Subaru 5mt front differential question

[Okie]

20211020_184449.mp4

I have mentioned this before, but I run a stock Subaru 5mt, that I have converted to 2wd, in my mid engine sandcar. I finally broke it last week. I think the diff broke in half, not sure yet. I have considered swapping to the sti ra 6 speed, but that creates problems at the moment.  I do not run huge hp or torque. Fairly light car. My research is getting mixed info, because it all comes from street guys. What do ya'all think about installing a LSD into a 5mt for strength? And which type? Clutch or bevel gear? Keep in mind, I am not actually educated on these. I don't need one for traction, but I assume they are stronger than a stock open diff. Is there a certain ratio-1 way, 1.5 way- that would be recommended? And would turning brakes still work? I can also weld stiffeners to the case.

 

[Grease Monkey]

IMO,

Stick with what you've built. Find a replacement transmission and enjoy.

I don't want to necessarily speak for all of us here, but what you have is not the norm and I doubt any of us will have the right answer. Maybe @John@Outfront

The question of using the oem transaxles has been asked many times in the years past and it always ends with "use a vw transaxle" or aftermarket Mendeola etc.

Not wanting to shut your question down either. Anyone have the knowledge please contribute.

 

[Okie]

I have another already converted and ready to bolt in. And another spare to possibly build stronger. I like to build my own stuff, out of the normal. I just hope to fix a few weak spots.

 

[John@Outfront]

Grease you are correct,  don't have much to add, just too few trying to do this setup.  i do have a question.  what size are your paddles and what gear are you typically in?  one of the biggest issues is the tranny was geared for street use with small tires, so with big tires and wanting lower gears i would assume you only use 1st-3rd and would never get into 4th or 5th?

the nickname for the 5 speed Subaru tranny is the "glass box" with reason,  the 6 speed is super strong but super long and heavy too.  not sure the procedure to lock out the driveshaft portion of the tranny.

 

[Okie]

30" tall paddles, and I run a lot of air pressure. I like the "power slide". Yes, 1st -3rd gear. Large gap between 2-3rd, so I built a turbo motor to pull it. Worked out good. The job of converting these 5 and 6 speeds is fairly simple. I do it in my garage with a cut-off wheel and tig welder. I will probably try a torsten style diff (only for strength) and another 4.44:1 ring and pinion in a 5 speed. I have been running the old one for about 3 years. Our group was seeing how hard we could hit some whoops on the side of a bowl, and it finally broke this one. It was no surprise!

 

[fastestang]

Thank you for posting this. I have an old school vw buggy that I am planning on converting to Subi. My vw transaxle just barely grenaded this week, so it would be easier to get the whole power train out of 1 donor vehicle. I was torn on 5 or 6 speed. If I go with 5 speed (for size and weight) is there any simple upgrades to make them a little stronger? 

 

[SeanRitchie]

I don't want to sound like I am trying to convince you guys to not use these Subaru transmissions for your rails, but we took a pretty deep look into these Subaru transmissions about 10-12 years ago, but there is just not enough meat there to hold up to any decent use in even a 200 HP sand car. 

The biggest reason is that the R&P is still only about the same size as a VW bus R&P which limits using taller tires and anything more than about 200 HP. There are also some internal housing issues that are just not strong enough to withstand the abuse of bouncing across rough terrain. 

Albins did make an assortment of lower ratio's 1st-5th/6th gearsets for these, but they were still somewhat tall and tailored for rally use, and were also quite expensive at $5k+ per 5 speed set.

I know everyone is looking for a less expensive, production vehicle type gearbox for these things, but we have not found any mass produced manual gearbox that can withstand the abuses of off-road use without having to spend many thousands of dollars on new gears and strengthening components. This is reason why we decided to go all in and develop the HV-2 transaxles that are built specifically for this type of use. 

 

[Rockwood]

To answer the question on limited slip: do you use the turning brakes?  If you do, I'd steer clear.  Even if you don't, unless the limited slips are stronger (the more enclosed cases often support the R&P better), I'd still steer clear. 

Reasoning: torsen works well to help pivot the car (gear type will push power to the outside wheel to help rotation) under throttle, but it will peg-leg if you lift a tire, so it won't be 100% consistent lockup wise in the types of terrain we encounter.  Clutch type will always behave the same, but the improved traction comes at the cost of understeer until you get wheelspin.  Since we're not after lap times, I'd stick with open diff unless you're having issues lighting up the inside tire (doubtful) or it gives some other benefit.

1 way would likely be best, since again, we're not after lap times and don't want stability under braking (I only use them for "OH chit" moments where I'm locked up anyway, or to set the car up to drift where I WANT it to rotate).