The Getrag F23 Tutorial (by EMC209i/L67)

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The Getrag F23 Tutorial (by EMC209i/L67)

Postby Emc209i » Mon Jun 04, 2012 9:31 pm


This article will familiarize you with the Getrag F23, its strengths and weaknesses, and supply detailed instruction for installing it and the necessary equipment.

The F23
Getrag’s newest iteration of their five speed transaxle is the F23, which has been built from 2000 - 2010. It is of three shaft design, features a self adjusting internal throwout bearing, a synchro'd reverse, a variety of gear ratios to choose from, and most importantly - bellhousing variety; GM metric (60 degree), Opel/Vauxhall/Saab /122 pattern, and Ecotec pattern. The F23 is rated to withstand 230nm of torque (170ft/lb), but is known for its renowned strength in high power circles.

Why you should install the F23
The first and foremost reason this transmission is a viable option is its low mile availability. The F23 using the GM metric pattern is found in 2000-2002 J bodies equipped with the 2200 series engine, which statistically have been driven far less than the 25 year old M282 and HM282 / NVG-T550 of the 80's and 90's. The newer ecotec engines come mated to the F23 in many instances – a bonus for those doing an ecotec swap. The F23's mannerisms are mild, and uncharacteristic of the Getrag we know in our own circle; the M282. Shifting effort is easier, engagement is less "notchy", and the reverse gear will never grind. Servicing the F23 is much easier task than the M282. Having disassembled both, I would prefer to split the case of two F23’s, than a single M282, and I could do two of the former faster. Parts and LSD options are readily available. The power potential the F23 continually handles reliably, an option those of you with high output builds value most. Lastly, the F23 is an easier, cheaper, and better geared, swap than the F40.


GM technical specification on the F23: Released 2006
The Getrag F23 is a three-axis conventional transverse 5-speed manual transaxle with fully synchronized reverse gear. It features compact packaging, broad low-torque applications, and reliable operation.

The F23 has two gearsets on each of three parallel shafts – the input shaft, the output shaft, and the intermediate shaft. This three-shaft (also called three-axis) design results in a very short axial length for better packaging. There are three separate shift fork shafts, which hold three shift forks to activate the synchronizer rings for the two gearsets on each of the three gear shafts. The shift forks are activated by a cable system. The clutch release bearing is operated by a concentric slave cylinder that surrounds the input shaft in the clutch housing. A concentric slave cylinder allows more linear clutch feel than an external lever-actuated clutch and release bearing. The input shaft carries the 3rd and 4th gear synchronizer, the intermediate shaft carries the 1st and 2nd gear synchronizer, and the output shaft carries the 5th and reverse gear synchronizer. The aluminum case contains a conventional final drive gearset.

There are sintered bronze double-cone blocker rings on the synchronizers for 1st and 2nd gears, while 3rd and 4th gears use carbon fiber blocker rings, and 5th and Reverse gears use molybdenum on their synchronizers. Carbon and molybdenum are extremely durable friction surfaces that remain stable even under extreme heat.

2010 Getrag F23 (M86): 5-Speed Transaxle for Small FWD Car and Truck Applications
• 3.63 Final Drive Ratio for Chevrolet Cobalt offers exceptional fuel-economy.
• 3.84 Final Drive Ratio for Chevrolet Cobalt offers sportier vehicle performance.
• 3.95 Final Drive Ratio exclusively offered in Chevrolet HHR.

• The F23 uses DEXRON VI ATF and is filled for life. No fluid changes are required for normal duty cycles.
• The F23’s clutch is actuated hydraulically. This allows the clutch system to automatically compensate for wear, so no clutch adjustments are necessary.

The Getrag F23 is a conventional three-shaft (three-axis) transverse five-speed manual transaxle with a fully synchronized reverse gear. It features compact packaging, broad low-torque capabilities, and reliable operation. 1st and 2nd gears are located on the intermediate shaft, 3rd and 4th gear are located on the input shaft, and 5th and reverse gear are located on the output shaft. 1st and 2nd gear have double-cone synchronizers while 3rd, 4th, 5th, and reverse have single-cone synchronizers. The intermediate rings in 1st and 2nd and the blocker rings in 3rd, 4th, and reverse are all lined with carbon friction material. The blocker ring in 5th gear is molybdenum coated. Carbon and molybdenum are extremely durable friction surfaces that remain stable even under extreme heat. The F23’s gear sets are actuated with a remote shifter that is connected to its internal shift system via shift cables. Its output shaft is mated to an open differential. The F23’s clutch has a smooth, linear feel because its release bearing is operated by a concentric slave cylinder. Getrag builds the F23 transaxle in Bari, Italy for both European and North American applications.

