727 front clutch orifice restriction size

Posted By: clemford

727 front clutch orifice restriction size - 05/26/23 11:44 PM

Im wondering what size to reduce the front clutch because of the hard thumping into 3rd at light throttle and overlap on manually 1-2 shift for the last 48 years.

I removed the shuttle rod and put back in the d pocket ball bearing. I might even put the accumulator spring back in after seeing the cheap fairbanks (plate kit) didnt even have an accumulator blocker rod, but it was still in straight. I'll use the fairbanks separator plate.

This still has the stock original line psi spring. A&A told me maybe go a turn more over stock 1 5/16 inches. ,spring is much weaker than b&M, etc.

y07a66 here said .093 was good size for him a few years back but he had a transgo 2 spring really cranked up so im thinking my weak spring psi will need a bigger hole, at least 100 . A&A thought might be good. the b&m were .140 which wasnt small enough with big spring. Any guesses as these headers and sore back make vb removing miserable. I can put up with manual shift overlap and 3rd gear clunk rather than downshift flare up. Its just a guessing game.
Also i put a a&a part throttle kit in . That will be interesting. Also pulling tailshaft tomorrow to do the rear pin o .ring. It would have been easier to have pulled tranny out. Thanks in advance.

Posted By: John_Kunkel

Re: 727 front clutch orifice restriction size - 05/27/23 06:52 PM

I'm confused, the thumping into 3rd is related to the front clutch but "overlap" on a manual 1-2 upshift has nothing to do with the front clutch. By "overlap" do you mean delay?

Posted By: clemford

Re: 727 front clutch orifice restriction size - 05/27/23 09:39 PM

'
Im going by yo7a66 post 8-04-19. He had the 1-2 shift thump at low throttle too. Carburge and dave rs23 said what you are feeling is vb not releasing the front band before applying psi to the front clutches that causes that problem.

You yourself (John Kunkel) said lots folks consider the orifice restrictor a band aid, but if it works so what and its the cheapest and easiest way to mitigate overlap. Start of small at .080.
I think just getting rid of the shuttle valve blocker will help a lot. The70 factory manual says shuttle valve !'st function is fast release of kickdown band and smooth front clutch engagement on light foot upshift from 2 to 3.
Way back in 3-21-09 u (J K) said with r band apply max flow often causes severe overlap on manual 1-2 shift since rear band cant release as quickly as kd band applys . U said leave d ball in place and adjust the size of the servo feed orifice for good shift without overlap. ( Whats the servo feed orifice?). You said without the accumulator it can shift so hard it can shear the aluminum front pinion.carrier splines. Then you said jack r end up and shift 1-2 at 1500 and tires will stop for a second. I think mine did. Hard to remember 14 years ago. Plus i have a sinus infection? I think i might just go .140 on the trans case that yo7a66 used the factory manual calls it front clutch apply. He used >093.

Posted By: TJP

Re: 727 front clutch orifice restriction size - 05/28/23 03:10 AM

Originally Posted by clemford

'
Im going by yo7a66 post 8-04-19. He had the 1-2 shift thump at low throttle too. Carburge and dave rs23 said what you are feeling is vb not releasing the front band before applying psi to the front clutches that causes that problem.

You yourself (John Kunkel) said lots folks consider the orifice restrictor a band aid, but if it works so what and its the cheapest and easiest way to mitigate overlap. Start of small at .080.
I think just getting rid of the shuttle valve blocker will help a lot. The70 factory manual says shuttle valve !'st function is fast release of kickdown band and smooth front clutch engagement on light foot upshift from 2 to 3.
Way back in 3-21-09 u (J K) said with r band apply max flow often causes severe overlap on manual 1-2 shift since rear band cant release as quickly as kd band applys . U said leave d ball in place and adjust the size of the servo feed orifice for good shift without overlap. ( Whats the servo feed orifice?). You said without the accumulator it can shift so hard it can shear the aluminum front pinion.carrier splines. Then you said jack r end up and shift 1-2 at 1500 and tires will stop for a second. I think mine did. Hard to remember 14 years ago. Plus i have a sinus infection? I think i might just go .140 on the trans case that yo7a66 used the factory manual calls it front clutch apply. He used >093.

