TheSamba.com :: View topic - Subaru transmission with TDI engine in a syncro

Wed Jun 29, 2022 2:55 am

Hi All!

I'm tired of rebuilding my gearbox every year. I have a mTDI engine with stock syncro petrol gearbox (with some parts from Weddle), but still too weak.

So I'm planning a Subarugears update. The ideal candidate would be a cable shifted 6MT from a diesel Subaru (Outback or Forester). At the same time, I'll upgrade the engine to 110 HP TDI, all stock, but with a mildly chipped pump.

The new engine will produce about 140 HP and 300 Nm torque. It's less, than the 2.0D Subaru boxer diesel (150 HP, 350 Nm), so it will probably not kill the gearbox, which is the most important thing for me.

The reversed R&P is 4,86 ratio which is shorter than the stock Subaru, which compensates the weaker engine. The wheels are almost identical size (less than 1 cm difference), and the car weight is also close enough (both Subaru and Vanagon are about 1500-1600 kg).

So I think, the final driving experience will be close to a diesel Forester, except top speed, and noise. Top speed will be lower, but that's not a problem. As I calculated, rpm 2600 will be at cruising speed 120 km/h. It's ok for me, and the engine.

I know, I'll lose the differential lock, and granny gear, but I almost never use these stuff anyway. It's enough for me to have a correct awd system for winter, and low rpm highway cruising. I don't crawl on rocks, my offroading is just looking for camp spots, and shortcuts on dirt roads (or not roads).

So, in my mind, this is the ideal setup for me. But I'm a bit worried about this setup, as I read in some posts (here, facebook, or other sources):
- 6MT gearboxes are made of glass, they are weaker, than original VW boxes (it's hard to believe, as boxer diesels are stronger engines)
- Subarugears R&P-s broke sometimes (but maybe this problem is fixed with re-designing, and maybe it was a problem with more powerful engines)

My question is, that is there someone, who uses Subaru gearbox for a long time? What are the experiences, any issues?

Ideally a TDI user would be the most helpful, but I'm curious about any other high torque application user experience.

Thank you, if you share your thougths!

Wed Jun 29, 2022 6:08 am

Curious, what did Subarugears say to these questions?

Wed Jun 29, 2022 6:21 am

I called Subarugears a few months ago about compatibility of the reversed R&P with the AWD transmission and they said it was not compatible.

Wed Jun 29, 2022 6:53 am

vanis13 wrote: Curious, what did Subarugears say to these questions?
Todd emailed me about, this gearbox is ok for this application. I'm sure, he tested it, and his product is good. But I'm curious about long term experiences.

Wed Jun 29, 2022 7:05 am

Pchill2 wrote: I called Subarugears a few months ago about compatibility of the reversed R&P with the AWD transmission and they said it was not compatible.
Maybe I'm using the terms incorrectly... I'm thinking about these products:

conversion kit:
https://www.subarugears.com/product/kit-for-syncro...ing-pinion

plus adapter for tdi:
https://www.subarugears.com/product/vw-tdi-adaptor-only/

and of course, everything else, what is necessary.

Wed Jun 29, 2022 7:08 am

What components keep breaking in your current gearbox? I think I'd check with some of these renown transaxle builders to find out what they're doing to beef them up.

Wed Jun 29, 2022 7:24 am

krumelmonster wrote: Pchill2 wrote: I called Subarugears a few months ago about compatibility of the reversed R&P with the AWD transmission and they said it was not compatible.
Maybe I'm using the terms incorrectly... I'm thinking about these products:

conversion kit:
https://www.subarugears.com/product/kit-for-syncro...ing-pinion

plus adapter for tdi:
https://www.subarugears.com/product/vw-tdi-adaptor-only/

and of course, everything else, what is necessary.

Disregard my statement. I do remember inquiring on the dual range gearbox with reverse R&P. I believe that is not compatible.

Wed Jun 29, 2022 9:41 am

Sorry you caught me in a (too common) procrastination cycle and here I am typing another book. :roll:

krumelmonster wrote: - 6MT gearboxes are made of glass, they are weaker, than original VW boxes (it's hard to believe, as boxer diesels are stronger engines)
Thank you, if you share your thougths!

My thoughts are with regards to the duty-cycle.
The comparison of weight and engine torque is just the front side, the numbers.
You have to look "behind the curtain" where the rubber meets the road to estimate longevity of the wear items.

The FIRST graph is related to your first drive with your new conversion engine. !! 8) 8) !!

The Second graph shows the Duty-Cycle.
The area under the curve is the usage at the necessary torque output and produces the gearbox "wear response".

There are other contributors to longevity.
Pulsations, lugging.
Lubricant cleanliness provided over this lifetime.
Overload produces more metal in the oil (.....no ifs, ands or buts :shock: ).
What is your program to remove this contaminant from the lubricant?
These contributors have a fantastically higher effect on longevity when the drivetrain component is over-loaded at or beyond its mechanical limit (of the gear and bearing physical sizes).