Bellhousings The Getrag F23 is constructed out of two aluminum case halves. One half has the bellhousing pattern and houses the flywheel, and the other half houses the gears. There are four bellhousing case sides in existence – 60 Degree, Ecotec, Opel, Saturn Vue (MG3). It is important to understand that each of these bellhousings is different from the other; mounting points, external case design, also the Opel + Vue have different shifter linkages. But it is my understanding that all of these case halves are interchangeable – IE. An Ecotec half could be matched to a 60degree half, if desired. All of the internals are 100% compatible with any case.


Flywheel The Getrag F23’s input shaft is the same spline as the older Getrag, albeit minutely shorter. Because of this, the flywheel type and contact surface may remain the same, with a distance between the flywheel face surface and engine bellhousing surface of .820”. The transmission can be used just like any other Fiero transmission. The original (correctly balanced) flywheel can be used for the Duke or 60 degree engines, the machined Fbody flywheel is retained for 3800 swaps, swaps would use whatever flywheel is normally used, and the Ecotec flywheel can of course remain in place when using an Ecotec. The one known exception is when the V8 adapter plate is used, such as with the 4.3, SBC, and LS series. The problem is double faceted. The first problem; the distance between the flywheel contact surface and the adapter plate bellhousing surface is now shorter; .600”. A spacer will be needed from SPEC to shim the HTOB to the clutch surface so that the bearing does not overextend. The spacer I used from SPEC was .270". I've drawn the illustration below for the visual learners out there.


Here is a picture of the spacer installed on the throwout bearing:


Secondly, the Centerforce flywheel that has been supplied by Archie for the SBC swaps is too large, and will need to be modified in order to clear the differential housing protrusion on the bellhousing. As many of you know the Centerforce flywheel is very deep and very wide, and because of this and the adapter plate, the ring gear rides on the outside of the bellhousing, very close to the surface. This wasn't a problem with the Fiero transmissions, because the surface of the bellhousing was flat, and there wasn't a raised area for the differential. With the F23, the differential housing and axle seal housing are raised, and get in the way of the ring gear.

Here is the difference between transmissions:


In the picture below, the transmission is not and cannot be completely seated because of this interference. It is at least, if not more, a half inch from full seat.


There simply is no way to remove enough material from the transmission housing to clearance this flywheel, without breaking through or severely weakening the case. The Centerforce flywheel uses a 153 tooth ring gear. I decided to take the opportunity to remove useless rotational mass, and decrease moment of inertia, by having the flywheel re-machined for a smaller ring gear. After a drawn out conversation with FieroGuru (many thanks), I had my alternatives.

Teeth - O.D. - Application
153: --- 12.837" --- Centerforce
148: --- 12.400" --- 91 Camaro
142: --- 11.910" --- 84'-88' Fiero

After doing the math, the Fiero ring gear was the only size which would fit. This suited me, I wanted to remove as much weight as possible. Aside from the ring landing, the face of the Centerforce flywheel also has a great deal of unused real estate. So I measured the pressure plate and drew up a schematic that I could hand my machinist.

This is that schematic:

The ring landing is .020" larger than the ID of the ring gear for a press fit. The ring gear I used is part number FRG-142W, and cost $20.00. After the flywheel was machined and the ring gear installed, I had the machinist angular inch-oz rebalance the wheel to zero - this balance is not the same for all engines, be sure you have the correct balance.

The flywheel will be noticeably lighter when returned, and will be tailored for a perfect fit. Here is the clearance once installed after machining (note: I took a very small amount away from the diff. housing, which wasn't required).


The starter will now need to be adjusted to reach the flywheel. I had the aluminum mounting block slotted, rotated the starter towards the flywheel, and shimmed to the correct position.


I also built a compact copper extension for the oil adapter for additional clearance when the starter was rotated. I found the supplies to build it at Lowes Hardware.


I might as well mention something else here while I'm at it. There will be a small amount of grinding required only for the SBC. One of the starter mount bolts gets in the way at the front side of the engine. The housing can very safely be clearanced to make room.


And again at the rear, a small amount of grinding is required to clearance the corner of the SBC.


