Silicone tech

Crosley.In.AZ · August 09, 2008, 08:50:36 AM

We had a trans come in with a complaint of leaks. It was not a warranty problem , just a new customer with a problem he tried to fix himself.

The customer had installed a fresh pump seal to stop the leak and the leak was actually worse after the repair.

In the photos , you can see the silicone was goop'd every where. The cavity around the seal internally is filled with silicone.

Also , part of the leak was the fact that the pump bushing had moved forward into the seal. This will not allow the seal to function correctly too.

wayne petty · August 09, 2008, 11:44:35 AM

a question for the trans pro...

do flanged seals or unflanged torque converter seals stay in better?

in your opinion...

and do you put them in dry

Crosley.In.AZ · August 09, 2008, 12:47:14 PM

Quote from: "wayne petty"a question for the trans pro...

do flanged seals or unflanged torque converter seals stay in better?

in your opinion...

and do you put them in dry

That depends on the seal design.

Most transmission flanged seals have a coating on them that is a type of sealant. Most DIY folks do not know this coating is a sealant. When I remove these seals , usually the coating remains on the surface of both seal and the part

The non-flanged seals like on a C-6 pump usually have no coating , so I use some red locking chemical agent on them.

Some folks use the red locking chemical on all seals and I have used the red stuff too.

The durprene paper type of trans pan gaskets have a sealant coating on them too. If the surfaces are clean and smooth , these gaskets can stick very tightly.

Then...... you get into the seal designs that are silicone printed with a ridge of silicone material around the sealing surface. An eggzample is the 4R70W aluminum pump & others.

Some of the transmission valve body gaskets are printed with lines of a sealant on the paper to aid in reduction of cross leaks. I view this as an indicator that these parts are too thin of a casting , so they move / warp easily. The gasket design is a band aid fix - cure ....... IMHO.

wayne petty · August 09, 2008, 02:56:00 PM

thanks... that is most of the info i needed...

my thoughts were not complete... i have had them pop out at rare times... mostly do to in my opinion flanged seals into pumps that have too much relief cut so there is not enough bore to get the seal into far enough to get a really good grip...... or the seals that were packaged were too narrow for the application...

i worked at a transmission shop in 1981... i still remember being able to take a step and slide all the way across each bay... taking my work boots off and finding my socks red from the bottom up.. loaning my boss my IR231 impact.. he spun a socket off the end of the tranny stick that must have bounced around in there for 30 seconds... all i could do was laugh...

Crosley.In.AZ · August 09, 2008, 03:23:24 PM

Often the cause of a seal pop out on a transmission is too much pressure behind the seal... this usually is a result of several items.

A common procedure to perform on trans pumps of several OEMs is to drill out the relief / drain back hole behind the seal.

you probably know that if you increase a hole size by 1/3 (33%) , the volume of oil through the hole doubles IF all the same parameters remain the same........ per the pressure and temps of the oil flowing through the hole

kb426 · August 09, 2008, 04:43:51 PM

Silicone is your friend, until it isn't. I took a sbc apart years ago that had no oil pressure. The builder had used so much silicone that it plugged the oil pump screen.

enjenjo · August 09, 2008, 09:51:33 PM

Years ago, some one where I worked decided that we would no longer use gaskets, silicone would do the job. In a few months, everything was leaking every where. Took a couple years before that junk worked it's way out of the system.

Mac · August 10, 2008, 12:42:10 AM

Back around `75 I learned that silicone is not a good gasket sealer for anything fuel related. I used it on a gas tank sender and within a few days the engine began dieing at highway speeds. It might have taken me longer to diagnose if I didn't have some clear fuel line just before the pump and noticed a telltale blue wad inside.
:oops:

zzford · August 10, 2008, 05:30:36 PM

Quote from: "kb426"Silicone is your friend, until it isn't. I took a sbc apart years ago that had no oil pressure. The builder had used so much silicone that it plugged the oil pump screen.

Ditto on a small block Ford, in my case. Most silicone should be used for breast implants. That would make all men and most mechanics happier.