Hawk's First 727 Transmission Rebuild

[Dave6T4]

Thanks. Yes, I have the good red clutches and good steels, so hopefully that will be fine.

Right now the clearance on my front drum is .112" I have read the spec is .050" to .150". This still seems on the looser side, but I only have two choices for the top snap ring. The thin wavy ring (.112" to the top of a "wave") and an old style solid snap ring. I don't remember the exact measurement of that, but it was less then .050".

 

[66Satellite47]

Hawk, the wavey snap ring is not the correct part to use on the front clutch drum. Mopar sells a select fit package of different thickness solid snap rings. You want to be around .040-.060.

EDIT: The wavey snap ring is for the rear drum.

 

[Gunner1]

Just read this. I learned a bunch. I also know I'll never do this. LOL way to much to learn. Great job Hawk. I just had mine done and they used all Turbo Action parts. I was always an engine builder. Auto trans were Voodoo magic stuff. Looks like your well on your way to being able to do more of these.

 

[HawkRod]

@Dave6T4
You gave a red X for an earlier post and then tried to reply (there was no reply). Was there something you disagree with or did you just have computer issues?

Hawk, the wavey snap ring is not the correct part to use on the front clutch drum. Mopar sells a select fit package of different thickness solid snap rings. You want to be around .040-.060.

EDIT: The wavey spring is for the rear drum.

So my 73 340 Drum had the wavy spring. Per the Carl H Munroe book: "Note that later units have a wavy snap ring on the top of the pressure plate to soften the clutch apply." There is also a picture of the way to take the measurement:

Based on that, and for a performance transmisson, it seems that I perhaps should use a solid snap ring. Having said all that, the book doesn't have a table of specs for what it should be (wavy or solid). The best I have gotten from the internet is somewhere between .050" and .150".
In your experience, have you used a spec of .040" - .060" clearance with a solid ring? If so, I might be able to make that happen if I swap out and put the solid ring in it.

 

[Dave6T4]

@Dave6T4
You gave a red X for an earlier post and then tried to reply (there was no reply). Was there something you disagree with or did you just have computer issues?


So my 73 340 Drum had the wavy spring. Per the Carl H Munroe book: "Note that later units have a wavy snap ring on the top of the pressure plate to soften the clutch apply." There is also a picture of the way to take the measurement:
View attachment 1209255

Based on that, and for a performance transmisson, it seems that I perhaps should use a solid snap ring. Having said all that, the book doesn't have a table of specs for what it should be (wavy or solid). The best I have gotten from the internet is somewhere between .050" and .150".
In your experience, have you used a spec of .040" - .060" clearance with a solid ring? If so, I might be able to make that happen if I swap out and put the solid ring in it.

 

[Dave6T4]

Hawk, I did not mean to leave you a red x. I meant to leave a comment about not using a wave spring in the front clutch. They are only used in the rear clutch to keep the Belleville spring in place. I use .020" clearance per clutch, so 4 clutches x . 020" = . 080" clearance. I was also going to mention that Chrysler parts departments have flat snap rings in varying thicknesses. I think . 060" , .075" , .090" , .105" .
I would measure the thickness of the flat ring you have and record it. Then, snap this ring into the groove and measure the clearance between the top pressure plate and this ring. This is the total gap you have to play with between the top of the pressure plate and the bottom of the snap ring groove. As an example, if this measurement comes out to about . 150" , you would need a .075" snap ring to achieve a . 075" clearance, which would be acceptable. Sometimes I have had so much clearance here, that I have had to use a spare steel plate as a spacer to get the right measurement.
Since post # 142 covered some of this, I just left it, as my post somehow failed. It might be just me, but I seem to have more trouble now, since the big crash a while ago.

 

[66Satellite47]

Probably should have said .050 to .065. A .040 is getting a little tight. I've had a box of the different solid snap rings forever. I may have got the select fit package from the Mopar dealer when I did my 1st 727, if not, it was when I built my 1st drag race 727. Then kept adding to the assortment with each core I picked up. Again, Mopar used many different internal parts combinations for the different car/trucks.
That Mopar snap ring package is very nice. I presume they still sell them. The high end of the factory spec is WAY to loose for a performance build.

