rb25det gearbox on rb30det -

[Boostin']

rb25det gearbox on rb30det -

Hi guys,

my r33 that my brother and I converted to rb30det was tuned over the weekend and we installed a heavy duty organic clutch hoping to have that as the weak point to not put so much strain on the driveline and it's getting bent over anywhere above about 420bhp so basically were going to take it out and install the triple plate I've got for it but I'm concerned having a direct clutch how much power the gearbox and diff (both in good nick but both standard) are going to be able to stand up against. Ive been told the gearbox is the weak point and will break sooner rather than later once you get over 400-450bhp area especially with the triple plate clutch so if anyone could clarify or correct that I would appreciate it. It will mostly be a street/weekend car but it will definitely see the drag strip a few times and maybe Wakefield so if I go with the triple plate how far can I turn it up before I'm going to break everything behind it? Anyone have any alternatives? Car made 424hp on wastegate pressure before the clutch started slipping 

[Boostin']

[Boostin']

L

Edited September 4, 2017 by Boostin'

[blind_elk]

Fitting an even heavier clutch is going to improve your chances of breaking the gearbox or other driveline component. The clutch needs to act like a fuse - it needs to slip before more power is transmitted further down the drive train.

You surely need to strengthen all the other driveline components before you consider upgrading the clutch (fuse). Otherwise, it will be like using a 6" nail as a (house) fuse, and then wondering why the kettle blows up.

[Ben C34]

Yeah nah.

There are a thousand clutch options, certainly not a single organic or a triple plate.

 

Call a clutch place. Talk to them.

Don't expect a clutch to really protect the driveline if making big power. The clutch job is to hold the power, not to protect. The gearbox's are not that bad.

 

[Birds]

Tyres are the other weak link that protects the driveline. Keep in mind that slicks or semis increase pressure on the gearbox as you improve grip.

Aside from wear through failed or faulty bearings, or some sort of pre-existing structural damage to the cogs, catastrophic gearbox failure / stripping teeth usually occurs from two things: 1. too much torque transferred through the box with resistance at the other end, e.g. lots of engine power and the tyres are gripping, or 2. too much torque instantaneously transferred / shocked through the box, e.g. dumping clutch or harsh pick up.

So boxes do have their limits for what they handle power wise, but it goes a long way to treating the box kindly. You can baby around a drag car with a T5 gearbox or you can kill a Tremec TKO with a stock LS1 and horrible driving. If you're insistent on running a certain power level then I would talk to a clutch specialist like NPC, tell them your power and application (street or strip) and they will sell you a clutch that suits. But be prepared, down the track you may need a stronger box.

[Boostin']

Thanks for the feedback guys, I'll make a call to npc tomorrow and see what they say, as far as strengthening components what are my options if I want to keep it h pattern ? 2 or 3 speeds auto is completely out of the question and I haven't got 20k to spend on a sequential 

[Birds]

Strengthened gearset put in existing box, e.g. OSGiken, PAR or PPG. Do some research though, as there are issues with certain brands and I've also heard of breakages with all of them. But they will certainly be stronger than the standard gearset. You can get these in dog engagement or synchro and straight cut or helical. Recommend synchro and helical for street car. You may realistically only need the first three gears as 4th won't break and 5th is for cruising.

The gearset alone can be anywhere from 3k - 7k (been a while since I've tried to source one) and you'll need to recondition the gearbox it's going into, so budget another $1200-$1500 on top of that.

Keep an eye out, second hand strengthened boxes pop up from time to time.

This is where power starts getting expensive

[KiwiRS4T]

Gearbox will not break if you treat it right.

[donut_kng]

If the tyres are mega sticky third gear will go eventually, I have done this three times doing anything from simple changes launching to just a light clutch pump. I run a direct twin plate so there is zero slip.

Slip is annoying as hell especially when you've built the thing to have power.

[Birds]

Third gear is the weakest part of the box, but more common for it to go in GTRs.

[niZmO_Man]

Max torque applied longer on 3rd gear compared to 1st and 2nd gears + g-forces pushing the oil away from the gear ?

[Birds]

From memory the transfer case design had something to do with it; creating more pressure on third. In weak gearboxes, 2nd is usually the most likely to blow because we spend the most time in it and it's the "thrash" gear. Variety of other reasons for third to go in a GTR/GTS-T box, including:

- lower boost in 1st gear (at least on factory vehicles)

- second more likely to wheelspin than third (wheelspin protects the cog itself, but not the gearbox bearings!)

- physically smaller cog on third than 1st and 2nd

- taller ratio with more rolling and air resistance at higher speeds

- as above, longer time opportunity to exert pressure/forces on cog

- 4th gear would probably do the same if it wasn't a simple locking of input shaft to output shaft (creating the 1:1 ratio)

For reasons above, 5th and 6th overdrive are the gears most likely to blow when towing, which is why you always tow heavy loads in 4th. Incredibly rare to blow 4th in a gearbox because it would take forces capable of snapping the input or output shaft itself.