Hawk's First 727 Transmission Rebuild

[HawkRod]

I been watching you rebuild this trans. And I have decided to try my luck at it myself. Thank you for this thread.

I'm glad this thread helped.

The great part about threads like this is the member doing them gets help from the vast FBBO knowledge base, and others can learn too simply by referencing the thread later, so it's a win-win. I certainly could not have done it properly without all the support I have received!

 

[HawkRod]

I have started the transmission swap. I'll leave this thread solely about the transmission rebuild process so I don't water it down with other aspects of transmission removal/replacement. The transmission swap, however, is going slowly. First of all, removing some of the bolts out of the bellhousing has been more than difficult. It's easy when the K member is down and the whole assembly can easily be reached! But when the body of the car, headers, torsion bars, etc. are in the way, it gets harder and much slower to get them out.
Additionally, we have had some bad weather here. I don't have enough room for all my cars, so I have to stack my 73 and 70. I don't want to leave the 70 outside in bad weather to work on the 73, so I need to have good weather to continue with the work (no rain or snow).

Hopefully I can finish by the end of this weekend coming up.

 

[451Mopar]

9/16" swivel socket and extensions you can reach the bellhousing bolts from under the car (on a lift.)

 

[HawkRod]

9/16" swivel socket and extensions you can reach the bellhousing bolts from under the car (on a lift.)

Thanks - used that for a couple (a good L O N G extension is a lifesaver in many cases!). A couple others just didn't work well to get at that way. One somehow ended up with a cupped washer so I couldn't get a good "bite" on it. At any rate, the ones I needed are out. Now I'm back from my father-in-laws and will try to make some progress tomorrow.

 

[HawkRod]

So after a few challenges, I finally got the old transmission out of the car (covered in my restoration thread - I'll try to keep this thread on point for transmission building specific posts).

As a reminder, I have built up the new transmission will all the parts I need except the valve body. I really like the way the valve body that was in the car worked, so I will use that one in the new transmission. So here is the valve body I will use, along with a new torque converter and cleaned, deep pan.

The torque converter is a 2000 RPM stall speed converter, rather than the 3000 RPM converter that I had in the car. The 3000 RPM stall speed converter was not a good combination with an overdrive that runs less than 3000 RPM on the highway.

I will go through the valve body in additional posts below as I verify that it is in good working order. By the way, there was a question about if this had a spring for the accumulator, and the answer is no, there was no spring for the accumulator; it had been removed as expected. So when this valve body goes back into the new transmission, it will be without an accumulator spring.

 

[66Satellite47]

Who made the converter? The accumulator spring makes the shifts softer for standard driving car. You sure don't need it.

 

[HawkRod]

Who made the converter?

It is a B&M "Tork Master" with a 2000 RPM stall speed. Not a high end unit by any means, but it hopefully will do the job OK.

 

[66Satellite47]

Hope that works well for you. BTW "Stall speed" is a very relative, almost meaningless term IMHO. Good luck.

 

[HawkRod]

Hope that works well for you. BTW "Stall speed" is a very relative, almost meaningless term IMHO. Good luck.

Yes, I realize. They really should use "K" factor.

For others reading this thread and potentially referencing it in the future:
Stall speed is really a variable. The constant that really describes the way a torque converter will behave is the "K" factor. The equation for K factor is:
K = Stall Speed / Square Root(Torque)

So my torque converter with a stall speed of 2000 is really dependent on the engine torque. If they measured the 2000 RPM stall seed with an engine (or a device) that had 350 lb foot of torque, then the K factor would be as follows:
K = 2000 / Square Root(350)
K = 2000 / 18.708
K = 106.9

Let's assume my 416 stroker engine makes 450 lb foot of torque. Then the same torque converter, with the K factor as calculated above, would have a different stall speed.
K = Stall Speed / Square Root(Torque)
Stall Speed = K x Square Root(Torque)
Stall Speed = 106.9 x Square Root(450)
Stall Speed = 106.9 x 21.213
Stall Speed = 2268 RPM

So in this example, my 2000 RM stall speed torque converter might actually stall at 2268 RPM for my engine.

The problem is, there is no way to know what torque was used to get the original manufacture stall speed of 2000. Was it 350 like I assumed? Who knows? They don't tell you that. Of course, another variable is the torque of my engine. My little 416 stroker has never been on a dyno, so I don't know what torque it makes either.

It really would be beneficial if torque converter manufacturers started advertising K factor, but almost none do. So, it becomes a guessing game. The number I used above are my best guesses for how the torque converter will behave. All things being relative, this new torque converter should be better suited for my application than the 3000 RPM torque converter that I had in the car.

Sorry for all the mathematics, but I hope this helps folks understand torque converters better.

 

[66Satellite47]

Yes, I realize. They really should use "K" factor.

