TH400 shifting issue

[Norwester]

Hello Folks! I have a transplanted TH400 put in by a PO. I've had the truck for 3-4 years and it's always shifted beautifully.

About two weeks ago, I started experiencing a problem. I would select "R" and nothing would happen. I'd move the selector to the left just a little bit and it would go into reverse. Ok, I can live with that. Yesterday, I took off from a stop sign and the truck would not go into 3rd gear. I moved the selector to 2nd and it felt like it wasn't hooked up at all. I messed with moving the selector through the 3 gears and finally it caught and went into 3rd and then drove fine.

My first thought was that I had a linkage issue but my non-mechanic mind doesn't really know. I'll be putting it into a shop but I'm hoping one of you people can give me an idea of what I'm dealing with.

I do appreciate any comments.

 

[AuroraGirl]

The reverse thing makes me think linkage. My dad has a 75 and the entire time hes owned it(20 years) the gear shift never indicates the proper gear. Always off, to the left. Except park is proper. Do you feel the physical shift where the lever locks in ever so slightly. You should have, to my understanding, P R N D 2 1. If you select 2 I believe it puts you in 2nd gear, otherwise D uses 1 2 3 and 1 limits to 1st gear. Dont quote me, its been a few years. It might say like D D2 D1 possibly. But the other gears.. hmm. If the gear lever moves into nice grooves, but it doesnt line up, and seems to work, Id say its the indicator spring that wears out and doesnt pull the needle with the right force, in that case too little force from years of use. If 3rd didnt seem to work right away I bet it was in 2 but showed 3 or D whatever.

 

[Norwester]

Appreciate the reply.......and what are doing up so early? Yes, the indicator reads P-R-N-D-2-1. I replaced the indicator itself when I bought the truck because while the transmission was replaced, the indicator wasn't. It had the 700R indicator and it just bugged me.

 

[AuroraGirl]

I dont sleep, pretty much. Could ask you the same. There are square bodies to save. And just generally a lot of other work to get done. Whats the indicator look like? And very possible the current indicator has to be different to match transmission linkages. Im not sure, I dont have a automatic in my driving, finished square body.

 

[Norwester]

I don't believe it's the indicator. Yesterday, when I put it in "D", I felt a positive "clunk" Just wouldn't go into 3rd. Even if the indicator was broken, I'd still be able to feel when it went into gear. Not much of a mechanic so I'm sure I'll put it into a shop.

 

[AuroraGirl]

Well what I did in my 77 ford LTD that didnt have an indicator was start from the left and go right. you should get a clunk in the trans and gear selector for R, then again in N. Which neutral should have higher rpms and you go no where. Then one more over to thr right SHOULD put you in drive which SHOULD allow 3rd gear. If that is still the problem it sounds very much like your trans has issues. Fluid on the right hash area according to the owners manual and nice and red? Not black?

 

[Norwester]

Good idea....I haven't checked the fluid in a while. I get lazy because every time I check it, it's fine. But even if the level is fine, that wouldn't explain why I have to move the indicator a bit to the left when I'm looking for "R". I very much appreciate your comments.

 

[AuroraGirl]

The TH350 in my 77 Buick Electra calls for checking fluid at ambient temperatures or with mild warming up, never on a running engine(like a lot of modern vehicles) so you for sure want to know the proper procedure because that can change everything very quickly. I only saw it casually browsing the manual.

 

[Matt69olds]

There is a difference in columns between 3 and 4 speed transmissions. The detents for the gearshift are spaced differently, I think the spacing between neutral and drive is closer on the 4 speed than 3 speed. When they added the 4th gear everything had to get closer to keep the shifter range of movement equal.

basically, what I’m suggesting is maybe the entire time you have been driving the truck the trans wasn’t fully in reverse. It may have in reverse according to the shifter on the dash, but the manual valve in the valve body wasn’t fully in the reverse position, causing a fluid leak in reverse. Since the direct drum is used in both reverse and 3rd gear, the clutches may be cooked.

Drop the transmission pan, hopefully the fluid isn’t burnt, and there isn’t much crud in the pan. Change the filter. Unhook the shifter linkage, put the trans in drive. Put the shifter on the column in drive, loosen the adjustment bolt, and assemble the linkage and tighten the bolt with the trans and shifter in drive. Then put the shifter in reverse, look at the detent spring in the transmission linkage in the transmission. If the detent roller isn’t fully in the detent for reverse, then your going to have a internal fluid leak. You may be able to find a happy medium with the adjustment, as long as the shifter fully engages in park, reverse, and drive the trans will be happy. Assuming the damage isn’t too severe

 

[Norwester]

Matt, thanks for the detailed response. If the issue is as you described, would that possibly account for the fact that I put it in "D" and it wouldn't go into 3rd? Also, would that account for when I put it in "R" and I have to move the gearshift slightly to get it to engage?

 

[Matt69olds]

I would not be surprised if the problems are related. Once the pan is off you will be able to see the detent roller on the rooster comb, the detent roller needs to be bottomed out in the rooster comb for each gear.

 

[Norwester]

Thanks for the input, Matt!

 

[Norwester]

Took the truck to AAMCO and they found that the linkage was practically "going to fall out" They adjusted and tightened it all up and it shifts wonderfully now. Thanks to all who replied.

 

[Big Chip]

Wow, blast from the past there! I wasn’t aware AAMCO was still in business.

 

[Matt69olds]

And that they were able to fix it without a complete overhaul. For those that don’t know, AAMCO stands for All Automatics Must Come Out.