1964 Grand Prix Downshift Issues

Orzel

New member
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Michigan
Hi all, have a question about the infamous "Slim-Jim" roto hydramatic. I'm not very transmission-literate, so bear with me here.

For a quick bit of background, I've planned to rebuild my '64 GP's 389 for awhile now; have had the dreaded oil light flicker for about a year now and have determined it's the main bearings. Still runs relatively well but I don't wanna do too much damage to anything considering the block is original to the car, blah blah blah. Well I figured since the motor's going to be out, I may as well get an adapter plate and swap the dreaded Slim-Jim to a TH-400, though I only have enough cash as of now to square away the engine and would rather get the engine done anyway since I wanna drive it. Of course with that being said, I'm going to have to make the most out of the Slim-Jim until I can get the cash for the swap.

So this brings us to the main issue at hand. In the case my roto, it's surprisingly decent for what it is. While it does leak a tad bit and the 1st-2nd shift is pretty rough as with any roto, it shifts well through all the gears and I think I've got the TV rod, at least at the carb, dialed in decently well. The big problem, and has always been a problem, is the downshift quality. When rolling to a stop, the trans takes waaay too long to downshift, to the point where the RPMs drop very low; the RPM drop has actually caused my car to stall a couple times when driving it out cold.

To tell you the truth, I'm not completely sure if it's the nature of the transmission, something's badly worn, something's not adjusted right, etc. It's got plenty of fluid, though the only I can think of is that I don't totally have the TV rod dialed in, as I've only adjusted the linkage at the carb. I'll have to get my hands on the 1963 service manual and do my own homework on adjusting that blasted TV rod, but I'm just curious about your thoughts and experience.

Thanks!
 

melsg5

Staff member
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Are you sure the issue isnt carburetor adjustment related? As far as your transmission is concerned not too many people dealing with that transmission on this site. See if you get any comments concerning it.
 

Orzel

New member
5
0
1
Michigan
Are you sure the issue isnt carburetor adjustment related? As far as your transmission is concerned not too many people dealing with that transmission on this site. See if you get any comments concerning it.
Hard to say if it's a carb issue, I've toyed with the carb numerous times and am pretty sure I've had it dialed in, excluding the TV rod at the carb. Granted the motor's pretty worn of course too; I'll have to see how the performance changes once I get the engine sorted out. In any case, considering the obscurity of the transmission, I don't quite expect to get much if anything but it's worth a shot. I'll have to do a bit of searching around to see what I can dig up.
 
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