1996 Saturn with 90,000 miles suddenly lost reverse. I checked the input shaft nut, it was tight, so I installed a rebuilt valve body and changed the fluid and filter. Still no reverse. Does anybody have a suggestion what to do to fix it? The valve body came from Ken Partin, could it be defective?
Thanks in advance for your assistance in this matter!

 

You are most likely on the correct path to repairing the issue.

The following is key:

If the ONLY issue is with Reverse and there are NO other issues with shifting between any gears ---> usually valve body
If the issue is with Reverse and there ARE other shifting or behavior problems --> usually input shaft nut issue.

That being said, there are many Saturn TAAT driven vehicles that refuse to follow the rules of thumb above,
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Valve body -- 1st pass check

1) You can test the resistance of each solenoid with the valve body installed or out of the car. Out of the car is much easier, but in car can be done, and since you will want to check the solenoids both hot and cold, I'd try doing it in the car.
2) You want to do a cold test and hot test (operating temperature), as some solenoid problems only show up under heat stress.
a) The resistance of each solenoid/actuator in the valve body should be in the 4 to 6 ohm range, with 5 being ideal when engine is cold AND all solenoids should be within 1 ohm of each other. Usually, the cold results are in the low 5's.
b) The warm results will probably push into the low 6's. 4-6 is an approximate range. If one is greatly different from the rest, it's probably bad. You're looking for general consistency in generally the right resistance range.

Note: This resistance test MAY uncover bad or failing solenoids, but only based on whether their resistance is too high for the solenoid to actuate properly.
Solenoids can malfunction in other ways, like the plunger (the part actually being moved) can get stuck, causing it to not actuate at all.

Look at It includes the layout of which pins correspond to which gears and the which correspond to the line pressure solenoid, etc. for the resistance test.

Post the cold and hot test results here and we'll see if anything looks suspect.

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Input Shaft Nut

Apparently, the valve body design is flawed in that the pressure needed to engage reverse takes too much time to build up in the valve body. Other aspects of the car's computer control system alter shift points and such so that you don't realize that it's slowly loosening the input shaft nut. Once it backs off far enough, you feel the reverse slam. The rebuilt valve bodies will eventually suffer the same fate, Basically what I'm getting at is that the valve body issue leads to the input nut shaft loosening, Hence both should be addressed at the same time. If you read threads where one is done and the other is not, this is almost definitely why.

Torquing the input shaft often a difficult procedure in this A/T without special tools because in order to do so properly, you need to fully immobilize the clutch pack and shaft in order to properly remove the old nut and torque the new Input shaft nut on a spotlessly clean input shaft (with threadlocker to spec (123 ft lbs, revised spec from GM, original 111 ft lbs). Even if you tighten the old one, it is likely to back off again (Alas, read on....)

Losing reverse entirely usually takes place after a period of reverse slam issues, but in re-re-re-researching for this post (haven't answered a TAAT Reverse question in a while), I did come across several cases where people had 2 reverse clunks and reverse was gone in the span of 3 minutes, and several cases where reverse works while cold but disappears when warm, and several cases where reverse vanished with no prior ill symptoms whatsoever, and......

Personally, I do not know how far the input nut needs to back off in order to wreak havoc, so even if it seems tight by hand, it may be partially backed off and corroded into its current location. You just don't know. I hate when people answer mechanical questions like that, but this has been a wild animal since 1991, and experience is your best friend.

Unfortunately, most A/T Saturn owners only go through this experience once, and in the case of the input shaft nut, you don't know if it's backed out or properly torqued until you take things apart to check. Once you've gone to that much trouble, you might as well replace the input shaft nut while you're in there. (see below for the bad news)
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Here is a link to a thread which in turn has links to three other threads with detailed instructions on the input shaft nut replacement process. Much of the information centers around what NOT to do so that you don't wreck things, and little hints to make annoying parts of the process much easier.

Some thoughts on tightening the input shaft nut - SaturnFans.com Forums (Old Nuc Post #9) Sucks b c some folks linked their photobucket pictures into the posts instead of just putting in the links. but it helps.
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Here's a youtube link of some dude only retightening. Didn't replace the gasket (bad move if you ask me)
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As the Input shaft nut has been discontinued by GM and the parts scene has dried up, I think your options are down to removing the nut and chemically cleaning the nut and shaft to ensure a threadlocker will grip them or just retightening periodically, knowing that the original threadlocker has by definition already failed. Problem is cleaning the nut without removing it -- you really can't. Also, it is a special type of nut that must be torqued to spec in one continuous uninterrupted motion. That and the threadlock are why GM advises using a new nut.

