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Quote:
Originally Posted by tctnd View Post
You cannot reverse the rotation by altering the R&P pitch in any way. You must either flip the ring to the other side or flip the whole box over.
regards,
Phil
I am always surprised when such a definitive answer like this is posted from an engineer especially since it's dead wrong. Not only can it be done, it has been done and successfully by this company Home. One of the main problems with subaru conversions in VW' based cars has been the gear box needing an adapter, this gentleman came up with a solution based on common sense. Marine drive units have been using opposite pitch gearboxes for ever so why can't it be done in a automotive transmission? I never said it was an easy thing for a lay-person to accomplish, I simply made a suggestion based on empirical knowledge that it in fact was possible. I hope to have my own conversion driving out my garage tonight or tomorrow morning

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Last edited by MarKoBrow; 07-18-2010 at 12:34 PM..
Old 07-18-2010, 12:26 PM
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Here is a picture. The new one is the on top.

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Old 07-18-2010, 12:31 PM
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Originally Posted by MarKoBrow View Post

Home:-
We make a reverse-cut ring & pinion to suit Subaru transmissions and fully remanufactured reverse drive
What's that in red?
Old 07-18-2010, 01:27 PM
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I was under the impression that was something to marine technology, just for clarification I will send a note his way and ask. When I receive an answer I will post it.
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Old 07-18-2010, 05:10 PM
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I've been lingering on this thread because its a very exciting project which hope fully we will get to see some pictures of one day!
MarkoBrow, I think you need to read about the subaru R&P a little more thouroughly before you tell tctnd and blue 72 they are wrong,

Quote from their website: A new crownwheel and pinion shaft have to be engineered that re-align the teeth on the gears so they mesh in the flipped position.

The differential is still moved to the opposite side of the transmission, a new R&P has been machined to rectify the problem of the hypoid gearset not meshing once the diff has been flipped.

keep looking for solutions blue72.
Old 07-19-2010, 01:48 AM
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Hey Reuben I understand what you are saying as i thought exactly the same thing when I read a forum post about that setup, in fact before I bought and installed my own i was under the impression that you had to flip the differential and I was prepared to do so. The differential stayed in it's original position. I think there may be more of a problem with authors explanation. I will however carefully document a second transmission conversion I am doing in late August to visually explain how it all fits back together. The Subaru transmission and the Porsche G50 share the same problem you can not flip the differential in the trans at all.
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Old 07-19-2010, 02:59 AM
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MarKoBrow
If you want to cite the authority of an engineer, well I am a mechanical engineer and I'll tell you that if you wish to reverse the rotation, the ring gear MUST be flipped to the opposite side one way or another. This only sounds definitive because it is.
I looked at the subarugears site determined that the R&P set you refer to is intended to allow the use of an engine that rotates the opposite of a Subie (like VW or Porsche) without destroying the gears. Installing such an engine in a Subaru would give you a car with one forward gear and five in reverse, but the intention is to turn the whole thing around for use in a rear engined car. If you simply put the reverse cut gears into a stock Subie, the car would still have five foward gears as normal, but the R&P lifespan would be very short.
regards,
Phil

Last edited by tctnd; 07-19-2010 at 10:12 AM.. Reason: more info
Old 07-19-2010, 09:38 AM
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Quote:
Originally Posted by tctnd View Post
MarKoBrow
If you want to cite the authority of an engineer, well I am a mechanical engineer and I'll tell you that if you wish to reverse the rotation, the ring gear MUST be flipped to the opposite side one way or another. This only sounds definitive because it is.
regards,
Phil
Phil,

A hypoid gear set can be manufactured to twist in either direction, the basis for using a hypoid gear is they are quiet and strong. I was suggesting to someone to basically manufacture a ring and pinion set for the G50 transmission as it can be designed to twist in either direction. Just for the record I was not stating the authority of an engineer nor do I think it is important enough to continue down this path because it's really not. My other statement about the subaru transmission was based on my own project that I am working on, since that car has not driven out the garage yet, we shall see if it holds together in the mean time it went together as I stated.

I get that there is a need to be right and if I hurt your feelings I am sorry.

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Old 07-19-2010, 10:22 AM
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Mark,
My feelings are not hurt and this has nothing to do with the "need to be right". If your car uses a Subaru engine and transaxle mounted in the rear Porsche style, you are going to have one forward speed and five reverse gears regardless of which R&P you use. I sincerely hope that is not what you are doing.
regards,
Phil
Old 07-19-2010, 01:06 PM
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I believe he is using the Subaru in a WRXSTi
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Old 07-19-2010, 04:54 PM
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Quote:
Originally Posted by blue72s View Post
^ If you use a reversed R&P set (pitch reversed) you will be driving on the coast side, and coasting on the drive side of the R&P - it probably won't like that long term.

