Converting a GT3 engine to reverse rotation? - Page 6

johnman001 · johnman001's Garage

Quote:

Originally Posted by Reuben.L

John,
901/914/915 gearboxs have no offset so you are correct in stating that the diff in these boxes can be flipped with no effect on the way the gear teeth mesh. However we were talking about GT3 and subaru gearboxes, and the GT3 gearbox (g96), has a 10mm (i looked it up in the factory workshop manual) offset. The pinion shaft is offset 10mm lower than the diff center line, which means the gear teeth will not mesh when the diff is flipped.

BING!

The light bulb came on. That is information that I did not have before. Which is why I specifically called out the basis of my statements and that they may be the exception and not the rule.

Since my limited knowledge does not apply here, I respectfully will be quiet now.

Carry on.

I am interested in the answer as one dream I have is putting a GT3 engine in a 914 and I will need a trans that will take the punishment, but I'll probably invert a GT3 trans.

MarKoBrow · 07-21-2010, 11:00 AM

Quote:

Originally Posted by johnman001

BING!

The light bulb came on. That is information that I did not have before. Which is why I specifically called out the basis of my statements and that they may be the exception and not the rule.

Since my limited knowledge does not apply here, I respectfully will be quiet now.

Carry on.

I am interested in the answer as one dream I have is putting a GT3 engine in a 914 and I will need a trans that will take the punishment, but I'll probably invert a GT3 trans.

Not to start a new round, The Lambo replica builders all are pointing at the latest Audi 6spd 2wd transmission used in their TDI models, it is supposed to hold up to a lot of torque

Reuben.L · 07-21-2010, 12:28 PM

John, I'm glad we cleared that up for you. Just remember if you do invert the gt3 box you will need some sort of oil pump and sprayer onto the r&p because otherwise they don't get enough oil. The result is pretty messy. I brought an older g50 out that had been in a lambo replica and it had broken teeth on the pinion which were then forced out the side of the box as they jammed in the reverse gear idlers!
A tdi box sounds promising because it may be able to handle the torque that the lambo guys love from their v8's.
Maybe we can get this Back on track for blue72.

blue72s · 07-25-2010, 08:46 AM

Quote:

An answer to your question will be forthcoming on Saturday as I plan on starting the car and driving it around the block. If when I attempt to drive the car, I will report back to you exactley what it does.

If it goes backwards believe me I will be the first to tell you, until Saturday then

Well?

MarKoBrow · 07-25-2010, 09:26 AM

Quote:

Originally Posted by blue72s

Well?

I did in fact drive the car around the block 4 forward speeds and reverse, I now have to figure out what I may have done to my shifter assembly so I can get into fifth gear. Next radiator and water management.

Did you happen to see the note I left about the Audi 6speed 2wd TDI trans? I am curious to hear your thoughts on that transmission assembly.

Flieger · Flieger's Garage

Is that the one in this Audi V8 mid-engine 356?

Amazing 356 build

MarKoBrow · 07-25-2010, 11:27 AM

Quote:

Originally Posted by Flieger

Is that the one in this Audi V8 mid-engine 356?

Amazing 356 build

I just read it and yes it's the same one. I have a neighbor that has a Lambo kit with a BMW V12 in it and he just bought one to exchange the 5 speed he is using now. That came from an Audi 100. The one thing that got me to think was his car is driven hard and I never heard him complain about transmission problems with the five speed.

blue72s · 03:59 PM

Quote:

Originally Posted by MarKoBrow

I did in fact drive the car around the block 4 forward speeds and reverse,

You may have 4 forwards speeds but unfortunately you are driving on the coast side of the R&P

. Just wanted to warn you before you wear it out even further so you could try to send it back for a refund. Good luck. Don't believe me? Check your R&P.

Quote:

Did you happen to see the note I left about the Audi 6speed 2wd TDI trans? I am curious to hear your thoughts on that transmission assembly.