For others reading this thread and potentially referencing it in the future:
Stall speed is really a variable. The constant that really describes the way a torque converter will behave is the "K" factor. The equation for K factor is:
K = Stall Speed / Square Root(Torque)

So my torque converter with a stall speed of 2000 is really dependent on the engine torque. If they measured the 2000 RPM stall seed with an engine (or a device) that had 350 lb foot of torque, then the K factor would be as follows:
K = 2000 / Square Root(350)
K = 2000 / 18.708
K = 106.9

Let's assume my 416 stroker engine makes 450 lb foot of torque. Then the same torque converter, with the K factor as calculated above, would have a different stall speed.
K = Stall Speed / Square Root(Torque)
Stall Speed = K x Square Root(Torque)
Stall Speed = 106.9 x Square Root(450)
Stall Speed = 106.9 x 21.213
Stall Speed = 2268 RPM

So in this example, my 2000 RM stall speed torque converter might actually stall at 2268 RPM for my engine.

The problem is, there is no way to know what torque was used to get the original manufacture stall speed of 2000. Was it 350 like I assumed? Who knows? They don't tell you that. Of course, another variable is the torque of my engine. My little 416 stroker has never been on a dyno, so I don't know what torque it makes either.

It really would be beneficial if torque converter manufacturers started advertising K factor, but almost none do. So, it becomes a guessing game. The number I used above are my best guesses for how the torque converter will behave. All things being relative, this new torque converter should be better suited for my application than the 3000 RPM torque converter that I had in the car.

Sorry for all the mathematics, but I hope this helps folks understand torque converters better.

Hawk, math is good on paper.
What makes the converter work is the design of the cover (11", 10", 9", 8 3/4"), fins and stator. And the sprag design dramatically effects durability.
K would be some empirically derived number based on the actual engine combination the vendor used to test a particular design.

 

[HawkRod]

Valve Body
I cleaned up the valve body and verified that the shift kit I installed way back in the early 80's was still there as I remembered.

First I removed the screws holding the two half together. There are lots of small steel balls in there that you have to be careful with.

To make a long story short, I pulled out all the valves and springs. When I was done, the "exploded" view looked like this:

To keep this organized, I laid the parts out exactly as they came out, oriented to where they came from. I'll tell you, I don't know who came up with this maze of passages and valves, but they were either a total genius or totally crazy. Maybe both. I certainly do not understand how each of these work, so I simply carefully followed directions for cleaning and reassembling. A note here that was made in a video and in other instructions: All the valves should move very easily inside the valve body. They should essentially fall out of their corresponding holes. If not, you need to work on them carefully to make sure they are not sticking. Sticky valves will lead to problems shifting!

Shift Kit: It turns out that my shift kit was installed exactly as I remembered it. Below is a spot that was to be drilled out according to the shift kit directions, and it was. There were also other modifications with respect to omitting a steel ball and adding one in another location. I won't go into those specifics here, as each valve body can be a bit different. If you are installing a shift kit, follow the instructions carefully.

Here is the other half of the valve body.

My fingers point to locations that need to be drilled larger than they were. These were also done.

So everything was cleaned with solvent and then reassembled. I also replaced the small gasket in the shift linkage right below the kickdown lever shaft. I found that installing the shift linkage can be a pain. A video I watched suggested pulling the spring and ball out from the back by pulling up on this spring, then reinserting once it was all back together. This worked well for me and I recommend this method.

So here is the cleaned up and finished valve body assembly ready to go back into the transmission.

I'll continue in the next post with additional pictures.

 

[HawkRod]

I then installed the valve body into the transmission. I found getting the park lever into this GV tail shaft quite difficult. Stock ones are not bad, so the machining must be a bit different.

I checked an adjustment for the throttle pressure. A 1/8" drill bit should just touch the two surfaces, so the Allen key is used to adjust the screw up or down as needed.

Here is the transmission with the filter installed. After this I installed the pan.

Since I had changed almost everything in this transmission, I needed to re-shim the Gar Vendor's unit. This shaft adapter must be shimmed with the round shims shown to get end play to less than .020".

After that, I installed the overdrive unit.

It is now ready for installation back into the car. Hopefully I did everything right and it all works as it should - this has been a much longer process that I had originally planned for.

Installation of the transmission will be covered in my other thread, but I will follow up here with any transmission drivability results, concerns and issues (hopefully none).

 

[66Satellite47]

Hawk, FYI, getting the park rod in place often takes a little tweaking of the output shaft. Turning the shaft slightly to allow the lug to line up with the notch on the park sprag.
Very impressive detail on your valve body re-assembly. The TransGo shift kit I used on my tow vehicle 727 in '80 worked perfectly, just follow their instructions, which were very clear & easy to understand.
Great job!!

 

[HawkRod]

RESULTS

OK, I took a quick drive (just around the block) and I have some initial results.

The good:

• No major leaks seen so far (although this is very preliminary - I could have some minor leaks that will show up once I drive some more).
• No strange noises in any gear.
• All forward and reverse gears work.