A significant number of our 'weak gearbox data' comes from 'rebuilt' gearboxes.....
-re-used old parts of unknown remaining lifetime (zero to xx,xxx miles). A gear that has only has 20,000 miles remaining can destroy the new bearings, and quickly if nobody's watching the magnet and upping the maintenance. Watching the magnet is not 'easy'. And gearbox death is inevitable anyway at that point.
-part-quality (of new parts)
-customer instructions WRT final cost
-build quality of the re-assembly
All this coupled with the conversion environment (driving style, duty cycle and maintenance).

----------

If you are driving a Subaru Forester and a Vanagon at the same speed, same grade, same headwind, the Vanagon will require more power.
It will consume more fuel than the Sedan. Burning more fuel ---> more gearbox wear.
The throttle position will be deeper on the vanagon and the drivetrain will experience this higher duty cycle (continuously).

A Diesel Forester that pulled a travel trailer its entire lifetime (continuously) would be a good comparison for longevity.
Smaller trailer: to compare a Doka, Tintop
Bigger trailer: to compare a Camper.
Even bigger trailer: compare to heavy campers, tall campers, campers with many items attached to the outside.
I don't think there is any way to get longevity data for a Forester that pulled a permanent trailer its whole life.
My mom's forester is still fine at 212,000 miles, that's about all we get (grandma/grocery getter etc).

Weddle gears had some trouble a few years ago with longevity. Big-tooth gears are stronger for racing, to be replaced after a season or two. For 'longevity' you need smaller, quieter teeth (like OEM gears). I don't know if Weddle has addressed the longevity complaints, or is even interested, as their focus is racing. Weddle's racing parts happen to fit our gearboxes so we use them, then try to drive 'far'.

VW created a "Dual Mass Flywheel" system to soften Diesel engine pulsations.
I will 'guess' that it was an alternative to increasing the size of the gearbox.
VW went to a lot of trouble to create this cushion, and must have deemed it's additional cost & complexity as "necessary".
?Waldo?, AlikaT3. SyncroandDestroy have incorporated the DMF to their Diesel conversions, likely some others too.

Wed Jun 29, 2022 10:18 am

Would it be beneficial to cryogenically treat these transmission components (Weddle & Subarugears) before installation if they're not already to improve longevity? Or would that be pouring snake oil voodoo over a pile of money and lighting it on fire?

Wed Jun 29, 2022 10:50 am

Silverghost500 wrote: Would it be beneficial to cryogenically treat these transmission components (Weddle & Subarugears) before installation if they're not already to improve longevity? Or would that be pouring snake oil voodoo over a pile of money and lighting it on fire?

I don't know.
It looks like 'free lunch'.
Like if it worked, everybody would be doing it, including OEMs.

Wed Jun 29, 2022 11:46 am

Pchill2 wrote: I called Subarugears a few months ago about compatibility of the reversed R&P with the AWD transmission and they said it was not compatible.

I have a Subaru diesel 6 speed in my van now, yet its not running. The problem is the trans is to long and requires cutting the main rear wheel to wheel frame brace. The one under the rear seat. Its not for the faint hearted, yet its totally do-able. Check my thread in the signature for pics. (Page 10)

P.S. if you go these route, you need the LSD in the trans. It takes out some of the chance of R&P issues from what im told. O-Yeah, you also have to figure out the cable shift setup. Have to go aftermarket, yet its not crazy hard as your already in the rabbit hole at this point.

Wed Jun 29, 2022 3:33 pm

Sodo wrote:

These contributors have a fantastically higher effect on longevity when the drivetrain component is over-loaded at or beyond its mechanical limit (of the gear and bearing physical sizes).

It's surely hard to predict the longevity of a gearbox, as there are so many factors. So, I try to simplify it for myself.

The Vanagon gearbox is designed for max 170 Nm torque engines. It can be rebuilt, and strengthen, but for that amount, I can buy a kit and a Subaru gearbox, which is originally designed for double that torque. So it makes simpler from my point of view.

Can we say, that a Subaru gearbox is originally stronger, than an original Vanagon gearbox? And can we say, it's stronger, than a strengthened one? Or it's not that simple...

Wed Jun 29, 2022 3:35 pm

Silverghost500 wrote: What components keep breaking in your current gearbox? I think I'd check with some of these renown transaxle builders to find out what they're doing to beef them up.

A lot. Bearings, gear teeth, mainshaft. Once this, then that. I think, the rebuild prices (if it contains stronger parts) are higher, than the subarugears conversion. And the other probem is, that there are no renown builders in my neighborhood, as far as I know.

Wed Jun 29, 2022 3:36 pm

0cean wrote:
I have a Subaru diesel 6 speed in my van now, yet its not running. The problem is the trans is to long and requires cutting the main rear wheel to wheel frame brace. The one under the rear seat. Its not for the faint hearted, yet its totally do-able. Check my thread in the signature for pics. (Page 10)

Thanks, I checked, and, ooops... That's one thing, I surely not want to do. Yes, I'm faint hearted, in my country, it's an immediate execution on the MOT...

