Often overlooked as a potential area of pressure loss are the internal sealing rings. The rings are designed to seal oil delivery between rotating shafts and drum assemblies. These are usually found along the internal spine of the transmission. There are two main types of sealing ring material, cast iron and teflon. Both operate in a similar way. The sealing ring is pushed away from the pressure source and against the ring-groove sidewall, creating a seal on the outside face of the ring. In addition, pressure is directed under the ring, creating an outward force against the bore to provide a seal at the ring outside diameter and bore inside diameter.
If debris becomes wedged between or embedded in a sealing ring, the space created between the ring and groove will allow pressure to escape. If a ring-groove sidewall becomes indented or burred because of contact with the component bore, the same result would occur.
Ring-groove sidewalls must be square, flat and smooth or pressure will be lost. Ring wear will happen quickly as well. If the sealing-ring bore is tapered or out of round, then the oil pressure will leak at the ring O.D./bore I.D. Based upon sealing-ring operation, the ring in most instances must remain with the bore, meaning that if the ring bore – such as in a clutch drum – rotates, the ring must rotate as well.
If the bore is stationary, such as a case bore, the ring must be held stationary, meaning that only the ring groove rotates. If the scenario changes and the ring “sticks” to the ring groove, pressure will cause the ring to wear into the bore as well as wearing the O.D. of the ring.
Proper bore micro finish is important to enable the ring to bite the bore and prevent wear. Ring wear at the bore is different from ring-land wear, which results from the bore contacting the ring land groove due to excess endplay or bushing clearance. All components must work together to provide a good seal.
Some of the more common sealing ring problems seen include Powerglide and ZF4HP22 with internal stator bore wear caused by the turbine shaft sealing rings, C4 narrow pump ring being installed in to wide ring groove Mazda FN4AEL are very common for overdrive end cover ring failure.
GM 6L80E early pump stator was updated by GM to a rotational ring design to help correct 2-3 shift issues.
Early units had issues with the ring design, which lead to leaks, especially during cold operation. Generally, the customer would complain about a delayed or slipping engagement, usually going into reverse. GM updated the sealing rings on the support to address the issue.
The updated ring design won’t fit previous design pumps, so you’ll need to either replace the pump or have it machined, allowing you to install the updated rings. More detailed information can be found on pages 4 and 5 of GM technical
service bulletin number 09-07-30-004J.
Nissan RE5R05A suffer from centre support ring issues related to design and installation.
Good rebuilding procedure requires that all rings be carefully checked for correct depth and width sizing, that the ring groove is not worn and that the bore is not grooved, rings end should always be staggered when installed and well
lubricated to assist air check and initial application.
The performance aftermarket is aware of the importance of good sealing ring
operation and Transgo have developed a wire ring expander help keep teflon rings tight in the bore to ensure no pressure loss.
Cast iron rings were replaced by Teflon, then Vespel also known as Peek and now Torlon. The rings can come with various designs ranging from butt and hook joints to scarf cut and even solid endless rings that require sizing tools for installation. Teflon materials vary in how they are made.
One Teflon ring could have a high content of glass filler while another has a higher percentage of graphite. Ring composition will dictate how quickly the ring or component might wear.
The OEMs try to pick the best combination but could miss at times. Ring colour or markings sometimes denote composition; for example, a white ring usually has a high percentage of glass filler and should not be used with soft adjacent parts.
A good example, in 1999 Mazda and Ford released the 4F27E. Mazda chose to make the end-cover ring lands aluminium. Ford used a steel sleeve, only the Mazda suffer from end cover ring wear. From experience Ford knew better than to use rotating rings in aluminium parts.
Another design to try and overcome sealing ring issues is the introduction of tabbed stationary rings. Chrysler changed the ring design and added a tang to prevent rotation in the 62TE low drum to try and improve ring groove wear.