G50/01 rebuild?

[TC]

I am happy to announce that I now have a GT40. It has a G50/01 that has approx 92,000 mi on it and shifts very smoothly but was wondering if it should be rebuilt due to almost being 20 years old and it's mileage. Is this high mileage? It has a 74H01xxx serial number, which means built in 1987 and I believe it is from a 911.

Currently, it does not leak any oil from the seal (now on the bottom), but I am concerned about whether the main support thrust bearings, syncro's, seals, etc. should be replaced before I actually have a failure (which I would perceive as worse and more expensive than doing preventative work, plus getting stuck somewhere).

Additionally, it's gearing is as follows:

1st 3.50
2nd 2.07
3rd 1.41
4th 1.13
5th 0.89
final 3.44

So in addition to wondering what your experiences would advise on the necessity of a rebuild, do you think this gearing is acceptable? Turning this is a 331 stroked, 450hp, 400 ft/lb engine. (street and maybe a few track days). Any suggestions?

I live in Florida and would prefer a service locally if anyone knows of a great shop.

 

[flatchat(Chris)]

These boxes love to be driven hard, just change the oil annually with a quality Castrol synthetic. Most DRBs use this trans and they get "used"!,haven't heard of any problems in the last 10 years.

(check to see if the angine is braced to the adapter plate)

 

[TC]

Chris,

Thanks for the response, sounds like you have quite a lot of experience and time watching these G50's. I hope some others chime in as well.

Great photo of the brace and yes, mine is braced similarily. With DRB's motor mounts and braces, the whole engine/trans seems rock solid.

TC

 

[jmracecar]

It's hard to tell if we don't know more about the history (both use & service) of the transmission. If it has never been rebuilt, I would do so now. Much cheaper this way. Yes absolutely the 4-point bearings should be replaced if never done yet, and the syncros & dog teeth should all get a close look, replace any needed. I can do it up here, or in FL look up Rodger at Orbit Racing Orbit Racing

If you had a G50/50 I might be tempted to run it longer, but with the "small" G50.0x, I'd err on the side of caution and preventive maintenance.

Right, your trans was from a 911 originally, specifically the 3.2 liter Carrera. Those were nice cars, but they only made 210 to 230 hp. If you were still running that much power, and no track use, you might well run to 150,000 miles before overhaul. But with your power level, 97k miles is a lot. Obviously the first miles weren't running as much power... Still I think it's a good time to go through it.

 

[TC]

JM, Thanks for your input, and I value your opinion with your background and interests in G50's. Can you give an idea of what you would normally replace in a typical rebuild and some budgets for these items or anything else you would do if it was yours. Thanks for the lead on Orbit, I will check them out.

 

[jmracecar]

Well as I said, the 4-point bearings should be replaced if never done yet, and the syncros & dog teeth should all get a close look, replace any needed. That is the main list. The gear teeth should be looked at for wear, but I would not expect to see much if any.

Typical items to replace now would include the two ball bearings, often several syncros, maybe an operating sleeve or two, or not -- all depends on condition & how things are wearing. Steel racing syncros can be used for some of the gears, or just standard ones can be used.

If you have a limited slip diff, it will probably be ready for a set of new clutch discs.

It is impossible to give a dollar figure without opening it up, because you only would buy the parts needed. A complete list would be expensive and unnecessary.

One way to look at it, or budget it, is to see what is the labor cost to open it and have a look without replacing anything. The nose cover comes off first, then we remove fifth and reverse. Then the center housing can be removed. The diff housing cover comes off by itself, allowing the ring & pinion to be looked at. To really get a good look at the syncro teeth though it is necessary to remove the rest of the gears & operating sleeves from the input & output shafts.

To take it apart as above, and check everything, reassemble & reset the shift forks is something like a day's labor (roughly 8 or 9 hours). You could in theory decline any & all parts replacements that might be suggested. A gasket set & sealant is less than $100, plus 8 or 9 hours times a shop's hourly rate would be the basic budget to check it. There are a couple of non-reusable gear shaft lock nuts at $10 or $15 each.

 

[TC]

JM,

I am finally ready to address the rebuild and was looking at buying a G50/01 and rebuilding it, then swapping with the G50/01 in the car to avoid too much down time. My question then becomes whether I should take the opportunity to change to a stronger transaxle like a G50/50 or 52, rebuild it outside the car and then swap out with the G50/01.

Do these (G50/50 or 52) bolt up and fit exactly like the G50/01 currently installed?

Would I be better off just rebuilding and "beefing up" a second G50/01?

For that matter, is there any beefing up of the G50/01 that would get it closer to the G50/50?

Any thoughts or experiences from you or others would be appreciated.

