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I’ve been helping a friend bring back from the dead a ‘67 Bug he bought about a year and a half ago. Yesterday we installed a rebuilt Rancho transaxle that he bought through Chirco. The transaxle comes totally dry, obviously. When we top it off with the 80/90 hypoid gear oil; what is the procedure to break it in? I’ve read you need to change the gear oil after the first 300 miles and then every 30,000 but how exactly do you first put it into service? Just take it off the stands, start it, put it in reverse, back up from the garage and drive it down the street? I want to be careful because, like I said, the thing looked totally dry inside; want to make sure we do this properly. I know many of you have done this but funnily enough no one mentions these first few moments in a rebuilt transaxle’s life. Thank you in advance for your help.

Last edited by Impala
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If you're also breaking in a rebuilt motor you're in luck.  Just drive it like you would breaking in a motor; vary the speed and load, run through the gears, don't hurry the shifts.  Change at 3-500 miles, refill and Bobs your uncle. 

Be careful with what lube you run because of the yellow metal synchros. I've done a pant-load of research and found Swepco 202 is apparently the beans for our type of transaxle.  For the break in I wouldn't worry too much, but after that go as good as you can afford for longevity.  Here are a couple links for fun reading.


Swepco 202

The Bentley manual states to change the gear oil after 300 miles for a new or rebuilt unit. That's what I do. No other special behavior/usage is specified.

I use any cheap 75W90 or 80W90 for the first 300, then usually run something a little nicer for the next interval.

I know I'll ruffle feathers, but I used GL-5 Valvoline synthetic for a long time(30,000 miles). There was no excessive wear on any "yellow metals" i.e. the synchro rings or the reverse shift fork. The only wear was the main bearing(steel), of Chinese origin, put there by Trans West in 2002. That company is now defunct, and I bought the best German or Brazilian bearings available when I rebuilt it.

I'll also add that the synchro rings had NO WEAR, and sat on the synchro hubs with the same clearance as NEW. I put them back in the trans and ran it another 15K miles before I zinged the 3rd gear slider with a missed downshift. Trans shifted perfectly after rebuild.

Last edited by DannyP

This is a timely post.

I just (and I mean Tuesday afternoon) got the speedster back on the road with the 2110 meant for my bus, and a transaxle rebuilt by @Anthony in Kalifornia.

I put $11/qt Mobil 1 75/90 GL5 in it, as I always ran a cheap semi-sythetic GL5 and never had any issues. I could barely shift the thing when I rook it out for a spin (double clutching, etc.). A quick call to Anthony confirmed that he wanted GL4 (which I suspected). Apparently Brad Penn makes some GL4, but I can't buy it here.

All I wanted was some GL3 gear-oil like I used to crank in by the half-gallon, back in the day at Bruner Bros. Oil. In 2020, out here in flyover country-- finding something besides GL5 was like looking for shards of the true cross. None of the FLAPS had it (and I checked them all)-- everything was GL5.

I had a couple quarts of Swepco 201 in the stash, but it's GL5 as well, and I didn't want to drop another 2.5 qts of super-oil with the same result. Advance, Autozone, and NAPA had some $10/qt GM syncromesh GL3 lube of indeterminate weight, which I nearly bought-- but thought I'd try a speed shop as a last resort.

Winner's Circle Racing in Peoria had some Redline full synthetic GL4 75/90 for $17/qt-- which is pretty harsh for a break-in oil, but it is what it is. I just came back from a little 20 mi shake-down. The syncros are still pretty tight, but they loosened markedly from the start of the drive to the finish. Rev-matching helps considerably, and if it doesn't want to go into first, I just double-clutch. It'll be great as it loosens. I moved to a CB rhino nose-cone mount (from a Prothane)-- I was hoping it might be a bit quieter, but alas, no. This also is par for the course.

I suppose the snooty gear oil only cost an extra $30 for the RedLine (over something more generic) every time I change it, but it still sticks in my craw, as I'd already dropped $35 for the Mobil 1. I'm nearly $100 into gear-oil, and I've only driven 50 mi. We used to just about give this stuff away, way back when.

I'd love to know what cheap and readily available oil might work in a syncromesh transaxle for break-in. I can tell you with 100% accuracy that it's not Mobil 1.

Last edited by Stan Galat

Stan, I ran and still run Valvoline 75W90 Synthetic. Available at most any FLAPS. Shifts nicer when cold IMHO. I tried some really expensive stuff, can't remember the name, but I wouldn't recommend it so the name doesn't matter. Went out to the garage, it IS Red Line Synthetic High Shock-Load. Meh. Waste of hard-earned money.

I truly think your trans is new and tight and will loosen up with use. The CB Rhino nosecone mount transmits noise/vibration, but keeps the trans where it's supposed to be. 

Break-in? Anything cheap from NAPA or Tractor Supply. It's only gonna be in there for two tanks of gas. Dump it HOT, let it drain for a day.

Having a subie tran, I ran Total GL5 dyno in my subie for breakin, then Redline synthetic,  not cheap, but I did not find it shifted any better so I went back to GL5 Total dyno oil and I find it shift pretty good then I decided to try a little boron additive Archoil and it seems to be quieter shifting, not as notchy. 


I know a lot use GL5 Castrol#Syntrax#75w/90 

Jim, I never heard of it either. But common sense says that when a bunch of new parts are put together, there's going to be some metal shed from parts as they mate. So it's probably a good idea, especially since Ray has that nifty reversed ring and pinion from Subagears or whatever the name is.

It's interesting to me that someone else thought that the Redline didn't give them any better shift action. Thanks for that, Ray.

