Jacks Transmissions is a company which employs people with not only great talent, but with the engineering mentality to handle complex repairs.  We believe that a clean work environment and smart well paid employees give our customers the highest quality products on the market today.  This article will discuss the entire process, from start to finish, the rebuild of your GR6 GT-R trans.

After receiving the unit, we tear it down completely for inspection and cleaning.  The GR6 trans is very messy and allows particles to collect everywhere.  Our state-of-the-art cleaning equipment is essential to provide the level of quality our customers deserve to assure all parts are truly clean.  The unit uses 2 filters inside to try to stay clean, so assuring all is flushed and cleaned properly is very important for a long and trouble free service life of your trans.

Please click on any of the pictures below to see a full-sized version. You can also click on any links to read that article attached as well.


First, we remove the oil pan, sump filter, valve body and front cover:

1b1 1b2 1b3 1b4

Inside the front cover we have the oil pump assembly, clutch assembly and ETS (FWD,4wd) unit.  They are all torn down for inspection and cleaning:

<-Oil Pump Assembly->1b5 1b6

1b7<-Clutch Basket Assembly->1b8

1b9<-ETS (FWD) -> 1b10

Next is the removal of the rear diff assembly:


We are now able press all gears from the shafts, remove the oil squirters, remove sensors, remove the detents, and wash the rest of the parts.  Our pullers and multiple press assemblies are designed to remove the gears without chipping teeth or damaging any of the surrounding parts:

Output end of gear clusters:


Removing gears with special puller designed to hold proper without chipping teeth:


Gear cluster removed and ready for wash and inspection:


Main cluster assembly ready to be installed on the press for gear removal:


All parts are run through our parts washer first to get most of the junk off.  We then run the parts in our ultrasonic washer to loosen up particles we can't reach and finally blow any remaining debris out with our pulse jet.


Now that all parts are exceptionally clean, we can get a good look at what condition the parts are in and set them up on our clean assembly bench:

1b16 1b17


Inspection of all synchros, gears, engagement teeth, needle bearings, sleeves, detent balls, and bearings is critical at this point to assure a trouble free trans.  We check all synchro assemblies for proper contact and timing.  Check out THIS article about those details:


This is where experience counts!  The picture below is the final drive gear to the rear diff.  In most cases, they get a little wiped out and this is normal.  How much wear is normal and how much requires replacement?  After cleaned and inspected, we will make that determination and contact the customer if it needs to be replaced.  This gear is fine and would be happy in a 1000ft/lb torque environment all day long:


To make the GR6 reliable, we perform several modifications as standard procedure during the rebuild process.  The first to be modified and assembled are the gear clusters.  With our rebuilds including the 'Jacks Trans Spec' shaft retaining clip upgrades, we take the shafts to our lathe and modify the retaining ring grooves proper to accept a thicker and more robust heavy duty retaining ring.  The small and thin factory retaining rings are known to pop off and fail, causing catastrophic failure of the unit.  Our retaining rings are good up to 16,000 pounds of thrust!  This will allow the retaining clips to work like they should and never have a failure.  We like performing our own retainer upgrade as we believe it to be superior and more reliable than gear locks.  It's a lot more work, but worth it to have the piece of mind that it's done properly.  Details about the process HERE

This build is receiving our own unique 1st gear and shaft upgrade which requires the tear-down and assembly of the gear clusters.  Pictures below of the clusters coming together:

1b20 1b21 1b22

Jacks Trans input shaft in its new home:

1b23 1b24

Both clusters meshed together to be pressed into case:


Shift forks and rails installed:

1b26 1b27

Oil control doors checked and installed:


Reverse gear idler installed:


Gear oil squirters installed:


Note in the pictures below how the squirters need to be oriented to point straight at the gear teeth for proper lubrication.  In the second picture, you can see some of the tiny pin holes which will feed parts their oil.  This is one of the reasons why our cleaning equipment is so important for the GR6! The gear-set sit above the oil sump, so the gears do not receive any lubrication other than from the squirters.  If a squirter is clogged or dirty, a gear can fail in very short time.

