87 Dakota 2wd V6.
I came across the term “runaway upshift” while reading the auto trans section of the shop manual for the 87 Dakota. I googled the term, and while I found many references to it, I could not discover exactly what it is.
I found out how to adjust the upshift from 2nd to 3rd on this A-998 LoadFlite/TorqueFlite transmission. It is an adjustment to the throttle valve linkage. I am still try to discover how to adjust the upshift from 1st to 2nd. I would like for it to happen at a lower speed than at present, which is more than 20mph.
A ‘runaway upshift’ is where the valve body commands the shift to occur but the mechanical parts of the transmission tries to obey but it does not or cannot engage the next element. For example, on your 998 it would be a runaway on the Direct (Third) to Kickdown shift if the Kickdown/Intermediate band were left too loose to stop the common sun.
Thanks so much, R. That is really valuable knowledge. You explained it very well. One question: Is the intermediate band that you refer the same as the kickdown band or the low-reverse band? Those are the only bands that the shop manual refers to that are adjustable. I was very careful to adjust them according to the manual, with help from Rod_Knox here at Car Talk. I have to drop the pan to get to the low-reverse band. I put a drain plug in the last time to make future access less messy. I can drop and rebuild the valve body if that might be advantageous. This delayed shift only began happening after I changed the filter and fluid, and adjusted the bands in an attempt to deal with a sudden onset of slippage when first starting up in the morning. That problem no longer exists. The late shifting is not that much of a problem, not like the slippage was, and I could live with it, but if there is something I can tweak to get it to shift at slower speed I would like to try.
Jack
Do you think the throttle cable is properly adjusted now?
As a real case example of a ‘runaway’ shift, I was driving my parents 1968 Belevedere with an A727. When I went uphill the engine would rev but the car would slow down. I knew from the layout that the ‘HIGH’ clutch was not holding. If I had floored the accelerator just below ‘KICKDOWN’ the engine would have raced away.
The ‘KICK DOWN’ band is the same element as ‘SECOND/INTERMEDIATE’ band. You do the kickdown from ‘HIGH’. The second/intermediate engages from ‘LOW’.
The delayed up shift is because the throttle adjustment is not correct. When governor pressure overpowers the throttle pressure and spool spring, the spool valve will toggle causing the hydraulic shift completed by the mechanical elements. Your throttle pressure is too high.
I adjusted the throttle linkage to delay the shift from 2nd to 3rd. It was occurring before 25mph, which caused to the acceleration to get bogged down from 25 to 45. Now it shifts at around 30, which gives better acceleration. The excessive delay from 1st to 2nd began after I changed oil and filter, and adjusted the bands, but before I adjusted the throttle linkage (no cable). I am not sure if the throtle linkage controls both the upshift from 2nd to 3rd AND the upshift from 1st to 2nd, or ONLY the upshift from 2nd the 3rd. Do you know?
Thank you, researcher, that is very valuable knowledge for me. You guys are helping me keep one of the very few remaining 87 Dakotas still on the road. At least I don’t see any. It was the feedback carb that doomed that year to oblivion. There are no replacements for the feedback solenoid. I eventually replaced the Holley 6280 with modified NOS leanburn Holly 2280. Runs great and passes smog.
One thing I just remembered. The throttle pressure raises the line pressure. `So if you have slippage in one of the elements i.e. kickdown band or high clutch, the higher line pressure will clamp the band servo or clutch pack tighter obviating the slipping. So if you reduce the line pressure to get the shift points in line, you will probably get the slippage back.
If you feel competent and are meticulous, using the shop manual as reference, rebuild the transmission yourself. You can augment your memory by taking layout pictures of everything. Also look up various ‘youtube’ videos on ‘rebuild a 998 automatic transmission’. The expert there does a very good job of guiding; showing the disassembly and assembly of the gear body and valve body; and explaining the weaknesses and what to look for on various transmissions. `
I would love to take apart the transmission and rebuild it. Knowing there is a YouTube video is comforting, but I will wait until it demands to be rebuilt. Not there yet. But I WILL watch the video.
Sorry, no experience w/that transmission. Common sense suggests if that adjustment affects both transitions, if it is correct for the 2-3 then it must be correctly adjusted for the 1-2 also. One further idea, Hot Rod magazine has articles quite frequently on the how-too’s of adjusting the throttle cable on Chrysler automatic transmissions; suggest to surf over there and see what a website search yields.
Thanks, George, I believe I found just the article for this particular transmission. The article refers to the A727, but the adjustment of the throttle valve linkage is the same as on the A998. The article describes the correct adjustment in much more detail than the shop manual.