Hey, my car has this strange issue where the transmission has a delay when it shifts from 1st to 2nd. The delay is after 1st has been disengaged and before 2nd is engaged. This makes the rear tires burnout for a little. Is this normal during hard acceleration or should I have my transmission overhauled?

 

Are you sure the fluid is up to proper level? (Checked when car is on level surface and idling)

 

The fluid level is a little high by 1/2 inch on the stick. I haven't tested downshifting yet.

 

Car downshifts from 3rd no problem and I add then removed some transmission fluid, had no effect

 

Did you try adjusting the transmission throttle cable?
Did you check the modulator vacuum rubber line for cracks?

 

I have a mityVac will that do the job?
I can't find the transmission throttle cable, do you have a diagram or reference picture?
Is the modulator vacuum line in the carb or in the intake manifold?

 

Your profile says you have a 71.
The car did not come with a TH350 from the factory.
So are sure you dont have a TH400?

 

Yeah my bad it is a TH400

 

There is no transmission throttle cable on a TH400.
Does the engine rpm go up a lot during this delay in shifting?
When is the last time the filter and fluid were changed?
If recently was there a lot of material in the pan?

 

I'm not sure when the last time either one was changed, yes the engine rpm does go up a lot. (This is because the gas pedal is fully depressed)
The fluid color and level both look good, is the filter inside the transmission, or is it like the engine where it can be removed from the exterior?

 

As the engine is waiting for the delayed transmission shift does the rpm briefly go up and then drop down when the shift completes.
Trying to establish whether it is slipping between shifts.
The transmission pan has to be dropped to change the filter.

 

Yes, the rpm goes up after the transmission disengages 1st. There engine spools up and then the transmission engages second and because of the increase in rpm in between the shifts, the car does a brief burnout. This only happens when I mash the gas and not under normal driving conditions. I will drop the pan this weekend to see if I find anything alarming.

 

Be prepared for a very messy job. There's just no neat and tidy way to drop the pan without fluid going everywhere. Once the pan is off, don't be alarmed by a loose filter - that's normal. Before you start, have a new filter, pan gasket, and a couple quarts of new fluid on hand. Did I mention that you'll need dozens of rags to sop up the spillage?

 

Got it, I will make sure I have everything ready. I think a gallon will be enough and I'll take some pictures of the pan and filter and post them here. If everything looks normal I'll go to the local transmission shop and see if they have an idea of what's going on. The car has the base 270 engine and only 44k miles so I'm hopeful it will look normal. Also if I have to re-build it is it possible for me to pull the transmission without removing the engine?
Do I fill the transmission through the dipstick tube?

 

Yes, filled through the dipstick tube. I don't recall how much fluid to have on hand with a filter change, so might be good to look it up in a specs chart.
Also, yes, you can remove the trans without pulling the engine. Be warned though that it weighs a LOT (~150 lbs if I recall) and the car needs to be pretty far in the air for it to come out from below. Best would be to have a transmission jack but then you need even more clearance. Unless I were really jonesing to do it myself, I might opt for a trusted trans shop to pull it. (I've done it twice and that's plenty for me!)

 

Turbo 400 transmissions have a weird filter issue. Their cloth and as they age they can restrict fluid flow, and in some cases fall into the pan,

 

It sounds like you have a problem with the intermediate sprag. When the trans shifts from 1st to 2nd, the forward clutch remains engaged and the intermediate clutch is then applied with the reaction taken by the intermediate sprag. If the intermediate sprag slips, the rpm will rise until the sprag locks.

For better understanding, first gear (the forward clutch) does not disengage when going to second; only the second gear (intermediate clutch) is applied, but the reaction must be blocked by the intermediate sprag.

To fix this, the trans must be disassembled and overhauled.

 

I discovered that the connection from the vacuum line to the intake manifold was leaking and repaired it. What exactly does that vacuum line control?
Also when the car is in second at WOT it redlines instead of shifting to 3rd, is this normal or is it aTH400 flaw? I can get the car to shift into 3rd by letting off the gas a little. Could the kick down solenoid be preventing it from shifting?
I've decided to not drop the pan just yet. I might take it to get inspected at a transmission shop but I need to be sure before getting it overhauled.
The car drives fine in normal driving conditions and it comes out very expensive if I have to rebuild the transmission. My dad is already not happy with me fixing his car because it keeps costing him more and more

 

The vacuum line operates the vacuum modulator (on the side of the transmission). Its function is to 'adjust' the shift timing and shift points (up or down), depending on the throttle setting you have at that instant. If you are just driving normally, shift points are at a much lower speed and there is a smooth transition from one clutch to another. If you have the "pedal to the metal" (WOT), shift points will be near the engine's redline and shift timing will be very fast. And everything in between

I suspect the diaphragm inside the vacuum modulator ihas failed and that is how vacuum is leaking....thru that diaphragm and into the trans sump area. This is the cause for all "late" shifts you are experiencing. Replace the vacuum modulator. All auto parts places sell the 'generic' part for the THM-350 trannies. When you pull the defective unit out of the trans, some fluid will run out, but probably less than a quart. You can clean the outside area around that modulator first, put a pan under the work area, then remove the modultor and catch the overage. Once you install the new one (lube the O-ring with trans fluid before trying to push it into place), you can put the lock tab in place and tighten the bolt. Then pour the lost fluid back into the trans....assuming the pan was clean and no dirt or debris got into the oil. Otherwise, just add the same amount that you lost.