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1995 MPV Differential questions
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pipedreams
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PostPosted: Tue May 05, 2020 12:21 pm    Post subject: 1995 MPV Differential questions Reply with quote

Hi all! (whoever is still out there)

I'm wondering if anyone has done testing on their differential? Here's what I mean;

20 years ago I had a 92 4wd mpv. It was great. I remember that when I put it in 4wd and then locked the diff the thing stiffened up and felt unstoppable.

Cut to 2015 when I got a 1995 4wd mpv to relive the glory. It's great. But ever since I got it it feels like the diff isn't working. I put it in 4wd and it works great. but then I lock the diff and it doesn't feel different. If I get it a bit articulated in some deeper snow a front and rear wheel will spin. I'm pretty sure my 92 didn't do that. And in the manual it says that locking the diff makes the wheels locked. All four locked should turn together, right? Which doesn't seem to be happening. Anyone have any thoughts?




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poptop
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PostPosted: Wed May 06, 2020 12:58 pm    Post subject: Re: 1995 MPV Differential questions Reply with quote

Ah, the mystery's of 4X4. I am no expert, but I think our MPV's do not have limited slip differentials which would keep the power to both wheels no matter what. With our non limited slip differentials on normal surfaces the power ratio is evenly distributed between all the wheels. What I do not know is when one wheel starts slipping, I have read that then all the power goes to the spinning wheel although it doesn't seem to make sense.
The Center Lock switch locks the rear and front differentials. Have you tried turning in a tight circle and feel the steering binding up? If not, then I would suggest you verify that the Front Vacuum actuator is operating correctly. The actuator moves the front differential axle locking shaft.
An old post that might help:
There is a vacuum activated fork inside the front differential. This fork internally slides a locking ring to engage or disengage the front axle shafts. The main vacuum line comes off the throttle body thru a small one-way check valve up to the firewall vacuum reservoir then to two solenoids on the drivers strut tower. Here I think the manual maybe wrong It states the one closest to the firewall is the disengage solenoid and the one closest to the front of the car is the locking solenoid) . Then the two vacuum lines run down to the front left axle actuator. When you switch the 4X4 switch on and off the solenoids will allow vacuum to pass down to the actuator.This in turn moves the actuator rod either inward or outward which engages or disengages the internal fork. I never had a reason to do any troubleshooting on these parts but it looks like you may be able to manually disengage the 4X4 mode by pulling the actuator rod away from the pumpkin. To engage 4X4 push the rod towards the pumpkin.
Also when you select 4X4 mode you should hear a slight clunk which is the change motor moving. There is a small round indicator on the back of the transfer case with an indented arrow that moves, On mine it is covered by a metal bracket that needs to be removed to see this round indicator.
The best way to check the front axle actuator arm is working is to use one of those hand pump brake bleeding tools with the vacuum gage on it. You can use it at a straight vacuum gauge to see if vacuum is going thru the solonoid as you swtitch into 4X4 mode or you can pump it and visually see the actuator arm on the differential move back and forth. Very hard to see from above, but with a strong flashlight you can see the rubber protector stretch and compress as the actuator arm moves.

1990 4X4 V-6 5-speed
1991 2WD V-6
1994 2WD V-6
Scion Xb
A pile of old timing belts
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pipedreams
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PostPosted: Wed May 06, 2020 2:20 pm    Post subject: Re: 1995 MPV Differential questions Reply with quote

Ha! A mystery indeed! Well, thanks for those thoughts.

I do know the 4wd works. I use it all the time. If I'm on pavement with 4wd on it can't turn. Normal stuff. And I had read the post about the front diff actuator...interesting but not quite my issue...

But from 20 years ago I remember 4wd feeling stiff on pavement. Same as this 95 now. But from 20 years ago I also remember when I then locked the diff it felt WAY stiffer (on pavement also) to the point that I could feel the lack of turning on snow or soft dirt and sand!

With this 95 I don't feel or see any difference when I lock the diff. And again, the manual clearly says that the 4wd button puts it in 4wd and the diff lock button then additionally locks all the wheels at the same turning speed... and it cautions you not to use diff lock on pavement or other firm surfaces... as it should!

So... I guess my question is; Do you or anybody else out there have a 4wd MPV with diff lock? I would assume most people do who look at this since the 4wd mpv is the one to have I feel... Seems most mpv fans would agree... Can you or anyone do this test? As in, put it in 4wd and then play with diff lock to see if you can feel a difference? Or, if you're adventurous, get articulated on loose surface and see if you can spin a front and rear in just 4wd... then see if you can spin in 4wd with the diff locked?

I guess I'm asking someone to go out and do some MPV off-roading! Not the worst days activity when we're all chillin at home!

Point is, if anyone can do this test or knows they feel a difference with diff lock, I will be able to know if and what I might need to look into. I'm not that much of a mechanic myself... I did go to pick-n-pull and get an "actuator" looking thing with wires and vacuum lines that was bolted to the tranny/transfer case in hopes that it was the differential locker or had a part that would fix mine... IF MINE IS ACTUALLY BROKEN... which I think it is but still not sure...

