Last year I attempted a TransGo shift kit install on my '87 GT, but may have overestimated my ability to do it right. I took my time and was very careful throughout the entire process, since this was my first experience of disassembling the valve body. Unfortunately, the end result has been a slight 2-3 shift flare at medium throttle, delayed kickdown into passing gear, and soft and early gear changes.

I confirmed there is a low line pressure problem with a gauge. When the trans. is cold, all pressures are within spec except reverse (~40 PSI below spec) @ Max T.V. Reverse drops to around 115 PSI @ Max T.V when trans. is warmed up, when it's expected to be 230+ PSI. Drive, 2nd & 1st are all 20-40 PSI below spec, except Drive @ Min T.V.

Factory Pressure Specs - 7CPC - @ 1000 RPM

-------- Min T.V -------- Max T.V

P ------- 66-74 ----------- 66-74
R ------ 117-129 -------- 232-258
N/D ---- 67-74 --------- 133-147
I/L ---- 114-126 ------- 114-126

Line Pressure Test #1 - Trans. Cold @ ~850 RPM

-------- Min T.V -------- Max T.V

P --------- 78 --------------- 78
R -------- 115 -------------- 190
N/D ----- 70 --------------- 138
I/L ------ 120 -------------- 118

Line Pressure Test #2 - Trans. Hot @ ~850 RPM

-------- Min T.V -------- Max T.V

P --------- 70 --------------- 70
R -------- 113 -------------- 115
N/D ------ 68 ------------ ~100
I -------- ~95 ------------- ~95
L -------- ~75 ------------- ~75

I'm unsure where I've gone wrong. The trans. has never had an issue prior to the shift kit install at 120k miles. Fluid level is normal. T.V cable set correctly. No problems selecting gears. My main concern is whether I've taken too much material off the pressure regulator valve. TransGo instructions suggest grinding two flat spots flush with the spool, allowing fluid to continuously flow to the converter.



As a temporary fix, I increased the line pressure manually with the T.V cable which resulted in a harsh 1-2 shift, soft 2-3 (no flare), and higher shift points. I'm confident the T.V valve is working normally, but I still seem to be losing pressure somewhere. Any advice on this would be greatly appreciated, thank you.



------------------
James
RHD '87 GT 3.4L V6

[This message has been edited by James_GT (edited 01-18-2023).]

After pondering on this further, I'm thinking it has to be a seal that's leaking. Seems as the fluid heats up and becomes thinner, it's finding a way past a gasket and causing pressure loss. If it were a problem with the pressure regulator valve, I'd expect most pressures wouldn't be within spec when the trans. is cold. Only reverse appears to be down a significant amount when cold. Given that reverse is the gear with the highest pressure, it would likely amplify the leak problem. I now suspect one or more valve body bolts could be loose. Even though I used a 1/4" torque wrench to tighten them to factory specs, I'm questioning whether it's accurate.

Here's an excerpt from the service manual. I feel I can comfortably eliminate no. 1-4 & 7-10 as potential causes.



Will re-check the valve body bolts and whether my torque wrench is calibrated correctly.

[This message has been edited by James_GT (edited 08-07-2022).]

quote Originally posted by OldsFiero: First thoughts from memory; separator plate gaskets reversed, loose bolts, boost valve sleeve retaining pin positioned incorrectly on sleeve grooves. When I get time I'll try to look at fluid charts to see if there is anything else. DO NOT put the car under high load conditions until you locate the problem. Int/Rev boost valve sleeve retaining pin is holding the sleeve in the correct spot. Marc

Thanks for your help, Marc. Separator plate gaskets can be interchanged on either side, can't they? As long as the holes line up they should be all good? This is how my valve body looked before it was reattached, with small amounts of grease holding the gaskets and check balls in place.



In Line Pressure Test #2 above, where there's a ~ symbol next to the PSI reading the pressure gauge needle is flickering and not holding steady. Also during warmup, with the trans. in Drive, it would fluctuate between 70 & 110 PSI. Settling at 75 PSI when warmed up.

Still leaning toward loose bolts being the cause. I've had the valve body off twice now and had the same result, even after changing the separator plate gasket. I tightened the long torx bolt (valve body to drive sprocket support) by hand, so maybe that's causing problems here.

[This message has been edited by James_GT (edited 08-07-2022).]

quote Originally posted by OldsFiero: My bad. The VB gaskets are the same. I see that min line is OK even hot, so pump volume or leak is unlikely. You didn't mention whether lock up works or not. There is a bolt that goes through the auxiliary valve body that holds the bore plug and lock up control valve in place. If the plug is missing or the valve fell out when you took it apart, and was reinstalled backwards, the result would be no lock up and low line pressure. You have very little pressure rise which indicates a TV / boost problem. After looking at hydraulics, I think a missing #6 check ball is likely the problem. There are 5 check balls in the case cover. #6 is the uppermost one in a passage that connects to the manual valve. If it is missing, RNDL oil from the manual valve to the TV valve will leak into the detent circuit. Pretty sure it could cause your symptoms. Hope this helps, Marc

Thank you again, Marc. The lockup converter is working normally. Feels like it engages quicker than before the shift kit install.

That's a logical hydraulic diagnosis - though I'm fairly certain none of the check balls are out of place. I used a touch more grease to hold them in this time, ensuring all six wouldn't fall out while refitting the valve body. One other change I made during the shift kit install was to replace the steel check balls with Torlon, though I don't see how that would have any negative effects on the trans if they're the same size as stock (0.250").



I'll take another look at it over the weekend. If it's not a loose bolt(s) or a problem with the check balls, I may need to hand this over to a transmission shop. Don't really want to give up on it now, since it seems so close to success at this point.

[This message has been edited by James_GT (edited 08-12-2022).]

[This message has been edited by James_GT (edited 01-18-2023).]