Transmission questions

[silicon212]

TH700R4 from 1984 Caprice.

I put some new clutches in it and a new band, but I didn't perform a full rebuild as the old clutches/band seemed to be in decent condition with no burning. The reason it came out was because of a slip on the 1-2 shift. OD would also phase in and out, when going out it was neutral. This can be symptomatic of a burned 2-4 band, but that wasn't the case once the transmission was broken down. Niether was the reverse input housing (which the 2-4 band bears against) burned. When I took the 1-2 accumulator cover off, I noticed the spring was broken into 3 pieces.

Forward to now.

I put the new spring into the 1-2 accumulator and put it all back together to use as an interim in this car while I rebuild the 4L60 with the broken reaction sun shell. This isn't happening as fast as I would like - I need a better paying job.

The transmission STILL has that 1-2 slip, even with the new spring - and it also has 'neutral' OD.
3rd gear works very well, the 2-3 shift has a nice, crisp 'bite' to it, as does the 3-2 downshift as the car decreases speed.
Knowing what I know about the power flow through this transmission, I've determined the 3-4 clutch cannot be the problem as 3rd gear is rock steady and healthy.

I've determined the problem must be in the servo for the 2-4 band and this is a two-piece unit (one piston for 2nd, the other for OD).

If anyone has experience with these transmissions, my question to you is -

Does this seem plausible or is there something else to look for?

The TV cable is adjusted per the GM method and the shift points seem to occur at the proper times. The engine doesn't really "flare" on the 1-2, but there doesn't seem to be any power transfer during the shift - which itself is, well, 'spongy'.

[Blue Bowtie]

You mean it shifts like a Ford MXO (soft a a baby's behind)? Is reverse working properly and engaging firmly?

A few WAG -

• The "E" clip/lock ring under the 4th apply piston in the 2-4 band servo is missing or damaged;
• The oil passage in the band apply pin is clogged;
• The 3rd gear accumulator is not dumping on shift to 4th (valvebody or separator plate problem?);
• Leak past 'O' ring on outer piston or at center of outer piston to pin
• Oil leak between inner end of piston and case (right near the band end);
• It's cursed.

That's all presuming that you have 4th apply pressure. I've seen a few covers that have been converted with a brazed-on 90° fitting to take a pressure check right at the servo (doesn't help for 2nd gear).

[silicon212]

Originally Posted by Blue Bowtie

You mean it shifts like a Ford MXO (soft a a baby's behind)? Is reverse working properly and engaging firmly?

A few WAG -

• The "E" clip/lock ring under the 4th apply piston in the 2-4 band servo is missing or damaged;
• The oil passage in the band apply pin is clogged;
• The 3rd gear accumulator is not dumping on shift to 4th (valvebody or separator plate problem?);
• Leak past 'O' ring on outer piston or at center of outer piston to pin
• Oil leak between inner end of piston and case (right near the band end);
• It's cursed.

That's all presuming that you have 4th apply pressure. I've seen a few covers that have been converted with a brazed-on 90° fitting to take a pressure check right at the servo (doesn't help for 2nd gear).

The E-clip was there and intact, the oil passage through the pin was clear, the accumulator I didn't check, there could be a leak on the O ring on outer piston, could be leaking on the inner end, and I think it's cursed.

When I pulled the servo cover off and pulled out the contents, I noticed the inside of the case, where the outer piston rides, was worn to the point that it had a ridge, like a worn cylinder on an engine. It has to be a high mileage transmission - I don't think there's any hope for it. My seal change on all 3 components of the servo tightened up the 1-2 a little bit, and I mean a little bit, but at least it didn't go the other way. The OD is still a mystery to that transmission, however. I am not so sure that it's slipping - it seems that when the 3-4 shift occurs, I get engine braking! The car slows down unless I really punch it (which downshifts it into 3rd or 2nd depending on speed).

[Blue Bowtie]

Was the 3-4 clutch rebuilt? Not to question anyone's assembly prowess, but is it possible some of the steels and discs were mixed, so that the 3-4 stack-up depth is wrong? If the 3-4 clutch didn't fully release (too many/too thick plates) you might get that drag in OD. Do you recall if it was a five disc or six disc stack?
(Don't ask me how I know that can be a problem. )

[silicon212]

Originally Posted by Blue Bowtie

Was the 3-4 clutch rebuilt? Not to question anyone's assembly prowess, but is it possible some of the steels and discs were mixed, so that the 3-4 stack-up depth is wrong? If the 3-4 clutch didn't fully release (too many/too thick plates) you might get that drag in OD. Do you recall if it was a five disc or six disc stack?
(Don't ask me how I know that can be a problem. )

Yes it was, and it had 5 plates in it not 6. It is a possibility I screwed something up, so that could very well wind up being the problem.

Anyways, it's a non-issue for me now - as I've given up on getting this one good. I just want it to work as a TH350 (no OD) so I can drive it around the city until I get the other one done - 2 weeks.

[Blue Bowtie]

Run it in DRIVE and it might make it along just fine. If it is a tight 3-4 clutch pack, it should not be a problem in 1-2-3. If you run it in OD, it may grind some space off the discs, but that might turn into a problem. Baby it if you can, and fix the "good" trans for a later exchange.