Had a 92 4wd MPV
Have a 95 4wd MPV
Had 4 Subaru Justy's, all 4wd, a few Audi's, all AWD
Have a 91 Toyota pickup xtracab 4x4
Have a 2007 Suzuki SX4 AWD
Is it obvious I like power to all wheels? Wink
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vincentkou98
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PostPosted: Sat May 09, 2020 10:11 pm    Post subject: Re: 1995 MPV Differential questions Reply with quote

IIRC the MPV has a CENTER locking differential which just means the power is split 50/50 to the front and rear diffs. Both the front and rear are just open differentials which is concluded by having the car jacked up off the ground and spinning one wheel by hand (Turning one side and having the other side spin the opposite way means its open and if both spin the same way it is a LSD which our MPV do not have).
1997 Mazda MPV 4WD (Towing Package)
Black & Silver 2 Tone / 4 Channel Amp (Components & Coaxials) / Sound Deadened Front to Back / 55W HID Bi-xenon Projector Retrofit/ Front, Side, OEM Rear Wind Deflectors / NOS Mud Guards / Aluminum Cluster Rings / Running 235/70/15s
1997 Mazda MPV 2WD
Black & Silver 2 Tone
2019 Accord Sport 1.5T
Black
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pipedreams
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PostPosted: Sat May 09, 2020 10:46 pm    Post subject: Re: 1995 MPV Differential questions Reply with quote

vincentkou98 wrote:
IIRC the MPV has a CENTER locking differential which just means the power is split 50/50 to the front and rear diffs. Both the front and rear are just open differentials which is concluded by having the car jacked up off the ground and spinning one wheel by hand (Turning one side and having the other side spin the opposite way means its open and if both spin the same way it is a LSD which our MPV do not have).


Ok... Sounds possible... But why would the manual say that diff lock makes ALL the wheels turn at the same rate?

And why would diff lock even exist if it locks the front and back to 50/50? What does 4wd do? Lock it at 70/30? How would the 4wd switch do that? Certainly when it's in 2wd it's 100% rear. Then when you put it in 4wd, wouldn't THAT be the 50/50 mode?

I don't get it...

Had a 92 4wd MPV
Have a 95 4wd MPV
Had 4 Subaru Justy's, all 4wd, a few Audi's, all AWD
Have a 91 Toyota pickup xtracab 4x4
Have a 2007 Suzuki SX4 AWD
Is it obvious I like power to all wheels? Wink
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vincentkou98
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PostPosted: Sun May 10, 2020 2:34 am    Post subject: Re: 1995 MPV Differential questions Reply with quote

No, due to open differentials in both front and back the torque will go to the wheels with least resistance. Center locking just makes sure it doesnt all go the one end.
1997 Mazda MPV 4WD (Towing Package)
Black & Silver 2 Tone / 4 Channel Amp (Components & Coaxials) / Sound Deadened Front to Back / 55W HID Bi-xenon Projector Retrofit/ Front, Side, OEM Rear Wind Deflectors / NOS Mud Guards / Aluminum Cluster Rings / Running 235/70/15s
1997 Mazda MPV 2WD
Black & Silver 2 Tone
2019 Accord Sport 1.5T
Black
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pipedreams
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PostPosted: Sun May 10, 2020 10:28 am    Post subject: Re: 1995 MPV Differential questions Reply with quote

Really? I've never been able to create that scenario while driving...

You're saying that if I have it in 4wd without the differential locked I would be able to lose traction and all the power would go to the front or rear? (ie, power would all go to which ever end had less grip?)

I gotta say, I do some pretty aggressive off roading in this 'ol MPV, and I've never experienced anything like that. 4wd ALWAYS has power to the front and back no matter what I do...And I'm talking about 4wd only, not the diff lock. I've had this diff lock issue for 5 years, so I've played around with it plenty. Just like my Toyota with basic hi-low transfer-no matter what I do in that thing there's always power to at least one front and one back wheel. But it doesn't have a locker. So I expect the opposite spinning wheels in the Toyota.

The MPV has a locker. So either the button is just for looks, or something is not right...

Does your MPV have separate 4wd and diff lock buttons? I'm only familiar with the 95 body/interior versions

Have you had yours in 4wd ONLY and had one end get all the traction?

Thanks for the help!

Had a 92 4wd MPV
Have a 95 4wd MPV
Had 4 Subaru Justy's, all 4wd, a few Audi's, all AWD
Have a 91 Toyota pickup xtracab 4x4
Have a 2007 Suzuki SX4 AWD
Is it obvious I like power to all wheels? Wink
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vincentkou98
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Location: Walnut, California, United States of America

PostPosted: Wed May 13, 2020 4:39 pm    Post subject: Re: 1995 MPV Differential questions Reply with quote

I've never taken my car into anything that serious to be quite honest haha. But generally yes, power will end up to the path of least resistance. I don't mean you'll completely lose power to the wheels, but a big portion of it. My 97' does have the two separate buttons "DIFF LOCK" and 4WD". But yea, you'll know when you service the rear end of the car that the rear axle is in fact an open diff and that the front pumpkin that actuated by vacuum is to engage the two front shafts
1997 Mazda MPV 4WD (Towing Package)
Black & Silver 2 Tone / 4 Channel Amp (Components & Coaxials) / Sound Deadened Front to Back / 55W HID Bi-xenon Projector Retrofit/ Front, Side, OEM Rear Wind Deflectors / NOS Mud Guards / Aluminum Cluster Rings / Running 235/70/15s
1997 Mazda MPV 2WD
Black & Silver 2 Tone
2019 Accord Sport 1.5T
Black
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pipedreams
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PostPosted: Sat May 16, 2020 7:56 pm    Post subject: Re: 1995 MPV Differential questions Reply with quote

Gotcha. Thanks for the insight.

One more question; What does your manual say? Does it say that diff lock makes all the wheels turn at the same speed?

I'd be very curious to hear the exact sentence from the diff lock page in your manual to see how it compares to mine!

Maybe mine is working as it should???

Had a 92 4wd MPV
Have a 95 4wd MPV
Had 4 Subaru Justy's, all 4wd, a few Audi's, all AWD
Have a 91 Toyota pickup xtracab 4x4
Have a 2007 Suzuki SX4 AWD
Is it obvious I like power to all wheels? Wink
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