During my recent clutch replacement job, I decided to replace my transmission's detent compression springs and locking pins. My transmission had 174,668 miles on it at the time of replacement, so the hardware was likely original and needed refreshing. All hardware removed was still functional and intact. This is not always the case, as the compression springs can break over time. After replacing all detent springs and pins, I can confirm that gear selection feels more precise and solid. Given that the information I researched and used was scattered, I figured this thread might help those considering tackling the job or wanting to learn more. Much thanks to George Hill for the advice and tidbits he provided in another thread. I was able to source and order all parts for this DIY from FCP Euro.
The purpose of the detent compression springs in the Getrag 420G transmission is to create a positive, crisp shifting feel and to prevent the transmission from accidentally popping out of gear. The detent system works through spring-loaded pins or balls that engage with notches machined into the transmission's shift selector rods. How the system works:
Replacing the transmission's detent compression springs, pins, and other hardware can restore a positive shift feel. Over time, the factory detent compression springs can lose their tension, or the pins and sleeves can wear, leading to:
List of resources I referenced for this DIY:
This is the RealOEM diagram and parts list for reference:
Since I was replacing the clutch, I removed the transmission from the car. This provided ample space to access all the detent compression springs and locking pins. I highly recommend this for ease of access, although I did read of others replacing these parts with the transmission still installed.
The detent compression springs and locking pins (sleeves) at the rear and right side (if looking from the rear) of the transmission have a metal retention cap held secure by two 10mm bolts. This is #17 if referencing the RealOEM diagram. Remove these bolts to access the compression springs. Use a small magnet to remove the detent compression springs and locking pins from holes 1, 3, and 5, leaving the larger pins in holes 2 and 4 (do not remove these pins). Replace the three detent compression springs and locking pins. A small amount of gear oil or similar lubricant is recommended on the parts before inserting. Install the new retention cap, 10mm bolts, and washers. Tighten down in an alternating pattern until snug. Torque to 10 Nm.
The detent compression spring and ball for parts #14, #15, and #16 in the RealOEM diagram are located at the rear and left side (if looking from the rear) of the transmission. The #16 locking device requires a 19mm socket to remove. Use a small magnet as necessary to remove the detent compression spring and ball from the slot. Replace them with the new detent compression spring and ball. A small amount of gear oil or similar lubricant is recommended on the parts before inserting. Add thread sealant to the locking device threads before replacing. Tighten until hand-tight (snug). Other DIYers suggest a torque value of 10 Nm.
The detent compression spring, thrust pin, and locking pin for parts #8, #9, and #10 in the RealOEM diagram are located behind the gear position switch (GPS). Before complete removal, the GPS cable connector needs to be unclipped and removed from its bracket; otherwise, the unscrewing action of the GPS will bind the cable and potentially damage it. A 22mm wrench is needed to remove the GPS from the transmission. Once removed, use a small magnet to retrieve the detent compression spring, thrust pin, and locking pin. Note the orientation of the locking pin when replacing. The roller needs to be in the vertical position (see picture for reference). A small amount of gear oil or similar lubricant is recommended on the parts before inserting. The assembly should slide into position without resistance. Add thread sealant to the GPS threads before replacing. Tighten until hand-tight (snug). Other DIYers suggest a torque value of 10 Nm.
The last two detents are on the left side of the transmission and just above the slave cylinder position, if looking from the rear. The upper detent compression spring and locking pin are for the 5th gear. The detent compression spring and locking pin are secured behind a coated metal retainer cap. The easiest way to remove the cap is to gently tap a screwdriver into it until it is deformed and partially collapsed (see the pictures below). The snap ring can be removed with snap ring pliers. Otherwise, the snap ring can be removed by deforming as well. Replace with the new detent compression spring and locking pin. Note that the slanted portion of the detent locking pin faces downward. A small amount of gear oil or similar lubricant is recommended on the parts before inserting. The detent locking pin slides in effortlessly if in the correct orientation. Install a new retainer cap by using a socket slightly smaller than the inner diameter of the snap ring. While pushing the retainer cap down with the socket, install a new snap ring into the slot and release once the snap ring expands into the slot to lock everything in place.
The lower detent compression spring and locking pin are for the reverse gear. A word of caution: The reverse detent compression spring has a lot of resistance and may pop out given the compressive force it's under. The detent compression spring and locking pin are secured behind a coated metal retainer cap. The easiest way to remove the cap is to gently tap a screwdriver into it until it is deformed and partially collapsed (see the pictures below). The snap ring can be removed with snap ring pliers. Otherwise, the snap ring can be removed by deforming as well. Replace with the new detent compression spring and locking pin. Note that the slanted portion of the detent locking pin faces upward. A small amount of gear oil or similar lubricant is recommended on the parts before inserting. The detent locking pin slides in effortlessly if in the correct orientation. Install a new retainer cap by using a socket slightly smaller than the inner diameter of the snap ring. While pushing the retainer cap down with the socket, install a new snap ring into the slot and release once the snap ring expands into the slot to lock everything in place.
The purpose of the detent compression springs in the Getrag 420G transmission is to create a positive, crisp shifting feel and to prevent the transmission from accidentally popping out of gear. The detent system works through spring-loaded pins or balls that engage with notches machined into the transmission's shift selector rods. How the system works:
- Holds the gear: When a gear is selected, the detent compression springs push a pin or ball into a notch on the corresponding shift rod. This spring-loaded pressure holds the shift rod firmly in place, preventing the gear from disengaging on its own.
- Provides driver feedback: As you move the shifter, you must overcome the resistance of the detent compression springs. This produces a distinct "click" sound and notched feel when a gear is engaged, giving the driver a clear, tactile confirmation of a successful shift.
