $6.20 so you don't have to order the o-rings and your check valve and valve stem to ensure leak free valve. As for the port seal you can just make one from a 1/4 poly tube used on refrigerator ice maker, Just cut it straight and a little bit longer than the metal one and you can gain some fps on bigger port hole. If you are mechanically incline, you can install a flat top and it will shoot harder but your gonna be wanting more like longer barrel, steel breech etc.. My modded 1377 I did now shoot 707fps with 7.9 CPHP ten pumps. For plinking I only pump her 5X for 549fps.

[rocker1]

i have been a mechanic for almost 37 years  i build automatic transmissions  , i need to know why atf would harm the seals, i know for a fact motor oil that has been poured in brake master cylinders  swell the seals   terrible mess  and i know   the old wives tale of people putting brake fluid in auto transmission    which is a bad thing to  but it will help for  a short time  it will swell the seals terribliy sometimes almost impossible to get the pistons out of the drums  i have never knew atf or any auto transmission fluid hurting seals. these pumper rifles  are basically a hydraulic cylinder.

[spark22]

From what I've been told ATF is too acidic and from personal experience my 10 year old 2240 work fine till I ran out of pelgun oil and started using ATF after a few uses the seal on the valve stem let go and all the co2 would blow out the barrel.From all of the co2  and multi-pump guns I have repaired the ones that had holding problems were from using the wrong type of oil in them.There is no replacment as good as pelgun oil but the next step down would be ND 30 wt motor oi.Pelgun oil is a paraffin based red tinted ND 30wt motor oil made by Lubrication Engineers Inc. under the name of MONOLEC GFS 8430 motor oil.

[rocker1]

you are absolutley right   what the manufacturers call for is correct. my point was atf would not harm seals   by itself  .  if it is contaminated with oil or some other  types of lubricates it will  ruin seals in most anything  but the viscosity would not be proper for air guns .