automatic made into standard having problem on pavement in 4

[yppg]

I bet this is already a discussed topic but I could not find it through the site search.
After the front differential went out on my automatic tercel I had it switched over to the 5 speed transmission with the extra low range gear. There was much talk about gear ratios, but my mechanic thought it could be done. The "new and improved" tercel is running great with one glitch. The problem has occurred twice when I tried to run the car in 4wd on pavement. The front end tightened up. The car did not want to go. That is the best way I can describe it. These are the only two times I have run it on pavement in 4wd.
Question: Is this the possible mismatched-gear-ratio problem manifesting? Could it be caused by my running different tires (but not sizes) at varying rates of inflation?

[ARCHINSTL]

Welcome to the Club!
Your mechanic thought it could be done? Did he actually check it? There are several threads here about how to check it -and the '83-'84 cars had a different front and rear from the later cars.
And even with the correct and matching ratios, with different sizes of tires it can be difficult to enter/exit 4WD -and funny things can happen as well - also reported in some threads, and Toy is emphatic on using the same size tires.
I think a couple members have also commented on some awkwardness when using different tire pressures and brands (not absolutely positive about this, though - my memory is fuzzy sometimes...).
The tire circumferences can vary from brand to brand, even with the same sidewall sizing. Just go to www.tirerack.com, punch in your brand and size and check out the differences.

OT - but how much did this cost you? Had to be some major bucks.
Tom M.

[Petros]

Welcome to the list.

I have used different brand tires, all the same size, and did not have a major issue if the pressure was pump up to 36 psi, though it was more difficult to shift in and out of 4wd unless I was moving over about 10 mph, as compare to when I have all the same brand tire. If I had a low tire it would act like this too, this system does not tolerate much difference in rolling dia. If you can tell which tire is larger dia, you might be able to run lower tire pressure than in the other tires as a test, but I would not recommend driving around that way.

It does sound like you have different front and rear ring and pinion ratios, what year did the manual trans come from? And do you know what ratio the auto had in the rear? They have to match front and rear ring and pinion ratio. You have to check this out, easy to do by counting revs of the driveshaft vs. front and rear tires with all 4 tires off the ground (engine off, turn the driveshaft by hand, use chalk marks).

Changing the rear diff 3rd member is not too difficult if you change it out as a unit with one from a wrecking yard. but you have to verify what ratio you have first. 1983-84 had the 3.73:1 ring and pinion in the manual trans car, and 1985 and newer had 4.1:1. I do not know what the auto tran has, it might be different.

good luck.

[yppg]

Thanks for the responses and welcomes. I wish I had known this site existed a few months ago. In defense of my mechanic, he did research it on the internet enough that he felt the gear ratios were compatible. And, yes, it cost some bucks. My rationale was that it would still be cheaper than buying an older Outback (the only other car I could consider suitable.) The donor car was an 86 or 87. He still has it so I could get the rear end also. Yet more bucks.
How serious is this gear ratio disease? Could I just use the 4wd sparingly in off road/dirt road situations and get by for the next 100,000 miles?
There is no problem shifting into 4wd. I have to reverse it twice to get it out (not a problem).

[ARCHINSTL]

Take a look at this Sticky in the General Forum (actually, in the header of every Forum): http://www.tercel4wd.com/forums/viewtopic.php?f=2&t=930
Still, no info on the AT front or rear ratios, if different. I have a suspicion they are the same as the MT cars, though - can't imagine Toy's beancounters at the time would countenance having two sets for the same car, regardless of the transmissions - it would increase the SKUs...
Tom M.

[xirdneh]

You should not drive in 4wd on pavement even with proper ratios
you can get away with it only if driving straight with no turns.


if ratios are wrong the front vs rear will be off one revolution per ten
thats around a 6 foot difference in travel over 60 foot of distance (with 24" diameter tires )
i would not put my car thru that even on dirt

jack up one side of car
mark both tires
put in 4wd and in nuetral
rotate a tire and count front vs back revs
if ratios are wrong you will notice a difference on every revolution
until you are 1 rev off at ten

[splatterdog]

The auto's final ratio is an interesting topic. I could see 3.73 being used on auto's for all years. With out overdrive or even a lock up converter, can you imagine the engine rpm's on the freeway?