 

[HawkRod]

So I went to a transmission place today. My front drum snap ring was .106". I picked up a .074" solid snap ring there and now I have .082" clearance in the clutch pack. Hopefully this will work OK. This is almost exactly the .020" per clutch spec mentioned by @Dave6T4 , although it is certainly a bit looser than the .050" - .065" mentioned by @66Satellite47
If anyone has any serious concerns let me know. Otherwise I will now move on to the pump and try to get this transmission over the finish line!

Thanks,

Hawk

 

[66Satellite47]

Hawk, which springs did you put in the front servo with the 3.8 lever? It appears you have a single outer spring. Also the late model apply piston (which I generally prefer). I would normally use the early outer spring and inner spring combination in the servo. There were a few combinations used by Mopar. The large outer spring varied over the years and applications IIRC.
I tested the early style outer, two new model outers on my valve spring tester. Some difference. Not sure they would be noticeable. There were two inner springs used, standard inner or the longer Hemi softer style. The Hemi 727 used only the tall light spring, no outer spring. A single large outer spring was used on many of the SB 727's.
The characteristics of the valve body make a noticeable difference on which servo spring combo should be used.
My math says the .106 snap ring puts you at .050. I'm sure .082 will work though.

 

[HawkRod]

Hawk, which springs did you put in the front servo with the 3.8 lever? It appears you have a single outer spring. Also the late model apply piston (which I generally prefer). I would normally use the early outer spring and inner spring combination in the servo. There were a few combinations used by Mopar. The large outer spring varied over the years and applications IIRC.
I tested the early style outer, two new model outers on my valve spring tester. Some difference. Not sure they would be noticeable. There were two inner springs used, standard inner or the longer Hemi softer style. The Hemi 727 used only the tall light spring, no outer spring. A single large outer spring was used on many of the SB 727's.
The characteristics of the valve body make a noticeable difference on which servo spring combo should be used.
My math says the .106 snap ring puts you at .050. I'm sure .082 will work though.

The entire servo (spring included), is a new performance "red spring" servo I got from @Dave6T4

I don't know the specifics of the servo though besides it is a later style with a beefier spring.

Thanks,

Hawk

 

[66Satellite47]

Hawk, use that servo combo, see how it works, that's what I've done for many, many years. Again, it really depends on what the valve body likes. With 10 springs in the front clutch, it should be good.

 

[451Mopar]

I haven't read all 8 pages, but you can add an extra steel to take op some clutch pack clearance if it is real loose.
You can also get thicker steels like this:
https://transmissioncenter.net/shop...els-for-forward-and-direct-these-measure-085/

The rear direct clutch is better to setup on the tight side, I think around 0.025" - 0.035"
Front clutch is a shifting clutch, so needs more clearance. Depends on number of clutches, I think around 0.085" - 0.095"
Number of front clutch springs varies on valve body pressure. Manual reverse and trans brakes valve bodies get all the springs.
I usually use 9-10 with the Trans-go TF-2 shift kit. 3.8:1 lever or 4.2:1 lever.
I don't use a restrictor in the case to the front clutch. Tried the one Trans-Go supplies, but removed it later.
When replacing parts, double check all the end clearances, gear train and pump/input shaft.

For checking clutch clearance, I put the pump up-side-down on a paint can and install the drum, then set a dial indicator on the clutch plate and use air through the pump to actuate the clutch. Make sure the drum does not lift with the air pressure.
Then do the same with the rear clutch pack. Checks clutch sealing rings, seals, and clearances.

 

[HawkRod]

Sorry for dropping this thread for a bit. The holidays plus losing our one cat Zoe has meant that I have had limited garage time.

When we last left this, my front drum was completed and had .082" clearance, so I am considering that to be done. The rear drum is now also complete.

Here it is after the clutches have been removed and before disassembly of the piston.

Here are the clutches and order they go into the drum.

I disassembled, cleaned and checked all the parts. Really a pretty simple task of removing the bottom wavy snap ring. The piston, like the front drum, has seals that need to be replaced. Once I replaced those, reinserting the piston can be a bit tricky. You need to make sure the downwards facing lip seals appropriately go into the drum. I used a narrow .012" feeler gauge to slide around the seal (lubed, of course!). You have to do this on both the outer and inner seal, slowly working the piston down until it slips in.

