Transmission Issues

[Ron Luchene]

I just posted this in the Riviera forum but since my transmission is common to other Buicks I thought I would post here as well.

I have no issues looking for a reputable transmission shop but I always hate giving up a chance to save some money and learn something at the same time. Admittedly I have zero experience with transmissions but I am mechanically minded and typically successful when pointed in the right direction.

I have a '65 with the ST400 transmission. Based on a previous thread I have determined that the transmission is a BR code out of a 66. In addition, for some unknown reason when the transmission was rebuilt by the previous owner they installed a single wire case connector instead of dual so I do not have switch picth control and at present do not know if the option is even still installed in the case.

As for the issue...the transmission will not come out of 1st gear. Here is the background info.

1. From the time I bought the car 3 years ago, there has always been a slight shutter when shifting from 1st to 2nd especially under load.

2. The transmission would never kick into passing gear but I had a long list of things I had been working on and I never paid it much attention. Last week it kicked into passing gear for the first time but I could not get it to do it twice.

3. The next day I went for a drive and it kicked into passing gear but when I stopped and then started again it wouldn't shift pass 2nd. I shifted manually through all three gears and then it acted normal for the next 10 miles. Then, when accelerating from a stop light it wouldn't shift pass 2nd again. I could shift it manually through all three gears again but it would not shift automatically.

4. Took it out the next day and it would not shift pass 2nd. In addition, I could no longer shift through all three gears manually.

5. I have good vacuum so I changed the modulator yesterday. I took it for a spin and now it will not come out of 1st gear.

6. I was thinking that the kick down solenoid might be stuck but with the engine off and the key on I can hear the kick down solenoid actuate when I push the accelerator to full throttle.

So what's next? Does this sound like an issue with the kick down solenoid, govenor, vacuum modulator or valve body? I would think I could deal with any of these issues with the trans in the car? If it is beyond that I think the trans shop is my best bet but would like some advice first. If I need a rebuild what should I expect to pay?

Sorry for the long post...let me know your thoughts.

Thanks - Ron<!-- google_ad_section_end -->

[NTX5467]

To me, this sounds like a valve body issue. Either some of the ballchecks are not seating firmly or the particular seats in the valve body have "worn". Or there could be some (possibly) clutch material which could have come loose and is somewhat preventing them from seating correctly.

IF the switch pitch function is still there, that should not be an issue with what you've described. Remember that it takes a front pump and switch pitch converter to make those things work as a team. Still, though, that should not be an issue with your shifting problems.

I bought a '77 Camaro new. At about 3000 miles, one night on the way home on the Interstate, crusing at 60mph, the rpm suddenly jumped to 3000rpm, from its normal 2000rpm cruise at 60mph. I thought that was unusual and backed out of the throttle . . . the rpm dropped to idle rpm. When I eased back into the throttle, the rpm came back up as if the trans was in Neutral, "catching" at about 3000 rpm. I pulled over to the shoulder and stopped. It still went in to "D" and "R", but I could hear a slight rattle in the pan area. Still, it would move so I drove off, carefully. This time, though, it took nearly 5000rpm for it to get out of 1st gear in "D" (which uses different "things" than 1st gear in "D"). Then it'd go into "second" in "D". I could drive it in either 2nd gear (2.56 rear axle gears) so that wasn't really an issue per se.

The next day, it still acted the same way on the drive to work (at the selling dealership). When I checked on it later in the day, they told me what had happened was that the check ball seat in the direct drum was not cut correctly and it bleed-off fluid pressure, which prevented it going into 3rd gear, but that it needed all new clutch friction items. Being under the basic warranty, no cost to me.

Sometimes, valve bodies can have "issues" even if the vehicle just "sits", although there migth have been anythings wrong with the trans previously. In one case, a friend had a THM400 built for a car he was rebuilding. He sat it on the garage floor as he finished the car, which took about a year or so. When he put it in, it hit all of the engagement gears, but when he was driving it to the muffler shop, whenever it tried to go into second gear, the trans would lock-up. Think drag racing trans brake where two gears were trying to engage at once. He took it back to the trans shop and they found a gunked-up an corroded valve body.

