SMT maintenance

[fawtytoo]

The SMT variant of the MR2 Roadster is becoming scarce in the UK primarily because most mechanics (including Toyota) don't know how to fix or maintain them. So I just wanted to share my experience with mine and what I've done to it in order to keep it functioning properly.

1. Check the fluid level and/or replace it if it hasn't been done. £100 currently from Toyota for a litre which allows for 3 complete fluid changes. The reservoir can be found under the air box.

2. The HPU (Hydraulic Pump Unit) should take no more than 30 seconds to prime. If so, then the pump can be considered as working properly. If it takes longer, you may want to check the fluid reservoir and top up the fluid if necessary. This is the pump that starts when you open the drivers door. Mine took 22 seconds.

3. The GSA (Gear Shift Actuator). Somebody else here might be able to help with more info on this bit.

4. The ECU. This can be reset and re-learnt (re-calibrate). This is normally only done if you replace a part, but I did it on mine anyway given it's 20 years old.

I want to point out that mine has only had the fluid changed and an ECU re-learn but was well worth doing. It went from the occasional clonky gear change, slipping clutch and irregular gear change speeds, to a very smooth consistent gear change every time even when cold.

If anyone has trouble with their SMT, I highly recommend the fluid change and ECU re-learn BEFORE condemning the gearbox entirely. It might be all it needs.

According to howmanyleft.co.uk there are 155 left in the UK as of 2021. They weren't popular in the UK and some have been converted to manual.

[Petrus]

MerryFrankster at Spyderchat offers a kit with all the seals and includes an extensive how to.

[cyclehead]

MerryFrankster at Spyderchat offers a kit with all the seals and includes an extensive how to.

I'm not aware of repair seals from Frank.  But I have seal kits for sale
https://www.spyderchat.com/threads/fs-repair-seal-kits-for-gsa-and-hpu.120921/#post-1733313

[cyclehead]

Excellent summary fawtytoo!   I think your item #1 is the most important for longevity of the system.  I've studied the SMT fluid pretty carefully and concluded that brake fluid is actually better, and cheaper than the expensive Toyota SMT fluid.   
I'll paste my thoughts and reasons in the next post...

[cyclehead]

SMT Fluid discussion

Toyota sells some very expensive, proprietary fluid for the SMT system.   I believe that straight DOT3 or DOT4 brake fluid will provide better results. 

Discussion follows:

Toyota provides zero support, details, data or information about the fluid; and provides misinformation about parts of it:
There is absolutely no maintenance schedule recommended by Toyota, for changing the SMT fluid.  Ever.
The Toyota SMT system maintenance instructions require "depressurizing the system" prior to unscrewing the reservoir cap.   However, the plastic cap has a vent hole that is open to the atmosphere!  Incorrect information from Toyota.

Chemists posting on Spyderchat (among others) have analyzed the magic Toyota SMT fluid and confirmed that it is simply brake fluid, with some additives.  Castor Oil (not castrol motor oil) is the primary additive.  Castor oil is used in some Rolls Royce  and Peugeot braking systems as a lubricant.

The rubber seals in the SMT system are made from EPDM, which is compatible with brake fluid.  Quite a few SMT systems have been destroyed by pouring various oils into the reservoir (hydraulic oil, gear lube, power steering fluid etc).   The rubber (EPDM) seals will swell significantly in the presence of any oils, and will quickly cause leaks and catastrophic failure of the system.  (Usually less than a week.)  The most destructive result is the rupture of the bladder inside the hydraulic accumulator.  Second and third: the orings in the quick-connect joints will swell and obstruct fluid flow, the o-rings on all four solenoids will swell and leak internally upsetting control-fluid pressures to the clutch and shift actuators. (This is based on my first-hand experiences with three destroyed SMT systems)

The SMT system is designed and manufactured by LUK in Germany.  If you look at any of the four solenoids that are used in the system, you will see a black sticker with silver letters that say "Brake fluid".   These stickers are applied by LUK during manufacture of the system.

