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  #1  
Old 12-01-2011, 07:19 AM
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Huskymaniac Huskymaniac is offline
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Wynndi got me thinking about transmissions

He got great mileage out of his 1996 which, as we know, had all of the Subaru upgrades. The fact that beefier components helped is not a surprise. And I can rationalize why they may not have put better components in the earlier trannies. Cost. They may have, incorrectly, assumed that the components they had were good enough and when cost pressure mounts, you don't put more expensive components in unless you absolutely have to.

One technique people have used to improve reliability in the older trannies was to open up the passages in the valve body. So my question is, why wouldn't the Subaru engineers have made these passages larger in the first place? It doesn't cost more to make holes bigger. Is there any reason why they wouldn't have wanted these passages to be larger?

The thing that got me to this question was that my 1996 with 89K on it seems to be running quite well. There has been talk recently on what the right type of external cooler is. I noticed on my drive to work today that my TC took about 5-7 minutes to lock up. The temperature outside was 35F and I am running just through the stock cooler in the radiator right now. Most of that time was on "city" roads. Seems to me that my tranny is running quite cool with the stock cooler.

Given that, I would think increasing fluid flow would be more important than improving cooling, assuming that the tranny is in good condition. That has been my assumption all along and it was reinforced today. So an external cooler with lower flow resistance would seem to be a much better choice than a high capacity cooler. In fact, a high capacity cooler may be a negative as it will keep the TC from locking up and degrade fuel efficiency. Therfore, a low capacity cooler with low flow resistance would seem to be the way to go and that points to a small tube and fin cooler.

Once you get past that decision, one then naturally wonders what else would improve flow and line pressure and that brought me back to those valve body modifications. It makes sense with the exception that one has to ask why the Subaru engineers didn't just make the passages larger in the first place. It makes me wonder if there wasn't a logical reason for wanting them smaller.
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  #2  
Old 12-01-2011, 08:13 AM
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Re: Wynndi got me thinking about transmissions

Regarding the valve body holes, my feeling is that they were unprepared for how theory and reality seldom mesh as one expects. It's possible that on paper the valve body had sufficient flow, but in reality that flow is restricted by debris build up or some other interference. Maybe Subaru rushed the 4EAT into production too quickly and short-cut the durability testing.

I don't drive my SVX in the winter anymore, but it always took a good while to warm up to the point of T/C lock, to the point that I didn't like getting on the highway too soon and winding it up to 3000 RPM to keep up with traffic. With an external cooler I think you'd want to have a block-off plate for winter driving.

Actually, now that I think about it, I've driven my car on days so cold that the transmission would unlock every 10-15 minutes on the highway to re-heat itself. Obviously in cold weather the 4EAT doesn't have heat issues.

I think the ultimate solution would be to have a thermostat controlled external cooler. I would like to see the trans fluid running through a warming circuit during the initial part of driving to get quicker lock up and better mileage, then switching to a cooling circuit as required to maintain the minimum lock up temperature.
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Old 12-01-2011, 04:31 PM
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Re: Wynndi got me thinking about transmissions

I don't have much experience with the SVX, but in general, I know that when a company designs a car much more ambitious than their past models, chances are that they don't make a good car...I mean how can you know that your tranny will overheat unless you try it...some things can't be calculated
I don't know but maybe they were in a hurry in some sort and didn't have enough time to test the parts out
Reminds me of what McLaren did with their Mp4-12c...They designed the car, gave it to the press, and fixed the issues for a year or so...now they sell a car with far less problems than it might have had one year ago
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  #4  
Old 12-02-2011, 06:34 AM
dcarrb dcarrb is offline
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Re: Wynndi got me thinking about transmissions

I realize that these transmissions had a number of shortcomings out of the gate, but weren't the vast majority of premature failures due to a screen in the ATF cooler loop becoming blocked by bits of friction material?

dcb
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Old 12-02-2011, 10:58 AM
1986nate 1986nate is offline
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Re: Wynndi got me thinking about transmissions

The earliest failures were from bad torque converter linings which were prone to "wearing" quickly and particles getting clogged in the screen, causing a lack of flow, lack of pressure, therefore causing slipping, causing heat and the process quickly got out of hand causing failures. The very earliest 92's also had low/reverse clutches/drums that were much to small leading to reverse failures.

Most of the holes drilled in the later transmissions were actually in the clutch drums/hubs and not the valve body to allow more fluid to reach the friction discs in the clutch pack. Keeping them lubricated and working better. Also, by the time the 95+ were around, the word was out to watch the transmissions. Fluid/filter changes were kept more aware which also leads to longer transmission life.

All in all, there are a huge number of factors and variables.

They also had no reason to believe there would be transmission issues. It was the same basic transmission that had already been out for a few years in their other models without a high catastrophic failure rate. They used the existing design but upgraded the amount of clutch packs which in theory should have worked. The same 4eat are used in all other subarus of the 90s that go well into the 200k+ mile range and much higher with transmissions that are technically weaker than the SVX one. Keep that in mind.

Last edited by 1986nate; 12-02-2011 at 11:00 AM.
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Old 12-02-2011, 12:31 PM
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Re: Wynndi got me thinking about transmissions

Quote:
Originally Posted by 1986nate View Post
The earliest failures were from bad torque converter linings which were prone to "wearing" quickly and particles getting clogged in the screen, causing a lack of flow, lack of pressure, therefore causing slipping, causing heat and the process quickly got out of hand causing failures. The very earliest 92's also had low/reverse clutches/drums that were much to small leading to reverse failures.

