Tranny Shifting Problem

[sirhk100]

My tranny has about 10,000 miles on it. A4ld that's been completely rebuilt and has an aftermarket shift kit. It still shifts good and hard. The only problem is that from first to second it seems like the shift point has jumped up about 1000RPM when just barely on the gas and if I get into it, it won't shift up at all till I let almost all the way off it. Any ideas? I'm going to go crawl under and see if all the lines and wires are still hooked up. Would the vacuum modulator on the side cause this?

Khris

 

[Opera House]

And is the reverse ok?

Your low/reverse band could have broken. This is a double warp band that is cast. Since you say it was rebuilt, I assume they put new seals in the low/reverse servo. This is easy to check and get at if you drop the pan. Do you really know that it was completely rebuilt? Sometimes just a quick job is done to replace what has gone bad.

Try this test. Find a steep hill and point the car down it. Put reansmission in low (1). Take your foot off the brake and don't use the gas. Should accelerate but the engine will be doing some heavy braking. Tach should go up over 2K easily. If not, then it is the band or servo that is bad.

 

[sirhk100]

The shop I choose to take it to was based on word of mouth and is supposed to be very reputable. They build a large number of SoCal offroad racers trannys and judging by the pictures signed with thanks on the wall they build the who's who of off road racing. So based on that I'd hope they installed everything they did.

I crawled under tonight and everything was still hooked up. I called the shop this morning and first they said to check to make sure the OD cable was sticking open. That checked fine also.

Did the test you suggested and it went up to 3000RPM before I had to brake on the hill I tested it on. Also had lots of engine braking.

Any other suggestions? I'll be calling the shop tomorrow again to see what else they suggest.

Khris

 

[Opera House]

Sounds like basic internals still ok

That high rpm with little gas threw me off. Sounded like the band was hardy working at all. The two things that change shift point are the vacuum modulator and the speed governor.

The vacuum modulator is on the side of the transmission and has a line that runs up to the vacuum tree on the drivers side of the manifold. Hose should be easy to find. Pull it off and see if there is any oil inside. If it develops a leak, transmission fluid is sucked up. In the vacuum modulator, there is a small orifice that can slow response time if there is fluid in it. Depending how long you have had the problem, fluid may not have made it up to the vacuum tree. A mity-vac on this line with a gauge is a better test to see if it holds a vacuum since there could also be a hose split. This would also effect shift points in other gears. Any engine problems would also change the vacuum.

A shift point change in only first to second indicates that the speed govenor is sticking. This part is located in the extension housing between the transmission and the transfer case. I wondered just how hard it is to remove the governor from the transmission while it is still in the car. So I decided to take mine out of my 92. Removed both drive shafts, and dropped the cross member holding the transmission. Support the transmission with a jack. After removing the bolts to the transfer case, I pulled it out a little an let it swing down. Then I pulled it out more and let it drop to some folded carets. Had to remove the tranny mount to get at the transmission extension bolts. Transmission extension bolts to the transmission and mounts the transfer case. The only internal connection is the parking pawl. The governor valve is then just mounted with two bolts. If you are talented and lucky, you can probably pull out the valve without removing the extension housing.


Remove it carefully, all the pieces will fall out. There is the outer weight, close to the shaft. followed by a spring, then the primary valve that goes into the governor body. The steel valve gets little scoring marks on it. Valve should move freely from its own weight.

Although mine worked, it was very sticky. You could see wear marks on the steel piston. I polished it by hand with some very fine wet or dry paper and oil. Also the aluminum surfaces. The piston now operates freely. If yours is sticking, it is because of wear and not contamination. I think I have seen this part new for about $30.

Not a hard job at all. I think a lot of these are on the brink of failing. The only tricky part is getting the parking rod back into the extension housing. Remove the shift cable so you can operate it yourself from under the car. Put in park to extend rod, then shift slowly into low to bolt on the housing.

 

[sirhk100]

Thanks for the reply. I'll check for vacuum on the modulator tonight when I get home. Can I check for vacuum up in the engine compartment on that line or should I do it down at the modulator which is almost a joke with the exhaust there!!!

It's only maybe been shifting like this for maybe 100 miles so I'm not sure if that's enough time to see fluid. Also the modulator was replaced with the tranny rebuild about 12,000 mi/5 months ago. It was replaced with one of those adjustable ones. Any chance of a temporary quick fix by adjusting that? Also from the way it still does shift and run I firmly believe that the internals are good. Other then the first gear shift point rising everything else is still good and it still busts the rear end loose in the dirt when it shifts under hard power because it was built so agressivly.

The speed govenor that your talking about? Is that the thing that is in the cavity between the transfer case and the end of the transmission. If you drop the transfer case and look into the tail of the tranny it's to the upper left of the output shaft if I remember right? When I got the tranny back installed I could hit redline in first if I just floored it. They said I needed to change the weight on that thing and gave me a chart of various weights to run depending on my symptoms. Now that I think about it, yeah, if it were stuck from what I understand it doing that could be the cause. I'm taking it to the desert tomorrow night for 4 days. I'll just be carefull with it. Next weekend though I'll probably tear into that and see what I find.

Let me know if you think I'm describing the same thing as you?

Khris

 

[Opera House]

thats the part

There is an internal spring but that is just to take up vibration. You are balancing the centrifical force against the pressure of the fluid on the valve. Haven't heard much about changing weights, Who spends that long in first. If you take weight off, you have to adjust the weight of the counterbalance or you could get vibration. Those adjustable vacuum modulators are nice, just got to remember that it is still an A4LD and at higher rpm and torque bad things can happen. Modulator is probably good but the connector hose could always get a little slit. Still that would show up on other shift points. How many K did this transmission have before a rebuild. Have you checked the kickdown linkage? Maybe it got hit.

 

[sirhk100]

Yeah, I had my pops crawl in and hit the gas for me last night and the kickdown linkage all still looks fine. The tranny had 115,000 on it at rebuild and now has about 123,000 on it. They went through and did the entire OD, upgraded to some of the newer parts that I guess are found on newer trannys, did a shift kit, and also put in some custom needle bearings or something where there used to be thrust bearings. Basically they built it the same as a couple of the off road race A4LD trannys that some of the locals are running in their 7S class trucks. I do definately swear by the temp guage that I installed and basically my driving tends to be based around what it's reading. I'll be taking it easy this weekend. Once it's outta 1st it works fine so I guess this will be more of a high speed weekend then a crawling weekend. Oh well I did some more suspension stuff that I wanted to beat on anyways.

Khris