Hello & All Trac 4wd System question

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Re: Hello & All Trac 4wd System question

Postby 93celicaconv » Mon Oct 07, 2019 10:59 am

The brake test, as you described it, when testing the front wheels, provided the speed of the front rollers drove the front wheels slowly (say 1-2 miles per hour) for 5-8 seconds should have been OK. The handbrake would have prevented movement of the rear wheels (provided the hand brake was functioning properly.

The brake test, as you described it, would not work for testing the rear wheels. The hand brake cannot be engaged (it would prevent the rear wheels from turning). If the hand brake was not used on the rear wheels, when the rollers turned, the front wheels would have turned with it, unless the car body was somehow restrained, or the roller speed turning the rear wheels was exceptionally slow (turning the rear wheels puts force to turn the front wheels in this situation).

The test I mentioned was to check the viscous coupling. The front wheels are locked (because with the engine off and the transmission in first gear, the front wheels cannot turn without the engine turning). You want the front wheels locked to see how easy it is to rotate the rear wheels. If one rear wheel was not restrained, that unrestrained rear wheel would turn easily in the opposite direction the wheel being turned by hand would turn.

You could do this test with only the rear wheels off the ground, as the front wheels on pavement would prevent them from turning. But still have the transmission in first gear - don't want the front wheels to move while the rear wheels are elevated above pavement.
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Re: Hello & All Trac 4wd System question

Postby ATSTodd » Mon Oct 07, 2019 11:58 am

My cousin took her all-trac to be emissions tested many years ago. The technicians failed to realize the car was all wheel drive and strapped the car to the emissions dyno. The rear tires were on the ground while the front tires were spinning. They stopped the test when burning transmission oil began to pour out of the car. I assume it was heated by the viscous coupling. That car was never checked out by anyone afterwards and drove for thousands of miles. I imagine the VC fluid is damaged but who knows? Just one anecdotal story to say the OP's VC is probably not worth worrying about.
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Re: Hello & All Trac 4wd System question

Postby Celicast185 » Mon Oct 07, 2019 12:01 pm

93celicaconv wrote:The brake test, as you described it, when testing the front wheels, provided the speed of the front rollers drove the front wheels slowly (say 1-2 miles per hour) for 5-8 seconds should have been OK. The handbrake would have prevented movement of the rear wheels (provided the hand brake was functioning properly.

The brake test, as you described it, would not work for testing the rear wheels. The hand brake cannot be engaged (it would prevent the rear wheels from turning). If the hand brake was not used on the rear wheels, when the rollers turned, the front wheels would have turned with it, unless the car body was somehow restrained, or the roller speed turning the rear wheels was exceptionally slow (turning the rear wheels puts force to turn the front wheels in this situation).

The test I mentioned was to check the viscous coupling. The front wheels are locked (because with the engine off and the transmission in first gear, the front wheels cannot turn without the engine turning). You want the front wheels locked to see how easy it is to rotate the rear wheels. If one rear wheel was not restrained, that unrestrained rear wheel would turn easily in the opposite direction the wheel being turned by hand would turn.

You could do this test with only the rear wheels off the ground, as the front wheels on pavement would prevent them from turning. But still have the transmission in first gear - don't want the front wheels to move while the rear wheels are elevated above pavement.


I understand, I'm going to test the rear wheels as the way you described, thanks!

About the brake test for the rear wheels, your observation is very smart, I'm totally agree, but I think that this test could be done because rollers were located at not the same level of the ground, I mean, they are located in a type of "hole" and no in the normal horizontal of the road, its like you were driving and then you get stucked in a big depression, obviously not so big, but maybe enough to prevent the advance of the car.
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Re: Hello & All Trac 4wd System question

Postby Celicast185 » Mon Oct 07, 2019 12:05 pm

ATSTodd wrote:My cousin took her all-trac to be emissions tested many years ago. The technicians failed to realize the car was all wheel drive and strapped the car to the emissions dyno. The rear tires were on the ground while the front tires were spinning. They stopped the test when burning transmission oil began to pour out of the car. I assume it was heated by the viscous coupling. That car was never checked out by anyone afterwards and drove for thousands of miles. I imagine the VC fluid is damaged but who knows? Just one anecdotal story to say the OP's VC is probably not worth worrying about.


:cry: What a terrible situation! but, how much speed did those cars killers put in the front axle of the car? That test sounds like the car was with the gearbox engaged in 1st or 2nd gear, accelerating and then the failures happened ...
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Re: Hello & All Trac 4wd System question

Postby ATSTodd » Mon Oct 07, 2019 12:29 pm

If I remember correctly they would do a low speed test and a high speed test. I think the high speed test was only like 25mph. It was still plenty to heat things up!
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Re: Hello & All Trac 4wd System question

Postby underscore » Mon Oct 07, 2019 6:41 pm

93celicaconv wrote:At any rate, you can get a feel of condition by getting all 4 wheels of the ground at the same time, engine stopped, transmission in 1st gear, then someone holding one rear wheel still (to allow no rotation) while another tries rotating the other wheel. It should be possible to turn the one rear wheel in this case, but only very slowly and with significant resistance. If this is what you find with the test, chances are high you are OK. But if one rear wheel turns freely in this test, your viscous coupling is gone.


Don't forget he has an RC which should have the torsen rear limited slip diff still in it. I don't know enough about the functionality of those to comment on how it might affect this test though.
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Re: Hello & All Trac 4wd System question

Postby 93celicaconv » Mon Oct 07, 2019 7:00 pm

underscore wrote:Don't forget he has an RC which should have the torsen rear limited slip diff still in it. I don't know enough about the functionality of those to comment on how it might affect this test though.

Good point. I know manually rotating one rear wheel with both back wheels lifted off the ground will cause the opposite side to rotate freely in the opposite direction (just like the USDM open rear differential, which we tested on an uninstalled Torsen rear differential we have as a spare), but when one side is held, I don't know if it will act the same.
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