 

[Lynn Larsen]

TC,

The issue with G50/50 is going to be finding one. G50/52 not as hard, but....there are a couple of different bell housing widths, etc. etc.

Two things come to mind re: beefing up: billet side cover and shift parts, both available and will address two weaker areas fairly easily.

Beyond this, I'll let Joel address; he is the expert!

Gear ratios: they are available, but very $$ ($1750-$2000 for the gears themselves the last time I checked, which was a while ago.) How happy are you with the ratios thus far? I know 1st is a touch short, but behond that?

Lynn

 

[jmracecar]

Doin' fine Lynn. There are cheaper gears though, e.g. from Guard Transmission, or PowerHaus II. Oh wait, you may mean for a set of gears, in which case, no argument. The only alternative there is to hunt for used ones, which can still run $400 to $500 per ratio.

If the diff is not limited slip, or if the LSD friction plates are worn out, this would be the time to address it.

One way to answer your larger question is to take apart your G50/01 and see how its wearing. If its wearing fine, and all you need are a few bearings and syncros, and a gasket set, then that suggests you don't need a G50/5x. You can then choose between a spare /01 or an occasional rebuild of your existing one.

There is not a clear-cut line on what is too much power for a G50/0x. It has a lot to do with the way the car is driven. Even in track use, there are some wild swings of how easy or hard one is on the gearbox.

If no gears grind when shifting, and only some balkiness when really cold in the low gears, then the syncros/dog teeth/op sleeves are probably still runnable for awhile yet.

Re: gearing, is first too short? Do you use 5th much? Do you run out of revs in 5th at your track(s)?

 

[TC]

Hi Joel,

The diff is not a LSD. It serial number is G5001 1J02677. Is that even a modification that would be possible or worthwhile for a diff mainly on the street with limited track days?

I have been speaking with Rodger at Orbit and hopefully he will be taking it apart very soon and going thru it, replacing items as you discussed earlier in the thread. I think with only 5,600 miles of the total estimated 90,000 miles on the trans, it would be hard to evaluate whether the G50/01 is going to be strong enough for a V8 and my driving style, which is fairly aggressive, but certainly no high rpm clutch dumping, but lots of hard acceleration including some from stops and some light track days, no real competing, just playing on tracks at some speed, like Homestead, Sebring, Moroso.

No gears grind when shifting, but some balkiness when cold in the low gears is an excellant description. I think while apart, I should replace some or all of the syncros with steel racing versions for strength and better mesh/shifting, and certainly if that is one way to beef up the unit or address any weaknesses.

Speaking of beefing it up, I have read that the deflection of the side cover is another weakness that I would like to address while apart, perhaps with a billet side cover as Lynn suggested. Any other areas for improvement in the strengthening?

Gearing seems to be an area that could use some improvement. 1st gear is very short duration and due to the balkiness of shifting into second, takes away even more from the time under acceleration. 5th is important to run on the street (read:highway speed) to reduce noise/rpm and yet keep the rpm above the min 2,400 rpm necessary for this lumpy cam. I have also read that a closer ratio set would make the driving and acceleration a lot funner. Does one have to replace all gears to properly re-gear and address these items?

Being that I already own the /01, spending $1,500 to 3,000+ is totally acceptable if I end up with a stong enough trans that will handle my style of driving. It would seem a better route than spending $5,000+ on a /50 or /52 plus the cost of a rebuild/refresh. I would like piece of mind that I have a strong and quick trans. I apologize about beating this topic into the ground, but I am new to these transmissions and really enjoy the thoughtful and expert input from all of you guys.

TC

 

[Lynn Larsen]

TC,

From your description I would say, don't leave out the billet shift forks. LSD or no LSD that is highly personal. After going with an open diff because I was building a street car, I though better of it after talking with a lot of guys who use their cars for street/light track. But, I guess if you've never had an LSD, you won't miss it, now will you ;-)

Lynn

 

[jmracecar]

As before I agree with Lynn.

Rodger is one of my mentors, so, far be it for me to tell you to tell him what to do. You are in very good hands. I am sure he will go over whatever makes sense. I am ultra-curious to hear what he recommends, if you don't mind updating us. Especially his take on a rebuild vs a G50/5x replacement. In general he is a "do it right" kind of guy.

I do recommend an LSD though. The whole idea of an open diff sending the power to the wheel that has the least grip just blows my mind, given the time, attention, & detail we and the factories put into the rest of our cars.

Now, gearing. The thing we call the mainshaft or input shaft has another name. It's called first gear. So changing that is more trouble (cost) than one might have wished. They do exist though with other ratios, e.g. from Guard Transmission, and Rodger can review that with you. Look at the bright side, the six speed streetcar mainshafts have 2nd formed and cut right on them as well.