200r4 not holding 1st gear

[southpaw]

Hey there,

New to the forum and thought I would start it off with a real head scratcher. I have a 200r4 from a GN in my 1979 malibu. For the longest time everything was perfect until recently when I went to the track. Now when I hold in 1st gear the transmission automatically shifts to second around 3000 rpm even with the shifter still in 1st! I have no clue why this would happen but its costing me serious time at the track. Is anyone able to help me with this situation? Oh I should add the only thing that changed during this time was I added a new transmission filter and changed the oil....so not sure if its something to do with that.

Regards
SP

 

[RockSS]

Check your TV cable ... did you disconnect it? or did it possibly break? ... its not a kick down cable like on a th350 it controls fluid pressure start with that ... is it adjusted correctly .. thats all I got good luck

 

[AlanB]

Welcome to the forum. That is a tough one. I had to pull out my 87 Olds manual and do some digging because I never heard of this problem. If you leave it in D3 or D4 and go full throttle, does it do the same thing, shift to 2nd at 3000 RPM? Have you recently made any significant changes in gear ratio? At what speed (mph) does it shift?

I would take a look at the shift linkage to make sure that 1st gear is fully engaged. If you are using stock GM 3 speed linkage, the bar that runs from the bottom of the column to the shift linkage on the trans can hit the firewall preventing full movement into low. The bar for a 4 speed car is slightly longer and will clear fine, allowing full engagement of manual low.

As RockSS mentioned, I would definitely check the TV cable adjustment.

Things get more difficult from there. Next step would be to check line pressure and compare against the specs. My manual shows pressure for an 87 BRF should be 123-138 in manual low. There is something called a 1-2 shift valve that is held closed in manual low by hydraulic pressure and the 1-2 shift spring at speeds below 30 mph. I suppose if the spring broke it would allow premature shifting to 2, as would low line pressure. Also, I would think a malfunctioning governor could cause this problem if too much governor pressure was applied to the 1-2 shift valve, overcoming the line pressure and spring tension. I would expect a malfunctioning governor to cause a late shift though (low pressure), not an early shift (high pressure).

That's about as far as I can go with limited knowledge and an open book. One of the best resources for 2004Rs on the net is turbobuick.com. You might try asking over there. There are some transmission pros lurking in that forum.

 

[JBreu]

Could be many things...When you took the transmission pan off was the TV plunger dislodged accidently? Is it a floor or column shifter? maybe a linkage issue??? Possibly even a govenor issue that your now noticing...Has it been to the track prior to this?? I'm partially thinking the tv cable isn't adjusted properly or possibly a bad valve body???