For us 85 and up manual owners, that would be like driving somewhere between third and fourth gear.

[tercel4wdrules]

The problem is a mis-matched rear differential. It seems to me that your mechanic did not do a thorough job of researching this. The front and rear diff final drive ratio on the A55F automatic transmission for the Tercel 4WD is 3.909 as stated in the 1985 Factory Service Manual on page AT-17. The regular A55 automatic has a 3.583 diff ratio. If I were you I would contact the mechanic, point out the problem, and see if he can correct it without charging you since it was something that was overlooked by him.

I can't imagine if they had used the 4.10 final drive ratio, if I'm right, the car runs around 3,600 rpm at 62 mph with the automatic trans, but I have no way to find out since I don't have a tach. With the automatic T4WD I have been able to get over 30 MPG on the highway, I was impressed since it was rated around 27 MPG on the highway. The downside is that it's fairy noisy, but oh well...

[splatterdog]

There you have it! One more useless fact that will be stuck in my head.....

I would ask for/demand a pretty good deal on the rest of the conversion.

[tercel4wdrules]

I became intrigued on the subject awhile back and I searched until I found my answer. I was just browsing a scanned article from a Japanese magazine in Dec '83 posted on here by terceldude. Oddly, it lists 3.727 as the final drive ratio for the automatic. However, a quick search reveals that production for the automatic T4WD for North America commenced in Feb of '84, which has the 3.909 as the diff ratio. Another search yields that in Japan, the Sprinter Carib (AL 25) was produced from Oct of 1983, which I will presume came with a 3.727 diff ratio, until whenever they switched to 3.909. It seems like 3.909 is a good compromise between 3.727 and 4.10, although an overdrive gear would have been very beneficial in this case. I try to drive 55 mph in the far right lane when I drive the automatic on the highway, mostly alternating between 55-60, but cruising at 65 mph can be done, it's just too noisy.

[Barto]

Also read and memorize this site as it will tell you what was in your car (so your rear end) and go look at mechanics but if it was an 86-87 then it had 4:10's.

useful info so you can just read the vin plate
http://www.toysport.com/Technical%20Inf ... ations.htm

[yppg]

Once again, many thanks. This site is great.
Responses:
I will definitely try the revolution test for a final diagnosis.
Before the demise of the automatic I too was able to get 30mpg highway. With the new transmission I've gotten up to 37mpg. The thing runs incredibly well in 5th gear. I have no tach so I can't monitor rpms.
No one in town would tackle this change over project except the young mechanic that did it. His shop is pretty basic, no lift or anything. Most of the work was done outdoors. His internet savvy is probably about on par with mine- not exceptional. He must not have been able to access the info. you all have. If I ascertain that the gear ratio is indeed the problem (sounds like it is), I'm sure he will swap out the rear end for a very minimal charge.
I do generally try to avoid running on pavement in 4wd. I will try harder in the future.
In the meantime I will avoid using 4wd. Since the change over I have driven about 4000 miles. Very, very little of that was in 4wd. Hopefully the components haven't been stressed too badly.

[xirdneh]

The info on the tire rotation test i described above applies only to the 3.73 vs 4.1 ratio differentials
per tercel4wdrules there is a 3.9 ratio that i was not aware of (tercel4wdrules is great with the details)
but the test will still show a difference in revolutions (front vs rear)
i just do not know how much

[yppg]

Test complete. Diagnosis: gear ratios
The rear wheel was close to 1/2 a rotation off after ten rotations of the front. Must be the 3.7..
Anyone looking for a rear differential for an automatic?
Much thanks to you all.

[ARCHINSTL]

I know I am stating the obvious, but...
This is a great Club with helpful and knowledgeable members.
It's a perfect example of "We're all in this together, so let's make it work."
Tom M.