Trimatic Faults

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Original submission by T:

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253 Trimatic showing the Filler Neck and where it enters the gearbox. Note that it enters at 90 degrees to the casing. Also shown is the breather (white plastic at the centre of the image), the kickdown connection (plastic and brass centre left) and the Modulator (brass coloured and to the rear of the valve body). The gear selector shaft is next to the Filler Neck immediately to its left. Click to enlargen. Photo by Kangahx.

Faults, Symptoms and Fixes:


Oil Level:

Secure the vehicle from moving by following the steps in Securing the Vehicle. As simple as it sounds, the oil level in a Trimatic is critical.The gearbox oil level should be checked with routine driving and at the first sign of any abnormal behaviour.

Oil Pump Test:

Withdraw the Dipstick when the Engine is stopped. The Oil Level must be way over the Full Hot Mark. Start the Engine, reinstall the Dipstick and take another reading. The Oil Level must have dropped to Full Hot if the Engine is hot, or lower if the Engine is cold. If the Oil Level hasn't dropped, the Oil Pump is not working.

Alternative Oil Pump Test:

Alternatively, loosen one of the Oil Cooler Lines at the Radiator while the Engine is running and test for Pressure . Copious amounts of Oil can emerge so make sure there is Bucket there to catch the Oil. Thanks to HQSS and HQ308Belmont for sharing the idea.

No Oil Pressure:

Without Oil Pressure no Gear can be selected.

No Oil Pressure Causes:

No ATF or the ATF level is low. Failed Oil Pump, stuck Pressure Relief Valve, or failure of any device in the Line Pressure Circuit. Remove and test the Modulator and its Shift Valve.    

A 3.3 Engine from a VC or VH Commodore with an EST Trimatic Gearbox. Note the thickness of the boss on the Bellhousing where the Dipstick support Bracket bolts up. Varying thicknesses here requires different Dipstick tubes to match the Trimatic involved. Also note the Hole in the top of the Bellhousing for the EST Crank Angle Sensor. Click to Enlargen. Photo by SleakVH.
Early Type 6 Cylinder Trimatic. Note the Dipstick top Bracket is bolted to the Bellhousing Boss and that the Boss is thinner than in the image to the left. Click to Enlargen. Photo by VernonV.


Early Type 6 Cylinder Trimatic. Note that the Dipstick enters the Case squarely. Click to Enlargen. Photo by VernonV.


Early Type 6 Cylinder Trimatic. Note that the top two Bolts are much closer together than with the V8 Bellhousing. Click to Enlargen. Photo by VernonV.


Trimatic Governor. The Governor Valves are mounted on the rear of the Governor Housing and held on by 2 bolts. Click to Enlargen. Image by Juls9.
Trimatic Governor. The image shows the large Primary Valve and smaller Secondary Valve. Only the Secondary Valve uses a spring. Without oil pressure the valves normal position is outmost. Oil pressure pushes them inwards and centrifugal force extends them outwards. The balance position determines the road speed oil pressure. Click to Enlargen. Image by Juls9

Servo Cover removed from a neglected Trimatic.  Click to Enlargen. Image by Veight.


Trimatic Kickdown Solenoid.  Click to Enlargen. Image by Deefa.


Trimatic Kickdown Solenoid and Gasket.  Click to Enlargen. Image by Deefa.
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.


The Column Shift Neutral Safety Switch with Reverse Light Switch (far left) Click to Enlargen. Image by One TunnaLova.


Burned 3rd Clutch Plates.  Click to Enlargen. Photo by Twin Turbo HT.


The red Arrow shows the Oil Pressure monitoring Bolt. Remove the Bolt and screw in an Oil Pressure Gauge to measure the Oil Pressure. Photo by Qute. Click to Enlargen.