The following thread describes what other people much more familiar with the A/T in the s cars are discussing using as replacement threadlocker.

Input shaft nut availability - SaturnFans.com Forums
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Hopefully, this condensed research, mostly from saturnfans.com, will provide you enough guidance to deal with the input shaft nut.


Part number references below
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Parts References (OEM GM Part Numbers) CHECK THESE FOR FITMENT BEFORE ORDERING (I pulled them from another forum)
Transmission gasket and nuts part numbers
21003202 is the valve body cover gasket. This fits 96-02
21001684 is the end cover gasket. This fits 91-02
21001680 is the input shaft nut. this fits 91-02 DISCONTINUED. Available on E bay (price gouging for kit containing it) This thread discusses alternative strategies Input shaft nut availability - SaturnFans.com Forums I would think any reputable tranny shop could cross ref it to something
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Skinny 23mm deep Socket (Required for clearance to get the socket onto the input shaft nut:
Need socket end OD of 1.200" (30.48mm) or smaller.and MUST be 12 pt socket

* Snap-On FM23, 3/8" drive 23mm 12-pt std: 29.9mm OK
* NAPA 23mm 12-pt thin-wall, special order: sorry no part# OK
* Armstrong 3/8" drive 23mm 12-pt, std #38-123: 30.2mm OK
* Armstrong 3/8" drive 23mm 12-pt deep, #38-323: 30.2mm OK
* Armstrong 1/2" drive 23mm 12-pt deep, #39-323: 30.2mm OK
* NOT Snap-on 1/2" drive 23mm 12-pt #SWM231: 31.2mm NO
* NOT Armstrong 1/2" drive 23mm std #39-123: 30.9mm NO
Snap-on FM23 (expensive) or NAPA (logical choice) for 23mm thin wall
****Specs current as of 5/2017 to the best of my knowledge.*****
Shaft immobilizer thingy: Apparently available as part of the price-gouged kit. If you purchase, you can probably resell the immobilizer on ebay at a reasonable price as used, but without the nut and keep many Saturns on the road (giving it forward)
You will be able to sell it, as the hardcore guys will figure out alternatives but the average DIYer will not try the alternative immobilization methods out there as they risk irreparable tranny damage. Your call.

Keep those oldsters on the go! The service you provide is appreciated more than they can express and more than you know.

OK, back to my normal life......what is normal, tho?

 

Thanks derf for the thorough and informative reply.

The loss of reverse happened very quickly with as far as I can tell no notice of the problem. A couple of times after the initial loss of reverse, reverse did work, but now is completely gone. I don't think there were any clunks or slams when engaging reverse prior to the initial failure. The car drives and shifts well going forward.

When I checked the nut, it was not loose and I put a torque wrench on it to 111 lb-ft and it did not move, so I left it alone.
I purchased a rebuilt valve body from Ken Partin Sales. They use a Sonnex kit to sleeve the pressure regulator with steel. The stock pressure regulator bore is the same as the valve body casting, aluminum. Apparently the aluminum body erodes under the high pressures required for reverse to function. The steel sleeve sounds like an ideal and long term solution.

Ken Partin Sales has been very cooperative and helpful, messaging me with some ideas as to what might be wrong, but so far no resolution is in sight. Rats! I just knew the rebuilt valve body would fix it! I was wrong, it made no difference. The car drives very well in the forward gears. Ken Partin sales told me to check some fuses and make some other electrical tests, which I will do as soon as I can see the car again.

Any other thoughts anybody has regarding this problem, I will be happy to entertain them!

Thanks in advance Saturn Forum members for all your concern. What a great bunch of folks!

David Hollinger

 

Dang it. Forgot to mention to check
1) the TRS fuse in the underhood junction box,
2) the TTS (Transmission Temp Sensor). I think the TTS only locks out forward gears when it fails, not sure.


