Trimatic Periodic Maintenance

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Page created by T Oct 7th 2009:

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Trimatic Service Kit. Outermost is the Pan Gasket. Top left is the Oil Filter. Top right is the Servo Cover Gasket. Centre left is the Detent Solenoid Gasket. Centre right is the Oil Filter Gasket. Bottom of the photo is the 7AT4 Tool and a Warren and Brown in/lb Torque Wrench. Click to enlargen. Photo by 383HGBroughgam.

Trimatic Periodic Maintenance:

Periodically Trimatic Gearboxes need the Oil and Filter changed as well as the Band re-tensioned. This page explains how to change the Oil, Oil Filter and re-tension the Band. 

7AT4 Band Tensioning Adaptor fitted to Warren & Brown in/lb Torque Wrech. Click to enlargen. Photo by 383HGBrougham.
7AT4 Band Tensioning Adaptor and Warren & Brown in/lb Torque Wrench Click to enlargen. Photo by 383HGBrougham.
The 7AT15 Modulator Spanner. It is 1 1/4" AF and 3.0 mm thick. Click to Enlargen. Photo by T.
The 7AT15 Modulator Spanner. It is 1 1/4" AF and 3.0 mm thick. Click to Enlargen. Photo by T.
Early Type 6 Cylinder Trimatic showing the Modulator and Vacuum Pipe at the left side of the Image. Click to Enlargen. Photo by VernonV.
The Detent Valve is to the right of the Modulator. Click to Enlargen. Photo by HQ_SS.
The red Arrow marks the Detent Valve. Click to Enlargen. Photo by HQ_SS. Arrow by T.

For a Commercial Vehicle the Maintenance period should be every 12 months. For a Private Vehicle Maintenance period should be every 24 months.

The Servo Cover is at the left hand side of the Image (1). It's bolted to the Valve Body by 4 Bolts. Click to enlargen. Photo by TooL.

Before You Begin:

You must drive the Car forwards and backwards at low speed to test that the Car rolls freely. If the Car feels as though the Brakes are dragging it could mean that the Band is too tight.  It could also mean that the Brakes are dragging. You must adjust the Brakes before you do the Trimatic Oil Change so that you can test the Band is operating correctly. If the Car isn't dragging then drive it for 30 minutes to make sure the Trimatic and its ATF are hot enough to Drain properly during the Service. Check to see if there is an Oil Leak from the Detent Valve. If there is, plan to replace the Detent Valve O Ring during this service because it can only be done after the Pan has been removed. You will need to buy a Detent O-Ring and the 7AT15 Spanner to remove the Modulator as mentioned under Items Needed.

The Servo Cover is bolted to the Valve Body. The Valve Body is the large Cast Iron fitting bolted to the bottom of the Trimatic. Click to enlargen. Photo by TooL.

Modulator Gasket Leak:

Good information there T.
Can I also mention the paper gasket on the modulator which should really be changed while the modulator is off to replace detent o-ring. Forgive me if I'm wrong but I didn't see it mentioned anywhere. Not sure if all auto places do this but we would change pan gasket, detent o-ring, modulator gasket and selector shaft seal routine on every Trimatic service. Stops getting caught out later with pesky leaks.
Cheers Dave

Selector Seal Leak:

As Dave eh has also said the selector shaft oil seal can leak and when it dose it drips down on the pan edge and looks like the pan casket is leaking... wombat.

Items Needed:

All 4, 6 an 8 Cylinder Trimatics use the same Pan Gasket, Oil Filter, Oil Filter Gasket and Detent O-Ring.

1. 2.5 Litres of Dexron I , II or III Automatic Transmission Fluid (ATF). 2. A Service Kit containing the Pan Gasket, Servo Gasket and Filter Gasket. This can be bought for around $25 from Repco. 3. If the Detent Valve is leaking the Detent Valve O Ring will need replacing. The O Ring has an Outside Diameter of 21m, an Inside Diameter of 18mm and the rubber is 1.5 mm thick. 4. The 7AT4 Trimatic Band tensioning Tool. This is a 3/16" Allen Key with a 3/8" Drive Socket. Also available from Snap On Tools FA6E 3/16 Allen Key 2 1/16" long. Snap On Tools FA6E 5. The 7AT15 Modulator Tool. This is a very flat Spanner. It allows you to get between the Modulator and the Trimatic Case to unscrew the Modulator. 6. Drain Tray. This should be large enough to fit the entire Pan inside. 7. 3/8" Drive Torque Wrench that can handle 40 inch lbs (4.5 NM).

