Clearance with dry vs wet clutches

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Uncle Bob

Shiny paint causes stress.
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I've got a 727 that creeps in neutral to the point it will actually move the car. Yes the shifter is adjusted correctly.

Right now the trans is apart and I find the clearance on both the front and rear clutch packs are .020 to .030 too tight based on the spec provided by the VBA builder.

The book I refer to describes checking the clearance with dry frictions and steels. I didn't see any mention of that in the FSM. These parts are not dry and they don't need replaced so buying dry frictions just to use for checking doesn't make any sense. Is there a measurable difference between checking clutch clearance with dry vs wet clutches?
 
The rear clutch is too tight if it’s going forward in N.

just wipe them all off so they don’t have any fluid coming off them anymore and measure them.
 
I found early on (I was 16) a little loose is better than to tight... First trans I did was a 727 cable shift... I searched everywhere for selective snap rings so I could set both clutches at the minimum spec... And had a trans that had severe shift overlap and that burned up the clutches in 5000 miles

As mentioned, wipe them off & check them... Most professionals don't really measure it at all, they simply feel the clearance with their fingers... The apply piston can easily move .125 so a little loose works fine & lives....
 
The rear clutch is too tight if it’s going forward in N.

just wipe them all off so they don’t have any fluid coming off them anymore and measure them.

I found early on (I was 16) a little loose is better than to tight... First trans I did was a 727 cable shift... I searched everywhere for selective snap rings so I could set both clutches at the minimum spec... And had a trans that had severe shift overlap and that burned up the clutches in 5000 miles

As mentioned, wipe them off & check them... Most professionals don't really measure it at all, they simply feel the clearance with their fingers... The apply piston can easily move .125 so a little loose works fine & lives....
Thanks to both of you.

I had it apart before and remember thinking tighter is better because it's race use only, but wanted to get it right before using it in a street car.

The rear clearance is .047 with a spec of ,070-.080. The front clearance was 0.10 with a spec of .030-.040.

Both snap rings measured about .086 and it looks like the thinnest I can get is about .062. I'll double check my measurements before ordering but it looks like I need .062 pick up another .024 or so and put me right in range.

Thanks again!!
 
I've thrown the pressure plate (end plate) in the lathe and cut just the snap ring area to allow more clearance
 
I've got another question - I think I was measuring my front drum clearance wrong because my front top pressure plate has a step in it. Not my photo, but like this:

1670935423429.png


Munro mentions machining the pressure plate but if he mentions how to measure one that is cut I didn't find it. It seems like I need to use an allen wrench instead of a feeler gauge so I can get under the snap ring without the thicker part of the plate interfering, right?

It has 5 frictions in it so per Munro it should be .075. I can get a 7/64 (0.109) allen wrench between the pressure plate and the snap ring. If that is the right way to measure the stepped pressure plate then it is too loose, not too tight. In my case there is .02 clearance per friction instead of the recommended .015. The transmission worked fine (other than the creeping reverse) so I wonder if I need to worry about that?

I get the feeling that whoever originally set this transmission up just slapped new parts in it and didn't measure anything.

If it matters, there are 15 springs in it.
 
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I always install the pump into a vise and use air pressure to apply the clutches. I watch how much the piston moves to determine clearance. You can vary the pressure to the direct clutch so the snap ring isn't compressed; either way. But I use enough pressure to squeeze the excess fluid out of the frictions. Using a set dimension "per clutch plate" is ridiculous. And a piston being able to move ".125" is not a consideration. Too much clearance can cause a delayed forward engagement, a delayed reverse engagement, and even a 2-3 spinup.
 
I always install the pump into a vise and use air pressure to apply the clutches. I watch how much the piston moves to determine clearance. You can vary the pressure to the direct clutch so the snap ring isn't compressed; either way. But I use enough pressure to squeeze the excess fluid out of the frictions. Using a set dimension "per clutch plate" is ridiculous. And a piston being able to move ".125" is not a consideration. Too much clearance can cause a delayed forward engagement, a delayed reverse engagement, and even a 2-3 spinup.
OK but how do I use that info to figure out when I've got enough clearance to prevent the car from moving in neutral?
 
Neutral creep is caused by too tight forward clutch. Set clearance to 0.04" you should be good.
On direct use factory spec or 0.06".
Pressure plates can be turned to gain clearance.
Forward lower plate can be modified to gain clearance to direct pack.
 
Neutral creep is caused by too tight forward clutch. Set clearance to 0.04" you should be good.
On direct use factory spec or 0.06".
Pressure plates can be turned to gain clearance.
Forward lower plate can be modified to gain clearance to direct pack.
I've got .047 in the forward (rear) clutch. It doesn't make sense that it creeps.

