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Originally Posted by wolf_walker
The two valves on top of the valve cover are shot, that's your downshift clunk, the injection pump vac valve($170) is probibily shot as well, giveing eratic shifts out of spec. Sucks don't it?  |
Well it sucks that's for sure. I just completed replacement of the two valves (my old ones were shot for sure) but the clunks remain.
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Originally Posted by Cateaux
The downshift "clunk" is generally caused by not enough vacuum being sent to the modulator valve via the vacuum control valve on the injection pump. When new, the valve should have 19 or 20"Hg going to the transmission when at idle (accelerator not depressed). If you have less than 15"Hg or so, the transmission thinks that you are trying to accelerate, so it downshifts into first gear, hence the clunk. When operating properly the transmission will stay in second gear when you slow to a stop, and will only shift back down into first when you hit the accelerator (and the vacuum signal to the trans drops).
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Seems like the two of you (Cateaux and wolf_walker) are on top of this. My clunks seem to have reduced as observed from a brief 5 mile city only test drive I conducted after the replacements. However, I still get clunks quite a lot. In fact, my 2-3 shift is not only hard, but it seems like all my downshifts have the clunk with them. So, I guess my problem lies in the vacuum control valve on the injection pump. What is this thing anyway? And also, what does it involve to measure all those vacuum levels you mention? Do I need a mityvac or something? Sorry but I'm new to this vacuum business. I think it is about time I got into the vacuum business on this car since everything has some vacuum attached to it.
Edit: The car I'm currently dealing with is my 1984 300SD with 166K miles. My other 300SD shifts so smoothly and rarely experiences those clunks. I guess someone worked on it sometime in the past.