The Detent Retainer Pin can be seen hanging down to the left of the Kickdown Solenoid (2). Click to enlargen. Photo by TooL.

Maintenance Interval:

Trimatics need the Oil and Filter changed as well as the Band retensioned. Over time the Oil becomes contaminated blocking up the Filter and Galleries. It causes poor shifts and reduces the life of the Trimatic. The Band wears and needs to be retightened. A loose Band causes the Trimatic to bang when shifting between Gears.

The white object in the centre foreground is the Speedometer Driven Gear and is not involved in a Periodic Service since it bolts into the Tail Extension Housing. Click to enlargen. Photo by TooL.


The Engine must have immediately done a 30 minute Drive to ensure that the Trimatic is hot enough. If the Trimatic is drained cold the full benefit of the Oil Change will not occur. Raise the Car on a Hoist or alternatively drive the front Wheels of the Car up onto Ramps. If using Ramps pull the Handbrake on, put the Gearselector to Park and chock the Wheels so that the Car cannot roll. Shut the Engine off. Place a Tray large enough to cover the area of the Pan under the Trimatic.


ATF is a flammable fluid. Don't allow it or any Rags that have soaked in it to come in contact with the Exhaust System or Fire can result. Take the normal precautions against Fire. Have a safety policy like keeping an appropriate Fire Extinguisher handy.

Drain Bolt:

 Early Trimatics had a Drain Bolt in them. If yours does, simply remove the Drain Bolt and allow the Oil to drain into the Tray.

Without Drain Bolt:

Place the Drain Tray under the Trimatic Pan. Loosen all the Bolts that hold the Pan on until they are just  finger tight  but don't remove them.  Create a controlled leak at the Rear of the Trimatic by removing the Rear Bolts and slowly loosening the Front and Side Bolts. Allow the ATF to slowly drain slowly out of the Rear of the Pan by loosening the front Bolts as required.

Remove The Pan:

Once the ATF has ceased flowing out remove the Pan Bolts and the Pan. Place the Pan in the Drain Tray which now has about 2.5 Litres of Oil in it.  Soaking the Pan in the old ATF while you continue with the rest of the Service will clean the inside and outside of the Pan making it easy to wipe clean later on.

Remove The Oil Filter:

The Oil Filter is made of pressed Tin Plate and is Bolted to the Trimatic Valve Body. Loosen and remove the 3 Bolts that hold the Oil Filter on then place the Oil Filter and its Bolts into the Drain Tray to clean.

Servo Cover:

The Servo Cover is at the nearside rear of the Trimatic and is held on by 4 Bolts. Remove the 4 Bolts and the Servo Cover and place them all in the Drain Tray to soak in the old ATF.

Band Re-Tensioning:

After the Servo Cover has been removed you will see a 9/16" AF Lock Nut screwed onto an Allen Bolt. Using a 9/16" AF and a 1/2" AF Spanner to hold both the Nut and the Servo Mechanism, loosen the 9/16" AF Lock Nut but don't allow the Allen Bolt to rotate, or mark it to make sure you don't lose it's position. Fit the 7AT4 Tool to the Allen Bolt and slowly turn the Bolt clockwise counting the number of turns until it bottoms using Finger tight pressure. Do not remove the Circlip from the Servo Mechanism. 

Band Re-Tensioning Turns:

If it rotated 4 turns or more but less than 5, you will use 4 turns to tension the Band. If it rotated 5 turns or more but less than 6, you will use 5 turns to tension the Band. If it rotated 6 turns or more but less than 7, you will use 6 turns to tension the Band. Fit the Torque Wrench and torque down the Allen Bolt to 40 inch lbs (4.5 NM) by turning it clockwise. You want the Allen Bolt to be tightened to 40 in/lbs. Note the position of the Allen Bolt after you've torqued it, then turn it anti-clockwise by the exact number of Band Re-tensioning Turns you worked out (above). Note that your turns must be exact so take careful note of the position of the Allen Bolt as you rotate it.