Starter Aside from the SBC starter (covered above), all other engines can use the same starter as if the standard Getrag, Muncie, or Isuzu were used. This of course excludes the LS4.

Clutch Any clutch can be used with the correct flywheel, however it is important to keep an eye on pressure plate height because the differential housing extends into the bellhousing interior, reducing headroom. Some clutches have reported to scrub. This is a non issue with engines using an adaptor plate, because of the extended clearance.

List of known working clutches & pressure plates (engine installed on):
[*]SPEC Stage 3+, and Superclamp flywheel (3800).
[*]Clutchnet 6 puck sprung hub, and a 2x "red" pressure plate (SBC - .270" HTOB shim).
-- I will update this list as clutches & pressure plates with working clearance are discovered.

Speed Sensor The Getrag F23 uses the newer 24,000 ppm magnetic hall effect sensor, which can be found in other newer GM four cylinder transmissions. To correctly configure this input for the Fiero's 4000 ppm speedometer, a PCM which can filter the 24,000 ppm signal must be used to interface the signal along with the infamous conversion circuit. If such equipment is not available per application - say a carbed engine, the Dakota Digital SGI-5 box can be used to control the speedometer.

An example using the 3800 and its OBDII computer:

Installing the Dakota SGI-5:


We will need four wires to correctly plug in the SGI-5; switched power, ground, Yellow VSS from sensor, Yellow VSS to speedometer. The yellow wire is connected to the C203 at pin "G". I recommend splicing into the yellow VSS wire on the cabin side of the C203 connector, here:


Switched power goes to the first input, ground goes to the second, the VSS input from the transmission goes to "input", and the feed to the speedometer should be connected to "OUT 3". The four toggle switches should be "down"


I will quote forum member Trinten's directions for configuring the box:
Originally posted by Trinten in "Trinten's 'MMTS' build."
First thing I did was use one of the "quick presets" to get it closer to where it needed to be -- I used the formula in the directions to find that my output signal had to be .33. One of the quick presets is for .5. So to do this, with Key off, push pin three to "On" (up). While holding down both the up and down buttons, turn key to On.

Did that, confirmed that I was in the ballpark and that it took. So shut the car down, key off, and put it in "Fine Tune" mode. To do this, with key off, hold the "down" button, turn key to on, that puts it in the right setting. I then got on the highway and up to 2500 RPM (my 70 MPH point) and held the "down" button again, and the speedometer gradually dropped to the right speed.

Clutch Hydraulics The HTOB can easily be adapted to the stock Fiero line using Roger Thelin's adapter. Roger's website. The adapter will connect directly to the Fiero's braided flex section on the clutch hydraulic line. I couldn't believe how affordable the adapter was from Mr. Thelin.


Mounts How you mount your transmission will depend on which bellhousing you have.

The Ecotec bellhousing is very straight forward, and again, Thelin offers a plug and play 1/8" stamped steel set of brackets that use the stock Fiero's transmission mounts. These should work very well for the Ecotec.


60 Degree:
The 60 degree bellhousing is not as accommodating as the Ecotec. The front anchor points for the mounts on the Ecotec are not found on the 60 degree bellhouses. The only mount provision is underneath the transmission at the end.


The rear anchor points are still there, but the holes are not tapped, as seen here:


Rear Mount:

The first thing to be done is to drill the holes for the rear mount with an 8.5mm bit, and tap each hole with a 10x1.5 mm tap. At this point, Thelin's rear mount for the Ecotec will work. However, because I was working with a heavy, high torque engine, that needed to be solid mounted, I built my own out of quarter inch steel. Here is the rear mount I built, which will see compression loads as the drivetrain tries to rotate over the axle due to driveline torque about the differential:


Front Mount: I did not like the location on the cradle that aligns with the mount point at the end of the 60* case (it is directly over the control arm, and there isn't much room), so I used the bellhousing as a mount point. Again I built the mount out of quarter inch steel, hoping to stay well within the elasticity limit. This mount will see both compression and tension axial loads as the drivetrain tries to rotate over the axle and return.


Shifter Cables The F23 is designed for FWD cars, and subsequently, the cables are coming to the transmission from the wrong direction per our application. In the Fiero, there are currently three solutions.

- Roger Thelin sells a kit which will rotate the shaft into an orientation much like that of the Isuzu, so that the cables will interface from the firewall. This requires the shifter assembly be removed and taken apart to install the new shaft. I small triangular piece is substituted for the up down operational leverage of the shaft. A cable mount will either need to be made or ordered from Thelin. I'm not sure which cables are ideal for this setup.