Turbine Splines on a good 202 Torque-Converter. Photo by T. Click to Enlargen.
Yellow Arrow shows the Turbine Splines on a good 202 Torque-Converter. Photo by T. Click to Enlargen.
Sheared Turbine Splines on a failed WB style Torque-Converter from a 202 Engine. Photo by T. Click to Enlargen.
Electric Kickdown Solenoid. It's retained by bendy tags at the connection end. A rubber O'Ring seals in the Oil . Photo by T. Click to Enlargen.
Electric Kickdown Solenoid. Always bolt this to the Trimatic and never allow it to hang by the Wire or the Wire will break. Photo by T. Click to Enlargen.
The Washer at the top of the Dipstick can break loose from the Dipstick. False readings can be caused by the Dipstick being pushed too far down the Tube. Click to Enlargen. Photo bySamWB .
The Trimatic Dipstick can have its spot welded Washer break away from the Dipstick Rod. As a result the Dipstick can extend too far into the Gearbox and cause the level to read higher than it really is. The result can be slipping clutches due to Oil Starvation. Reweld the Washer to the lowest position or replace the Dipstick. Photo by BIJ. Click to Enlargen.


Many times a Trimatic only needs an oil and filter change and to have the band retensioned.

Cannot Engage Any Gear:

Cannot Engage Any Gear when the Engine is running. Do the Oil Pump Test on this page. If there is Oil Pressure it likely means there is a loss of drive between the Torque Converter and the Input Shaft. The Turbine Splines have sheared off inside the Torque-Converter.  See the accompanying Photos. Symptoms: The Trimatic will show normal Line Pressure because the Oil Pump is turning and making Pressure, but 1st, 2nd, Drive and Reverse cannot be engaged while the Engine is running.  Park will work normally. If the Torque-Converter appears to have failed, replace it and do a normal Service on the Trimatic. Inspect thoroughly for debris inside the Pan, Servo Cover and especially in the Filter. If any debris is found, dissemble and clean the Trimatic.  

Erratic Shifts:

Trimatic gearboxes are vacuum sensitive devices. If their source of vacuum becomes blocked or disconnected then any shifts will become unpredictable and unreliable.
On many occasions Trimatic gearboxes have been needlessly dissembled and rebuilt when the only
problem they were experiencing was a blocked Vacuum Pipe.

Checking the Vacuum Feed:

At the rear of the Trimatic Gearbox on the Driver's side there is a round device with a metal pipe
plugged into it. The device is called the Modulator and the Modulator is responsible for developing
an Oil Pressure that matches the Manifold Vacuum. The Engine has a high vacuum at Idle
and a low vacuum at Full Throttle.
Secure the vehicle from moving by following the steps in Securing the Vehicle.
With the Vehicle secured and the Engine running in Park and the Handbrake fully applied, remove the Metal Pipe that fits into the rear
of the Modulator and confirm that a strong Vacuum is present. If not the source of the trouble will have to be investigated.
The problem is usually Exhaust Gas Recirculation Ash blocking the Pipe's connection to the inlet Manifold. The blockage will need to be cleared and the Pipe re-connected. EFI VK Commodores suffer from blocked vacuum lines caused by the ram air intake being
placed below the front bumper.
EFI VK Vacuum

Checking the Detent (Kick-Down Switch) Operation:

Secure the Vehicle from moving by following the steps in Securing the Vehicle.
The switch is located just above the Accelerator Pedal. With the Engine shut down, the Handbrake on, the Gearlever in Park and the Ignition on, floor the Accelerator. A faint click should be heard from inside the Transmission every time the Accelerator Pedal reaches Full Throttle. If there is no click the Kick-Down Switch will need adjusting. Sometimes the switch can stick in the pressed-in position, causing the Transmission to be reluctant to shift out of Low Gear. If it still won't work check the Fuse or replace the Kickdown Switch as necessary.


If the Oil Level is too high the oil will get into the Gearset and become frothed.
The frothed oil will become pumped in to the system and cause erratic operation including erratic shifts.
Removing the Modulator and letting some oil drain out is the easiest way to return the fluid to its correct level.
See Replacing the Modulator for steps on how to achieve this.

