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Discussion Starter #1
I just had my tranny rebuilt for the second time in its life (I really like the car). One of the complaints going in was that in addition to slamming into second gear indicating worn clutch packs the car would not engage in first gear from a stop. I would sit at a stop take my foot off the brake and the car would not roll until I dropped the shift lever into 2, once rolling I moved back into D and everythig was OK

The problem was getting progressivelty worse as the old clutch pack wore out. Since the rebuiild last week it has continued to do the same thing but less often. Since it is an intermittent probelm that the shop has not experienced I hooked up my AutopTap kit and ran for a week to capture the data for the shop. AFter reviweing the data the do not not belieev there is anything electrically wrong with th trany but will be pulling the tranny tomm to look at/replace the "sprague" which the mechanic described as a mechanical diode.

What is this and what does it do, should this have been replaced as a part of the overhaul last week?
 

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A "Sprag" and "Mechanical Diode" are both incorrect terms. The AX4S/AX4N both use a "Roller Clutch"

All three parts do the same thing, but each does it in a different way. It is an overrunning clutch that allows part of the transmission to freewheel one way, and lock the other way. If that breaks then you generally lose forward movement.

Its not a wear item, but is a weak point in the transmissions. They can fail, and all it takes is a handfull of "neutral drops" or a couple very hard shifts.

Tell your mechanic to replace it with the overdrive roller clutch from an E4OD truck transmission. It has more elements on it, and is a much stronger piece. And it can be used as a direct replacement for the intermediate roller clutch that is broken on your transmission.

Hope this helps,

Jeramie
 

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Discussion Starter #3
Will pass the info to the mechanic, wil let you know what final result is.

Is there any way to test the "roller clutch"?

Dave
 

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Yes, if you put the trans in "D" (or OD depending on your model) and it does not move forward, but DOES move forward in "1" then you have a disintegrated roller clutch.

When in "1" the transmission engages a band to secure the drum, to allow both acceleration AND engine braking (locks it from moving at all).. Normally in "D" it just relies on the roller clutch.. The roller clutch locks when under acceleration, but freewheels when you take your foot off the gas.

Here's a pic of an AOD transmission (similar, but not exactly what your transaxle looks like)

Here's a roller clutch dis-assembled: http://members.tccoa.com/92bird/AOD/intermediate%20roller%20clutch.jpg' alt='' width='640' height='480' class='attach' />[/url]

Here's a band and how it secures the drum: [url=http://members.tccoa.com/92bird/AOD/OD%20band.jpg][img]http://members.tccoa.com/92bird/AOD/OD%20band.jpg' alt='' width='640' height='480' class='attach' />[/url]

ITs also very possible for the band to break, in which case you'd have no forward movement at all if the roller clutch is also broken.

Jeramie
 

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I would sit at a stop take my foot off the brake and the car would not roll until I dropped the shift lever into 2
The "2" function engages a different band that holds second gear stationary, just like first gear.. So from what you described I'd say your roller clutch is bad.
 

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Is this "roller Clutch" the same as the "forward clutch piston"? In the picture posted it looks like it(3rd item from left).
 

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Thanks for the pics and explanations Jeramie, I'm always interested in learning more about the inner workings of our trannies. It's the one part of cars I still don't completely understand.
 

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Discussion Starter #9
Thanks for great info and pics. AFter original posting the problem occured again and this time I dropped all the way into "1" on column at mechaics request to see what would happen, there was no movement until I cam e back up to "2"

Does this add anything else to the problem?

I talked to mecahnic this AM and they have already replaced the roller clutch but also found a bad valve in the valve body. They hae had to orde the ream adn tool to fix thre problem.

On a related subject--- since I pointed out this problem to the shop when I first delivered the car for overhaul and they quoted me a fair price to fix, which I paid, should I expect to be billed for this additional work since according to Jeramie's email a roller clutch is not normally replaced in an overhaul.. My gut feeling is to not pay siince I had poiinted out the problem at initial drop off.
 

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A stuck valve? that shortly after a rebuild?

Sounds like contamination somehow got into the fluid supply. Did they flush out the cooler lines when they re-installed the transmission? They should have replaced or at a very minimum flushed out the torque converter too. The tq converter and the cooler lines hold old trans fluid (and whatever was in the old trans fluid, like metal shavings, dirt, seal fragments, etc..) so when you build a new transmission you need to clean that out so that it doesnt' get re-circulated back into the transmission.

My guess it they did a very basic overhaul. A complete overhaul to me means taking every part out and examining it. Taking every valve out of the valve body, spinning the valve against your thumbnail to see if there are any knicks or scores, and replacing all parts that could potentially be a problem. An automatic transmission is a very sensitive piece of equipement..

The low/intermediate roller clutch is about $26 retail at the dealership, more like $15 costs for a parts shop. Its a known weak part on the AX4S and AX4N, and for $15 or so its just dumb not to replace it. Unless you specified you wanted the cheapest rebuild possible..

Let me give you this as an example.. My friend took his Thunderbird SC (AOD rear wheel drive) to a shop for a new transmission. It continued to have problems even after being "repaired" under warranty 4 times.. That's right FOUR times..

After a 5th failure, he decided to let me play with it. So I did a complete rebuild.. Just started fresh.. His was the very first automatic transmission I ever rebuilt. I followed the directions on the manual, got the special tools, spent a lot of time checkign all the details, and then re-assembled it. I found all sorts of stuff that was missed by the so-called "professional shop".. LIKE THEY DIDN'T EVEN REPLACE SOME OF THE CLUTCHES! .... AND, they re-used parts that should have been replaced. The boost valve was scored to all hell, and a chunk of the rubber seal lip on the reverse/low servo was missing..

I completed the rebuild and the transmission works flawlessly.

So have each and every trans I've rebuild so far..

How is it that a beginner can build a better transmission than a shop?

My guess is a shop takes lots of shortcuts, or they are just too lazy to do the job right..
 

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Discussion Starter #11
It is beginning to sound like they may have taken some shortcuts. They replaced the converter as part of the overhaul, hopefully they flushed all the lines.

I now know to ask so leading questions for the next tranny rebuild (hopefully not this car for a long time) like do you pull and inspect all the valves Maybe I will get brave and try it myself someday.

I went to this shop because they were the only ones in town (Norfolk VA area) that had the ATRA certification.

Based on the $26 cost of the roller clutch I don't think there will be any agruement from them when pick up the car, they can eat the $26 as far as I am concerned.

I did get them to comp me lower ball joint replacement (I provided the parts) since they already have the hub pretty well torn down to remove tranny.

Will get aligned next week

Thnkas, if anything else comes up I'll let all know
 
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