The front clutch pressure plate has been modified to allow 5 clutches in a 4 clutch pack, so it's hard to measure because there's a step in it. That's why I asked abive if using an allen key is OK because a feeler gauge won't work. Thinking it over I'm pretty sure that's a good enough way to do it, but I'm always happy to be wrong.

I'm thinking to just put it back together and throw a wheel chock in the trunk in case I need it.
 
Remove clutch discs. Measure between piston and snap ring.
Then measure stacked cluches and pressure plate. Substract from measure taken from clutch.
Or Make measuring gauge from wire of suitable thicnes. Hammer or file to fit the gap then measure with caliper.
 
Neutral creep can also be aggravated by a tight convertor or a high idle speed; especially on an engine with a lot of idle-timing and/or a bad T-port sync.. This is NOT the cause of it, but is an aggravation of a pre-existing condition.
The transmission worked fine (other than the creeping reverse) so I wonder if I need to worry about that?
I don't get it; With the stick in reverse it has to creep, lol.
Or do you mean that she creeps backwards with the stick in Neutral, which seems contrary to what you said in post #1, which was;
that creeps in neutral to the point it will actually move the car.
If the car , in Neutral, actually creeps backwards; then you have more than one problem
 
how do you know you are on the flats of the Allen wrench or on the high spots? In accurate measurement is highly possible. I’d use a round rod and bend it to the L shape.

Also you can measure anyplace you can get the gauge in there, it doesn’t have to be at the top of the snap ring. It can be under there on a friction disc, but use a flat feeler gauge so you don’t gouge the friction.

I like .100 with 5 frictions
.075 seems on the tight side.

do you need 5 Discs? 4 is plenty for most applications.

maybe you have pressure to the rear clutch in P or N? What is the valve body and the mods done to it?

I can rev to 3000 doing timing and they don’t creep forward.
 
Neutral creep can also be aggravated by a tight convertor or a high idle speed; especially on an engine with a lot of idle-timing and/or a bad T-port sync.. This is NOT the cause of it, but is an aggravation of a pre-existing condition.

I don't get it; With the stick in reverse it has to creep, lol.
Or do you mean that she creeps backwards with the stick in Neutral, which seems contrary to what you said in post #1, which was;

If the car , in Neutral, actually creeps backwards; then you have more than one problem
Yeah you caught me there. It creeps forward in neutral, not reverse.

Not a tight converter, not an excessively high idle speed.
 
how do you know you are on the flats of the Allen wrench or on the high spots? In accurate measurement is highly possible. I’d use a round rod and bend it to the L shape.

Also you can measure anyplace you can get the gauge in there, it doesn’t have to be at the top of the snap ring. It can be under there on a friction disc, but use a flat feeler gauge so you don’t gouge the friction.

I like .100 with 5 frictions
.075 seems on the tight side.

do you need 5 Discs? 4 is plenty for most applications.

maybe you have pressure to the rear clutch in P or N? What is the valve body and the mods done to it?

I can rev to 3000 doing timing and they don’t creep forward.
On the allen wrench - I guess I don't know for sure that I'm on the flat, but I can kind of rock it on the bend of it and it seems like that would put it on the flat. Maybe not.

Do I need 5 discs? Probably not but it's got them and the pressure plate to fit them. I probably don't need the 15 springs or the super sprag either, but they're there. I don't know how to begin to estimate the engine HP, but it ran 7's in the eighth in a stripped out light weight b-body. 450-500? Maybe less?

The valve body is a Cheetah, AFAIK it's box stock but it came in the trans with the car. I'm replacing that with a Coan LBA VB.

The trans worked and shifted fine, other than it wanted to run away when it was idling in neutral.
 
Does this happen even after it's warmed up to operating temp? I have always set (rear drum) forward clutch pack tight .020-.040 range with no issues.
 
Does this happen even after it's warmed up to operating temp? I have always set (rear drum) forward clutch pack tight .020-.040 range with no issues.
I don't remember any difference in it, cold or warm.

It sure doesn't seem like it's really a problem with the clutch pack.
 
Is the belleville spring putting pressure on the piston? Or does the direct engagement hub just sort of flop around?
 
Is the belleville spring putting pressure on the piston? Or does the direct engagement hub just sort of flop around?

I noticed there is some play in something about it. If you pick it up just right you can feel the play, and if you shake it around you can definitely feel and hear it clunking. Could that be the direct engagement hub flopping around? I will look at it closely and try to figure that out.
 
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