I have disassembled dozens of HPUs and GSAs in the course of measuring and creating repair seal kits for these units.  I routinely notice there are flakes of crud inside the HPU reservoir - both stuck to the sides and floating in the fluid.   Coincidentally, I have never seen similar contaminants in any automotive braking system (which also use DOT3/4 brake fluid).   Furthermore, I am finding yellow crusty deposits adhered to the aluminum pistons in the GSA actuators.  I have seen these deposits on the o-ring lands.  It is reasonable to suspect that these deposits interfere with the o-rings and seals, and will promote hydraulic leaks.

For reference - MonkeyWrenchRacing has cautions posted on their website:
"*Note* – Use only approved fluid in the SMT system! Some people online have recommended using brake fluid. This will quickly destroy the GSA and HPU ($$$!!!). Use only Toyota OEM SMT fluid."   
My comments:  This statement is simply false.  I have personally used DOT3 brake fluid in my spyder for 6 years now.  In addition my children have three more SMT spyders, all running brake fluid in the reservoir.  None of these four spyder have had any SMT system problems.  I proposed to MonkeyWrenchRacing that perhaps they meant to say "Hydraulic oil" or "Gear lube".

To be thorough, MonkeyWrenchRacing mis-states some other facts:
"GSA leaks:  This is generally from the clutch actuator rod rusting, destroying the seal. The rod and seal cannot be serviced so the GSA must be replaced. At this point there is generally other internal rust from neglecting the fluid changes so the unit is not in good shape overall."

My comments: Again the MonkeyWrenchRacing statement is inaccurate.  There is no clutch actuator rod in the SMT system.  (There is however a clutch actuator cable that is coated with plastic, but it never touches any of the rubber seals.)  The clutch actuator rod's function is served by a hydraulic actuator, that uses a bare aluminum piston, with a rubber (EPDM) seal riding on a hard anodized aluminum rod.  With one caveat - there are no steel parts inside the clutch actuation system, nor the entire GSA that can rust.  The only possible exception is the solenoids, that appear to be made from stainless steel.  I have seen very minor rust on them when I leave them exposed on my workbench for months and months.

I have emailed MonkeyWrenchRacing and confirmed that they do not have any factual information that I have overlooked.

Last thought:  The owners manual hints that accelerated wear will result if you don't use genuine Toyota fluid.  This is plausible if the replacement fluid is simply brake fluid - and the genuine fluid has an added lubricant (like Castor oil).   

I suspect the crud I'm seeing in the reservoirs is likely in 20 year old fluid!   

The decision you must make: which is worse - less lubrication to avoid the formation of crud?  Or more lubrication, and risk crud formation. 

OR...shoot for the best of both worlds:  Use added lubricant to minimize wear, and assume that periodic fluid changes will preclude crud formation? 

If you want to take the "added lubrication" path, the accepted lubricant is castor oil.  (Not castrol motor oil!).  Mix in a ratio of 8% castor oil, to 92% brake fluid. 

Folks have used both DOT3 and DOT4.  I've read that DOT4 has better performance at high heat levels, but worse affinity for water. So I've been using DOT3 brake fluid, without any problems.

[Petrus]

I'm not aware of repair seals from Frank.  But I have seal kits for sale
https://www.spyderchat.com/threads/fs-repair-seal-kits-for-gsa-and-hpu.120921/#post-1733313

Oops, my bad 

[fawtytoo]

@cyclehead Thanks for your feedback. That's some great information there especially knowing that most internal parts are aluminium rather than steel therefore reducing the worry of rust forming. Seeing as the OEM fluid is still available, I'm ok buying it as you get 3 complete changes from it. Should it become difficult to get, perhaps I'd go the brake fluid road.

Is the castor oil the same stuff you can buy in shops? I've read it's supposed to be "propoxylated ethylated" and god knows where you get THAT from.

[Petrus]

Is the castor oil the same stuff you can buy in shops? I've read it's supposed to be "propoxylated ethylated" and god knows where you get THAT from.

This thread reminded me it needs to be refreshed again so ordered DOT3 and castor oil. The latter is ricinus oil which is available through health shops in unadulterated form.





The problem with the OEM stuff is that it is hygroscopic and  thus does not keep well. I would rather replace with fresh DOT3 than with 1 or more years ago opened OEM fluid.