Slipping clutches burn and produce black ATF. Neglect caused a loss of Oil Pressure due to a choked Oil Filter which made the Clutch Packs slip. Slipping Clutch Packs caused the Oil to burn which exacerbated the problem. Click to Enlargen. Image by Veight.
Pieces of broken old Pan Gasket are stuck to the Rim of the Pan. This will have to be scraped off and the Pan completely cleaned before the new Pan Gasket can be fitted to the Pan. Click to Enlargen. Image by Veight.
12 Bolts hold the Pan to the Trimatic. Click to Enlargen. Image by Veight.

Locking Down the Band:

Once the Allen Bolt has been unwound to the exact number of turns, tighten the Lock Nut so that it cannot come loose. The Band Lock Nut is tensioned to 15 ft/lbs.

Servo Cover removed from a neglected Trimatic.  After soaking in the old ATF this will be easy to clean. Make sure it's spotless before reinstallation. Click to Enlargen. Image by Veight.
4 Bolts hold the Servo Cover to the Trimatic Valve Body.  Click to Enlargen. Image by Veight.

Servo Cover Gasket:

Clean the area where the Servo Cover fits by removing any traces of old Gasket. Scrape any pieces of old Gasket away until you have clean bare Metal.

Refit the Servo Cover:

Remove the Servo Cover from the Drain Tray and wipe it absolutely clean with a clean Rag. Note that the dish part will have old Band material in it that looks like Graphite. Make sure all of this is removed. Remove the 4 Servo Cover Bolts and wipe them clean. Place the new Servo gasket on the Servo Cover and refit it to the Trimatic using 2 of the Bolts. Note that the Servo Cover is an odd shape and only goes back on one way. Once the Servo Cover is in place, fit the remaining 2 Bolts, tighten all 4 of the Bolts down Finger tight. Then torque the 4 Servo Cover Bolts to 18ft /lbs. gradually increase the torque evenly on all the Bolts.

Fit The New Oil Filter:

Clean the area where the Oil Filter fits on to the Valve Body making sure the Oil Filter Gasket area is absolutely clean. Remove the 3 Oil Filter Bolts from the Drain Tray and wipe the clean. Note that the new Oil FIlter Gasket is often an odd shape and doesn't seem to be the correct item. Check to see that the Gasket will cover the 2 square Holes and be able to seal them off OK once fitted. Fit the new Oil Filter Gasket to the new Oil Filter and place 2 of the Oil Filter Bolts through the Oil Filter to hold the Gasket in place.  Fit the Oil Filter and Gasket to the Valve Body and tutn the Bolts just far enough so that the Filter won't fall off. Fit the 3rd Oil Filter bolt them tighten all the Oil Filter Bolts finger tight. Torque the Oil Filter Bolts to 15 ft lbs.

Detent O-Ring:

There is a small O-Ring in the Detent Valve. This O-Ring can only be replaced while the Pan is removed so now is a good time to  do this.

Removing the Modulator:

Remove the Vacuum Hose from the Modulator. Using the 7AT15 Spanner  unbolt and remove the Modulator.

Removing the Detent Valve:

Looking inside the Trimatic you'll see a small pin near the Pan Gasket area. The Pin is easily twisted and pulled out. Once the Pin has been removed the Detent Valve can be levered out of the Trimatic. Note it only has to be pushed out about  0.75". Once the Detent Valve has been pushed out a little way the O-Ring can be seen. Lever the old O-Ring off with a small screwdriver. Don't score any part of the Detent valve. If the O Ring has gone hard cut it with a Razor Blade. Make sure you don't nick the Detent Valve. Soak the new O-Ring in ATF and fit it to the Detent valve. Slowly push the Detent Valve back into the Trimatic and replace the Pin.

The Photo shows the Detent Retainer Pin to the Right Hand Side of the Modulator. Note the Kick Down Solenoid has been secured by a Bolt to prevent the Wire from being damaged. Photo by T. Click to Enlargen.
Removing the Modulator using the Special Tool. Photo by T. Click to Enlargen.
After removing the Pin with Pliers the Detent Valve can be eased out about 0.5", just far enough to replace the O'Ring. You will need to rotate the Detent Valve slightly if you want to remove it completely.  Photo by T. Click to Enlargen.
The O'Ring will most likely need to be cut with a Razor Blade to remove it without damaging the Detent Valve. Smear ATF over the new O'Ring to help it fit on and smother the O'Ring again with ATF so that it will pop back into the Case without tearing. Photo by T. Click to Enlargen.

