GTM Transaxle

[tfraz]

Hi all,

I started a GTM build in February this year (2021) and wanted to pick the brains of some fellow builders and share my experience in trying to obtain a gearbox. By far, the biggest challenge I've had putting the kit together is sourcing a transaxle. I prefer not to go with a G96 due to the gear ratios, though we'll see as my search continues. I ordered a Mendeola SDR5 last November, but was ultimately unsuccessful in my dealings with that vendor, so looking for another option now. I have a LS3 376/525 installed on the chassis and so far all has gone well after having to change the water pump (chassis clearance) and modify the valley plate (for rotation of intake manifold). Looks like I'll have to swap the oil pan to increase ground clearance by a couple of inches. Otherwise, no issues, so far. Here is what I've looked at so far:

Mendeola SDR5 - no longer an option due to unavailability (moderate cost)
Porche G96.01 - still an option (lowest cost option)
Weddle HV25 - still a distant option but manufacturer is having difficulties getting them out the door. (moderate to high cost)
RBT 5DS25 - still an option (high cost but great quality)

Does anyone have any input, suggestions that would be helpful? Has anyone recently sourced a good option for their build? I seem to be leaning towards the RBT as I've found a viable source about 2-3 months out. I was also able to tour their production facility in South Austin, TX, and saw lots of activity including one build being tested on a dyno before shipment to a customer. I'm told the RBT is an old design originally made in Germany by ZF. Its a tried and tested gearbox used in racing circuits for the last few decades (with numerous wins) so reliability should be decent.

Comments regarding my tour of the RBT production facility: Noticed quite a bit of inventory as far as gearbox cases, R&P's, gear sets, etc, almost all of which is machined onsite using dozens of CNC's and other very expensive looking machines (I'm not a machinist). The staff spent two hours giving me a tour and were very interested in getting the news out to the GTM crowd. The folks there were very welcoming and interested in working with other GTM builders.

Hope this helps someone else and would be interested in any assistance myself.

[Ajzride]

Graziano, which are used in Audis are an option. Pretty pricey and the gearing needs to be changed for a V8.

[VRaptor SpeedWorks, LLC]

Have you considered the G96/50? It is a completely different transaxle than the G96/01.

The RBT looks interesting......I assume there are LS adapter plates/flywheels/starters available? What does it use for a clutch? Their website is pretty lite on info.....not a single photo that I see of an actual transaxle?

[tfraz]

Thanks. Should have included the Graziano in my list. I have recently reach out to Fran with Superlite (RCR) as he's the sole importer into the US, but he's backlogged on orders for his kit builders. Unfortunately, not an option.

[tfraz]

Hi Shane,

Thanks for the reply. I need to get a hold of you to order the GTM LS engine cover. I've looked into the G96/50 and it should work, but having trouble finding one in decent shape. If you know of one somewhere, let me know.

One other option for the future is the soon to be released Griffin Gearbox, which is to be offered in 5 and 6 speeds. Its is developed by the same folks at the RBT production facility I toured and discussed in my initial message. Saw cases and lots of gears in their inventory. Its a very clean and compact design using three cables for shifting. Unfortunately, not a current option and pricing hasn't yet been determined.

Tim

[cob427sc]

I would look seriously at the Porsche option unless you are planning some serious road racing. My GTM, an early kit used a 6 speed Porsche transaxle. Initially the original FFR shift linkage was not suitable and I switched to a cable shift. I sold the car in 2013 (I Think) and since then it has gone to Europe and back, Texas, and is now in California being used as a street/race version with I believe the original transaxle. They are pretty durable and the big issue has been trying to locate a used one at a junk yard. There used to be - maybe still is - a vendor who advertised on the site for these transmissions.

[tfraz]

Kennedy makes the bell housing to mate the RBT to an LS. Standard LS flywheel is used and off the shelf clutches is what I'm told by RBT.

[tfraz]

Thanks cob427. Do you recall the Porche gearbox you installed?

[Jkviper]

Thanks. Should have included the Graziano in my list. I have recently reach out to Fran with Superlite (RCR) as he's the sole importer into the US, but he's backlogged on orders for his kit builders. Unfortunately, not an option.

HCFautoparts.com can get you a Graz, drop gears, clutch, etc. ask for John B.

[crash]

If you researched the Mendeola at all on the forums then you should have been prepared for a year or so lead time. That was BEFORE covid. I spoke with Ian about a week ago and they are still making and selling transaxles, so I am wondering why you would say that a Mendeola is not an option?

That Griffin has been promised for six or seven years now. I wouldn't hold my breath waiting for that one.

I was given a good sales pitch at SEMA for the RBT but truth be told, the gearbox was always the weak link in the GT40 program even with the "new" RBT at the time. What I was told was that the current version is the exact same "tried and tested" RBT that was in the race winning GT40s.

The practical options, as I see them, are not cheap.

Graziano- Massive and requires custom parts.
Porsche- Hard to find, and requires a regear.
Weddle- Long lead time.
Mendeola- Long lead time.

Remember, the first two options are USED parts. They are just as expensive as the last two but you really are throwing the dice on what you are actually buying. Weddle S5 and Mendeola S5 are essentially the same gearbox and they both have long lead times. I can tell you that Mendeola has hundreds of transaxles out there in kit cars as opposed to very few from Weddle. The Weddle HV has no stated HP ratings, but I do believe it is far lower than the Mendeola.

[RR46]

Thanks cob427. Do you recall the Porche gearbox you installed?

