804 Front Dum Fails Air Check HELP

[340inabbody]

I am stuck and need help on my overhaul. I have an air leak in my front drum and can not for the life of me figure out where the problem is.

I did an air check on my front drum mounted to the pump on the bench and I get hissing and no thump/piston movement at 40 psi. It takes more than 80 psi to get the piston to move up with what I believe is lots of air bypassing the inner seal area.

I did a full assembly air check and it failed to thump like the rear drum.

I have checked both new seals for orientation and made sure they were not twisted or bound up. They went in nicely and I didn’t stretch them either.

Bushing looks good in the pump as well as the new teflon seals. Bushing in drum looks good as well.

Refer to my overhaul thread here: Post 196

My 1970 904A REBUILD THREAD


Any thoughts on where the leak might be coming from?

 

[340inabbody]

I get good response of the piston at 10psi by itself as seen here. No discernible leak. So the seals must be ok?

Seems like the air test cannot overcome the spring force. This appears to be the issue also noticed in my thread. The clutches move fine with lower pressure without the spring.

This is consistent with prior testing and why I moved on to final assembly.

 

[Bobzilla]

Post a picture of the pump in the same orientation with that clutch drum out of the way, removed. Then post a picture of the other side of that clutch drum, close enough to look inside the bore where the sealing rings ride against it.

I don't see anything out of the ordinary in any of your pictures.

 

[4spdragtop]

Following

 

[340inabbody]

Here are some pictures. Let me know if there are any others you guys want to see.

Please note I have watched this video from Nicks (which is excellent btw) and his forward drum air test sounds good mine only air hissing. This is my only reference!

 

[Bobzilla]

This sealing ring is overlapping wrong. It is cut on an angle. The angles must go together correctly so it looks flat or straight, however you say it, so it looks like it does the rest of the way around it.

 

[Icetech]

This sealing ring is overlapping wrong. It is cut on an angle. The angles must go together correctly so it looks flat or straight, however you say it, so it looks like it does the rest of the way around it.
View attachment 1716537791

beat me to it

 

[340inabbody]

This sealing ring is overlapping wrong. It is cut on an angle. The angles must go together correctly so it looks flat or straight, however you say it, so it looks like it does the rest of the way around it.
View attachment 1716537791

Thanks Ill try reorienting it. After I took the picture I thought it looked funny. Will report back shortly!

 

[340inabbody]

Wow BINGO Bob!

Thank you very much! The drum now moved the piston and holds pressure in the transmission!

 

[4spdragtop]

I ended up leaving most of the sealing rings as they looked good, and the ones in kit didn't "lock" like the steel ones. Im assuming ones in kit were Teflon.
Glad ya solved the issue!

 

[340inabbody]

I ended up leaving most of the sealing rings as they looked good, and the ones in kit didn't "lock" like the steel ones. Im assuming ones in kit were Teflon.
Glad ya solved the issue!

I was hesitant to use them as they looked flimsy and can easily get caught up during assembly. I spoke to John Cope (I ordered the kit from him) during assembly and said that I should use them over the steel since I have more pressure with the valve body mods. He said they seal better under higher pressure and are considered an upgrade ( if installed correctly lol ).

 

[rbkt65]

We use them in ALL RACE TRANS and they usually don't do any damage like the cast rings can.

 

[VOETOM]

For street cars, I try to keep with the iron rings. Easier to air check sometimes too.

 

[340inabbody]

For street cars, I try to keep with the iron rings. Easier to air check sometimes too.

What do you mean easier? How?

 

[VOETOM]

For me, they are not as sensitive to the amount of grease and air pressure used during testing.

 

[340inabbody]

Sorry if this has been covered before. Which is the preferred filtered for street driving?

 

[VOETOM]

Dacron, large., top in this set of images.

 

[4spdragtop]

Dacron is bottom one Tom?

Dacron, large.

 

[VOETOM]

Tan or yellow.