The bad:

• My 2-3 shift.
  As the transmission shifts from second to third, it has a moment when it "goes into neutral". The engine revs increase for a split second, and then third gear comes in. A potential cause of this is the "dance" is the front band and front drum clutch pack/springs. If the band releases before the clutch pack has engaged, then this symptom will appear. This can be caused by too many springs and/or the band releasing too quickly.
  I discussed this action in post 87 here: https://www.forbbodiesonly.com/mopa...smission-rebuild.232272/page-5#post-912077477
  and in post 157 https://www.forbbodiesonly.com/mopa...smission-rebuild.232272/page-8#post-912115966

Maybe a simple band or other adjustment?
I will do some preliminary checks and some reading to see if I can make a simple adjustment. I'm not looking forward to the potential of having to pull the transmission to adjust the way these work.

Hawk

 

[66Satellite47]

The 2-3 shift problem can be a combination of several things. Looking back at the thread, not sure what servo lever ratio you actually used. I would not use the 5.0 lever in your build, 3.8 is the way to go. The front servo spring you showed is not something I'm familiar with, so I don't know. It appears you used 10 springs in the front drum, should be fine.
The valve body may be the issue. Maybe not enough line pressure??

 

[451Mopar]

should not "goes into neutral" as long as the rear clutch is applied.
Might hang in second, or bind going into third?
If using a shift kit with the front clutch case restrictor, I usually remove the restrictor in the case.
Front servo lever 3.8 or 4.2, not 5.0
I like the sealed billet front servo cover, with the smaller piston / sleeve kit:
https://transmissioncenter.net/shop/2nd-gear-super-hold-servo-kit/

 

[Dave6T4]

You could try turning the front band adjuster in half a turn. I am not sure what you set line pressure adjustment at.

 

[HawkRod]

Here comes the FBBO brain trust to save Hawk's butt - as always, I sincerely appreciate all your help!!!

The 2-3 shift problem can be a combination of several things. Looking back at the thread, not sure what servo lever ratio you actually used. I would not use the 5.0 lever in your build, 3.8 is the way to go. The front servo spring you showed is not something I'm familiar with, so I don't know. It appears you used 10 springs in the front drum, should be fine.
The valve body may be the issue. Maybe not enough line pressure??

I used a 3.8 lever in my build.
The front servo was a performance "red spring" servo, although I do not know the specs.
I do not know what my line pressure is - I'm not sure I have the gear to test this? But I have a restrictor that was built in to the case (see write up below). I'm thinking I need to remove this restrictor. I guess this is not line pressure but more rate that the pressure is applied. Since I have a timing issue, this seems to be a reasonable path forward.

should not "goes into neutral" as long as the rear clutch is applied.
Might hang in second, or bind going into third?
If using a shift kit with the front clutch case restrictor, I usually remove the restrictor in the case.
Front servo lever 3.8 or 4.2, not 5.0
I like the sealed billet front servo cover, with the smaller piston / sleeve kit:
https://transmissioncenter.net/shop/2nd-gear-super-hold-servo-kit/

I guess I used the wrong phrase "go into neutral". According to Carl Munroe, he calls it "engine flare", and this is what I have. A mod he talks about doing is installing a plug with a hole drilled into it. This is in the case that feeds the front clutches. He then goes on to say:
"If there is overlap or stiffness in the 2-3 shift then the plug can be replaced with one with a slightly smaller hole. This will slow the front clutch apply allowing the kickdown band to release fully. Should the 2-3 feel too soft or should the engine flare on the upshift, the size of the hole in the plug can be increased, speeding up the application of the front clutch."
The underlined text is my situation. So I think you hit the nail on the head about removing the restrictor in the case.
As stated above, I used a 3.8 lever, and my front servo is a "red spring" performance servo.

You could try turning the front band adjuster in half a turn. I am not sure what you set line pressure adjustment at.

I have not tried turning in the front band adjuster a half turn. Perhaps I should try that first.
I have not measured line pressure - just set things per the book. As stated above, I am not sure I have the fittings/ gauges to measure this.

Maybe I should try adjusting the front band a half turn first and see what happens. However, I think the most likely thing I need to do is drop the pan and valve body and pull out the below pictured restrictor. This seems like the most likely culprit.

As always, THANK YOU for you help and I welcome additional comments and suggestions.

 

[Dave6T4]

I never use that restrictor. I set the line pressure with a 5/16" drill bit or a pan bolt between threaded plate and cage.

 

[451Mopar]

Not sure what a red spring servo is?
Been awhile since I was really looking at the front servo release, but I thought the piston release is partly hydraulic with fluid going between the piston and cover, and that is why I liked the idea of the "O"-ring sealed servo cover? Also, the same servo release circuit is also the front clutch apply circuit, so leakage at the servo cover or drum seals will cause the servo to release slower and also apply the front clutch slower.