I then reassembled the spring and snap ring. Note that the unit had a plastic shim (holding in my hand). I replaced this with a steel shim (in the drum) as this is supposedly much better.

Here is the unit as I was assembling the clutches.

The final clearance of this was .036". This is a bit more than I hoped, but within spec. As @451Mopar stated, perhaps closer to .025" would have been better. I will leave this as is.

I then used air pressure to check the operation of both drums. Both seemed to work well, and shows that seals are in place.

I then reassembled the drums and rebuilt pump assembly into the transmission. This is the reverse of disassembly, so I didn't take pictures of this. I also installed the tailshaft to be sure I got a good overall endplay number.

My overall endplay is now .044", which is good.

The transmission is now pretty much ready to be installed. Next steps will be to pull the existing tranny from the car, pull out the valve body from that, inspect and reuse that valve body, and then install the whole new transmission into the car. This won't be until mid January, as I will be away from the garage for over a week.

We are finally getting close, but still some work to go!

 

[66Satellite47]

Hawk, .036 on the rear clutch is fine. I shoot for .030. So that's good. Overall end play at .044, not sure how you measured that. I always measure overall end play with the pump installed, using the pump support trust washer. That is my test. Many pump support thrust washer thicknesses available.

 

[HawkRod]

Hawk, .036 on the rear clutch is fine. I shoot for .030. So that's good. Overall end play at .044, not sure how you measured that. I always measure overall end play with the pump installed, using the pump support trust washer. That is my test. Many pump support thrust washer thicknesses available.

Sorry for the slow reply - I was out of the country on a trip for a few days - but back (and fighting jet lag) now...

Thanks for the confirmation with the rear clutch.

As far as overall end play: I measured my 0.044" end play once I installed all the parts back in the transmission (except the valve body but with all thrust washers in place). So the pump was installed. Additionally, I also installed the tailshaft since I believe it will affect the end play - the rear bearing is held in place in the case and limits movement of the output shaft so I believe this is necessary for a good end play measurement.

 

[F4R/T]

Hawk I appreciate you sharing this build and others for contributing... it’s been awhile since I’ve done one and it’s been a refresher for me.. I’m curious about which ratio arm you wind up staying with. I had one that had 5.0 but switched to a 4.2 per the recommendation of a friend..

 

[HawkRod]

Hawk I appreciate you sharing this build and others for contributing... it’s been awhile since I’ve done one and it’s been a refresher for me.. I’m curious about which ratio arm you wind up staying with. I had one that had 5.0 but switched to a 4.2 per the recommendation of a friend..

Based on the recommendations by folks here, I ended up using a 3.8 ratio for the kickdown band (a 3.8 or 4.2 was recommended).
I believe that a 5.0 lever would require more springs and perhaps a different fluid flow to balance everything out. When your transmission shifts from second to third there is a dance between the second gear/kickdown band and clutches in the drum. If mis-timed, you may either get a little slip or some binding. Slippage happens when the band has released but the clutches have not yet grabbed. Binding happens when the the band has not yet released but the clutches have engaged. So the timing that all this happens is important - that much I have learned. I think many have thrown a 5.0 lever in the transmission "because bigger is always better", or, "hey it was used for the Hemi so it must be better". However, if overall setup is not properly designed then problems may arise.

Hope this helps. This is what I have learned so far - I'm sure some experts will chime in and correct and/or expand on the above.

Hawk

 

[66Satellite47]

I used the 5.0 lever for many years because it was the "recommended" lever. It takes more servo travel to apply so the clutch timing is critical. It does need the high line pressure. The 4.2 worked well. The 3.8 lever does just fine with 12 springs in the front clutch and either the Hemi inner servo spring with stock outer servo spring or stock inner and outer servo springs. Either the red Rebestos band or the Turbo Action birch bark band do the job.

 

[charger chris]

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

 

[66Satellite47]

A 727 is not very complicated compared to a GM TH 400.
For a 727 you need to look at the FSM or other books. Understand how the different components work. Combination of the parts is very important. Mopar had many combinations they used for the different applications. For high HP/torque applications you need to carefully select parts.