How many mi on the tranny?
How many miles since last trans fluid and filter change?
What are you using for trans fluid? I believe Dex III is the only one ever officially qualified for the TAAT. Dex VI meets Dex III, but that does not mean you want to use it in this tranny. I'd stick to good ol Dex III

How did you hold the clutch pack and shaft from moving while torquing? New solutions from fresh eyes are some of the best ones.

You should also check the pins on the valve body that mate with the connector for corrosion/deposits, and the female sockets on the connector for the same. Also, a tight fit is desirable to ensure solid electrical contact.

But you still need to check the solenoids (new).
In fact, since they are all identical, you can play swap a solenoid with the new valve body to see if the one that controls reverse just happens to be bad,

If all of the solenoids seem fine irrespective of where they are in the valve body, then it is possibly an electrical issue. 2nd and Reverse share the same clutch pack; often when people lose reverse they also lose 2nd. But not always. So I don't think the clutch pack is an issue.

Maybe there is something restricting fluid flow to the valve body or in the valve body itself (would only suspect a restriction in valve body if you installed new valve body w/o changing tranny filter and fluid) such that the required pressure to actuate reverse is simply never reached. I am totally unfamiliar with how the fluid gets there--just a train if thought thang.

Also, check the connector and pins at the other end of the cable that connects to the valve body.

Oh, any SES codes?

 

Yes, I will check all the fuses. The people that rebuilt the valve body gave me a manual on this transmission, it shows all the fuses and locations etc., it should be a big help.

The car has 90,000 miles on it, my friends have only owned it for a short time. I do not know if the fluid was ever changed, it was nice and clear and did not smell burnt. I changed the fluid when I replaced the valve body.

I used Dexron III fluid and installed a new filter too. Actually the old filter that was on the car was from Carquest, so it must have been changed at least once in it's life.

I borrowed a holding fixture from a friend of mine, I could not believe he had it.


I plan on checking everything electrical this weekend. I will carefully examine the plug that goes into the valve body, the fuses and measure the resistance of the solenoids.

Yes there is a SES code, either P 0732 or P 0733, I do not remember which one. Both relate to a bad valve body I think.

The valve body I bought had the Sonnax repair done to the pressure regulator bore. This describes the Sonnax repair. It sounds good.
*****WITH OVER 25 YEARS EXPERIENCE IN REBUILDING AUTOMATIC TRANSMISSIONS.***** YOU WILL GET A REBUILT VALVE BODY THAT USES THE SONNAX SLEEVE TO REPAIR THE WORN PRESSURE REGULATOR VALVE BORE . I ALSO USE OTHER FINE SONNAX PRODUCTS DEPENDING ON THE CONDITION OF THE VALVE BODIES INTERNAL COMPONENTS. SUCH AS THE PRESSURE BOOST VALVE AND THE PRESSURE REGULATOR VALVE AND THE PRESSURE REGULATOR SPRING. THIS VALVE BODY HAS BEEN COMPLETELY DISSASEMBLED AND DRILLED AND SLEEVED WITH THE SONNAX SURE CURE SLEEVE. THIS BRINGS THE PRESSURE REGULATOR VALVE BORE BACK TO OEM SPECS. THIS ALLOWS FOR THE VALVE TO PRODUCE LINE PRESSURE EQUAL TO THE ORIGINAL FACTORY REQUIREMENTS OF 60 TO 70 POUNDS AT IDLE. WHEN THE BORE GETS WORN, OVER TIME AND MILES, YOUR PRESSURE DROPS AND THE SHIFT QUALITY IS GREATLY REDUCED. WITH THE SONNAX SLEEVE INSTALLED YOU NOW HAVE A NEW PRESSURE BORE THAT WILL CONTINUE TO PERFORM FOR MANY THOUSANDS OF MILES. WHEN THE BORE STARTS TO WEAR, IT WEARS VERY QUICKLY AND YOUR PRESSURE STARTS TO DROP AND THE SHIFTS BECOME ERACTIC AND REVERSE BEGINS TO BANG.WHY TAKE CHANCES. GET A FULLY REBUILT VALVE BODY THE FIRST TIME, AND ENJOY YEARS OF CONTINUED SERVICE FROM YOUR CAR!!!!!!

What is interesting to me is that I still have the exact same problem after installing the rebuilt valve body that I had before I changed it. Either the rebuilt valve body has a defect, or most likely I have not found the real problem. I am anxious to perform the electrical tests and check the fuses.

