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Rebuilt transmission (from Mofoco) leaking -- not sure why
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gears
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PostPosted: Fri Nov 06, 2015 4:45 pm    Post subject: Reply with quote

I think it's unfair to any trans builder to withhold information that could dramatically affect the longevity of his product. I would surmise that this transaxle has been held in 2nd gear at high rpm for long periods of time. Otherwise, the 1st gear needle bearing wouldn't be completely fried (which in turn led to any other damage).

A transaxle can be built for EV, but expecting an off-the-shelf unit to withstand being held @ 5,000 rpm in 2nd gear is folly.
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EVfun
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PostPosted: Fri Nov 06, 2015 7:50 pm    Post subject: Reply with quote

My transaxle has been handling EV duty since 2000, full of Redline MTL. Running at 45 mph in second gear (5100 rpm) isn't really that extreme. That is about what I hit running 70 mph in 3rd too (though I don't do that for very long.)

You should let your transaxle builder know it's an EV, but unless one is building a drag strip EV the power levels and the rpm range are not much different than stock. The extra low rpm torque, that mostly eliminates the need to use 1st gear, is about the only difference.
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gears
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PostPosted: Fri Nov 06, 2015 8:27 pm    Post subject: Reply with quote

While it may seem that you're operating only slightly above design parameters, the VW trans can easily be pushed too far. For instance, we've learned that rotary engines which operate at much higher rpms than VW will often fry the late model mainshaft needle bearing. The little needles literally weld themselves at a sustained 9,000 rpm.

In the OP's case, when held at high rpm in 2nd, a lot of heat is continually generated right next to a needle bearing that may have been set at only .004" clearance. Had the builder known the OP's use, he could have set at the high end of the factory's recommendations .. or even much higher without consequence. I'm not saying that I absolutely know this is the sequence of events, but at least I know what I'm looking at (a fried 1st gear needle bearing, not a failed R&P), and I hope I'm shedding some light on the possible cause.
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9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com
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corbin_dunn
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PostPosted: Mon Nov 30, 2015 8:17 am    Post subject: Reply with quote

gears wrote:
While it may seem that you're operating only slightly above design parameters, the VW trans can easily be pushed too far. For instance, we've learned that rotary engines which operate at much higher rpms than VW will often fry the late model mainshaft needle bearing. The little needles literally weld themselves at a sustained 9,000 rpm.

In the OP's case, when held at high rpm in 2nd, a lot of heat is continually generated right next to a needle bearing that may have been set at only .004" clearance. Had the builder known the OP's use, he could have set at the high end of the factory's recommendations .. or even much higher without consequence. I'm not saying that I absolutely know this is the sequence of events, but at least I know what I'm looking at (a fried 1st gear needle bearing, not a failed R&P), and I hope I'm shedding some light on the possible cause.


Hi,
I never said I held the transmission at high RPM in 2nd. I don't go around driving the car at 5000 RPM constantly, and I rarely (if ever) hit that RPM. I said I don't use first. I start in 2nd gear (which means a lot of torque -- but I never push it too hard to break traction), and shift before specific RPM points; usually around 4500 RPM (specifically, before 40MPH I shift to 3rd, and before 65 MPH I shift to 4th). These are safe RPMs and within the original engine's guidelines.

The failed R&P couldn't have had anything to do with this -- that failure happened after ~20 miles on the freshly rebuilt transmission.

To follow up on the original leaking problem: I did a lot of work to ensure the alignment of the main shaft was dead center with the adapter I use. That seems to have fixed the problem; I have about 800 miles on this setup so far, and it isn't leaking. More details at: http://corbindunn.com/plugbug

corbin
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nsracing
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PostPosted: Sun Dec 06, 2015 5:33 pm    Post subject: Re: Rebuilt transmission (from Mofoco) leaking -- not sure w Reply with quote

Nice!

First of all, you had a trans built and cooked it on an application other than a car engine where it was supposed to mount.

I will address the leak first. If you filled this trans while it was upright -YOU WILL GET ALL KINDS OF LEAK.

2nd, the alignment issue. The trans bellhousing centered on a 'lip on the case and secured by 4 bolts. If you are going to adapt the transmission to some other powersource, you MUST reproduce ALL of the specs of the engine case to accept the bellhousing.

For centering, you machine that red coupler you made w/ the same 'lip' dimension as the engine case. Otherwise, you will not be able to align.

...or you can use dedicated 'studs' or dowel pins to maintain center for the input shaft. then the bolts will go on just as usual.

You were probably better off w/ the BUS bellhousing as an adapter to the electric motor. And use a spacer machined centered to the electric unit, mount/studded to the bellhousing.

The input shaft has to go inside the bellhousing same depth as the stock engine where it will mount to pilot bearing w/c can be in the rotor shaft of flywheel (like in some busses).

The issue is w/ your RED adapter. I will just cut the weld, machine the diameter on the mill and mount/couple inside the trans bellhousing. See how much depth you want, and weld the shoulder where it sits.

Well, seems you are a machinist too. Cannot forget the basics, mounting, coupling, alignment, all the good studs.

my 2 cents.
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