The lack of upshift issues seem to make it sound like a governor issue OR loss of governor pressure (especially with the "no 1-2 upshift" issue).

Remember, too, that the various shuttle valves in the valve body are governor pressure-biased against calibrated spring pressure. These are different from the ball check valves previously mentioned.

In some of the 1978-era THM200s which found their way into Chevy Caprice V-8s, there were some ocassional shift issues. The "shade-tree" fix, when they did that, was to get up to about 60mph in "D" and then (gets those "guts" ready!) shift the trans into "R" momentarily and then back into "D", continuing on down the road. At the time, this sounded crazy . . . and gutsy . . . plus a little scary . . . but later on I realized that what was going on probably was the poorly-cut ballcheck seats in the valve body. Having the sudden pressure change would make the balls seat "firmly" enough to "reconfigure" their seating area in the valve body. Not unlike using an old ballcheck and a center punch w/hammer to ensure the carburetor's accel pump's ballcheck had a good seat to seat into, when the old ballcheck was replaced with a new one.

The other side of things is that I somewhat doubt that a trans cleaning additive and a fresh change of ATF and new filter/screen might fix.

From an area aftermarket trans shop suipplier, we found out that there's a place in the TX five-state area that rebuilds valve bodies. There might be one in your part of the world, too. I suspect they'll check the shuttle valve bores and ball check areas for wear and correct that.

Just some thoughts,

NTX5467

[Ron Luchene]

Based on your explanation, and since none of this started until the detent solenoid kicked in, maybe there was trash in the area of the detent solenoid that is now floating around the valve body. Is that possible? If I disassemble the valve body and I find some particles and flush them out, do I need to rebuild the valve body?

[Thriller]

A '66 ST400 should still be a switch pitch transmission FWIW. I'm not sure what you would need to do though to verify and get it back.

Good luck.

[NTX5467]

Based on your explanation, and since none of this started until the detent solenoid kicked in, maybe there was trash in the area of the detent solenoid that is now floating around the valve body. Is that possible? If I disassemble the valve body and I find some particles and flush them out, do I need to rebuild the valve body?

You'll probably need the valve body separator (plate?)-related gaskets, at the least. No "rebuild kit" that I know of for valve bodies, other than the gasket where the two halves of the valve body go together. You WILL need to know where each of the ballchecks do go, though, so they can be put back where they should be. Plus noticing which of the shuttle valve springs go where.

Also, be sure to check the flatness of the respective valve body halves AND the integrity of the separator plate gasket(s).

Happy Hunting!

NTX5467

[JohnD1956]

Could it be a broken kickdown switch? Is this the one with the switch on the back of the engine drivers side? I would try disconnecting that and see if the trans operates otherwise normally.

[Ron Luchene]

Success!

When the transmission was rebuilt by the previous owner they removed the Switch Pitch functionality. They installed a single spade case connector for the wire to the Kick Down switch instead of the dual spade connector for Kick Down and Switch Pitch control. The problem was that the wire now feeding the Kick Down switch was actually intended for the Switch Pitch control effectively feeding 12v to the Kick Down switch the majority of the time. This hadn't been an issue since the Stator Switch at the carb was dirty inside and not making contact. I had been adjusting the switch over time trying to see if I could get Kick Down control. I guess I messed with it enough to get it to at least make contact with the slightest bit of acceleration.

Anyway, I disassembled the switch and cleaned it up inside. It is installed and adjusted properly. The wires to the transmission case connector have been swapped and the transmission is shifting perfectly! While chasing the issue I went ahead and removed the valve body and cleaned it out. I installed a Transgo Shift Kit prior to assembly. I replaced the kick down switch as well. I am very pleased with the end results.

Ron

[NTX5467]

Thanks for the great update and information!! I'm glad it was an "easy fix", too!

NTX5467