So if the 6MT is only can be installed this way, then I re-plannig, and rather install an 5MT. Is the 5MT strong, like 6MT, or it's (originally) weaker, as it's for less powerful engines?

Wed Jun 29, 2022 3:52 pm

isn't having a Dual Mass Flywheel key in transmission longevity with a diesel? i truly don't know but from the number of failed trans WITHOUT a DMF it seems like it is imperative to use one.

Wed Jun 29, 2022 3:57 pm

DanHoug wrote: isn't having a Dual Mass Flywheel key in transmission longevity with a diesel? i truly don't know but from the number of failed trans WITHOUT a DMF it seems like it is imperative to use one.

I think it does, and it's a must. Whether it's a Vanagon or Subaru gearbox, I'll use it.

Wed Jun 29, 2022 6:38 pm

krumelmonster wrote: Can we say, that a Subaru gearbox is originally stronger, than an original Vanagon gearbox? And can we say, it's stronger, than a strengthened one? Or it's not that simple...

It's not simple because there are many ways to build a VW gearbox.
The good, the bad, and the ugly.
And none of the methods nor the gearboxes, are OEM.
I think/hope some can be better than OEM but the cost is "unreal".

We don't know yet if Subarus are stronger.
The Subaru R&P is quite a bit smaller than the Vanagon R&P.
The Subaru case is much thinner and lighter than the VW case.

Nobody is reporting mileages.

Typically those having problems (for whatever reason) may report problems.
But those NOT having problems are not reporting mileage either.
This makes sense....

But in any case there's not much info about longevity of Subaru sedan gearboxes pushing the brick.
Everyone is "hopeful" that it's a valid conversion.
I hear...... to drive with the 5 speeds...... that it is a dream👍🏽. ( And 6 speeds has to be even better. )

Wed Jun 29, 2022 7:09 pm

your weakest link will be that SG ring and pinion. they continue to break to this day. someone just posted on a FB group that they are on their 2nd r+p

Thu Jun 30, 2022 12:11 am

Thanks everyone! Keep posting please :)

Conclusions so far (corrections appreciated), from this, and other topics

1. Subaru gearbox is designed for stronger engines, than Vanagon, but no long term data yet (hopefully, because it's good).

2. Subarugears R&P improved, but sometimes, they can brake (like everything else), but the net is not full of horror stories, so it looks like a solid stuff

3. 5MT fits without body modification, with SG mountings, easy install, but it's not cable shifted, linkage modification needed (or conversion to cable shifted?), and it's not for a diesel subaru, which is a risk (diesel torque pulsation). I'd be happy to hear about 5MT gearboxes are strong enough, and easy to install of the shifter.

4. 6MT is designed for high torque diesel, so it would be ideal for me. It's also relatively cheap, as many diesel Subarus suffer from engine problems, and end their life too early injunkyards. But to fit, the transverse beam needs to be cut. Is there any other solution for this? In this topic, it looks like a solution:

https://www.thesamba.com/vw/forum/viewtopic.php?t=...p;start=20

But it's a different engine, than mine, and I also need adaptor plate. So is there a setup to use 6MT:
- without cutting the beam,
- and stock(ish) drivetrain height?

Thu Jun 30, 2022 11:21 am

krumelmonster wrote: Thanks everyone! Keep posting please :)

Conclusions so far (corrections appreciated), from this, and other topics

1. Subaru gearbox is designed for stronger engines, than Vanagon, but no long term data yet (hopefully, because it's good).

2. Subarugears R&P improved, but sometimes, they can brake (like everything else), but the net is not full of horror stories, so it looks like a solid stuff

3. 5MT fits without body modification, with SG mountings, easy install, but it's not cable shifted, linkage modification needed (or conversion to cable shifted?), and it's not for a diesel subaru, which is a risk (diesel torque pulsation). I'd be happy to hear about 5MT gearboxes are strong enough, and easy to install of the shifter.

4. 6MT is designed for high torque diesel, so it would be ideal for me. It's also relatively cheap, as many diesel Subarus suffer from engine problems, and end their life too early injunkyards. But to fit, the transverse beam needs to be cut. Is there any other solution for this? In this topic, it looks like a solution:

https://www.thesamba.com/vw/forum/viewtopic.php?t=...p;start=20

But it's a different engine, than mine, and I also need adaptor plate. So is there a setup to use 6MT:
- without cutting the beam,
- and stock(ish) drivetrain height?

Yeah, its mostly correct. The only change i would make is its not really about 6 speed vs 5 speed, yet its about AWD vs. 2wd when it comes to length of the trans box and fitting in the space.

P.S. You cant move the engine backwards to make room for the trans, because you exceed the CV's acceptable angles. Even with Porsche CV's.