'94 Q45 shuddering under acceleration

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RustyBucket
Posts: 143
Joined: Mon Dec 28, 2009 2:04 pm
Car: '94 Infiniti Q45

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Recently, I've been noticing that my Q will shudder when I am accelerating away from a stop. It does not feel like it is coming through the steering wheel. It happens under light throttle and when the speed is around 20KM/H (12mph). It doesn't matter if I am accelerating in a straight line or turning, it happens. It also happens in both 1st and 2nd gear and does not appear to be interrupted by the gear change. If I apply more throttle, the shuddering is not as noticeable, which I think is because I pass the speed range where it happens more quickly.

I am thinking it could be a few things, but I'm not sure and would like NICO's input:- Transmission? Could it be clutch chatter? The fact that it happens in both 1st and 2nd without interruption on the gear change makes me question that though.- Engine/Transmission/Subframe mounts? This could cause vibrations, but it only happens when accelerating from a stop- Differential? Clutch chatter in the VLSD? The fact that it happens both in a straight line and while turning makes me question that as well.- Alignment?


Q45tech
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Posts: 14365
Joined: Tue Apr 30, 2002 3:19 am
Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl

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First thing to ask: When were engine and transmission mounts last replaced?When was transmision last replaced? The 90-93 and 94-96 have shorter life compare to 97 and newer.16+ years is a long long long time for a oem tranny about double the usual life depending on miles.

Per se there is no clutch [in normal sense] in a VLSD compared to mechanical LSD.

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RustyBucket
Posts: 143
Joined: Mon Dec 28, 2009 2:04 pm
Car: '94 Infiniti Q45

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Well, in response to your questions, the only answer I have is "Probably not since 2005", since there is no record of it in the maintenance receipts.

The car has 268,000KM on it (about 166,000 miles). It's been on the flat prairies since at least '96, so going up "hills" bigger than 30 or 40 feet has probably been an uncommon thing 14 or so years, which would help transmission life. The climate, which varies beween +35C in the summer and -35c in the winter doesn't help, however.

I've done reading on here about transmission lifespan, so I am defintiely putting aside a "transmission contingency fund". I got a transmission cooler on the weekend, so I'll check out the mounts when I'm putting that in and replacing the external trans. filter.

I've also read that this could also be caused by problems with the parking brake.

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goody90q45
Posts: 3679
Joined: Wed Aug 17, 2005 2:07 pm
Car: 1992 Q45 (sold)
Location: Orangevale, CA

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I had transmission shudder in my first 90Q very similar to yours and more noticable when climbing hills. It didn't happen in 3rd or 4th gear. I did the fluid flush and filter change, tried Lucas and Lubeguard additives and never got much improvement. My conclusion at the time was a bad torque converter but I never replaced it.

Has the TRANSMISSION MALFUNCTION warning in the odometer display come on at all? Have you done the tranny self-check from the AT section of the FSM? Anything electronic will show up stored as a code.

A new transmission mount and exhaust hangers will get rid of vibrations you never knew you had. Check the exhaust hangers (they're attached to the tranny mount) and see if the rubber block is torn away from the bracket it's bonded to. With your cold weather you'll see similar cracks in the tranny mount rubber.

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RustyBucket
Posts: 143
Joined: Mon Dec 28, 2009 2:04 pm
Car: '94 Infiniti Q45

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I've never seen the "TRANSMISSION MALFUNCTION" display and I haven't run the transmission self-check from the FSM. It looks like my motor mounts are alright, as the motor barely shifts under load.

After this weekend, I am starting to wonder if the cause may actually be the fuel pump. After doing some unrelated work (DRL fix, injector ohming and troubleshooting a problematic trunk tamper switch), the car would not start. It turned over, but would not catch. I unplugged the FPCU and shorted the pin to ground, forcing the pump to run on high. The car started with a little persuasion and appeared to run better with the pump on high. I shut it off, plugged the FPCU back in and the car has been running fine since. The pump has also been making noise, though, so a replacement is on its way from IOS.

3Q Jay
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Car: 94 Q45a
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my '94 active did something similar until i replaced the alternator (genuine nissan remann'd only, please). old alternator had a bit of roughness in the bearing.motor mounts would probably help a lot, too though.

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RustyBucket
Posts: 143
Joined: Mon Dec 28, 2009 2:04 pm
Car: '94 Infiniti Q45

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I replaced my fuel pump over the weekend and it looks like the shuddering has gone away. The engine was also sluggish to rev up before I changed the pump; I didn't really realize how bad it was until I started it up for the first time with the new pump.

I'll have a look at the mounts next time I'm underneath the car, but it looks like the shuddering was being caused by fuel delivery issues.


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