Rb20 Manual Gearbox Problems Behind Rb25 Engine

[liampire]

Hi all,

My friend has a 32GTST with a RB25 engine conversion. He has kept his RB20 gearbox and has run it for over 12 months, gearbox started to develop a noise and recently a gear broke. We put another RB20 gearbox in and it worked beautifully but now has problems shifting into 3rd and 4th gears, just grinds. Car has a brand new exedy HDB clutch kit. The car rarely gets driven and is not really raced or driven hard.

A local workshop said that the clutch fork pivot ball is the problem and to change it to a RB25 pivot ball and possibly use a washer or two behind it so the clutch can be adjusted properly.

I know ultimately the best thing to do would be use an RB25 gearbox.

Has anyone else experienced this problem when using an RB20 gearbox behind a RB25 engine?

Thanks,

Liam.

[liampire]

BUMP

[blind_elk]

I have the original RB20 gearbox sitting behind a RB25DET in a 32 GTS4 - never have any problems.

[bubba]

I have the original RB20 gearbox sitting behind a RB25DET in a 32 GTS4 - never have any problems.

RWD conversion? Because the GTS4 box behind the RB20 isn't the same as the RWD RB20 gearbox..

I didn't have any problems (other than the input shaft bearing dying) with my old RB20 box behind the 30, was also using a clutch that came off an RB25.

Edited October 24, 2008 by bubba

[sly32]

Hi all,

My friend has a 32GTST with a RB25 engine conversion. He has kept his RB20 gearbox and has run it for over 12 months, gearbox started to develop a noise and recently a gear broke. We put another RB20 gearbox in and it worked beautifully but now has problems shifting into 3rd and 4th gears, just grinds. Car has a brand new exedy HDB clutch kit. The car rarely gets driven and is not really raced or driven hard.

A local workshop said that the clutch fork pivot ball is the problem and to change it to a RB25 pivot ball and possibly use a washer or two behind it so the clutch can be adjusted properly.

I know ultimately the best thing to do would be use an RB25 gearbox.

Has anyone else experienced this problem when using an RB20 gearbox behind a RB25 engine?

Thanks,

Liam.

it shouldnt matter man,

rb25 pivot ball wont fit in a rb20 box, the thread size is different,

if the pivot ball was broken it would have heaps of movement and not work for any gears,

washers isnt going to help anything, if you can change gears no worries in all the other gears except 3rd to 4th, then its nothing to do with your clutch setup at all,

its your gearbox, either the syncro is going, or the selector fork inside the gearbox for that gear is stuffed,,

so its the gearbox you got, and as u said tb20 gearboxes arnt the best, the are very crunchy when they start to go,

25 gearbox would be the go,

hope that helps

JV

[liampire]

Hey guys, thanks for your responses. We are going to play around and use a washer to space the pivot ball a little. And see how that goes.