• Overheated fluid
  • Damaged parts & planetaries
  • Overheated converter
  • Burnt parts & planetaries
  • Premature lockup
  • Inadequate lubrication


Wear at the cooler bypass valve bore due to continuous valve oscillation allows leakage and can prevent proper stroking of the valve.


This oversized valve restores hydraulic integrity, provides greater sealing capacity and has added stability throughout its stroking range in the casting bore.


Oversized Cooler Bypass Valve Kit
Part No. 63741-07K

Also fits Hyundai/Kia A5SR1/2 and Subaru 5EAT.

You need this if... View Instructions Find a Distributor

In Jatco/Nissan RE5R05A units, the cooler bypass valve is designed to allow excess oil to bypass the cooler circuit when required. However, if there is excessive wear in the bore, it can allow converter and/or lube circuit leakage and prevent the valve from stroking to the bypass position if needed. This can result in increased ATF temperature causing bushing and sealing failure, planetary destruction and converter or part overheating and damage. Severe wear prevents the valve from stroking properly, simulating a cooler restriction and increasing converter charge pressure. Sonnax oversized cooler bypass valve kit 63741-07K allows the bore to be refurbished to restore hydraulic integrity and has multiple design improvements to prevent reoccurrence of the failure.

  • Hardcoat anodized aluminum valve combats premature wear
  • Annular grooves added to hydraulically center the valve in the bore to prevent wear
  • The lengthened valve provides over twice as much sealing contact area as OE
  • Stability of the valve in the bore is greatly increased due to the critical spool diameter being over twice as long as OE

Some RE5R05A valve bodies do not contain a cooler bypass valve. Units can be identified by empty cooler bypass bore, blocked separator plate holes and separator plate code (Chart below). Do not install Sonnax product into units that do not require cooler bypass valve.

Units with No Cooler Bypass Valve (Do NOT install this part)
Valve Body Design See link for identifcation guide Separator Plate Code
1st AK
2nd BD
3rd EH
4th E1
  • Valve
  • Spring

Sonnax valve body layouts provide a detailed overview of individual units making it quick and easy to determine what’s available for the specific valve body you’re working on. See all Sonnax valve body layouts.

Jatco/Nissan RE5R05A Valve Body Layout

Jatco/Nissan RE5R05A Valve Body Layout
  • RE5R05A Oversized Cooler Bypass Valve Kit 63741-07K
  • RE5R05A Oversized Cooler Bypass Valve Kit 63741-07K
  • RE5R05A Oversized Cooler Bypass Valve Kit 63741-07K details

You need this if...

Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.

RE5R05A Oversized Cooler Bypass Valve Kit Vacuum Test Locations