It was a 1998 G50.20 (it's the exact one I am listing for sale here on the forum since I am the current owner of this car, for sale bc I am upgrading motor and gearbox). G50.20 is a six speed and is an excellent choice and shifts very nicely with the cable shift kit. The issue with these are since they come from the last aircooled Porsche and the last 6 speed aircooled Porsche, they are extremely pricey and rare. So probably you're best off finding a 996 Turbo (G96.50). They do pop up from time to time.

[tfraz]

Hey Crash, thanks for the info. My experience with Mendeola is based upon honest and open communication from my end to Ian and Mike, but not reciprocated in the least bit. Don't like to be disparaging, BUT based on my conversations with Ian and Mike I was mislead, then again mislead, and then after that mislead several times. Not sure I'd believe what Ian or Mike tell you without seeing it with your own eyes. If the lead time is a year or more, then they had a responsibility to disclose that upfront when I asked and not tell me I'd have the gearbox by June 2021. I don't like being lied to. They have whole gearbox kits, including R&P's, sitting on manufacturer shelves (saw those with my own eyes) that they won't pay for when they have customers who've paid good money for a gearbox. Maybe I'm unreasonable and naïve, but it just seems questionable to me, which is why in my mind they are not a feasible option. Don't want to get into a pissing contest over this, but I can only share my experience for what its worth.

Was told earlier today that the hold up with Weddle's HV25 is the second gear syncro. They are working out a bug and hope to start production again in October. We'll see

[crash]

To be fair and honest, and most people know this from reading these forums over the years, I run a Mendeola S5 in the race car I drive.

My opinion is that while the lead times are long, and sometimes longer than wanted and or expected, the product is a work of art. We have literally tried to beat the Mendeola to death and it just keeps working. I can tell you with pretty good confidence that I have less expectations with any of those other listed gearboxes than I do with the Mendeola.

As I said, they have hundreds of these out there and, as far as I recall, I have not seen one post where someone has complained that they broke a Mendeola. Yes there have been some "break in" issues with some of the synchros, but I have never heard of someone dropping the hammer and ending up with gears falling out the back of their car. The Mendeola is strong, built with all new parts, but requires patience when ordering. And the price isn't bad.

This reminds me of that sign some of us have seen in shops...

Fast
Cheap
Done Right

You Can Only Choose Two

[tfraz]

Appreciate the input. Checked out your website. Great looking cars.

[Jkviper]

Here is another lead for Porsche gearboxes. I’ve heard good things about this company…

https://californiamotorsports.net/

Also hcfautosports last I read can get new Graziano gearboxes, but to Crash’s point they are relatively larger than other choices.

[tfraz]

Hi All,

Here's an update of where I'm at currently. Decided to go with the RBT 5DS25-2 gearbox. Not the cheapest option ($15,000), but it worked out as far as sourcing something new. Fairly easy installation up to now. Had to modify the rear support bracket to connect to the case using the FFR supplied isolators, angle and tubing, and cut one of the support bracket ears on the lower chassis cross member to make room for the shifter cable mount. Had it re-powder coated when done so it looks decent. It fits in with plenty of room in the normal upright (not inverted) position. Used a Kennedy bell housing and McKeod dual clutch with a hydraulic TO bearing. Will post some photos once I have it all together.

Here's my last hurdle to get over. I need a supplier for a set of axle shafts as the FFR supplied set is too long by about .5". Stock corvette shafts are too short. Need them to be an overall length of no more than 22.5", 22.25" would be best. Does anyone know where I could source an axle shaft set with this length? Same splines on both sides.

[crash]

http://myraceshop.com/Driveline.html

[tfraz]

Thanks, I'll reach out tomorrow.

[tfraz]

Wanted to give an update on the RBT 5DS25-2 gearbox I selected for my GTM. Had help from "myraceshop.com" in getting it installed and so far, it's working great. As you all likely know, the kit wasn't specifically designed for this gearbox, but it went in without any major issues; it actually fits quite well with lots of space around the chassis. I have the advantage of living about an hour away from the RBT build site in South Austin (High Performance Gear), so I was able to visit their production facility where the majority of the components are manufactured and the gearboxes assembled. As with most custom gearboxes, I was able to select my gearing and a few other options. Cost was around $15,000, not including bell housing (Kennedy Engineering, $250), clutch and T/O bearing (Mcleod $1600), shifter and shift adapter (CNC Performance $1000). Used the kit cables that came with the FFR GTM kit.

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In order to install the gearbox, I had to modify the bolt-on rear gearbox support. This entailed cutting off the diagonal bracing that went to the lower set of dual tabs on the low cross brace. I then fabricated a duplicate upper cross support on the top of the assembly that I could use to bolt the rear support rubber isolators and a set of vertical hangers to bolt to the gearbox. Hope this makes some sense. Photo below is before powder coating. This photo was taken with a mock gearbox case installed that was loaned to me while the real one was being built. This allowed me to do all the fabrication before receiving my gearbox.

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Here's the final installation.

160247

The cable set up was straight-forward, and it shifts cleanly and crisply. It's a tight gearbox and brand-new, so it will loosen up with time. Gearing is: 2.23, 1.61, 1.21, .958, .704, R&P 3.56. I hope this information is helpful to someone else looking to install a new gearbox in their GTM build. Please forgive the inverted photo above; no matter what I tried, it always came out inverted.

[tfraz]

I also should mention that RBT is developing a "spec list" of what we found works on this installation in a GTM. They are in the process of making standard GM splined input shafts that will facilitate more clutch options. I had to use the BMW spline used in Panteras and GT40 installations with required a special order to McLeod for a dual clutch kit that would work in the Kennedy bell housing. The bell housing is designed to mate the ZF/RBT gearbox to a LS but requires a small block clutch mounted on an LS sized flywheel. Wasn't hard to get from McLeod!