Most of the holes drilled in the later transmissions were actually in the clutch drums/hubs and not the valve body to allow more fluid to reach the friction discs in the clutch pack. Keeping them lubricated and working better. Also, by the time the 95+ were around, the word was out to watch the transmissions. Fluid/filter changes were kept more aware which also leads to longer transmission life.

All in all, there are a huge number of factors and variables.

They also had no reason to believe there would be transmission issues. It was the same basic transmission that had already been out for a few years in their other models without a high catastrophic failure rate. They used the existing design but upgraded the amount of clutch packs which in theory should have worked. The same 4eat are used in all other subarus of the 90s that go well into the 200k+ mile range and much higher with transmissions that are technically weaker than the SVX one. Keep that in mind.
If I hear you correctly, there is no benefit to opening up the valve bodies on the new trannies (post-1994). Is that correct? If not, and there is a benefit, my real question is, why wouldn't they have opened them up? Is there a tradeoff by opening up the valve bodies?
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Old 12-03-2011, 05:22 PM
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Re: Wynndi got me thinking about transmissions

Quote:
Originally Posted by 1986nate View Post
The earliest failures were from bad torque converter linings which were prone to "wearing" quickly and particles getting clogged in the screen, causing a lack of flow, lack of pressure, therefore causing slipping, causing heat and the process quickly got out of hand causing failures The very earliest 92's also had low/reverse clutches/drums that were much to small leading to reverse failures.

Most of the holes drilled in the later transmissions were actually in the clutch drums/hubs and not the valve body to allow more fluid to reach the friction discs in the clutch pack. Keeping them lubricated and working better. Also, by the time the 95+ were around, the word was out to watch the transmissions. Fluid/filter changes were kept more aware which also leads to longer transmission life.

All in all, there are a huge number of factors and variables.

They also had no reason to believe there would be transmission issues. It was the same basic transmission that had already been out for a few years in their other models without a high catastrophic failure rate. They used the existing design but upgraded the amount of clutch packs which in theory should have worked. The same 4eat are used in all other subarus of the 90s that go well into the 200k+ mile range and much higher with transmissions that are technically weaker than the SVX one. Keep that in mind.
It was the faulty Converter clutch facings that sealed its fate. Their reluctance to do a recall at that time, allowed it to become widespread.
This cooler flow problem had nothing to do with line pressure. This oil is returned to the mainshaft for cooling and lubricating the gear trains that overheated with out it, causing the early failures.

Quote:
Originally Posted by Huskymaniac View Post
If I hear you correctly, there is no benefit to opening up the valve bodies on the new trannies (post-1994). Is that correct? If not, and there is a benefit, my real question is, why wouldn't they have opened them up? Is there a tradeoff by opening up the valve bodies?
First, Subaru did not design this box; it was Jatco's box that Subaru used for their application.
The holes that are drilled out larger, are the restrictor holes that have more to do with the timing of the operation of the clutches. These are used to slow the speed of engagement, to make it operate smoothly. Opening these will allow faster, but rougher operation.
An example is in the restrictor plate behind the C solenoid/transfer assemble. The restrictor holes there slow the engagement of the transfer clutch so that it does not engage with a bang, but because of it, it lets the front wheels start spinning before the clutch engages to drive the rear.

Harvey.
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Old 12-03-2011, 11:55 PM
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Re: Wynndi got me thinking about transmissions

Quote:
Originally Posted by oab_au View Post
First, Subaru did not design this box; it was Jatco's box that Subaru used for their application.
The holes that are drilled out larger, are the restrictor holes that have more to do with the timing of the operation of the clutches. These are used to slow the speed of engagement, to make it operate smoothly. Opening these will allow faster, but rougher operation.
An example is in the restrictor plate behind the C solenoid/transfer assemble. The restrictor holes there slow the engagement of the transfer clutch so that it does not engage with a bang, but because of it, it lets the front wheels start spinning before the clutch engages to drive the rear.

Harvey.
That makes sense. Does opening up those holes also improve flow and line pressure or does it only really increase the speed of the shifts? I was under the impression is does both. It sounds like the tradeoff was between harshness and speed (and maybe reliability).
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1996 Polo Green Subaru SVX LSi, 168,XXX miles, Redline D4 ATF, Redline 75W90 gear oil, K&N HP-4001 Oil Filter, Mobil 1 5W50 FS (3qt) and 5W30 High Mileage (4qt) Oil Blend, Motul RBF600 Brake Fluid, AC Delco A975C Air Filter, NGK BKR6EIX-11 plugs, Centric Rotors, Power Stop Evolution Carbon Fiber Ceramic Brake Pads
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Old 12-04-2011, 04:06 PM
oab_au oab_au is offline
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Re: Wynndi got me thinking about transmissions

Quote:
Originally Posted by Huskymaniac View Post
That makes sense. Does opening up those holes also improve flow and line pressure or does it only really increase the speed of the shifts? I was under the impression is does both. It sounds like the tradeoff was between harshness and speed (and maybe reliability).
Yes it is a comprise to get a smooth operation, though when they are modded with a Transgo kit, they are not too bad, as long as the shift accumulator springs are not increased. They don’t do any thing for the line pressure.

The line pressure is a continuous flow of oil through the valve body, and mainshaft. It leaks oil through all the clutches and valve body drains. Instead of turning pressure on to a servo to move it, the drain is turned off, to allow the pressure to build up to move it. There is really no problem with the line pressure flow. As I have said before, that is solely a TCU control problem, made worse by the high final drive ratio.

Harvey.
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