The RB25DET had two different versions of manual Gearbox. First was the push type 5 speed manual found in the R33, second was the pull type 5 speed manual found in the R34. Both have similar internals however it is rumored that the R34 variant has stronger synchros than it's predecessor. Other than that, the main difference between the two was the clutch engagement type. The R33 is push type and the R34 is pull type.
Push and Pull type refer to the action required to manipulate the clutch. A Push type clutch does just that, it pushes against the pressure plate diaphragm to release pressure on the clutch discs, disengaging the clutch. A pull type does the opposite, it pulls on the diaphragm to disengage the clutch. There is no argument that when it comes to handling power, the pull type clutch is superior in design. However pull type clutches are more expensive, complex, and do not have the same level of aftermarket options as the push type alternative. For these reasons, many choose to run push type clutches, especially in the oem RB25 gearboxes.
So if you've got a R33 gearbox, you are all set, but if you've got a R34 box, then you need to make some changes in order to use a push type clutch. But don't worry, the conversion is not as difficult as it may sound. To do the conversion you will need the following OEM Nissan parts:
- OEM R33 Slave Cylinder (30620-21U23)
- OEM R33 Front Cover Assembly (32110-05U11) & Gasket
- OEM R33 Clutch Fork or upgraded R33 clutch fork
- OEM R33 Pivot Ball
- OEM R33 Throw out Bearing
- RB push type clutch of your choice.
The R34 Bellhousing is drilled and tapped for a pull type slave cylinder however there is already a flat casting where the push type slave would be positioned towards the front of the bell housing. This location simply needs to be drilled and tapped to install the new push type slave cylinder. Next you will need to remove the front cover from the R34 box and install the R33 cover. Keep in mind there is a gasket here that should be replaced as well. Next install the R33 pivot ball, clutch fork and throw our bearing and don't forget the clutch fork boot! Install your push type clutch on your RB and install your transmission. Depending on which chassis you have, you may be required to modify the cross member and driveshaft. Last step is to bleed the clutch.