C4's leaking again

[Axle Roads]

My transmission is leaking again. It's not the pan gasket this time (I've fixed that leak, twice) but, now it's coming from where the dipstick enters the pan. I'm thinking that I busted the O-ring while replacing the starter. Now, I'm real temped to smear on Permatex black on the dipstick, push it back in and top it off with silicon. Can someone give me a good reason why I shouldn't.

Would I really have to drop pan to replace the O-ring? I've never replace the O-ring before so any instructions would be helpful.

67' Mustang, 200

 

[Mercury Mike]

You unbolt the one bolt that holts it on where the starter bolts up, then just pull the dipstick up and out. The O-ring takes two seconds to swap, and then just put it back in the pan. Put a little bit of trans fluid on the seal before you put it in so it's lubricated. Don't silicone it. If you ever have to take it out and some falls in, it's back to pan gasket. Take your time, it won't take long. =) And be gentle.

 

[Falcon Ranch]

DON'T USE SEALANT!...if any gets into the trans it could cause shift problems or clog up an important orifice...it really isn't that hard to change an O-ring...one bolt and it pops out...you can pick up one of those universal O-ring set from harbor freight real cheap...that little box has saved my life several times...works on the dizzy, dip stick and used one to seal a leaking water hose...the trick is to just jack up the passengers side so no fluid will spill out when you pull the tube...I did one in about 20 minutes...getting the bolt out is the hardest part, but if you got one of those fancy box end ratchet wrenches it is much easier.

 

[ludwig]

Make sure it's not the shift modulator leaking around the hole. It will work out and you can't tighten it by turning the outside rim of the diaphragm housing. You need to snug it up with a thin wrench.

 

[PaulS]

The o-ring on the dipstick yube is easy to replace. Let me help with some tech stuff here:
1. NEVER use silicone on or in an automatic transmission.
.... ATF will turn RTV into jelly after a short period of time.
.... When it gets into the pan it will plug the screen and if it gets through the screen it will mess up the valvebody and is difficult to get out.
2. Normally when you put sealant on an o-ring it keeps the o-ring from sealing - it does not help at all. (in the case of a fixed part like the dipstick tube the only exception is Loc-tite or Permatex 518 sealant.) It will seal the dipstick o-ring and act as a lubricant to help the insertion. Use no more than a thin film (.010") on the o-ring before placing it onthe tube. Any more than that and you risk contaminating the transmission.

 

[Axle Roads]

Ok, no RTV. Would a nitrile 0-ring work best here? I think they're black or green.

I have Permatex anti-seize lubricant 80078 around, would that work instead of loc-tite.

Where is the shift modulator exactly? Is that the round cylinder stinking out the rear of the pan? This maybe the source of a tertiary leak and next on my to-do list.

 

[ludwig]

Modulator sticks out of the side of the case just behind the bell housing on the passenger side. It is a round, flat housing with a nipple for the vacuum hose to the carb.

 

[PaulS]

Ok, no RTV. Would a nitrile 0-ring work best here? I think they're black or green.

I have Permatex anti-seize lubricant 80078 around, would that work instead of loc-tite.

Where is the shift modulator exactly? Is that the round cylinder stinking out the rear of the pan? This maybe the source of a tertiary leak and next on my to-do list.

Permatex 518xx (the last two numbers are the size of the tube), loctite 518 and Vaseline are the only things I would put on that o-ring.
Yes the modulator is is just above the pan on the passenger side of the transmission at the rear. Up to 1970 they were screw-in and after that push-in with an o-ring seal. You can use the same sealer on it but it is rarely necessary.