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Thread: Disabling AWD on 95 AllTrac

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    Disabling AWD on 95 AllTrac

    Hey Folks, new member here.
    I've found myself in the unfortunate position of having two '95 Previas that seem to be acting out the parts of the two hound dogs in Where the Red Fern Grows. First one (LE S/C RWD) blew the head gasket and I don't have the time, equipment or energy to tackle that after reading Tim's thread on changing it. Second one (LE S/C AWD) waited three whole days before almost simultaneously losing the low beam circuit on the headlights (lots of unhappy Hoosiers coming toward us at night now) and starting a very loud growling/grinding noise out of the front differential. Sound frequency follows vehicle speed so I know it's not SAD shaft or anything else engine-related.
    I think I can rob the parts off the first Previa to fix the headlight problem (from the diagram I'm almost sure it has to be that the low/high beam switch has stopped grounding the circuit), though from the looks of the mess attached to the steering column I might as well change the head gasket instead. My real problem is the AWD. We have found ourselves short on transportation and I need to get this thing back on the road as soon as possible. Finding a replacement axle isn't an option right now due to short supply and needing the van on the road. I can fairly quickly remove the front axle assembly and the drive- and half-shafts, but I thought I read somewhere that the t-case needs to be locked out somehow. My repair manual doesn't cover AllTracs so I need to borrow somebody's clue, but just for a day or two. Anybody know what's involved in converting an AllTrac to permanent RWD? Thanks!
    --dan

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    Re: Disabling AWD on 95 AllTrac

    Hi Dan & welcome to TVT. Removing the diff and the axles would reduce drag a bit, & might even be necessary depending on how bad the problem is. If the problem is a bad viscous coupling inside the transfer case (the more common issue) all you need to do is remove the front most drive-shaft. It's pretty easy and straight forward. I drove mine for a while with that shaft removed and everything seemed fine. I didn't mess around with locking the t-case, I think that's just for testing......but to be completely honest I'm a little vague on that.

    I haven't had a headlight issue with a Previa yet, but the 1st thing I'd check would be the connections between the switch and the harness. Pull apart the connectors that go up to the steering column and check the conductors inside for burn marks. Tim

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    Re: Disabling AWD on 95 AllTrac

    The headlight circuit on the USA-spec Previas is a weak point--they didn't use a dimmer relay (but even among North American Previas, Canadian models did use a relay, so this problem is specific to USA-Previas only). In the USA-spec Previas, the lights are tied to a fuse and switched to ground. The HI-beam indicator is in series with the low-beam filaments, tied to ground on the other end, so when the low beams are switched off, they source a small current (too small to light those larger bulbs) to the HI-beam indicator, and when the low beams are switched on, their ground point bypasses the HI-beam indicator.

    To confirm, ground the ground side of one of the low beams while the lights are on; the low beams should come on and the high beam indicator will go off.

    I think a sealed relay is more reliable than the stalk switch for high-current switching, but unfortunately Toyota didn't go that route with the USA Previa headlight circuit. I think your problem is probably in the stalk switch, which carries the full current of both headlights. I think the part number you'd need is 84140-32140 for one 95 that I checked, or try finding it used from a junkyard? (could be tricky...I don't see many S/C Previas in the U-pull yards around here).

    As far as running in RWD mode, I've never done that. I know some members of the Yahoo group have run their vans in that configuration for short periods, but I can't recall if they locked the transfer or not. You can confirm a bad transfer case by turning tight circles in a parking lot and feeling for wheel binding/lock-up. If it turns smooth circles, the transfer is OK. Eric

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    Re: Disabling AWD on 95 AllTrac

    Thanks fellas.

    With regard to the headlight issue, I'm pretty sure it's the stalk switch itself, since the high beams work and the high beam indicator stays on when in low beam mode. At least the wiring diagram I have seems to indicate that both positions share a common ground path wire, that's why I'm figuring it's the switch. Question: if I just permanently ground the low beam lug on the lamp, that'll make the low beams work, and the high beams should also work when I switch to the highs, but the lows will stay on with the highs like the signal position of the stalk (pulling toward me). Do you think there's any harm doing that long term, ie will that overheat the bulbs?

    My son just pulled the driveshaft off. Tim, re-reading your post just now I think you're saying that I needed to break the shaft just ahead of the intermediate bearing, right? I noticed that when Nik pulled the splined shaft out of the transfer case it appears to be sealing the internals, right? So I'm thinking that we need to reinstall the rear half of the driveshaft to the transfer case before taking it out on the road.

    I'm quite certain the noise is coming from the front diff. Returning home the last time, I crawled underneath and the diff was quite hot from a relatively short trip. I changed out the fluid last week and the magnetic plug had a fair amount of metal filings on it (say, 1/8 tsp). There also seems to be a bit of radial play on the left side output flange. And the noise is loudest at my feet rather than my rear (some would say that's unusual). So I'm expecting that removing the driveshaft won't change the sound at all, but we'll see.