Blocked Oil Filter:

A blocked filter can result in erratic shifts and operational behaviour. Ultimately it will
result in burnt out clutch packs due to the lack of oil available to make them engage properly.

Fluid Loss:

Apart from Oil Leaks, which are covered in another section,
a Trimatic can lose fluid through a faulty Modulator. Occasionally a Modulator will generate a hole in its internal diaphragm. Backfires can cause this.
When this happens, ATF will be drawn into the manifold and burned by the engine.
Consequently a pharmaceutical smell appears when the engine is running. The fluid level
goes down as the engine burns it off.
The fix will involve replacing the Modulator.
See Replacing the Modulator for steps on how to achieve this.

Slow to Engage Reverse:

This is a symptom of a worn out reverse gear clutch pack. A delay of 5 seconds is considered
tolerable. A slight blip on the throttle will pick up the Oil-Pump pressure and reduce the engagement time.
Note that an excessive application of power during a reverse engagement
will accelerate the wear of the reverse clutch pack or possibly even shatter the pack.
Once the clutch pack is destroyed the clutch will run metal to metal which is undesirable.
Repairing a worn reverse clutch pack involves a full rebuild of the Trimatic.

The Engine Will Not Crank:

Trimatics are fitted with a Neutral/Safety Switch. It's the job of this switch to ensure
that the engine will only crank when the gear level is in Park or Neutral.
This switch can wear and need re-adjusting and/or replacing.
The new switch can come with a piece of plastic inserted into it. The strip of plastic prevents the switch from being activated and is there to make installation easier.
Replace the switch while the Gear Lever is in the Neutral position. Adjust the switch's position left or right until the engine cranks reliably.
Now tighten the screws. Activate the Gear Lever through its range. Moving the gear lever thus
breaks the plastic securing tag.
Check the the Neutral/Safety switch permits cranking in Park and Neutral only and that the reversing lights come on only when the car is in Reverse.

The Reverse Lights Don't Come on:

The Reverse Lights are activated by the Neutral/Safety Switch only when the car is in Reverse
and the Ignition is turned On. If the lights don't come on, the fault can be caused by a worn out or badly adjusted Neutral/Safety Switch.
Since the most critical adjustment of this switch is the Neutral and Park positions,
only replacing the switch can remedy any internal wear that prevents the switch from being activated when the gear lever is in Neutral.

Reseating the Torque-Converter:

If the Torque-Converter has been moved forward while the engine is removed it will
most likely have become unengaged.  Engagement of the Torque-Converter is vital since it ensures that the elements inside
it (notably the Turbine and Stator) and the Oil-Pump (outside it) make proper connection.
To re-engage these components the "3 click" method is used.
Remove the Torque-Converter completely from the gearbox to ensure you will feel the 3 clicks.
Refit it Torque-Converter to its shaft.
Rotate the Converter as you push it back into the bellhousing.
With the engagement of each element you will hear a click and the converter will move further
into the housing with ease. When it's all the way back, you're done.

First Gear Judder on Departure:

When driving off from a standing start a Trimatic can judder.
The judder is caused by having the wrong spring in the band servo. A lighter or stronger spring solves the problem.

Trimatic Spring Replacement:

Permalink Submitted by 3 wheel (not verified) on Thu, 01/09/2016 - 11:07.
Trans guru said to me that it's a well known issue for trimatics. after a while the trimatics 'nominal pressure' gradually decreases which usually means needing a softer spring. He said if a trimatic was pulled out for whatever reason they change the spring to a softer one even if it isn't juddering yet.. End od submission by 3 Wheel.

Slipping in Top Gear:

A restricted or blocked Vacuum line to the Modulator will cause very slow shifts especially into top gear.