Once again derf, thank you for so generously sharing your knowledge and time to assist in this matter.

David Hollinger

 

Derf is awesome, David. I've learned a LOT about Saturns over the years from him and Andy, and I don't even own one anymore. I just like the site and consider these guys family. Derf goes way beyond what most mods or admins will on ANY other car forum I'm a member of and that's several. Hang in there with derf and run those tests. Odds are that you'll find what your problem is.

 

I looked on the Sonnax site and the have a very informative tech support article which deals with no reverse problem. Obviously the loose input shaft nut and defective valve body are the primary culprits, but they offered another possible cause for no reverse. I have copied a section of their website here.

Another common no-Reverse condition is a faulty or defective vehicle speed sensor. The input from the VSS to the PCM should always read less than 5 mph. This allows the PCM to command high line pressure, which in turn will move the servo apply valve ('93-later models only) to an open position, thus opening up the passage to allow oil to the Forward/Reverse servo piston. If the VSS is defective (reading 5 mph or above on your scan tool), the PCM will command low line pressure, thus not feeding oil to the Forward/Reverse servo piston. In turn, the slider assembly will not move, causing a no-Reverse condition.

VSS is vehicle speed sensor, PCM is Powertrain Control Module.

This sounds like a safety feature where you cannot shift into reverse when the vehicle is moving forward. Apparently when the sensor is defective, the PCM thinks the vehicle is moving forward and does not allow the transmission to switch to the high pressure mode required for reverse to engage. WOW! I ordered a sensor and will let you know the results when I install it. This would fit my scenario, as I have checked the nut and changed the valve body with no change in reverse gear performance.

 

I had seen VSS mentioned only once in another forum, and I did not understand the rationale behind it.
I do not pass on information I do not understand, as I cannot answer any questions about it if someone asks.
I should have included it in my write-up for completeness, with a disclaimer. I hate initiating costly wild goose chases in the wrong direction.
The explanation indeed sounds plausible, but I would think the shifting of the forward gears would be affected in some way, unless the line pressure required for those shifts is below the line pressure set as you described.

I assume you meant the VSS should read less than 5mph with the vehicle at rest (not "always"). If it reads above 5mph, reverse is indeed locked out as a gear choice.
I would think a defective VSS could be detected by cross-checking the ABS wheel sensor speed and calculating speed from the rotations and tire diameter and throw a code when 3 or more of the wheels say the car is not moving but the VSS says it is AND is moving above 5mph.

Also, if the VSS was defective, in the manner you described, I would expect the speedometer to be erratic with the car at rest and in motion, though the PCM is in between so who knows what programming logic was used for this situation.......
I would also expect a P0500 VSS Circuit Performance code, unless the V's generated by the sensor are changing smoothly with speed and are reasonable as far as the PCM is concerned. The evil case.


I did a little more research and found a Saturn tech stating that since 2nd and reverse share the same clutch pack, it is possible that there is a leak in that clutch pack preventing it from building sufficient pressure required for reverse, which is higher than for 2nd. He also stated that the reverse piston servo (the forward-reverse servo piston) assembly could be leaking, again not allowing sufficient pressure to build to move the piston into the "reverse position"

Do the doors lock automatically above a certain speed on this vehicle (by design)?
The ABS piston self check occurs above a particular speed. Is this still occurring with the vehicle?

Before you remove the existing VSS, see if you can get a V reading off of it at rest with the car running for comparison w the new sensor.

For the record, all three of my S cars have been 5 speeds -- back to 1992 -- I have driven nothing else since as a DD. This also means I have not personally experienced your issue but have tried to learn as much from others as possible in order to help the Saturn community.

 

Good morning derf! Once again thank you for your insight and generous sharing of knowledge and logical thinking. You have accumulated an amazing amount of knowledge on these vehicles.

This vehicle does not have ABS or automatic door locking.

This weekend I will see the car again and check fuses, wiring, solenoids and change the VSS sensor if it arrives in time.

I also do not see how it can give an erroneous reading. If it is a simple inductive sensor, It should give pulses as an output. I just thought it was worth a try. So far I have not helped the situation at all and am feeling kind of desperate to help out my friends.

Have a wonderful day and thanks again for your concern and assistance!

David Hollinger

 

1996 Saturn .....which model?
SL, SL1 SL2, SC1, Sc2