AT modulator - vac sucking ATF into engine possible ?

[Stanley]

73' 240 Z with automatic. My ATF is very low and I don't see a leak. I don't know how the modulators are built. Is is possible for the vacuum line to the modulator to be sucking ATF into the engine ?

And if so, could it dilute the break-in oil for the new engine ?   I think it would just burn up in the cylinders, but not 100% sure.

Edited August 1, 2018 by Stanley

[gwri8]

You said new engine.  Does your new engine oil look odd?  Did you pull the old engine and transmission out together?  

Edited August 1, 2018 by gwri8

[Stanley]

I paid a shop to R&R the engine; they didn't pull the trans. Oil looks clean and correct level, didn't see any red in it.

[gwri8]

By no means am I an expert, but I don't think there is any way ATF can get into your engine oil unless you put it there. The reason I asked about the rebuild (since you did not give a timeline or details) is that it is not unusal to pull the engine an trans together. Some people find it easier.   If the engine/trans were removed, like at an angle, there is a fair chance that ATF leaked out of the transmission and was not put back in.   With that assumption, I would just refill ATF and monitor it for leaks as a start. There are a lot of variables so it's just my opinion.

[Stanley]

The modulator on the AT is connected to a fitting at the back of the balance tube where it gets engine vacuum for automatic downshift. It seems to be working OK for shifting. Some modulators for other cars can leak, pulling ATF into the engine, but I don't know if its possible with the ones used on the 240Z.

[EuroDat]

I can remember in Australia in the mid eighties, holden used the Nissan RB30E and the RB30ET with the 4 speed jatco automatic (Nissan code 4N71B). The were known for using oil through the modulator valve.

You couls very wel have this problem. Easy to check it. Pull the steel tubing from the modulator valve and check if it has any oil. It should be dry.

You could buy a sports kit for the automatic to make it a more performance transmision. The datsun guys use to use the kits too.

https://www.ebay.com.au/itm/Commodore-VL-4N71B-4-Speed-Automatic-Transmission-Vacuum-Modulator-Non-Turbo/322484179317?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D52946%26meid%3D4327a240619b4a2e9d10680aaba0be2f%26pid%3D100623%26rk%3D1%26rkt%3D4%26mehot%3Dlo%26sd%3D222255979018%26itm%3D322484179317&_trksid=p2047675.c100623.m-1

 

[Stanley]

Thanks EuroDat. You were right. I pulled the hose off the balance tube fitting and there was ATF.

I've noticed the A/F ratio occasionally goes rich, with a puff of smoke from the tailpipe. I thought it was a sticky float bowl valve but maybe it was choking on ATF.

I looked at that link, didn't see performance kit for the Jatco 3 speed but maybe I didn't look at everything yet. They have a lot of stuff. I've read about mods for Z car AT but thought the parts were NLA.

Wonder if the 4 speed 4N71B bolts up to a 280Z engine ?