1b31 1b32


Below are the gear clusters with Jacks Trans 1st gear and input shaft upgrade, Jacks Trans spec retainer upgrade, forks, squirters, doors and case all assembled and ready to go!


Now it's time to install this cluster assembly in the main case:

1b35 1b36

Note how clean the case is below:

1b37 1b38 1b391b40 1b41 

Everything coming together perfectly:

1b42 1b43

Install of detent ball assemblies:

1b44 1b45

Install of gear sensors:


Assembly of the forward final drive gears and sensor:

1b48 1b48 1b49 

The forward drive gear is known to have retaining clip failures.  The OEM clip can start to pull away from the splines which will damage them and allow them to break.  After enough splines break off, the gear will wander forward and begin to cause damage to many oil pump and clutch components in the front housing.   This is where our 'Jacks Trans Spec' retaining clip prevents this from ever happening to anyone:



Next we will focus on the ETS (AWD clutch), known to fail in any application at any time.  Tech article about the ETS can be found HERE.  It's a good read and a must for any GT-R owner!  We check and modify the unit in ALL of our rebuilds.  Drag packages get a completely rebuilt ETS unit as part of the deal!

1b51 1b52


Next we work on the clutch assembly.  We build our own 14, 16 and 18 plate clutches in-house.  We are able to machine the housings and fit each clutch into the carrier perfectly with the thickest steel plates possible.  This allows for a clutch which is very durable, can withstand a lot of heat, and will live a very long time. The clutches are well balanced and will shift faster and cleaner with no noise.  Perfect for the track, yet will behave very much like a factory clutch on the street for your trip back home!

We laser weld the clutch baskets so you will never have a break at the weld, and we set up the clutches to work perfectly via the correct clearances for the application. 

Please note we offer billet baskets if you are not comfortable with the laser welded baskets.  This option is only another $800 per basket (trans takes 2).  This is near half the price of any other basket on the market.

 1b53 1b54

Front cover is then installed and torqued down.


A clean and healthy main valve body is important for proper operation and long life.  The valve body is the reason why shift forks break and synchro sleeves are damaged.  We tear the valve body down, clean all 7 filters inside, check and clean all solenoids and clean the shifting pistons.  On top of all this, we also modify the shifting pistons so they will not damage the forks or sleeves.  The shifting piston is what moves the forks and engages the synchros and gear.  The problem is the shifting piston tries to force the fork and sleeve too far as it has no internal stop.  In time, the forks and sleeves will fatigue and break.  We modify the pistons with a stop so it will not put unneeded pressure on the parts.  This works very well and completely eliminates the possibility of broken forks or sleeves for the life of the vehicle!  This added effort solves 2 of the biggest issues associated with the trans and we perform this work to ALL builds.

1b55  1b55

If that wasn't enough, the piston has another issue with wear.  If they wear at the corner circled below it can cause either an error code, or if you are very unlucky, the piston can kill the shift fork and/or synchro sleeve causing thousands of dollars in damage.  We install a TSB clip update to the pistons to avoid this problem. Once this update is installed, the issue will never be a problem for the life of the vehicle.


We tear down and clean the clutch valve body.  There are 2 filters inside which are known to clog and cause clutch pressure issues.  In fact, we have seen units with only 2k miles and with at least 1 filter nearly completely clogged.  We clean these as standard procedure in all builds.  Picture below of a clogged filter on the LEFT and clean filter on the RIGHT:


The pick-up sump filter is also flushed and cleaned properly with our ultrasonic and pulse wash, and installed.



Unit complete and ready to either be installed at our location or shipped back to customer!  We provide a number of shipping options to make things very easy!


GTR 600 Complete Rebuild Service 

Have any questions or comments?  Please feel free to EMAIL us at any time!  We would love to hear from you!

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3920 North Weber Street Colorado Springs, CO, 80907

Hours: Mon-Fri 8:30AM-7PM MT