700R4 Lock Up Converter Talk and Diagnose

[89Suburban]

I know what you're saying here. I really wish it were sprags, but actually it's roller clutches in the books IIRC, which are much weaker than sprags. It's a nit picky difference in lingo I know, but if the guys who aren't transmissions guys go looking for sprags in the book, they'll likely never find it, so being politically correct, roller clutches.

This is also why when diagnosing transmissions, you also use manual selected gears. Many are not aware that using manual selected gears uses a different fluid circuit and actaully uses a different method to create the gear. Same goes true when diagnosing a band. You might have 2nd this way, but not have it this way. Whichever way you have it and don't have it can tell you if it's a band or not. Bands actually aren't used near as much as most think. I'd have to look at a flow chart since i don't momorize that stuff since different trans models are different, and the minute you think you got it, it's no wait, that's the Th400, not the Th350 or vice versa.

A good example of this is when you're in D and the trans is in 2nd gear. When in D and trans is in 2nd gear, drop it into manual 2nd gear. It'll feel a bit like it downshifted, but NO it didn't. It changed the routing of how it's getting 2nd gear. At any rate, good point to bring up Jake.

Got pics so I can comprehend that better?

 

[89Suburban]

Yeah, get this fixed already wouldja Dawg??? Curiosity is starting to kill me on this deal. I'm about ready to pull the Th350 out of the K1500 and put this 87 700r4 that's supposed to work into the K1500 just to play with Lock Up TC. Of course it's going to be different cuz mine will work off activation by Vac switch on the firewall, yours will work off signal from the ECM. Of course that doesn't really matter. The signal goes to the same place, just gets its from a different source.

I don't recall the pinout on the connector, but I'd almost like to see your run a hot wire from the battery thru a toggle or push button swtich to the connector so that you're making your own signal and see if it works. What this will do is, confirm if the problem is in the transmission in front of the connector, or if the problem is behind the connector which would be in the wiring or the signal source. Know whudda mean???

So if you hook up a hot wire and it works. The you know the problem is NOT in the trans and the problem is BEHIND the connector.
If it still dont' work and you've confirmed you wiring and signal from the ALDL, then most likely the problem is in FRONT of the connector and inside the transmission, most likely to be the TCC solenoid.

I need to know what those 3 wires are for. Then maybe I can start diagnosing from there.

 

[HotRodPC]

Lemme see if i can dig up what I'm talking about Dawg. I'll look for an apply chart. That tells you what servo's are applied, which roller clutches/sprags are active and no active etc. This way you can pinpoint what is wrong.

Me, I've not gotten deep into those. Reason being, once you do a few checks, you can usually tell if it needs to come out and rebuilt or not. So if it's to far gone, doesn't really mattter since you going ot reupid it or not.

 

[HotRodPC]

Got pics so I can comprehend that better?

Here you go Dawg.

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[Jims86]

Yeah, get this fixed already wouldja Dawg??? Curiosity is starting to kill me on this deal. I'm about ready to pull the Th350 out of the K1500 and put this 87 700r4 that's supposed to work into the K1500 just to play with Lock Up TC. Of course it's going to be different cuz mine will work off activation by Vac switch on the firewall, yours will work off signal from the ECM. Of course that doesn't really matter. The signal goes to the same place, just gets its from a different source.

I don't recall the pinout on the connector, but I'd almost like to see your run a hot wire from the battery thru a toggle or push button swtich to the connector so that you're making your own signal and see if it works. What this will do is, confirm if the problem is in the transmission in front of the connector, or if the problem is behind the connector which would be in the wiring or the signal source. Know whudda mean???

So if you hook up a hot wire and it works. The you know the problem is NOT in the trans and the problem is BEHIND the connector.
If it still dont' work and you've confirmed you wiring and signal from the ALDL, then most likely the problem is in FRONT of the connector and inside the transmission, most likely to be the TCC solenoid.

He would have to get into the trans, and ground the TCC solenoid to the VB If he runs a switch. TCC is activated on the ground side, Pos is always hot when the key is on, unless your foot is on the brake. separate ground wire would be the fashizzle on an existing ECM commanded system.
Either way, I think it would be a safe bet to install a new solenoid...I really think that diode possibly being bad is why it popped the fuse when he grounded it. Its the only explanation I can find in the diagram.

 

[89Suburban]

Here you go Dawg.

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OK, only difference I see in that chart in 3rd gear is an "Override Clutch" is engaged in drive but not in OD. What is that?

He would have to get into the trans, and ground the TCC solenoid to the VB If he runs a switch. TCC is activated on the ground side, Pos is always hot when the key is on, unless your foot is on the brake. separate ground wire would be the fashizzle on an existing ECM commanded system.
Either way, I think it would be a safe bet to install a new solenoid...I really think that diode possibly being bad is why it popped the fuse when he grounded it. Its the only explanation I can find in the diagram.

Can you post that diagram here?

 

[HotRodPC]

It's an OverRun clutch. A roller clutch aka one way sprag. That's how you have downshift holding power if you were to manually kickdown a gear. So so you're going down a hill and you go into 3rd or even 2nd to help slow you down, but it's like going into neutral instead, then you can determine your roller clutch/sprag isn't holding and need replaced. If everything else is working OK, I think you'd still be able to drive forward, but no holding power when you let off the throttle. You'd just go into coast.