Changing Up Too Late:

If the Modulator line loses its vacuum and becomes open to the air,
the gearbox will assume the throttle is wide open even when it is not. As a consequence the gearbox will stay in 1st and 2nd as long as it possibly can. Re-connect the vacuum line to fix this fault.

Hanging in Gear:

If the Selector Lever pinch bolt has worked loose, the Gear Lever can indicate the wrong gear has been selected. The Gearbox might be in Second when the Gear Lever says Drive.

Won't Change Out of 1st Gear When in Drive:

The Governor is not producing oil pressure in proportion to the road speed.
It's likely that one of the centrifugal valves is stuck shut or open.
 The Governor can be identified once the rear of the Trimatic has been removed because it has indents in it with which the park pawl engages.
Remove, clean and inspect the Governor and valves. If you find nothing wrong then put the Trimatic back together and take the car to a Trimatic expert. Can also be caused by disconnected Vacuum Source to the Modulator.

Drops Back to 2nd From 3rd and to 1st From 2nd Once Warmed Up:

The Kickdown Solenoid is jammed open, is leaking or has failed causing continuously low Detent Pressure. Can be fixed by removing the Pan and replacing the Solenoid.

Drops Back to 2nd from 3rd Once Warmed Up:

The 2nd - 3rd Shift Valve has become scored and needs burnishing with fine Emery Paper or replacing. Can be repaired without removing the Gearbox from the Car.  The Valve Body may need to be removed to gain access to the Shift Valve.

Won't Upshift to 3rd Gear:

If the 1-2 shift is fine, I think T is on the money, the 2-3 shift valve is likely the problem. Other potential problems like the modulator etc would also affect the 1-2 shift so it seems the cause of your problem is specifically linked to the 2-3 shift. Depending on your skill level this is potentially something you may be able to fix at home. The first thing I would do is remove the pan (sump) from the trans (carefully as it's full of oil) To remove the pan loosen all the bolts half a turn, then remove the row of bolts across the back. Then starting at the back remove a bolt from each side working towards the front of the pan. By the time you get to the front, the back of the pan should have dropped down a little and the oil will be coming out, if it hasn't you may need to carefully lever it to break the seal. Loosen the front bolts a little more until the pan hangs down at the back and wait for it to drain. You'll need a decent size tray to catch all the oil. After you get the pan off you'll see a bowl shaped piece held on by 4 bolts, take that off and it's almost guaranteed you'll find a small piece of plastic sitting in the bottom. This is one half of the dump valve. Now you need to find the other half which has likely jammed the 2-3 shift valve. At this point have a good look at the colour of the trans fluid and take note of any metal or clutch material in the bottom of the pan as it'll give a good indication as to the condition of the trans and whether it's worth repairing, if it looks good and you think you have the skills continue on. This is where it gets a little more involved, you need to remove the valve body, taking careful notice of how it connects to the shift linkage. You need to also remove the separator plate with it(the plate above the valve body) Find yourself a nice clean space on the work bench and layout some clean rag (an old towel would be perfect) This is where my memory is a little vague (it's been 20 years since I worked in a trans shop) You'll need to strip the valve, laying all the valves out carefully on the rag so you can remember where they all go. Keep your eye out for the other half of the dump valve and other foreign materials (e.g. clutch material) As you remove each valve, make sure it doesn't stick in the valve body, if it does clean it up with a little wet and dry or emery cloth. Once you've stripped the valve body and your happy that none of the valves are sticky (and hopefully you've found the other half of your plastic dump valve) Thoroughly clean and dry the valve body. One at a time, clean each valve, lubricate it with a little trans fluid and put it back into the valve body making sure it moves freely. You can now re fit the valve body with a new gasket either side of the separator plate. Make sure the gear shift works correctly to ensure it connected the right way at the valve body. While you're at it adjust the band (see Holdenpedia) then refit the cover, fit a new filter and refit the pan. It's a reasonably involved job but with plenty of patience and care it is possible to do it at home. If you're not confident try finding another trans shop to look at it for you. Hope this helps.

