727 problems with 2-3 upshift

[jauringer]

Needless to say I'm a little angry. It's like playing whack a mole. The more work I put in, the more issues pop up.

I'm getting an intermittent slip at the 2-3 upshift. 1st, 2nd, reverse, and kickdown are all fine. It's just 2nd to 3rd. It's happening about 90% of time. It won't happen if I floor it or if I'm going really slow. (maybe I just can't feel it?) but anywhere in between I'm getting about 100-200 rpm climb and then it catches. (is this what runaway is?) it happens very fast and isn't very noticeable most of the time but its a slip. (or runaway if that's what that means)

a little history:

I bought this truck 5 months ago. The po had been driving like a manual because it would shift straight to 3rd gear at 5mph. When I got it home the throttle pressure rod was laying on the bell housing. I obviously repaired it but I have no idea how long it was like that.

2 months ago while driving I had a very large slip occur. They were within a few minutes of each other, it was from 2nd to 3rd, and it took a couple releases of the gas pedal before it caught. It scared the heck out of me so I started doing a little research and read that a transgo tf2 will help firm the shifts up and decrease 2-3 overlap, I installed one last month. (thread in this forum and no, I didn't think it would magically repair damage that already existed, but I was hopeful that it might help keep any additional damage from happening.)

besides the one occurrence I mentioned above and today, the tranny has been acting perfectly normal.

I'm about to go ahead and adjust the bands and change the fluid even though it was just done. Before I crack the pan, I would like to have a plan in place so that I know what I need to look at. Below is kind of an outline of how I'm thinking this through. Any help or corrections to my information would be greatly appreciated.

1. Fluid is brand new , full (not overfull) (B&M trick shift), and is not burnt.
2. Band are adjusted
3. Throttle linkage is adjusted to factory spec. (I did have to go back in and readjust this after tf2 install but it is spec now)
4. Gear shift control linkage is exactly the way it's supposed to be.
5. Stall test @ 1700
6. The rear clutch is engaged at any forward gear so if it was bad I would be experiencing other symptoms.
7. 3rd gear is created by applying the rear and front clutches simultaneously. The front clutch is also applied with the l/r band for reverse. Reverse is acting fine so that leads me to believe the front clutch is not the problem.
8. When governor pressure increases on the 2-3 shift valve, the line pressure is forwarded to the front clutch and the outside of the kickdown front servo. When pressure on both sides of the front servo are equalized, it retracts under it's own spring tension which releases the kickdown band. (2nd gear)

based on the stall test, and lack of additional symptoms to indicated a clutch problem, would it make sense that the front kickdown servo might be the issue here. If it's not retracting properly in it's bore and the kickdown band is not releasing in time. Would that cause a slip/ruanway?

If this all makes sense, what am I looking for in a bad servo? Lastly, monroes torqueflite book states that it makes no sense tearing out a 727 without first doing a pressure test as it May be something that can be repaired in the vehicle. Where would I find the equipment to perform a pressure test? (can I make my compression gauge work?)


any help would be greatly appreciated.

 

[jauringer]

One more item I wanted to add as I just found some info that sounds exactly like what's going on. Sorry for all the info here, just trying to think out loud.

Quoted from Tom hands guide @ allpar.com

"I'll explain the 2-3 shift function again. When the torqueflite shifts from 1st to 2nd, the kickdown band locks around the front clutch retainer to stop the sun gear driving shell. To make the 2-3 shift, the kickdown band has to hold until the front clutch is applied and then it has to be quickly released. This timing is very important; too early of a band release causes the engine to "rev up" until the front clutch is applied. Too late of a band release and/or too early of a clutch apply is more common; this gives a "putting on the brakes sensation" which is actually called shift overlap (since the rear clutch is applied in both 1st and 2nd, and nothing has to be released, kickdown band timing is not as critical in the 1-2 shift). Delay in the kickdown band-release and premature clutch-apply both cause overlap and, therefore, friction material wear.

How would I change this timing? It sounds like my front servo is releasing the front kickdown band just a fraction too early. There is now a plug in the front clutch apply orifice via transgo, which would slow the engagement of the front clutch right?

 

[Michael Mayben]

Now I know the whole story!

First off, I'd never install a valve body reprogramming kit in any 727 that was not performing perfectly. While they do an outstanding job of "fixing" known design issues regarding the shift timing and sequence, they also place a considerable amount of strain on the transmission overall that is not in perfect repair. Many transmission shops won't deal with 'em unless they are installed when the transmission is rebuilt completely.

On the other hand, I'd personally never run a 727 in my vehicles that had not been built and had a shift kit installed. That is because of the serious use we apply to these units in towing, winching, longterm highway travel heavily loaded, etc.

What you have is a plain old worn out transmission! It simply needs all the frictions replaced along with any other wear item that doesn't meet spec. Screwing around with making "adjustments" is something that was never done in the old days, the various forms of "shift kits" took care of those type issues.

The transgo tf-2 kit took care of the mods that the valve body needed, the timing of shift points and their characteristics have already been set for best possible use. Now the rest of the transmission needs to brought up to snuff. Once it's properly built, the tf-2 kit can really make 'em shine and you will have a unit that will run the rig for many years to come.

 

[jauringer]

Thanks for the response Mike. I had a feeling you were going to say that and I knew it was just a matter of time. As a matter of fact as soon as I read how terrible it was for my po to be driving without a throttle pressure rod, I started interviewing tranny shops.

Question. I've been following the rebuild here by newcscout. I'm close but not sure if I'm quite ready for a rebuild, as I was hoping I could get a little more knowledge under my belt first. Either way, I would want to provide the kit to whoever does the work.

I keep reading about these upgraded servo's, red eagle clutches, hd l/r strut, hd kickdown lever, bolt in sprags..... What do I really need to do this right? Does the B&M kit cover it all?

Thanks,
jason

 

[jauringer]

I guess if didn't learn the hard way, I wouldn't learn at all.

The good news is my transmission is just fine. The bad news is that I'm going to have to go ahead fess up that I'm a complete moron.

Carbs been getting pretty warm in this 110deg weather, so I installed a phelonic spacer to help with that issue. Obviously this changes the geometry of the throttle pressure rod and I thought I had made the necessary adjustments to bring it back to spec. What I didn't see was the return spring was no longer able to return the throttle rod all the way back to it's seat. There was about 3/8'' gap that the throttle would have to move before it even started applying throttle pressure to the transmission. Thanks goodness for the very direct guy @ transgo beating into my head that my tv valve was too short and there's lost motion somewhere or I would have probably rebuilt the dam thing only to install it and have the same problem. (I might never have admitted it if I had taken it that far.) other than the cost of 9.5 qts of trick shift, a waist of y'alls time (sorry about that), and most of my pride, all is well.

The only positve (I'm reaching) is I've now read just about every torqueflite document known to man so I have a little bit better understanding of how this thing works. That's twice now that the throttle valve/rod has gotten me so I think I'm going to stick to fixing oil leaks for a while.