Yes I have a 5MT subie tranny.  Subarugears can provide a brand new gear set and a R&P that is reversed, hence you want to break in the tranny with dyno oil.  I believe they want you to do it as well if it is simply rebuilt as well. 

BTW Danny, it was not the shock stuff but I felt that the shifting was good cold but worse when hot.   With my present combo it is a bit stiff cold and good when warm. 

Last edited by IaM-Ray


Yes, there will surely be some wear with a new or rebuilt manual tranny.  But, when you consider the use of break in dino oil for a transmission, I'm not convinced.  I can understand changing and inspecting tranny oil at 100 hours or so, but a tranny's moving parts get a free ride when compared to the temps, pressures, and speed of ring/cylinder wall contact.  Dino oil, then synthetic for a lower end engine rebuild makes sense to me, but not for a tranny.

Of course, there are some long-held beliefs that younger mechanics delight in trashing.  Many young engine builders say the time-tested means of breaking in a new/rebuilt engine, i.e., dino oil, vary the rpm's, don't go over 4,000, change oil at 50, 100, 300 miles or some variant, then only synth after break in, are outdated.  New machining techniques for cross-hatching cylinder walls and better metallurgy on rings mean that you should break in a new engine fast.  Don't baby it, smokehole it!  Some tuners even say a dyno break in for a new Subi engine is the way to go.  A couple hours on a dyno, and you're good to go. 

Of course, as we know, car guys can't agree on what day it is. 

Subaru manuals are silent about tranny break in.  Even for a new engine, they only say to keep it under 4000 and change oil at 1500 miles.  Nothing further needed.    


Seems like draining, examining and dumping less than three liters of gear oil is a small price to pay for peace of mind, and a likely best practice when settling in a rebuilt gearbox. 

When I had Bridget's transaxle replaced with one rebuilt to my specs for the Subaru engine I think the old one had the same oil in it since the Carter Administration. It was fine. The new one was fine. I changed the oil after the summer season and what came out was fine, so I put in new and drove on.

The Spyder box, having sat dry for a decade after its rebuild, then gotten re-worked again three years ago, will get the same treatment. I mean, why not?

Ed, the thing is, a VW trans is supposed to be drained and refilled after 300 miles according to the Bentley manual, which I'm thinking is the same as the factory manual. Nothing has changed as far as the metallurgy of all the gears and bearings, so I'd stick to that.

Jim, I'm not advocating for dino then synthetic. Cheap oil for break-in miles is common sense to me. And the synthetic Valvoline I use is available anywhere, and just happens to be synthetic. I notice much easier shift action when it's 40-50 degrees out, before the engine and rolling along warms the trans.

I buy the Valvoline Synthetic for the same reason I buy Valvoline 4 stroke motorcycle oil for the engine. It's available EVERYWHERE.

If Subaru doesn't recommend changing, that's fine. It won't hurt if you do.

When it comes to gear oil the big difference between Subaru transaxles and air cooled VW transaxles (and even Porsche transaxles up at least through 915) is the composition of the synchro rings. (drop to the bottom of the post right now for the cheap solution and to avoid annoying tech talk)  Most (not all) GL5 gear oils have extreme pressure (EP) additives that will attack the " yellow metal" synchros in the old German transaxles and wear them prematurely. From what I've researched they could reduce synchro life by as much as 50%.  This doesn't depend on the gear oil being a dyno oil base or a synthetic base as it's part of the additive package.  The thing that most does this is M0S2 or other sulfer based EP additives when they degrade with use/time. 

To measure this the test we want to see is ASTM D-130 which tests reactivity/corrosion on a polished copper strip. A gear oil does not have to pass this test in order to get a GL5 rating (it does to get a GL4), but if we can get a spec sheet we can see if it run through ASTM D-130. We are looking for a rating of 1a on that test.

That was why I mentioned the Swepco 202 before as it passes the ASTM D-130 with flying colors.  It is a true multi grade 75w90, not a 90w with a pour additive, so it will make it shift easier during warm up and in cold weather.  It  and gets raves for shifting performance from some folks on Porsche forums. I even stumbled across raves on International Harvester truck forums. The 201 version is similar. Should be able to leave it in there for a long time. Price is around $85 a gallon

The cheap option is Napa Performance Gear Oil 80w-85-90, GL3, GL4, GL5, Part Number #75-210 price is under $8.00 a quart. Slippery link

This is the stuff I use:

IL:71700000060668398&gclsrc=aw.ds&&gclid=Cj0KCQjwtLT1BRD9ARIsAMH3BtXIbmLFQtt9IDBT-nzB65uGVLVW20uAKzmGIlCidXQo1Hm7jfBwAAIaAlioEALw_wcB" target="_blank">

GL-4 and GL-5 rating. Available anywhere. Like I said, ZERO measurable wear on brass synchros for 30k miles or so. To measure synchro wear, you use a feeler gauge between the synchro ring and the hub. I'd have to look up the clearance, but mine measured no wear. So I reused them with no ill-effect. Shifted like butter.

Last edited by DannyP

A coda to my last post:

I got a few quarts of Brad Penn Classic GL-4 80w/90 from Summit a week or so ago, and dumped the $17/qt Redline oil to try this. I think this is better. The syncros are still tight, but loosening up. I'm at about 200 mi on the new transaxle (the weather has been horrible. Mother's Day was colder than Christmas 2019), and I'm only having occasional issues downshifting. I double clutch most times to get into first, but even that is loosening.

This is giving me practice rev-matching every downshift (it's a bit different with the 2110-- it doesn't spool up quite as quickly as the twin-spark motor).

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