You are absolutely correct. If you reversed the rotation of the engine and kept the ring on the same side of the transmission case without inverting the transmission, you would need the reversed ring and pinion to prevent you from driving on the coast side and coasting on the drive side.

That is exactly what the picture of the two sets of ring and pinion gears do. It allows the INPUT shaft to turn the other way and hence drive the transmission the opposite direction.

It would be easier just to invert the transmission and then deal with clearances....... just my $0.02.

If it was me and this was indeed a street car, I would use the stock Cayman box and buy some spares for when they go bang. You would be money ahead. As far as that goes, leave the stock engine in the street car.

Maybe you could find a 930 box and flip the ring and pinion.
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1971 914 (TBD).....................|

Last edited by johnman001; 07-19-2010 at 06:10 PM..
Old 07-19-2010, 06:08 PM
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Markobrow,
I think this needs to be discussed further because there is far too much misinformation on this site.
When you built your subaru gearbox did you follow the instructions on their website? Quote: In order to flip the differential in a Subaru transaxle, the gearbox casing must be relieved on the opposite side. As the crownwheel usually runs in the left side of the gearbox casing, the right side has some casting ribs and areas that need to be clearanced in order for the crownwheel to spin freely. Without this clearancing, the crownwheel bolts will hit the casing.
http://www.members.iinet.net.au/~ttriebler/index_files/Gearbox%20Relief.jpg
This can be undertaken with a die grinder or mill, being careful to only remove as much material as necessary and keeping all surfaces smooth without sharp edges. Use the left side gearbox casing as your guide.
Next step is to replace the standard crownwheel & pinion with the reverse cut one. Install the differential unit “flipped” so the crownwheel is in the right hand side gearbox casing. Ensure that you set up your differential for backlash and endfloat, using gear blue to ensure the contact pattern is correct. The Subaru factory manuals have all the specifications and excellent procedures to follow to set the diff up.


If you did not do this then i am unsure how you got the reversed pitched ring gear and pinion gear teeth to mesh?

If Blue 72 does end up running a gt3 engine backwards ( way to difficult IMHO) then he will need a reverse cut R&P in the stock position to maintain maximum strength.

Please do not take this as criticism, I just want to clarify.

Regards,
Old 07-20-2010, 12:49 AM
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Quote:
Originally Posted by Reuben.L View Post
Markobrow,
I think this needs to be discussed further because there is far too much misinformation on this site.
When you built your subaru gearbox did you follow the instructions on their website? Quote: In order to flip the differential in a Subaru transaxle, the gearbox casing must be relieved on the opposite side. As the crownwheel usually runs in the left side of the gearbox casing, the right side has some casting ribs and areas that need to be clearanced in order for the crownwheel to spin freely. Without this clearancing, the crownwheel bolts will hit the casing.
http://www.members.iinet.net.au/~ttriebler/index_files/Gearbox%20Relief.jpg
This can be undertaken with a die grinder or mill, being careful to only remove as much material as necessary and keeping all surfaces smooth without sharp edges. Use the left side gearbox casing as your guide.
Next step is to replace the standard crownwheel & pinion with the reverse cut one. Install the differential unit “flipped” so the crownwheel is in the right hand side gearbox casing. Ensure that you set up your differential for backlash and endfloat, using gear blue to ensure the contact pattern is correct. The Subaru factory manuals have all the specifications and excellent procedures to follow to set the diff up.


If you did not do this then i am unsure how you got the reversed pitched ring gear and pinion gear teeth to mesh?

If Blue 72 does end up running a gt3 engine backwards ( way to difficult IMHO) then he will need a reverse cut R&P in the stock position to maintain maximum strength.

Please do not take this as criticism, I just want to clarify.

Regards,


Please explain why you feel that it would be necessary to use the reverse pitched ring and pinion. If the engine rotation remains constant, when you rotate the ring gear (crown wheel) about the axis of the pinion shaft, the output rotation is reversed, but nothing has changed as far as coast side or drive side of the teeth.


This is exactly how we run 915 boxes with the standard ring and pinion flipped in 914-6's. (915 boxes require a minimal amount of internal clearance modification as well.) It is also how the factory used 901 boxes in 914's in the first place.
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2016 981 Boxster S.................| 1983 911 Turbo - (White)
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1971 914 (TBD).....................|
Old 07-20-2010, 05:36 AM
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Johnman is absolutely correct. At the risk of getting flamed let me try to clarify some of the basics.
If a pinion gear is rotating in, for example, a clockwise direction, the output (ring gear/axle) rotation is determined entirely by which side the ring gear is mounted on. Tooth configuration has nothing to do with it. Hypoid gears are typically used because they blend the transmission of force smoothly from one tooth to the next and are therefore quieter than straight cut gears. This comes at the expense of additional end thrust and drag (nothing is free). The direction the hypoid is cut is determined by the direction of rotation under power to minimize wear and cannot change the output direction. The practical effect of this is if you are using an engine that turns in the same direction as the one your transaxle was originally designed for, you need a "standard R&P" with the ring gear mounted on whichever side drives the car in the right direction. If your engine rotates opposite the original, you need a "reverse cut R&P" placed appropriately.