Yes. Stock 6-speed Boxster/Cayman cars have that transmission. The bellhousing is all wrong for the GT3 motor - it does not fit.

blue72s · 07-25-2010, 04:23 PM

Quote:

Originally Posted by Flieger

Amazing 356 build

Amazing indeed! Wow!

tctnd · 07-25-2010, 05:52 PM

I just went back and read the product description on subarugear's site. I was mistaken about the purpose of the "reverse cut" R&P. It is not made for reverse rotation engines but is intended to allow the the tranny to be reversed by flipping the R&P. The subie diff uses an offset pinion shaft (the pinion axis does not intersect with the ring gear axis) so the stock gear would not mesh if flipped. This product is ground to mesh when flipped to the other side. As your car has multiple speeds forward you can be sure that your shop followed the instructions and flipped the (new)R&P into the right case. These gears would not mesh of someone tried to install them in the stock (left case) location. Glad it's working out for you.
regards,
Phil

blue72s · 07:28 PM

Quote:

I was mistaken about the purpose of the "reverse cut" R&P.

No, you weren't. Look at this pic again.

MarKoBrow · 07-25-2010, 08:22 PM

Quote:

Originally Posted by blue72s

You may have 4 forwards speeds but unfortunately you are driving on the coast side of the R&P

. Just wanted to warn you before you wear it out even further so you could try to send it back for a refund. Good luck. Don't believe me? Check your R&P.
Since getting the drive train installed I have spoken to two builders that have completed and put miles on their cars and have had no problems thus far. If and when it wears out I will get on here and say so.

Yes. Stock 6-speed Boxster/Cayman cars have that transmission. The bellhousing is all wrong for the GT3 motor - it does not fit.

I would have an guessed adapter would be needed to make that happen. In the interest of your project did you ever come up with an answer to your problem?

tctnd · 07-25-2010, 08:50 PM

Blue 72
The pic you posted is of opposite rotation R&P sets (from what I don't know). The gears in question are shown in the enclosed images from the subarugears website. The first shows the stock R&P in the standard location (left case). You can easily see the pinion offset and why these gears wouldn't mesh if flipped. The second shot shows their custom ground gears mounted in the right case. They are ground to allow a mesh even though the pinion is now offset on the other side of the ring gear axis from the point of view of the ring gear. Note that the drive and coast faces remain in the same orientation and skew direction is the same.
regards,
Phil
p.s. I also have a blue '72

mike the snake · 07-26-2010, 06:48 AM

I was surfing the net and found Rodrico gearboxes. You should look into those for sure. They are the boxes used in the Ford GT. Price looks promising.

blue72s · 07-26-2010, 08:30 AM

Quote:

Originally Posted by tctnd

The pic you posted is of opposite rotation R&P sets (from what I don't know).

From Markobrow. He posted it on page 5.

Quote:

The second shot shows their custom ground gears mounted in the right case.

No, it's still the same R&P. Subgears was just showing why it doesn't mesh, that's all. If it was a custom ground R&P, the pinion would have a virtually straight bevel tooth with a slight curve in it to work in that position (before-centre hypoid).
However, motor car manufacturers never do that. Why I don't know.

tctnd · 07-26-2010, 09:23 AM

You are correct; I should have read the captions more carefully. However, the point remains; the reversal is accomplished by flipping the ring. The gears are ground to allow this.
regards,
Phil

Matt Monson · 07-26-2010, 10:54 AM

Quote:

Originally Posted by blue72s

Yes. Stock 6-speed Boxster/Cayman cars have that transmission. The bellhousing is all wrong for the GT3 motor - it does not fit.

And furthermore, as was previously mentioned, the box has some strength issues. I think they can get away with using this gearbox in the TDI cars because they just don't see the sort of stresses that are seen on a gearbox used on the track for extended periods of time.

blue72s · 07-26-2010, 10:57 AM

Quote:

Originally Posted by tctnd

The gears are ground to allow this.

You are talking about before-centre hypoid but is it good practice and if so, why do motor car manufacturers avoid it like the plague?

tctnd · 07-26-2010, 07:44 PM

I'm certain it is not good practice, but if you want to reverse the rotation, the ring gear must be flipped and this is the only way to do it other than turning the whole box over.
regards,
Phil

blue72s · 05:57 AM

Hello again guys,

Quote:

Originally Posted by Wayne at Pelican Parts

sounds like 962 is the way to go.

You are probably right but unfortunately the 962 casing has a "nose" around the input shaft. See pic below.

If I get one for my application, obviously I would have to cut its nose off completely and also make a bellhousing. The going value of these gearboxes in Europe is about 25,000 €uros, which is a lot of money. Naturally, I have to think about future resale, so what I need to know whether cutting the nose off would greatly devalue the gearbox or worse - render it useless for 962 cars?

I have located one for sale and I'm not sure whether I should buy it. What do you guys think? Is it too risky?