727 Rear Clutch Upgrade worth it?

Is it worth going to the more robust belleville washer and matching piston used in the later 727 rear clutch drums? Is the earlier, thinner cross sectioned ones problematic? My trans is a '73 so it has the thinner belleville...Im just using a Cheetah reverse pattern valve body so no sky high line presures. 600 hp approx... This is my first transmission job, so im a little in the dark...(pic from another thread on here)

We've used the thinner, pre '74 washer in the trans with no issues. Usually lives behind a 655, or a 572 motor when the reserve motor steps in.
HTH's

Thanks Tig!

Same here. I use the early one behind my 572 and Dizusters turbo motor. Never had a problem. Just make sure which ever spring you use it matches the correct piston.
Doug

I would upgrade while you have it apart. There are a couple of factors at work. The wave spring allows fore and aft movement, which effectively increases piston travel irrespective of clutch retainer clearance. Not all piston retainer to clutch retainer fit, is the same. The looser the fit, the worse the problem of excessive piston travel and consequential over centering of the spring. If you have a good selection of oem, and aftermarket snap rings, you will find that a combination of 2, will replace the wave spring nicely.

The early Belleville works OK when it's new but will fatigue with use and weaken more than the later one. HP has nothing to do with failures, line pressure kills them. Even if they don't break, the early ones can flex enough to allow the piston to pop out of its bore...very common failure.

I've seen a bunch of the early ones fail but never the later one. A worthwhile upgrade IMO.

I have used both style Springs. The only one I have ever had break was the thin style.

Thanks a bunch guys. Sounds like with the line pressures Ill be running Id be fine. But with wanting to buy a new belleville anyway, Ill just get the new style with the newer piston. Cheap upgrade.

Good Info

Andrews racing transmission, forward clutch video:

https://www.youtube.com/watch?v=eJsRtPhlwoA&t=9s

The video claims the early piston isn't any different than the late; I've found, by actual measuring, the late piston is taller. The casting number 2124834 ('62-'73) is .783" thick and the 3743623 ('74-later) is .830".

Just picked one up. Casting number 3743623AB. Measures .782 thick. Maybe the "AB" is a revision?

Most anytime you have letters following the numbers its
been upgraded and on yours with a AB it was down a
couple times

👍

In looking at both the pre '74 and 74up I see no differences between THESE two. The only small difference is a .060ish chamfer on the bore of the newer one. That's it.

Lay each on a flat surface and measure up to the OD of the piston.

Or take a mic and measure the top of that OD to the backside of the piston - on the back you will see a machined ridge, measure to it.

The piston rests on this ridge when in the clutch retainer. The inner bore does nothing In regards to the Belleville spring.

Not sure what you mean Transman....heres a couple more comparason pics..

Unless you mean overall height..

I just saw your last photo. - yes - depending how you measure.
Thickness is different - as long as you measure correctly using the machined register on the bottom of the piston ( the machined radial ridge ) to the top of the outer rim of the piston. EDIT- The way you are measuring in the last photo should show the different thicknesses between the two p/n's.

part numbers 623 and 834

Too cold for me to go to the garage again and I don't want to get snow on my pink slippers but .623 sounds pretty skinny. EDIT - sorry - thought that was your measurement. Mayberry I should have enlarged your image of the mic. 👀

Stay warm. Those two numbers 623 and 824 are the last 3 numbers in the part numbers. The thickness of both are around .785ish.

I have been upgrading these to late model piston and belvelle spring for years as the early skinny ear spring, a couple of the ears will snap off and piston will over travel and the piston seal comes out of bore and sticks the forward clutches on. The new style stronger spring has to be used with the new style, thicker piston. the 623 part# piston is .830" thick and the 834 part# piston is .780" thick. If you use a old style piston with new style spring you will have the same problem as if the ears broke off an early style spring. Made that mistake, piston over traveled and seal came out of bore and stuck forward clutches on.

Only explanation I can come up with is Kokomo machined the late casting to the early spec.
Maybe they ran out of service parts for the early application - stranger things have happened there.

I can image. I bought a dirt cheap, new old stock A1 Transmission hp rebuild kit the other day because it has the solid front red band, but it also has a brand new, early bellville in it. Temping to just use it.

If the Belleville is new I wouldn't worry about using it.
The number of cycles they go through, high line pressure, high clutch pack clearance is all additive to their failure.

The piston change was a coordinated change - the rear clutch retainer did too.

From the factory TF Service Bulletin, running changes for the '74 model year:

"Neutral to Drive shift quality

A-727 only

The N-D package for the A-727 also required the following changes in the rear clutch. The Belleville spring has a higher load and a reduced cone height and thickness. In the clutch retainer, the Belleville spring seat and cushion ring groove were moved forward. The over-all height of the piston was also increased. The piston and Belleville will not service prior models. The clutch retainer will service prior models."

I have found a couple sources for the later belleville spring anyone have a source for the later piston?

John, I believe you. And I believe my measuring tools as well..

Take both parts back to your supplier shop and
see if you got a bad part.. sounds like both
parts are the same

Just gonna mail it back to the ebay seller.They're a trans parts dealer...they can measure it.😂

Cancelled part#. Used, is your best bet.

Moving forward with the discussion on this upgrade...per John's post of the service bulletin, Do I need to do somthing to the piston retainer as there appears to be changes made there as well for the '74-up parts. How about the plastic cushion spacer? Is it the same or do I need 74-up specific one?

We went from metal to plastic on the spacer, they are interchangeable.
The piston retainer is the part with the clutch splines, also called a rear clutch piston support. I don't recall a change to it in 74.
The clutch retainer is what fits around the piston support and that is what had the groove location change made to it in 74.
As the bulletin states it is interchangeable. If you can - you might try to add another snap ring to the one just up from the spacer, it makes the retainer tight to the support if you find yours is sloppy.

As for the retainer - a retainer out of a 46/47/48 will fit the 727.

a&a trans offer a spacer that goes between the piston retainer and rear clutch shell. it is a clutch plate that has the material removed and outside turned down to fit into and remove the slop in the unit. i made my own by just using a wizzer tool to turn down outside. works great. a&a charged $10 for one so i just made my own. also qwkmopardan id correct about the piston pushing out of bore. have seen it a couple of times.

A&A no longer shows the billet piston or I couldn't find it.

I talked to the vendor that supplied this oddball piston and he alluded to the fact that there is *two* part numbers on it. He didnt say why, but he is right, there sure is two numbers on it indeed. Not sure if that's normal, but if it's not, then it might have something to do with it not being typical.

That's a 98 part cast date and a late model p/n starting with 52.
I doubt we went back to a thin piston so this piston is a fluke - I would just have him measure pistons until he finds a thick one and send it to you.
I've seen the plant send out parts of the later model dimensions but they had the prior part number still on them. But I can't recall ever seeing two part numbers like his - that's a process violation anywhere within the company.