- Have cables made that are long enough to span around the engine and mount at the back of the transmission. The cables would need to be two - three times longer than the longest Getrag cable. Additional length increases cable resistance. Not the best solution.

- Use the stock setup with a linkage modification, a mount I designed, one stock Getrag select cable, and a custom F23 cable I drew up and had manufactured by the company who makes cables for The Fiero Store. [/list]


The red arrow is pointing to a small section of armature that was welded on, and a ball linkage from the four speed Muncie was used at the end.

Below is the schematic for the bracket. It should be built out of 1/8" steel in order to correctly clip the shifter cables in. The holes for the cables were made with a 1" hole saw. Two studs can be used to fasten the bracket to the shifter housing.


Now the stock Getrag select cable, and the cable I had made, can easily be secured into place using the original Fiero C clips.


Let me talk a little bit about why I had a cable manufactured. Some have attempted to install the F23 (and F40) using two Getrag select cables. The transmission side of the cable is perfect; however, two select cables will not connect to the shifter mechanism correctly. Specifically, the Getrag select cable cannot be connected in place of the shift cable at the shifter, it doesn't have the range. Some have remedied this by cutting the cable and threading on a longer end. FieroGuru tackled this by chopping and rewelding the shifter plate for his F40. Because I was converting a car that came with the M19 four speed, I was going to need to order both cables anyway. So I decided to have a cable custom made for this swap, to make life easier for everyone.

I drew up this, a modified version of the Getrag Shift cable, with the correct end links and a much greater range of motion than the select cable:

I had the cable made, and have since called in several revisions. The cable is now 12.5 inches longer than the original Getrag shift cable, so it can be routed around the stock airbox for those of you who may be using this transmission with the stock engines, or a swap with the stock airbox. The cable neatly contours the firewall. I also bought a stock Getrag Select cable from the same company. Both are adjustable, so I was able to dial the shift in range.

I set up a merchant account with the company, and can have the cables drop shipped to you. The modified cable will cost $110.00 with free shipping. I can also supply the select cable they sell for $100 ($10 off TFS price, free shipping), should anyone want one that's adjustable or can't find a used cable. I will only offer the select cable to those who are also buying the modified cable - This is only for the community, and only for those installing the F23 - I'm not in the business of undercutting TFS. If anyone wants to put together a group buy, I can of course offer them cheaper.

Reverse Light The Getrag F23 uses a transmission mounted NO switch much like that of the Getrag M282 and Isuzu MT2. It is wired in the same fashion to the c500, C1 and E1.

Axles The Getrag F23's differential is designed for the same axle spline count as the Fiero’s. Stock axles can be used.


Service Bulletin: 02-07-29-001

A very small percentage of the older getrags have developed a rattle on the 4/5 gear assembly shaft. There was a technical service bulletin to overfill the the transmission with Saturn's equivelent manual transmission fluid to suppress the noise. Here's a highlight of the bulletin:


Some people swear that using the thicker Synchromesh quells the problem, so it really doesn't matter which you end up using - shift effort may change.[/HIDE]

Limited Slip Differential

There are two name brand units offered for LSD; OBX, and Quaife. I installed the Quaife differential inside the F23 that was installed behind the SBC.



Pictures of F23 Reassembly

Special Thanks

Trinten - For allowing me to document the transmission swap I performed while his car was at my shop, the complimentary meals, and his professionalism.

FieroGuru - For all of the helpful information he is always willing to give, for fielding my questions, and double checking my work when I needed it.

All of the pictures, sketches, and diagrams are my own (save for those I labeled Thelin). This article is 3500+ words, and took over 20 hours of my time to write, not to mention the hours I spent documenting and coming up with the designs I've shared. If the article was helpful, and we ever meet at a gathering, I like beer.

Best Regards,

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Re: The Getrag F23 Tutorial (by EMC209i/L67)

Postby Trinten » Mon Jun 04, 2012 9:44 pm

There is also some great information on an alternative way to do some/one of the transmission mounts, as well as info on measuring your HTOB to see what kind of spacer you'll need (if one at all) in this thread. It's covering how one guy is doing the F23 with the 3800.
1986 Pontiac Fiero GT, 355 cubic inch small block Chevy putting down 371 HP and 381 ft/lbs torque at the wheels, with more to come!
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