But for another example of diagnostics. Take a look at R and manual selected 1st. Then look at 1st in all other gears. So now, you lose reverse. It's safe to say, if you put it in Manual 1st gear and it doesn't work, but 1st works in all other gears, then it's safe to say you burned up your low/reverse clutch pack. Get it? It's all a process of elimination.

If get something narrowed down to say a band failure, then don't jump to conclusions and think the trans has to come out for a rebuild if you lost 2nd gear for example. It might just need the pan dropped, valve body dropped and you find a broken servo pin that activates that band, or some models, (NOT GM) that might just need a band adjustment. So the chart does help in some scenario's but usually by the time you need to get to this point, you know the damage is bad enough the trans has to come out and may as well tear it down and disect it thoroughly and go for the rebuild.

 

[Jims86]

OK, only difference I see in that chart in 3rd gear is an "Override Clutch" is engaged in drive but not in OD. What is that?




Can you post that diagram here?

Yarp!

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[89Suburban]

It's an OverRun clutch. A roller clutch aka one way sprag. That's how you have downshift holding power if you were to manually kickdown a gear. So so you're going down a hill and you go into 3rd or even 2nd to help slow you down, but it's like going into neutral instead, then you can determine your roller clutch/sprag isn't holding and need replaced. If everything else is working OK, I think you'd still be able to drive forward, but no holding power when you let off the throttle. You'd just go into coast.

But for another example of diagnostics. Take a look at R and manual selected 1st. Then look at 1st in all other gears. So now, you lose reverse. It's safe to say, if you put it in Manual 1st gear and it doesn't work, but 1st works in all other gears, then it's safe to say you burned up your low/reverse clutch pack. Get it? It's all a process of elimination.

If get something narrowed down to say a band failure, then don't jump to conclusions and think the trans has to come out for a rebuild if you lost 2nd gear for example. It might just need the pan dropped, valve body dropped and you find a broken servo pin that activates that band, or some models, (NOT GM) that might just need a band adjustment. So the chart does help in some scenario's but usually by the time you need to get to this point, you know the damage is bad enough the trans has to come out and may as well tear it down and disect it thoroughly and go for the rebuild.

I'm trying to understand though what gets damaged towing on OD, the sprag thing/Override Clutch? I got to look in your trans threads so I can see it....

 

[89Suburban]

Yarp!

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I am totally baffled by that diode....

 

[HotRodPC]

I'm trying to understand though what gets damaged towing on OD, the sprag thing/Override Clutch? I got to look in your trans threads so I can see it....

You burn up the 3-4 clutch pack. To much strain, less torque multiplication, fluid starts getting hot, clutches start gradually slipping, clutches getting even hotter, fluid starting to turn brown form the loose friction material coming off the clutches, getting even hotter still, the steals in the clutch pack start warping and coning and pretty much, by that time, it's all over with. Now without the 3-4 clutch pack, you non longer have 3rd or 4th gear.

 

[89Suburban]

You burn up the 3-4 clutch pack. To much strain, less torque multiplication, fluid starts getting hot, clutches start gradually slipping, clutches getting even hotter, fluid starting to turn brown form the loose friction material coming off the clutches, getting even hotter still, the steals in the clutch pack start warping and coning and pretty much, by that time, it's all over with. Now without the 3-4 clutch pack, you non longer have 3rd or 4th gear.

Yeah but why? I can't find a pic of the part you are talking about.

 

[HotRodPC]

Yeah but why? I can't find a pic of the part you are talking about.

WHY? Is because in 4th gear, you're putting the 3-4 clutch pack under more strain. Again, the same old example of a 10 speed bike and you're in that gear where your pedaling slow but it's very hard to pedal. So your actual rpms that you are turning the crank when you pedal are slow, but you're working you ass off to even keep those low rpms up. With me so far? Now you're doing the same thing up a little hill towing a wagon full bricks, now it get's even harder to pedal. How long do you think your legs are going to hold up for ??? Where as if you'd kick it down a couple gears on the sprocket, you will pedal a bit faster, but your taking the strain off your legs and you'll be able to do it longer without wearing out your legs.
It's the same exact type of deal in your transmission. You put it under strain and even though the rpms are lower, you're putting more strain on your motor and you're demanding that the 3/4 clutch pack to be held tight enough to hold that strain. If the clutch pack can't be held tight enough, then they are going to start to slip on the steels which creates heat. The more you slip, the more heat you create then the clutches start burning, steels start coning and it's all she wrote. That simple. The 3-4 clutch pack is in the front input drum of the transmission. Hope this helps.

 

[89Suburban]

What number in that diagram is the sprag thing you 2 guys were talking about a few posts back?

 

[HotRodPC]

You know what Dawg, I hope to hell someday we can get together to build a fuggin trans. When I was younger, and even now, if someone wants to allow me there to watch and learn a build of anything, like say a Cummins motor that I've never built before, I'd be all over that ****. My bro, my dad, my son, my son in law, I tell them when I'm going to building when I'm going to be building a transmission. I even hint around, it would be cool to have a little help with some parts cleaning to speed things up, or lift it up and down off the bench. Think they're interested in learning??? **** NO !! But you know what? I don't mind really. It's not like I can't do it myself just fine and I enjoy doing it by myself in peace and quiet just as much as doing it with someone and teaching them something, so the way I see it, it's more their loss than mine. But when their's breaks and they need a rebuild, guess who they call??? And guess how much of a hurry I'm in??? And you'd think they'd at least be interested in rebuilding their own. My brother wasn't, and I"ve built 2 for him for 2 different cars now.