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111 Posts
Discussion Starter #1
The pressure regulator valve was heavily worn, but everything looked to be in good shape. Because this was an early model transmission and does not have upgraded internals I drilled the holes in the separator plate conservatively.

hole 1 to .160"
hole 2 to .081"
hole 3 to .180"
hole 4&5 to .089"
hole 6 to .125"
hole 7 not drilled
hole 8 is used in this application and drilled to .238"
hole 9&11 drilled to .113"
hole 10 drilled to .089"
slot 1 was opened to .100" on the gasket

The valve body was cleaned and assembled with Sonnax pressure regulator valve, increase pressure spring, new boost valve and new gaskets and the updated bonded rubber 1-2 and 2-3 accumulator pistons were installed.
The transmission pan was upgraded from the flat style pan with the newer style pan that has a sump/dimple for the filter to pull from. Trans was re-filled with 10 qts of mercon V.

The result was a perfectly firm shift !


111 Posts
Discussion Starter #3
This thread is based on my experience, vehicle application and customer shift preference. Later on we installed the purple lower 1-2 spring to soften the 1-2 shift.

In the 91-95 valve bodies, pressure regulator spring was too weak. combine this with a pressure regulator valve wearing over time, it causes the main line pressure to drop be low the recommended pressure and caused erratic shifting and forward clutch pre-mature wear.

Installing the Sonnax valves and increased pressure spring is a requirement, in my opinion.

As Jerry mentions in his original thesis, you can not drill hole 6 larger than .125" because it puts too much stress on the roller style one way clutch.

Even if you rebuild the transmission and update to the mechanical diode clutch, you will need to install the spiral retaining ring. The OEM snap ring is notorious for failing under high load, high RPM.

Premium Member
649 Posts
Is it safe to say this thread includes everything updated in a basic JMod? Aside from the roller clutch to mechanical diode?
IMO this a GREAT JMOD Thread for Pre-96 Main Valve Bodies.

- I also verified I had the Jerry desired Orange (OR Brown) Spring in Converter Clutch Servo & OD Servo.

- I used the longer style Teflon 2-3 Accumulator Piston.

- NAPA has great price on Dimpled Pan WITH Drain Plug.

- I'm getting ready to do all this in my 95 - In addition to all the above & BELOW I'm thinking of stuffing in a new EPC.

Some 95 & older Sonnax P/N 's.



76948-02K Boost Valve & Boost Sleeve

7699-MED O Ringed End Plug Kit

76948-04k Bypass Clutch Control


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