Refit the Modulator and tighten it with the 7AT15 Spanner to 15 ft lbs. Refit the Modulator Hose.

Refitting The Pan:

Remove all the Bolts and the Pan from the Drain Tray and wipe them absolutely clean. Pour the old ATF Oil from the Drain Tray into an old Oil Container. Throw away the Old Oil Filter and Pan Gasket.

Pan Gasket:

The Pan Gasket is available separately. Permaseal KV148.

Refitting The Drain Bolt Type Pan:

Fit the Drain Bolt finger tight before fitting the Pan to the Trimatic.

Refitting The Pan Without Drain Bolt:

Place the new Pan gasket on the Pan in the correct position. Note the Pan Gasket only fits in one position due to the odd shape of the Pan. Using 2 Pan Bolts fit the Pan to the Trimatic by fitting the Bolts at opposite corners of the Pan. Turn the Bolts just enough to hold the Pan in place and to prevent it from falling and don't tighten them finger tight just yet. This makes fitting the remaining Bolts easier. Fit the remaining Pan Bolts and turn them all down finger tight only. Tighten the Pan Bolts a little at a time, first one on one side then one on the other going around until they've all been brought evenly up to 9ft lbs. You want the Gasket to be evenly tensioned.

Re-Torquing The Drain Bolt:

Torque down the Drain Bolt after all the Pan Bolts have been fully torqued down.


Some of the new Oil must be poured into the Trimatic Dipstick Hole before starting the Engine. Remove the Dipstick and slowly pour some of the new ATF down the Dipstick Hole monitoring under the Car for leaks. If no leaks, pour a total of 1.5 litres of ATF into the Trimatic. *Note* don't pour all the Oil in just yet. Refit the Dipstick. Start the Car and cautiously reverse it back onto level ground. Remove the Dipstick and note its reading. It will be some where near Low at this stage. Add more ATF until the level is about halfway between Low and Full Hot. *Note* don't pour any more ATF in yet. Leave the Engine running and check for leaks. If OK then do the tests (below). 


With the Engine running, move the Gear Selector through all gears including Reverse making sure there is a positive engagement  with each Gear and that the Car moves in the correct direction. Drive the Car slowly forward in Drive and then backwards in Reverse. You are checking to see if the Car drags. If it drags the Band is too tight. If the Band is too tight the Pan will have to be removed and the Band an extra turn anti-clockwise applied to the Band Adjustment. If the Car doesn't drag the Band tension is OK, but will have to be checked for Bang Shifts. Driving the Car is the most effective way to heat up the ATF. Be aware that a low ATF Level may cause slipping on cornering if you corner too hard. This will be caused by the ATF Level being slightly low, so take it easy.


Drive the Car locally and at low speed to heat up the ATF.  Check that the Gear Changes are smooth and do not cause a jerk when shifting. Once the Engine is hot do the Final Fluid Level Check.

Final Fluid Level Check:

Note that the Car must be on level ground, the Engine must be hot and idling with the Gear selector in Park and the Handbrake on. It's necessary to perform the Final Fluid Level Check with the Engine hot because the ATF expands with heat. An incorrect Level will exist if the Engine isn't up to temperature. You now want the ATF to be at the Full Hot Level as marked on the Dipstick. Add fluid a little at a time to achieve this if necessary. Remember that  the Car must be on level ground, the Engine must be hot and idling with the Gear Selector in Park and the Handbrake on when the ATF level reads Full Hot.


Overfilling is to be avoided. If the Trimatic has become overfilled, unbolt the Modulator and allow some ATF to run out. A small dowel may fall out. Don't forget to replace the Dowell into the Modulator before refitment. Refit the Modulator and re-check the ATF Level using the Final Fluid Check method above.

Final Road Test:

Recheck the Car with a final Roadtest. If the shifts were erratic on the previous test they may now be smooth due to the correct ATF level. Any erratic Shifts may be caused by the Modulator Vacuum Pipe having been left disconnected or the Pipe being blocked. See the Troubleshooting section for more info.

Ramp Angle:

The angle of the Car Ramps will have an affect on the amount of Oil drained. Steeper Ramps will drain more Oil than shallow Ramps.


Automatic Gearbox Service Tools

383HGBrougham's Shed


ATF is short for Automatic Transmission Fluid. This is the Oil used in Trimatics which has to be changed. Dexron I, II or III is used.


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