- Prevents simultaneous gear selection: The detent system also includes interlock mechanisms that prevent two gears from being selected simultaneously, protecting the transmission from damage.
Replacing the transmission's detent compression springs, pins, and other hardware can restore a positive shift feel. Over time, the factory detent compression springs can lose their tension, or the pins and sleeves can wear, leading to:
- Vague shifting: The shifter can feel loose and less precise, making it more difficult to find the correct gear.
- Popping out of gear: A weak detent compression spring may not be able to hold the gear properly, especially under load, causing the transmission to pop into neutral.
List of resources I referenced for this DIY:
- Getrag 420G secrets unveiled video: https://youtu.be/7iW1ECcfcm4?si=BOgYV4sehb62lr5Y
- Getrag 420G detent repair video: https://youtu.be/oDnoNxf_h2U?si=TFFT_JIfMWBaWtKg
- Getrag 420G compression springs thread: https://nam3forum.com/forums/forum/m...ession-springs
- Getrag 420G detent compression springs repair thread: https://nam3forum.com/forums/forum/m...nt-pins-repair
- Getrag 420G detent fastner tightening torque specs: https://nam3forum.com/forums/forum/m...ng-torque-spec
- Getrag 420G hard to get into reverse thread: https://forums.m3cutters.co.uk/threa...solved.250562/
- Getrag 420G shift pin replacement thread: https://www.m5board.com/threads/shif...t-info.491089/
- What else to consider when replacing clutch thread: https://nam3forum.com/forums/forum/m...i-do-my-clutch
- Getrag 420G detents explained: https://www.bimmerforums.com/forum/s...g-detents-work
- RealOEM parts list: https://www.realoem.com/bmw/enUS/sho...diagId=23_0887
This is the RealOEM diagram and parts list for reference:
Since I was replacing the clutch, I removed the transmission from the car. This provided ample space to access all the detent compression springs and locking pins. I highly recommend this for ease of access, although I did read of others replacing these parts with the transmission still installed.
The detent compression springs and locking pins (sleeves) at the rear and right side (if looking from the rear) of the transmission have a metal retention cap held secure by two 10mm bolts. This is #17 if referencing the RealOEM diagram. Remove these bolts to access the compression springs. Use a small magnet to remove the detent compression springs and locking pins from holes 1, 3, and 5, leaving the larger pins in holes 2 and 4 (do not remove these pins). Replace the three detent compression springs and locking pins. A small amount of gear oil or similar lubricant is recommended on the parts before inserting. Install the new retention cap, 10mm bolts, and washers. Tighten down in an alternating pattern until snug. Torque to 10 Nm.
The detent compression spring and ball for parts #14, #15, and #16 in the RealOEM diagram are located at the rear and left side (if looking from the rear) of the transmission. The #16 locking device requires a 19mm socket to remove. Use a small magnet as necessary to remove the detent compression spring and ball from the slot. Replace them with the new detent compression spring and ball. A small amount of gear oil or similar lubricant is recommended on the parts before inserting. Add thread sealant to the locking device threads before replacing. Tighten until hand-tight (snug). Other DIYers suggest a torque value of 10 Nm.
The detent compression spring, thrust pin, and locking pin for parts #8, #9, and #10 in the RealOEM diagram are located behind the gear position switch (GPS). Before complete removal, the GPS cable connector needs to be unclipped and removed from its bracket; otherwise, the unscrewing action of the GPS will bind the cable and potentially damage it. A 22mm wrench is needed to remove the GPS from the transmission. Once removed, use a small magnet to retrieve the detent compression spring, thrust pin, and locking pin. Note the orientation of the locking pin when replacing. The roller needs to be in the vertical position (see picture for reference). A small amount of gear oil or similar lubricant is recommended on the parts before inserting. The assembly should slide into position without resistance. Add thread sealant to the GPS threads before replacing. Tighten until hand-tight (snug). Other DIYers suggest a torque value of 10 Nm.
The last two detents are on the left side of the transmission and just above the slave cylinder position, if looking from the rear. The upper detent compression spring and locking pin are for the 5th gear. The detent compression spring and locking pin are secured behind a coated metal retainer cap. The easiest way to remove the cap is to gently tap a screwdriver into it until it is deformed and partially collapsed (see the pictures below). The snap ring can be removed with snap ring pliers. Otherwise, the snap ring can be removed by deforming as well. Replace with the new detent compression spring and locking pin. Note that the slanted portion of the detent locking pin faces downward. A small amount of gear oil or similar lubricant is recommended on the parts before inserting. The detent locking pin slides in effortlessly if in the correct orientation. Install a new retainer cap by using a socket slightly smaller than the inner diameter of the snap ring. While pushing the retainer cap down with the socket, install a new snap ring into the slot and release once the snap ring expands into the slot to lock everything in place.
The lower detent compression spring and locking pin are for the reverse gear. A word of caution: The reverse detent compression spring has a lot of resistance and may pop out given the compressive force it's under. The detent compression spring and locking pin are secured behind a coated metal retainer cap. The easiest way to remove the cap is to gently tap a screwdriver into it until it is deformed and partially collapsed (see the pictures below). The snap ring can be removed with snap ring pliers. Otherwise, the snap ring can be removed by deforming as well. Replace with the new detent compression spring and locking pin. Note that the slanted portion of the detent locking pin faces upward. A small amount of gear oil or similar lubricant is recommended on the parts before inserting. The detent locking pin slides in effortlessly if in the correct orientation. Install a new retainer cap by using a socket slightly smaller than the inner diameter of the snap ring. While pushing the retainer cap down with the socket, install a new snap ring into the slot and release once the snap ring expands into the slot to lock everything in place.
Attached Files
Comment