Moves Off In Second When D Selected; Jams When 1st Selected:

The Second Clutch is stuck on. Could be the Clutch itself jammed on or a Shift Valve that controls it. Moves Off In Second When D Selected

A 79 Gemini will probably have the plastic dump valve I mentioned. By grabbing manual low (1st) you've probably dislodged it from the valve but it probably still floating around in the valve body. Usually when the dump valve breaks the transmission will thump on the 1 - 2 change. By "thump" I mean it won't be a smooth shift, it'll be fairly harsh. If that sounds familiar I'd still take it to a trans place as that little piece of plastic will still be rolling around the trans and is likely to cause you more problems. If the trans guy knows his way aroung Trimatics the first thing he'll do is remove the pan, then remove the servo cover (where the band adjustment is located) and chances are he'll find half of the dump valve sitting in the bottom of the servo cover. He'll then need to find the other half, so he'll remove the valve body and he'll disassemble it and try and locate it. When he's finished servicing the valve body, he'll install a new dump valve in the seperator plate, refit the valve body (with new gaskets and a new filter) adjust the band and the problem will be solved. Cheers

Oil Leaks From the Breather:

The Front Plate has excessive wear and is allowing oil to leak through it when the car is in reverse. This can be caused by misalignment of the Bellhousing during installation. The fix is a gearbox rebuild.
A workaround is to avoid using reverse until the engine and gearbox warm up. Once hot, the expansion of the metals involved can reduce the amount of oil blown out the breather. If the Car has been High Towed expect Oil drops from the Breather. This doesn't mean there is a fault with the Trimatic.

The Inlet Manifold Vacuum Source located at the rear of the engine. Click to enlargen. The left most pipe provides a vacuum source to the Heater and Air Vent Controls. Photo by Vernonv
A common problem is this becoming blocked especially on EGR Engines. Causes slow and late upshifts. Often the last thing checked and not discovered until after a rebuild.  Click to enlargen.  Photo by Vernonv
253 V8 Engine. The Photo shows the Vacuum Source that supplies Vacuum to the Modulator on a 253 V8. Pressurewise the tap Source is underneath the Throttle. Photo by Energy4anarchy. Click to enlargen.

Kickdown Solenoid Loose:

This will cause the Trimatic to remain in 1st or 2nd Gear too long.  

"We also had a post from a guy who had a loose Detent Solenoid and had the same problem. The effect is the same as having the Kickdown stuck on." That's a fairly common situation (the solenoid coming loose) years ago when I worked at a trans shop we would always Locktite the solenoid bolts when we serviced Trimatics.  

Oil Only Level Appears On One Side of The Dipstick:

When checking the ATF Level after doing a Service, ATF can appear on the Rear of the Dipstick but not on the Front. The situation will occur if the ATF level is too low and ATF has recently been poured in.  The situation is caused by ATF that is still running down the Filler Neck covering the Rear of the Dipstick only. There is insufficient ATF in the Pan to reach the Dipstick and appear on the Front. Add ATF in stages until the Level is correct as per the Trimatic ATF check method (Handbrake on, Engine Running, Gear Selector in Park, Car on level Ground, ATF Hot, ATF Level to Full Hot as per Dipstick marking).

Front Oil Seal Repeatedly Blows:

Oil Cooler Lines are blocked.

Ground down Locator (left) caused the Trimatic Front Seal to blow out. See the Thread in the Links Section.  Good Locator (right). Photo by Cruisin_doug. Click to Enlargen.

Vibration Above a Certain Speed:

This can be caused by a failed Gearbox Mount. See the image.

