1998 ER34 GT into GTT details

[JC71]

I have a 1998 ER34 25GT 5 speed 2 door skyline. I have swapped engine for a R34 GTT RB25DET, along with GTT brakes and suspension,

and triple dash gauge. plus other things like seats, steering wheel, shifter and a bunch of other items that are no mechanical related.

 

my question for the SAUskyline community is what else is different between the 25GT and 25GTT R34 models

I know about turbo engine, HICAS ,Traction control, LSD rear diff, and the other things I already changed like brakes etc. but

what else is different?

 

thanks

 

 

 

 

please intelligent replies only

Edited May 27, 2020 by JC71

[KiwiRS4T]

I assume you don't have the 25DET big gearbox...

[Unzipped Composites]

When you say suspension, which parts of the suspension have you changed? The R34 GT uses an eyelet type mount on the bottom of the rear strut, same as R33 GTST's. The GTT uses a forklet on the bottom of the rear strut. 

 

Gearbox is different as mentioned. Because the gearbox is smaller, the driveshaft is shorter. So if you fit a GTT gearbox, you also need the driveshaft and diff. 

 

Off the top of my head, the rest is mechanically the same. 

[GTSBoy]

The chassis number will always be for a GT.

There is no sense in converting a GT into a GTT for almost any reason at all. But doing it for drift is the worst reason of all. If making a drift car, just drop an LS3 into it and be done with it. It will be 20x the drift car with a suitable engine in it.

[JC71]

so what are the differences in the transmission and rear diff?

[Kinkstaah]

The GTT has various under body braces that the GT does not. I can't be too more detailed (I swapped chassis about 5 years ago now) but I recall everything just looking more 'heavy duty' under the GTT. It was suprising.

Technically the gt also has no rear sway bar
The GT also has the ABS system from a S15
The diff by default is an open type diff with the same configuration and half shafts as a S15.

The gearbox is a weak piece of shit which is generally weaker. This theme is also apparent on a lot of different things you wouldn't ordinarily realise (or even notice unless you had the cars side by side on two different hoists).

[GTSBoy]

9 hours ago, JC71 said:

so what are the differences in the transmission and rear diff?

As Kinkstaah said above. The turbo box is about double the weight of the NA box.

You do know that you can google these things, right?  Google up the RB25DE gearbox and look at the images. Then same for the turbo box. There are even photos of them side by side.

About 4000000000 words have been written about these things on this forum in the last 25 years and that when you google you will get an endless stream of hits right here.

[JC71]

I will be replacing the trans with the "big box" 5 speed from a GTT.

anything else?

[Unzipped Composites]

Driveshaft, as I said above.

[JC71]

yes, drive shaft, trans mount, etc.  any other things not previously mentioned?

I found a brand new neo GTT RB25DET 5 speed trans but it doesn't come with anything...(wiring, shifter ,etc.)  will these items taken off of my current  FS5W71C  trans fit onto a FS5R30A ?

[GTSBoy]

The shifter certainly won't They are completely different gearboxes.

As to the wiring plugs....the wiring is part of the car. All you need to do is make the connections. If the plugs are different, get the right plugs.

My car has has an auto, an 20DET manual (and a 25DE manual) and a 25DET manual in it. I think I had to change the plugs on at least one of the switches on at least one of those conversions. It's not rocket science.

[Unzipped Composites]

The shifter does fit actually, as long as it is an R34 gearbox. The R34 pull-type gearbox and the RB20 gearbox use the same shorter nylon bush. If you get an RB25 gearbox from an R33 and try to use the shifter from an RB20 or R34 then it will actually fit, but it won't work nicely. The R33 push type gearbox needs a longer nylon bush on the shifter, so it will pop out of gear.

[JC71]

ok, so best to not try to "make" mine work. I will plan to get this then:

https://www.ebay.com/itm/CUBE-Speed-Premium-short-shifter-for-Skyline-R32-R33-R34-5-speed/223279617684?_trkparms=aid%3D1110001%26algo%3DSPLICE.SIM%26ao%3D1%26asc%3D225073%26meid%3Deaba7acfdd5e45e3bb22a4e1af95dc1e%26pid%3D100167%26rk%3D6%26rkt%3D15%26mehot%3Dpp%26sd%3D221840569882%26itm%3D223279617684%26pmt%3D0%26noa%3D1%26pg%3D5411&_trksid=p5411.c100167.m2940

 

question: would this give me everything needed, to replace entire shifter assembly or would I have to use some parts from my current shifter assembly to mount and make work?

Edited June 4, 2020 by JC71

[Unzipped Composites]

Looks like it will work fine, it seems to come with both size bushes so you use the one that suits the gearbox you are using. Shouldn't need to use anything from your current shifter, it looks like it's all there.

[GTSBoy]

Keep in mind that short shifters are, as a rule, f**king stupid. They are unpleasant to use, lead to synchro wear.

Stock is best.

[Unzipped Composites]

Feels off topic, but I really don't understand how a short shifter could increase synchro wear. All it does is change the throw at the top of the lever, the bottom of the lever stays exactly the same. 

 

Surely the only thing that effects synchro wear is engine speed vs gearbox shaft speed, ie. Not rev matching. So if your driving style smashing through gears, it doesn't matter what lever you've got, you'll wear the synchros with a stock shifter just the same.

[GTSBoy]

5 hours ago, Unzipped Composites said:

but I really don't understand how a short shifter could increase synchro wear. All it does is change the throw at the top of the lever, the bottom of the lever stays exactly the same.

 

5 hours ago, Unzipped Composites said:

So if your driving style smashing through gears

The latter quote happens more with short shifters. it is a proven fact. More synchros have died at the hands of clowns slamming gears with their hella epic short shifter (TM) than almost any other driving style.

[Unzipped Composites]

Ok sure, but that's not the fault of the short shifter. I've had mine in the car for the last 10 years, and it was in the old NA gearbox when I bought the car 2 years before that. Wouldn't have any idea how worn my synchros are, but they're still going. Get the odd crunch going from 4th into 5th after 5 or 6 laps, but that'll learn me for trying to use 5th gear on a race track. 

I think if you're the sort of person that drives like that then you're going to end up breaking things anyway, stock shifter vs short shifter is the least of your worries.

[JC71]

I will be trying to find a stock shifter setup for my new FS5R30A 5 speed gear box (GTT RB25DET) other wise I may have to go aftermarket, if I cant find a stock one, I do find the brand "Cube" shifter for a R34 RB25det , any one have any comments regarding that shifter? or recommend a different shifter setup?

 

Edited June 9, 2020 by JC71

[Dil-Dog]

Dont forget fuel pump