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    Re: Disabling AWD on 95 AllTrac

    Yeah, the shaft coming out of the TC needs to stay as it seals the unit. Just pull the front-most shaft. Tim

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    Re: Disabling AWD on 95 AllTrac

    Wow, that was a trip.

    I put the rear part of the driveshaft back on and took her out for a little run around the block. That shaft will whir like an A-10 until the coupling in the t-case decides to lock up. It does it sitting still in drive and unless I really give her a lot of throttle the vehicle accelerates like there's no fluid in the torque converter. Once it locks up, the whirring sound goes away and she's off like a rocket. My wife's first question when I came back in the house was, "Was all that noise you?" I might have a hard time getting her to drive it like this. I'll give the shaft a quick check but I'm pretty certain I lined the intermediate bearing up in the same spot it was originally. By the way, the front end noise didn't go away as expected, so I'll probably pull the half shafts and call that end of it done.
    The sudden lock of the t-case coupling under load isn't going to hurt anything is it? Any ideas on how to make it behave like a RWD with a working torque converter?
    --dan

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    Re: Disabling AWD on 95 AllTrac

    That isn't the way mine acted with the shaft removed. Mine drove like normal (even when I punched it). There must be something else going on with yours......or perhaps mine??? Keep in mind this is somewhat unknown territory for me, so take my advice with a grain of salt. Maybe you should start looking for another diff. I happen to have a spare for my 91. I swapped it out with a $50 salvage yard unit because it had a pinion seal leak. Too bad yours is an SC model because I'd give you my leaky one for a song & a smile (SC has a different gear ratio than NA). Tim

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    Re: Disabling AWD on 95 AllTrac

    BTW, based on what you describe, I wouldn't recommend driving yours like that as I think damage to the viscous coupling would occur. Maybe you could play with the TC lock mechanism. If you lock up the TC and it drives/feels normal (with that shaft removed) I would probably chance it. Tim

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    Re: Disabling AWD on 95 AllTrac

    Yeah, driving with a different final drive ratio in the front than the back would make it really exciting. ;-)
    Strangely enough, I took it out for a second drive so my son could experience it, and we couldn't get the darn thing to do it again. Wondering if the TC needs to warm up to get the coupling to lock? It wouldn't surprise me given the fact that every Previa I've ever owned (this is #4) won't go into overdrive until the coolant temp gauge reads quarter scale.
    Tim, when you mentioned playing with the locking mechanism, what do you mean? Is there something external that locks the coupling? My Previa doesn't have any diff lock button or anything like that on the dash, but if there's a button, bolt or rope to push I'll give it a try.
    Thanks again for this forum. It's nice to be among folks where the mention of the word Previa doesn't get me snarky replies.

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    Re: Disabling AWD on 95 AllTrac

    Here's where they talk about it in my 91 Previa service manual. I'm not sure if it's the same in 95 but would assume so. I've never messed with this stuff so I don't have any experience here, but I would think locking it and driving would be okay if the front drive shaft and/or other components were removed. The viscous coupling is only to control slip between the front & the back, so if you think about it your experience would indicate a working viscous coupling. Too much slip/heat however may cause failure. Tim






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    Re: Disabling AWD on 95 AllTrac

    Thanks, Tim, I'll put it up on blocks again tonight and see if the access plugs are there on my '95, and try locking it out. I did drive it to work today with no problems, and I think someone mentioned that I might feel a little bit of slip occasionally while launching from a stop, but it was very quick to lock up and go. Nothing of the scary stuff last night. Thanks a bunch for posting the procedure, that's really helpful.
    --dan

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    Re: Disabling AWD on 95 AllTrac

    My Previa is a 91 AWD manual. It is on its second transfer (first one loss of power and horrible clanging noise from within transfer, second one scuppering front wheels on tight turns) and I'm pretty much over the problems associated with AWD, so I'm looking for a permanent change to 2wd.

    I tried disconnecting the front shaft as described in the forum, put the car in gear, but no power to the rear shaft (seems like the coupling must work to some extent?) I didn't like the idea of the rocket take off if the coupling decided to lock, so I gave this up as a course of action.

    When I disassembled my first transfer to look for the problem within, I was surprised to see nothing obviously abnormal despite the dramatic noise. However, I did observe that the locking pin is a pretty small piece of steel and doesn't inspire confidence as a permanent solution.

    Has anyone actually driven theirs around for any appreciable length of time with the locking pin engaged and the front shaft removed?

    Any other suggestions for a permanent change to 2wd?

