Gearbox Breathing ?

[Strik3r]

hello all. Bit of a strange 'problem' to report. Recently rebuilt a gts4 gearbox to go into my GTR (taking advantage of the slightly shorter gears to match the gts4 diff ratio's i've put in). Used all new genuine syncros and bearings. All the gears were cryotreated for strength. gear set was assembled by a local gearbox mob, and we put the gearset into the housings and the assembled box into the car. Used nearly a full bottle (1 gallon) of Redline Shockproof Lightweight oil (had a bit left in the bottom). Gearbox worked perfectly, all shifts are silky smooth, no dramas at all.

Did some driving and put the car back up in the air. Noticed a fair bit of gearbox oil around the bell housing/gear housing and thoughtwe'd just overfilled it a little. Cleaned it up and did some more driving. More gearbox oil ended up around the housings. Pulled the gearbox out, the housings off and the gearset out and inspected everything. All looked normal. Gearbox went back together, back in the car, and we carefully filled it so the level was a cm or 2 below the filler plug. Ran new breather hoses up into the engine bay into a container so we could monitor the fluid the gearbox was putting out. Took it for a spirited drive, came back and checked - no fluid. Drove home and out to the track the next day and noticed about 150ml in the container (little to no boosting, no hard driving). Thought it might still just be a bit of extra fluid, so didn't worry about it. Did a few sessions at the track and no more fluid was added. Drove home and then down the highway and back home today and noticed another 150ml in there.

All the while, the gearbox is driving perfectly. no noises, no problem shifting/holding power etc. Its spat out somewhere between 250 and 350 ml so far from when we put it in the car and filled it last, so i guess it could still just be a bit extra fluid, but just wanted to see if anyone had any ideas/had experienced this before. I'll continue to monitor it and if it stops putting out fluid, i'll know it just doesnt like to carry as much oil as some other boxes.

[Ryan1200]

I had similar issues pumping redline lightweight out the breather tube in my ppg straight cut. I ran the normal breather to highest point but still pumped oil. I had the gearbox out for some reason and decided to add second breather to the inspection plate on top of the box and ran it up into the engine bay. This fixed my problem 100% and hasnt pumped a ml since...

Hope this helps.

[BIT SUS]

do you, (or anyone else) know if the transfer case on a GTR has a breather? I'm finding a fair amount of smurf's blood under the trans tunnel, above the transfer case on a freshly rebuilt PPG box...

[Strik3r]

yes, there is a breather at the back of the box which is the transfer breather.

[BIT SUS]

yes, there is a breather at the back of the box which is the transfer breather.

thanks man,

is there any way to stop it from spewing precious blood everywhere?

block it off? re-route it with some piping?

[Duncan]

nope....you want the breather because as it gets hot the fluid expands...when it cools it should run back to the gearbox.

one option I have seen is to extend the breather further and give it a little catch can up near the brake booster - I have a setup like this on the rear but am still using stock at the front

make sure it is not overfull, but in my experience smurf blood breathes a fair bit when hot

[BIT SUS]

Thanks mate, I can always rely on your extensive knowledge of GTRs!

Next time the box is out, I might get some fuel hose and make an extension like you suggested.

Nigel.