RBT in an SPF?

charlie c · 10-30-07, 12:12 PM

Hello kids -

Has anyone mounted an RBT 6-speed in an SPF GT40, and if so, what is the situation in terms of the bellhousing protruding beneath the pan, and clearancing/mounting issues? Is the RBT box really a drop-in fit, or will I need to mill ears and search out a new bellhousing to avoid scooping up Bott's Dots with my low-hanging trans?

I assume that if one is using the ZF box, that Bob Wood's (Safir) bellhousing and clutch setup is the answer... but what about RBT users?

Thanks!

Pat Buckley · 10-30-07, 12:15 PM

The RBT and the ZF are one and the same.

The 6 speed is just a little longer.

charlie c · 10-30-07, 02:25 PM

Right.... err.... so..... that means the RBT 6 is subject to the same concerns regarding the bellhousing protruding below the pan... and one needs to address this by means of a modifying or replacing the bellhousing.... yes?

(forgive my lack of knowledge! I'm a total noob, but I'm learning... slowly.)

Pat Buckley · 10-30-07, 03:09 PM

You are correct.

Everyone was a beginner at some point.

I had considered a 6 speed when I first got my car but drove a 5 speed and felt that it wasn't worth it.

Miles · 10-30-07, 03:56 PM

Charlie,

The original GT40 used a smaller diameter bellhousing and consequently a smaller diameter bellhousing. The ground clearance issues which have been raised relate to the larger diameter bellhousing protrusing below the chassis (there are piuctures on the forum somewhere which i pressume you have seen).

I have not seen the Safir bellhousing but bearing in mind its provenance i pressume it is pretty damn correct; John Wisher who posts on the Forum also produces an original bellhousing which is cast in aluminium and is availiable in the UK and (pressumably) overseas. This bellhousing incorporates the lower bellhousing mounts so the transmission is mounted to the "horseshoe top and bottom" rather than just the top pendulum mounts which some people have observed could lead to the transmission swinging like a pendulum.

Obviously the smaller bellhousing needs a smaller flywheel and clutch assembly and in the UK these are availiable from Southern GT.

The ZF and RBT 5 (and 6) speed share mounting faces so will mount to all thes bellhousings. One point you should check with Safir is that their bellhousing is of the six bolt variety. The GT40s had a dash 0 or dash 1 gearbox which had a four bolt mounting. the dash 2 has a six bolt mounting and this is what John's Bellhousing is designed to cater for.

I had considered the 6 speed ZF but actually struggle to find any merit other than in the numbers game. The Le mans winning cars had a 4 speed and with the torque of the engine needed no more to top 200 with flexibility. Surely the 6 speed will only add weight at the rear where you lease need it, why try the ZFQ which I believe is a few pounds lighter and a modern evoloution of the ZF.

This links to a previous thread on the subject. Bellhousing engine mount lugs

Miles

Miles · 10-30-07, 03:59 PM

Bloody computer keeps going to Error 404. Think that makes triple post and me a bit of a prat!

Miles · 10-30-07, 03:59 PM

Double post

charlie c · 10-30-07, 10:03 PM

Thank you, thank you, thank you! The transaxle fog is slowly beginning to dissipate...

As to 6-speed or not, I actually would prefer a ZFQ five-speed, but if I should chance upon an RBT-6 before the ZFQ is available, then who knows...

Again, thanks to all for enlightening and educating a noob like me!

Thread drift: I noticed on some hi-res pics of the SPF mkI that there are linkages (sway bar ends I think) that hang down dangerously low just inboard of the front wheels, coming to within a couple of inches of the pavement. Never mind the bellhousing, this looks like it could make serious contact with anything on the road thicker than a worm... Can anything be done about this, or is that extreme angle part of the original front suspension geometry? Just curious.

Ross Nicol · 10-30-07, 10:26 PM

Have a look at my build log.There are a few pics of my driveline in the early fitting stages.The bottom of my bellhousing is open and flush with the ring gear .I mounted the drivetrain so the bellhousing/ring gear is flush with chassis bottom and engine sump, being higher is well protected.
Ross

Mike Drew · 10-31-07, 03:18 AM

The one big problem in fitting an RBT six-speed in a GT40 is that the six-speed is about four inches longer than the five speed. There is precious little extra room to accomodate that length, and you would have to modify the back of the car to accept it--never mind the shifter/linkage issues.

The six-speed is also considerably more expensive than the already-expensive five speed, and really gains you nothing from a practical perspective.

I say skip it, and just worry about trying to find a five-speed!

Also, I'm at the SEMA show doing research for my someday Superformance build (among other things). I spoke at length with the head of sales for McLeod clutches about the GT40 clutch that Safir is selling (which they make). Specifically I asked them what makes it so bloody expensive relative to a conventional clutch. Turns out that the various components used in a conventional clutch are mass-produced stampings (the pressure plate, cover, etc.) whereas the components in the small-diameter clutch are all machined one at a time from billet, which drives the cost through the roof.

For my money, though, there's no substitute for a proper small-diameter clutch and bellhousing--I would try to ensure that it is as street-friendly as possible (i.e. built using reasonable friction material instead of full-race stuff).