    Jonny

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    Re: Disabling AWD on 95 AllTrac

    You could get a transfer case from a manual 87 - 89 van. These don't have the viscous couplings so you could just leave it in 2wd mode and not worry about it. If you wanted the ability to shift into 4wd mode (high or low), you could also get the shifter from same year range van and install that. This has been done before & it's a nice upgrade. Tim

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    Re: Disabling AWD on 95 AllTrac

    In another thread a while back there was an apparently still-unanswered question about whether transfer input / output splines and bolt patterns were the same for the corresponding models of vans and previas and thus whether it would be a simple bolt on part exchange.

    Since then has it been determined for sure whether, for example, the 4wd manual 5 speed 87 - 89 Van transfer has direct compatibility with the AWD manual 5 speed Previa transfer, without the need for modification (except of course for the routing of the shifter into the cabin).

    I ask this because I wonder if I am capable of anything beyond a simple swap out.

    jw

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    Re: Disabling AWD on 95 AllTrac

    Yes, swapping manual old style transfer cases to manual transmission Previas has been done and proven. I'm not aware of anybody putting an old school van transfer case on an automatic Previa, but pretty sure it can be done. If an automatic Previa, using a 2 speed transfer case would be a bit more complicated but should still be possible. Putting a single speed automatic t-case on an automatic Previa should be bolt-on, but then there's the vacuum/electric shifting to mess with. You could still use the old style 2 speed t-case on an auto Previa (presumably), but you would need to get 2 transfer cases (one auto & one manual), then swap the input shaft from the auto t-case into the manual t-case.......then it should be bolt-on. This is necessary because Toyota uses different splines in autos than they do in manuals (confused yet?). Here's another recent post where this was discussed. Tim


    Quote Originally Posted by timsrv View Post
    87 - 89 4wd TV vans with manual transmissions had 2 speed transfer cases. Same year range with auto transmissions had single speed transfer cases. These earlier generation t-cases are physically interchangeable with each other and with the Previa transfer cases. The only problem with putting a manual transfer case on an auto transmission is the input shaft splines (autos & manuals have different spline counts). A cool upgrade for 87 - 89 4wd automatic van owners is to find a t-case from a manual van & install it on their auto transmission. The only hiccup with this swap is the input spline issue. The good news is the input shafts on these TV transfer cases are interchangeable. Since they're removing a single speed transfer case with the correct splines, they can swap input shafts between the two cases & make this mod possible. The 2 speed case is shifted via a separate shifter and cable that is usually taken from the same donor vehicle as the t-case.

    This mod can also be done to the automatic Previa except you probably won't be able to swap input shafts. I say "probably" because I'm not aware of anybody who has tried this & don't know if the Previa T-case input shaft is interchangeable with the van T-case shaft (due to the viscous coupling I'm guessing not). There are at least 3 All-Trac Previa owners I know of who have successfully installed a 2 speed transfer case on their manual transmission Previas (without mods). If you were to attempt this on an automatic I would recommend having each flavor of TV transfer case available before starting the project. This will insure you have enough parts (input shafts) to complete the swap. Tim

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    Re: Disabling AWD on 95 AllTrac

    one last possibility is a full RWD conversion... that simply involves deleting the front axle components, including replacing the suspension knuckles with RWD versions... obviously slapping on the RWD trans and maybe the driveshaft too... it might be a good idea to get a RWD ECU too for the proper shift programming (for autos)

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    Re: Disabling AWD on 95 AllTrac

    My 85 toyota pickup with 395k on it is finally losing compression badly, so I was forced to do something with the previa (see my post above).
    Today I locked the transfer using the method from Tim's repair manual, posted above, and disconnected the front portion of the front drive shaft. Seems to drive normally, and the shuddering of front wheels on tight maneuvers has been eliminated. Hooray.
    I will report every couple of months on how this is working as a long term solution.
    If anyone has experience with this already, or knows whether this solution is dangerous, please post.
    Last edited by Jonny; 10-24-2014 at 09:54 AM.

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    Re: Disabling AWD on 95 AllTrac

    A few hundred miles later and no problems with the locked transfer mod.

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    Re: Disabling AWD on 95 AllTrac

    My 91 alltrac drove fine without the rear shaft, but I had to block the wheels when it was in park because it would roll. I came out of the doctor's one day to find it had rolled into someone's vintage car that they had just restored and taken on it's first drive. Fortunately for all it was only $100 damage, but man were they bummed.

    My 95 alltrac went one mile when I took the rear shaft out, then the driveline stopped spinning. It would not go another inch until I reinstalled it. .

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    Re: Disabling AWD on 95 AllTrac

    wouldn't have happened if you used the parking brake
    the "P" selection in the shifter is no substitute for the parking brake! You're depending on a piece of metal that's the size of a pinky finger that can break.... it has happened before and deaths had resulted!
    even if it doesn't break, it'll eventually break the engine or transmission mounts on any car because you're constantly putting a load on them

    frankly, not using the parking brake is a bad habit I've seen most people do

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