[silicon212]

Originally Posted by Blue Bowtie

Run it in DRIVE and it might make it along just fine. If it is a tight 3-4 clutch pack, it should not be a problem in 1-2-3. If you run it in OD, it may grind some space off the discs, but that might turn into a problem. Baby it if you can, and fix the "good" trans for a later exchange.

It actually seems to be doing fine with the selector in Drive. There is that issue with the tissue soft 1-2, which seems to soften up more the harder I give it gas (I've not even thought about doing any burnouts or anything with this thing, don't worry). Driving it around the parking lot at moderate speeds (up to 20-25MPH) will cause the 1-2 shift to occur at about 10MPH and there it actually has a little crispness to it, you can feel the shift. However, when accelerating up to about 40-45MPH, it will upshift between 15 and 20 and this is when it turns into a sponge. I've learned to take my foot off of the gas near the shift point. This is a habit that goes back to when this unit was in the car before. I miss that 4L60! That thing had great shifts. Until its final 1-2 shift that resulted in a broken sun shell ... Anyways, I got the rebuild kit for that thing tonight (master kit with band and steels), tomorrow I'm going to Cottman to get the replacement sun shell (SPX/Filtran Beast), the guy there is going to sell it to me for $30. I'm also going to spring for a new valve body spacer plate for it as well as the 1-2 accumulator spring (the old spring broke & bent the spacer plate).

I promise not to do burnouts in my nice heavy car with the fresh 4L60!

[GreyGoose006]

i know NOTHING about transmissions, but i am having similar symptoms on my th350 trans. when i keave the car in drive the 1-2 shift is normal until you give it gas. at full throttle the shift has a sort of gritty feel to it, like it is engaging, but slowly, and not all at once...
i usually do let off right before the shift and it helps a lot.

i dont imagine this will help you, but if you can recomend a quick fix it would be awesome, since we are on the subject of transmissions

(sorry for hijacking the thread)

[silicon212]

The good transmission - yes it was definitely the Reaction Sun Shell.

[silicon212]

UPDATE!

The POS 700-R4 transmission is now sitting in my trunk. I got the 4L60 finished over the weekend and decided to reinstall it tonight. It's absolutely perfect. Back home in its rightful place.

Doing a little more research into what happened, the sun shell broke when the transmission shifted late and hard. The 1-2 shift accumulator spring had broke and siezed the piston in its bore, basically removing it and the accumulator from the equation. The resulting hard shift is what did the sun shell in I believe.

[broughy84]

I don't see why that sun shell cant be reused.........I don't see anything a little stick of gum and some tape won't fix....

Okay so maybe a stick of Wrigley's won't fix it, but I bet a stick of TNT will!!!

[Blue Bowtie]

Yeah, I'm with him. A little J-B Weld and it should be good as new. Why waste the $30? (That's a heck of a deal on a good shell!) It's only a few hours labor to swap out anyway...

Looks like the planetary set hub was having its way with the shell too. Good thing you got in there when you did. You know the drill - Keep it full of clean, cool oil now and it will last forever.

[Blue Bowtie]

Originally Posted by GreyGoose006

i know NOTHING about transmissions, but i am having similar symptoms on my th350 trans. when i keave the car in drive the 1-2 shift is normal until you give it gas. at full throttle the shift has a sort of gritty feel to it, like it is engaging, but slowly, and not all at once...
i usually do let off right before the shift and it helps a lot.

i dont imagine this will help you, but if you can recomend a quick fix it would be awesome, since we are on the subject of transmissions

(sorry for hijacking the thread)

Check the free movement on the stem of the modulator. Check line pressure at idle in DRIVE and again at idle in Low and 2. If you start with the range selector in 2, does the trans even use LOW or start out in 2? Does manual 1-2 shifting make the shits any firmer? If hte oil pressure is good, an older trans may have wear at the separator plate and balls, and not be sealing properly. If you get that deep, you should also check the band adjustment (IIRC, TH350s should have that depending on vintage) and 2nd accumulator, piston, and 2nd servo.

[GreyGoose006]

if i start in 2, the trans starts in first, shifts to second and stays there. the shifts are no better.

let me repeat...

Originally Posted by GreyGoose006

i know NOTHING about transmissions

is this something i can live with, or is it a problem that will only get worse

is the modulator the thing that sticks out from the side of the trans on the drivers side?
i replaced something a while back because someone said i needed to
here is a "picture"

__
__| |__
|______|
|_ _|
||

one end plugged into the transmission, the other end went into a black rubber tube...

[silicon212]

Yes, that is the modulator.

It should be on the passenger side at the back on the area with the "cut out corner" in the pan. I've found that over the years with various TH350s that the best modulator to use with it on heavy cars such as the Caprice is the one with the red painted band on it. When you look into the vacuum connector, you will see a screw that you can turn with a small straight-blade "precision" screwdriver. This you can adjust to either soften or firm up the shifts. It's been a while since I've played with one, but IIRC, it's clockwise to tighten up the shifts. This adjustment is tantamount to the TV cable adjustment on newer transmissions.

Originally Posted by Blue Bowtie

Does manual 1-2 shifting make the shits any firmer?

I'm sure a doctor can help with that! LOL Anyways, the TH250 has a band adjustment, the TH350 does not.