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What Box Will Fit My Rb25det

180dftr
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180dftr Newbie

180dftr

Posted
Posted

hey,

i have an RB25DET in the car and the 5spd blew last night.....drove it home and sound really bad...i think there will be teeth everywehre when i take it out, its a daily and i dont thrash it so can if i make anything else fit for a bit cheaper....eg...rb20 box or 32gtr gears inside my case etc....

cheeers

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nizmonut Community Regular

nizmonut

Posted
Posted (edited)

Any model of nissan that came with a rb motor in it, just make sure you get the correct cross member to go with it.

ie laurel, vl commodore, cefiro, skyline, 88 to 98

i think the question should be what gear box will fit your car model. as any rb box will bolt to any rb motor, etc

your best bet if you've blown your box is go to the wreckers and pick up an auto box for the time being, you will get one really cheap....even if its a 50$ job from a VL commodore for the time being...then save up hard and get new, stronger gears, and box rebuild

straight cut gears these should set you back a 1000 dollars or so but you will never break it again and also the box will then be a selling point of the car.

i would say dog engagment but these are really expensive...

two reasons for the straight cut teeth is

the two cogs have a more contact surface area, and arent herlical, they will be noisey but this will be normal....that is the whole reason car manufacturers make the gears herlical as it reduces the noise from the drive train and makes for a smooth transition between gear changes......

also because the cogs have straight cut teeth the cogs can be narrower but stronger than standard, the upside to this is the sinchro's can be thicker/stronger. snchro ring gears are seperate from the cog itself giving the gearshift the smooth interchange you feel, letting the gear you are selecting catch up to the speed of the engine matching the teeth to engage correctly.

dog engagement is where two pins engage each gear and only spin about 240 degrees then lock that is why you can shift without using the clutch once you are moving because the "dog's" lock onto the gear as you select it once locked the teeth on the cogs are matched, then all you have to do is dump the clutch or let it do its thing while rolling.

ask any race car driver, this is why the gear stick almost gets ripped out of your hand if your not onto it.

this is where the term DOGBOX comes from,

the down side to this is driveability, it's like driving a normal car with a twin plate clutch....you'll get used to it,

knocking it out of gear while the box is under load at the traffic lights for example is a no no because you will crunch it to get it back in first, make sure the car is stopped with the clutch in full then move it

also the advantage to this is having straight cut teeth the shafts wont have as much sideways force and therefore less stress on the bearings and case of the box.

Edited by nizmonut
180dftr Newbie

180dftr

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Posted

awesome, are they the same length though? will my tail shaft fit all these gearboxes...is the lifspan of a dogbox going to be shorter. helical gears are lubricated slightly better due to the was they engage the oil can be pushed through instead of pushed out the sides?

also do you think if i bring the diff ratio down there wont be as much strain on the gearebox...hence an rb20 one might last a little while.

BHDave Grand Master

BHDave

Posted
Posted

First off; What car and what box? Based on your nic would i be right assuming its a 180 with engine conversion?

Confirm you don't have a 20 box in there first before shelling out for internals for a 25 box.

BHDave Grand Master

BHDave

Posted
Posted

Conversions done by someone else make it hard....

If the car was originally manual i reckon it's almost certainly the original VL box. If it was non turbo then the box would be very similar to an rb20 box and about the same strength.

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