regards,
Phil
Old 07-20-2010, 09:53 AM
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Quote:
Originally Posted by tctnd View Post
Johnman is absolutely correct. At the risk of getting flamed let me try to clarify some of the basics.
If a pinion gear is rotating in, for example, a clockwise direction, the output (ring gear/axle) rotation is determined entirely by which side the ring gear is mounted on. Tooth configuration has nothing to do with it. Hypoid gears are typically used because they blend the transmission of force smoothly from one tooth to the next and are therefore quieter than straight cut gears. This comes at the expense of additional end thrust and drag (nothing is free). The direction the hypoid is cut is determined by the direction of rotation under power to minimize wear and cannot change the output direction. The practical effect of this is if you are using an engine that turns in the same direction as the one your transaxle was originally designed for, you need a "standard R&P" with the ring gear mounted on whichever side drives the car in the right direction. If your engine rotates opposite the original, you need a "reverse cut R&P" placed appropriately.

regards,
Phil
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. When I bought the parts from Subaru Gears.com I had a transmission shop which is local to me, assemble the gears on the pinion shaft and I assisted in putting the transmission back together. At this point the car has been sitting while the wiring is sorted out as well as the radiator placement.

When I suggested that Blue72 look into that particular solution it was just a suggestion I am aware that he is planning on working with a GT3 motor and probily should have stuck with the "put an Audi 6sp 2WD trans in it" crowd. When I was looking at putting a Subaru engine in a VW Beetle I found a guy who put a Subaru engine and transmission in a bug using this setup it looked like a good idea. when I talked to him via the internet and phone what he had looked reasonable and I was pleased with his design and manufacturing process, I bought it and put my set-up together.

If it goes backwards believe me I will be the first to tell you, until Saturday then
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Old 07-20-2010, 12:25 PM
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Sorry we got confused there, in the original post, blue 72 asked about running a gt3 engine completly backwards, crank turning counter clockwise, thus reversing the direction the input shaft of the trans turns and so on. I agree with everything you guys are saying about hypoids gears and flipping the diff carrier to reverse the drive direction.
But a hypoid drive ring and pinion will not mesh if you simply flip the diff carrier because the pinion is slightly offset from the ring gear centerline. I will try to take a picture to clarify this.
Old 07-20-2010, 12:29 PM
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Mark,
is your project mid- engined or rear engined?
Old 07-20-2010, 02:39 PM
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Quote:
Originally Posted by tctnd View Post
Mark,
is your project mid- engined or rear engined?
Rear engined
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Old 07-20-2010, 03:09 PM
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Quote:
Originally Posted by Reuben.L View Post
Sorry we got confused there, in the original post, blue 72 asked about running a gt3 engine completly backwards, crank turning counter clockwise, thus reversing the direction the input shaft of the trans turns and so on. I agree with everything you guys are saying about hypoids gears and flipping the diff carrier to reverse the drive direction.
But a hypoid drive ring and pinion will not mesh if you simply flip the diff carrier because the pinion is slightly offset from the ring gear centerline. I will try to take a picture to clarify this.

I have a difference of opinion with you here. I have had no meshing issues when flipping the ring gear on 915 transmissions for use in 914-6 cars.

While I agree that the typical design for hypoid gear sets show that the centerline axis of the ring gear is offset from that of the pinion centerline axis, this does not seem to be true in regards to the 901 or 915 gearboxes (the only ones I have experience with). When setting the ring and pinion with the VW tools, the mandrel is placed where the differential carrier normally resides and the distance is measured from the mandrel centerline to the end of the pinion shaft. Now I have not measured the dead center of the pinion shaft once the magnetic spacer block is placed on the face of the pinion, I would assume that the measurement is pretty close to the center of the pinon shaft. This would indicate to me that the differential carrier centerline axis (also the ring gear centerline axis) is very close to that of the centerline axis of the pinion shaft (at least in 901 and 915 gearboxes).

Perhaps the offset is so minor that it does not cause a problem.

I do know that the 915 trans case and gears was once configured as a 916 gearbox for some of the early 1970's mid engine racing Porsches so maybe it was designed differently because of this to allow the ring gear to be easily flipped.
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2016 981 Boxster S.................| 1983 911 Turbo - (White)
1974 911 3.2 - Red Car...........| 1974 914-6 3.2 - (Silver)
1974 914-6 3.2, GT -(Red).......| 1974 914 - Unit Body (TBD)
1971 914 (TBD).....................|
Old 07-20-2010, 09:23 PM
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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.

Old 07-21-2010, 02:24 AM
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