Failed Trimatic Gearbox Mount from a 202 powered HJ Holden. Photo by WayneHGOwner. Click to Enlargen.
Failed Oil Pump in TH700. Similar to Trimatic. Caused by mis-alignment of the Pump and Torque Converter Drive during installation. Photo by BobHJWagon. Click to Enlargen.
Failed Oil Pump in TH700. Similar to Trimatic. Caused by mis-alignment of the Pump and Torque Converter Drive during installation. Photo by BobHJWagon. Click to Enlargen.
Typical Gearbox for many Old Holdens. Left failed, right new. Photo by Chopper75. Click to Enlargen.


DaveEH's Troubleshooting Tips:

Having answered a few questions about Trimatics recently, I thought I might start a Trimatic thread to empty my brain before I forget it all, and start a repository that others can add to and fill in any gaps in the 'pedia.
I spent a year at an auto trans specialist in 1995 when every third trans in the door was a Trimatic, so here's what I remember: The cases and gearsets are the same regardless of 6 or V8.
The V8 has a longer input shaft with a rounded end, the 6cyl is shorter with a machined step in the end. V8 converors are bigger.
HG cases have a kickdown cable rather than an electronic solenoid.
Early cases are RHS shifter, later (Commodore, WB floorshift, Torana?) are LHS. V8 and 6cyl have different bellhousings. Later 6cyl have a fully round bellhousing rather than half round. EST VK's have a hole in the top of the bellhousing for the crank sensor. 6cyl and 253 have the same number of plates in the clutch packs, 308 has more clutches and a servo piston and spacer that are smaller in order to fit them into the clutch drum. You can put 308 clutch packs into a 253 or 6cyl trans to give better clamping pressure (less prone to slipping, better towing capacity etc) V8's use a different valve body to the 6cyl though its probably just different tension springs in the shift valve to give V8's an earlier upshift due to more torque.
They are easy to modify with a shift kit - different springs ands a few holes drilled.
A broken dump valve in later trans will give a hard downshift into 1st when slowing down and can cause reverse to lock up if the broken bit of the plastic valve jams in the shift valves and locks a forward gear on. Delayed upshifts often mean a problem with the vacuum supply from the inlet manifold to the vacuum modulator on the trans.
Check and replace the rubber hoses and open a paper clip and its just the right size to clean the narrow vacuum supply hole in the (factory) manifold fitting.Gets blocked with gummy fuel residues. A split vacuum modulator diaphram can cause trans oil to get sucked into the engine and blow smoke. Check this before rebuilding your engine! Smoke smells distinctly like trans fluid. For street use a slight stall in the convertor with a brass internal washer rather than nylon works well. Oil leaks - If it looks like a pan leak, it may be more than that as oil from other leaks will drip off the pan. With the pan off take the modulator off and pull out the retaining pin of the detent valve next to it with side cutters. Lever the detent valve out a bit and replace the o-ring seal. Put a new gasket on the modulator or replace it if trans oil comes out of its vacuum fitting. Another problem area is the selector shaft seal. I've always used the factory tool which works well, others may know how to replace it some other way. You can't really rebuild them at home without the proper tools to to align the oil pump to the bellhousing or replace the clutch piston seals. If I was doing it at home I would take the oil pump/ bellhousing and the clutch packs to a trans shop to use their special tools to align the pump and replace the clutch piston seals. That's all I can think of right now. I'll edit or add more later when I've had a think.
Trimatics are a great transmission for standard or slightly modified engines. Big HP 308's in the hands of boy racers seemded to struggle a bit though recent inprovements in rebuilding and modifying Trimatics may have changed that. Some European cars have Trimatics that are the same except all measurements are metric apparently!
They built over a million of these and I've seen number 1,000,000 a V8 unit at Croydon Park TAFE. I've heard that good parts are rare now so if you find one with good gearsets and pump gears it might be worth hoarding. Feel free to add anything you think of.
DaveEH End of sub,ission by DaveEH.


DaveEH's Troubleshooting Link

Failed Gearbox Mount Thread

Failed TH700 Oil Pump Thread

Front Oil Seal Blowout Thread



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