I have a 1984 Buick Grand National with a replacement 200r4 tranny. The transmission is not an original GN – BRF transmission but it was rebuilt by a reputable builder to shift like a BRF, however it doesn’t shift like it should. I took it out and sent it back to the builder once and he made some improvements, but it is still not right.

I’d like to understand if my problems are just in the valve body, and it might be an easy fix, or do I have internal issues which require dropping the trans again. I don't have a lift, so I'd like to avoid dropping the trans. I really don't have time for that.

First let me say the following things work fine, with no issues:

- Overdrive/Converter lockup

- 3 – 4 Shift

- Full Throttle shifts

My problem is really with part throttle shifts on the 2-3 shift. At part throttle, the 2-3 shift always occurs at 22 MPH. It doesn’t matter if I am at 5% throttle or 40% this shift always wants to happen at 22. So, at 5% throttle where it shifted into 2nd at 13 MPH or something like that, then a 22 MPH shift to third might be OK, but at a higher throttle where it holds 1st gear until 20 mph, then it is almost immediately shifting from 2 to 3, when it should have held the gear longer. Once the throttle goes up over 50-60 %, then it will hold 2nd gear until a lot more RPMs, like it should.

The 1-2 shift isn’t perfect. Sometimes it will hold first gear too long, holding first gear until 3000+ RPM’s at very light throttle. Though that doesn’t happen all the time and that isn’t my real beef right now. If I could get the 2-3 shift corrected, I’d be much happier since that always happens and is very repeatable.

If I manually shift from 1 to 2 to D, it shifts fine, with no issue.

So does this seem like a Valve body issue or something more serious. And if it is the VB, what should I inspect/replace to fix this?
Thanks for any insights.

 

The Governor Pressure, and the TV pressures (MTV up and down, and the TV-Springs for each Shift Valve-Train) are going to determine when the Shifts will occur.

Do you know what you have for a governor (full throttle shifts will be changed here).

The TV springs can be changed for the 1-2 and 2-3 Valve-Train for shift timing (part Throttle).
The same goes for the 3-4 Valve-Train, but you said that you were happy the way that it is currently.

Does your Valve-Body use the Hydraulic TCC Lock-Up Valve-Train, or is it just an Electric TTC Lock-Up System?

 

Not sure about the governor.
The Torque converter lock up is computer controlled.

 

I realize it’s a little late for this but CK Performance would’ve been the right place to take your transmission. Getting shift points correct on a 200 4R it’s not an easy task. I took my OZ code apart four times and it still wasn’t 100%

 

The Governor is where you are going to want to start for full throttle Shifts.
It will determine what Engine RPM, the Shift will occur.

Jake's Performance out of Texas, can help you with anything you need for a THM200-4R Transmission.

 

Totally agree with this. But my full throttle shifts are good. They happen at the right RPM and have the right amount of firmness. My problem is part throttle shifting. Gears 1-2 and 2-3 only.

 

If you wanted all of the Up-Shifts changed this would be easier.
The Separator-Plate orificing could be changed for MTV UP Fluid if you were familiar with the Plate and would be willing to try different drill-sizes over and over to find the right combination.

With only the 1-2 and 2-3 Shifts being an issue for you...
I recommend that you try Jake's Performance in TX, and see if he has any 1-2 Throttle-Valve Springs, and any 2-3 Throttle-Valve Springs that he can sell to you.
You are going to have to remove these two springs from your Valve-Body, to measure the length and see if they still have any colored paint on them (for identification).
Then compare the Springs that you have, to what he may have... and go from there.

This would be easy if you brought the Valve-Body to a Transmission Shop that still does THM200-4R work.
To do this yourself, is probably going to be long and frustrating.

I honestly wish you the best of luck.