I bought a 1990 Infiniti Q45 that would move a few hundred feet and would stop moving. It makes a grinding noise when in neutral or park. I changed the ATF fluid and filter, and now the car can be driven around the block okay. It only makes the grinding noise in park or neutral and is quiet in gear. There were lots of metal shavings in the pan, and it looks like a bearing went out and threw these shavings everywhere clogging the filter. The car has 77,000 miles and the transmission case is painted blue, which makes me think it has been rebuilt before.

The junkyard has a 1998 Q45 that was in an accident. It has 274,000 miles and the fluid is a brownish red. Will that transmission fit my car? The only difference I see is that the 1998 has a transmission drain plug while the 1990 does not. I know that the 1998 has high miles, but I feel that the transmission was probably rebuilt some time in its life.

Is there some defect in 1990 Q45 transmissions? It seems odd that the one in my car is painted blue indicating that it was removed and rebuilt some time in its life and went out again.

Looking at Car-Part.com, it looks like the bell housing for a 1998 transmission is not the same as the one for a 1990 transmission. However, a 1995 bell housing looks like the same. Does anyone know if a 1995 Q45 transmission will fit a 1990 Q45?

the guts are all re4r03a for the g50 and the fgy33 platforms.
you have already identified the bellhousing bolt pattern b/n the g50 and fgy33 as being different.
within the g50 run, there was also a change somewhere in late 1992 whereby the planetary ratio changed. the 'early' g50 like yours has a 'wide ratio' 1st/2nd/3rd, vs. the later ones like mine that went close ratio. It's really only 1st and 2nd that have the different ratios, third is 1:1 in all versions.
The z32 platform with the TT (auto version) also used the re4r03a, with the wide ratio as yours came with.

here's a nico thread with some additional data:
re4r03a-transmission-t6915.html

oh, and yeah, the early g50s were fraught with transmission overheats. poor heat exchanger in radiator, 2nd gear start, etc.

Yes there was a defect in the 1990 and 1991 Q's transmissions. Mainly due to a heat issue.

I had 3 transmissions replaced under warranty to my first Q45 a 1991.

It was difficult to get the service department's to state a 'factory design' defect, but they finally did.

And corrected in later models.

Is it possible to install a 1992-1996 transmission into my 1990 so that I will not have transmission issues anymore? Would I need to swap the TCU? My plan is to install an external transmission cooler to prevent this from happening again. Would it be best to bypass the radiator heat exchanger or install the external cooler in line with the radiator heat exchanger?

Is it still possible to get a fragrance cannister on this car?

michaellong wrote: ↑

Mon Jun 07, 2021 12:14 pm

Is it possible to install a 1992-1996 transmission into my 1990 so that I will not have transmission issues anymore? Would I need to swap the TCU? My plan is to install an external transmission cooler to prevent this from happening again. Would it be best to bypass the radiator heat exchanger or install the external cooler in line with the radiator heat exchanger?

With a used tranny you're always best off getting the donor TCM with it if possible. It saves a lot of "re-education" headaches on trannies that have adaptive firmware or parameters stored in the Valve Body. I don't know if your Q requires any of that, but if you get the TCM then there's no need to find out.

You should install the cooler in series with the radiator heat exchanger, not instead of it. Running too cold will cause excessive wear in a transmission just like an engine, so you want the benefit of the heat exchanger warming the tranny. The best setup is to add a thermostatic bypass valve along with the cooler. They sell kits with them, or you can get one separately for about $50.

Michaelong, where are you located? I think if you're in Florida, just an external cooler would be fine. The recommendation on this fourm for years has been to just bypass the factory cooler unless you live in a very cold climate. I understsnd VStar's thinking though. I'd also be curious on VStar's take on the B&M cooler that supposedly bypasses the cooling plates until the ATF warms up?

A 90-96 transmission should be the easiest fits for your swap. If I remember correctly the 96 TCU won't play well with the earlier years though.

The old Q45s don't require TCU programming and matching like the later cars. I would recommend buying a 1st gear start TCU for your car to take advantage of the better performance and lower heat generation. I happen to have a spare out of a '95 that I tested, if you need one.

Q451990 wrote: ↑

Mon Jun 07, 2021 7:31 pm

I'd also be curious on VStar's take on the B&M cooler that supposedly bypasses the cooling plates until the ATF warms up?

If you mean the "SuperCoolers" with the bypass built-in, they're basically doing the same thing as a standard cooler plus an external bypass, but the H-valve is embedded into the core of the cooler. There's no real advantage to it other than convenience, but no big disadvantage either. The valve obstructs the core so it will slightly reduce cooling capacity compared to a "clear" core of the same size, but I expect Holley/B&M will have accounted for that in their BTU ratings. It does save 4 hose clamps and a bit of complexity in the hookup, which might be a big advantage on a car with lots of clutter around the lower radiator. The 'stats all use very reliable shuttle valves, and the combined price of a Hayden cooler plus a Derale or Dana H-valve is pretty much a push with a similar capacity B&M. So I'd say it's a "you pick" depending on your vehicle and preference.

I live in Los Angeles, so I don't need to worry about freezing temperatures. I usually hook external coolers in series with the radiator for extra cooling. It also helps in traffic and at idle when there is not much air moving past the cooler to keep the transmission temperatures down. However, I read that the heat exchanger gets blocked on these cars, and I was wondering if that means a blockage forms that prevents transmission fluid from flowing through the heat exchanger or if a blockage forms that prevents coolant from flowing through the heat exchanger.

Have any of you replaced a transmission on a Q45 before? I have removed transmissions from E46s BMWs, but I have never installed a transmission before. How long did it take you to replace a transmission on a Q45?

michaellong wrote: ↑

Tue Jun 08, 2021 3:44 am

I usually hook external coolers in series with the radiator for extra cooling. It also helps in traffic and at idle when there is not much air moving past the cooler to keep the transmission temperatures down. However, I read that the heat exchanger gets blocked on these cars, and I was wondering if that means a blockage forms that prevents transmission fluid from flowing through the heat exchanger or if a blockage forms that prevents coolant from flowing through the heat exchanger.

With a series installation, if the heat exchanger gets blocked then the whole cooler setup will be disabled. But the same is true of a blockage anywhere in the cooling loop. Since the flow stops, there's really no good way to automatically detect it and shunt around it. If that's a major worry (say, on an old trans with soupy fluid), the only thing you can really do is put in a tranny temp gauge and/or an idiot light to monitor it.

michaellong wrote: ↑

Tue Jun 08, 2021 3:44 am

or if a blockage forms that prevents coolant from flowing through the heat exchanger.

The coolant flows around the atf heat exchanger in the radiator end tank(s).
Some other g50 zenki versus kouki differences for your perusal: the zenkis had a single heat exch in the radiator, and no external ATF filter. The koukis fixed both of those issues.
Nevertheless, I have a hayden stacked plate cooler between the condenser and the rad on both my g50s (keeping the external factory [replaced once during lifetime] ATF filter). I also run a magnefine in series with the stacked plate cooler.

3Q Jay wrote: ↑

Tue Jun 08, 2021 8:03 am

michaellong wrote: ↑

Tue Jun 08, 2021 3:44 am

or if a blockage forms that prevents coolant from flowing through the heat exchanger.

The coolant flows around the atf heat exchanger in the radiator end tank(s).

Good catch, I didn't notice he said coolant and not fluid and presumed he meant the latter.