Yo' Clem,
John is well known as the resident Guru on 727's so might pay more attention to his advice and your sinuses

Posted By: John_Kunkel

Re: 727 front clutch orifice restriction size - 05/28/23 08:29 AM

Originally Posted by clemford

'
Im going by yo7a66 post 8-04-19. He had the 1-2 shift thump at low throttle too. Carburge and dave rs23 said what you are feeling is vb not releasing the front band before applying psi to the front clutches that causes that problem.

You yourself (John Kunkel) said lots folks consider the orifice restrictor a band aid, but if it works so what and its the cheapest and easiest way to mitigate overlap. Start of small at .080.
I think just getting rid of the shuttle valve blocker will help a lot. The70 factory manual says shuttle valve !'st function is fast release of kickdown band and smooth front clutch engagement on light foot upshift from 2 to 3.
Way back in 3-21-09 u (J K) said with r band apply max flow often causes severe overlap on manual 1-2 shift since rear band cant release as quickly as kd band applys . U said leave d ball in place and adjust the size of the servo feed orifice for good shift without overlap. ( Whats the servo feed orifice?). You said without the accumulator it can shift so hard it can shear the aluminum front pinion.carrier splines. Then you said jack r end up and shift 1-2 at 1500 and tires will stop for a second. I think mine did. Hard to remember 14 years ago. Plus i have a sinus infection? I think i might just go .140 on the trans case that yo7a66 used the factory manual calls it front clutch apply. He used >093.

You're taking what I said out of context i.e. you're asking about an "orifice restrictor" to cure both 1-2 and 2-3 overlap while the restrictor deals only with the 2-3 shift. Depending on the year (which you didn't state) the 1-2 overlap is usually addressed with a heavier return spring in the rear servo. In the years with a restrictor orifice in the rear servo separator plate, increasing the size of the hole will mitigate the problem but you state you have an aftermarket plate so that should already be the larger size.

Keep in mind that the front clutch orifice in the separator plate varies in size over the years so, in some years, the orifice in the plate is the restrictor but, again, if you have the aftermarket plate, the plate will have the larger orifice and a restrictor orifice in the case (supplied with a TF-2 kit) will help the 2-3 overlap. The orifice in the kit is a cup soft plug with a drilled hole but for home brewing it's common to drill the case and tap it for a 1/8" NPT plug...drill it with the orifice of your choosing .080" would be a good starting size.

Attached picture Air Check.jpg

Posted By: moparx

Re: 727 front clutch orifice restriction size - 05/28/23 04:48 PM

i have found that hole in the case is already the correct size for the 1/8npt tap.
i use a recessed hex plug, which is roughly 1/4" long.
when tapping the case, tap just enough so the plug goes just below the surface without you having to crank on it with a two foot cheater bar.
in other words, it should screw into the case easily with a shorty allen wrench, and doesn't need to be tight, just slightly snug.

Posted By: DaveRS23

Re: 727 front clutch orifice restriction size - 06/01/23 01:59 PM

Or you an use a tiny 'freeze plug' that just taps in. No shavings that way.

Dorman #555-115. 3/8" expansion plugs. To remove, just twist a screw in and pull out with a claw hammer or such.

I have done bunches of restrictions this way. Start small, say .090 to get a feel. Once you get close to a good size, make sure to test long enough to get the fluid to full temp because it will change the overlap or flair. And small changes can make a significant difference once you're in the all park, so make as small a change at a time as possible. Like .002" at a time. And it will never be perfect for all conditions and fluid temps. But with a little trial and error on the orifice, you can get it good for the majority of conditions.

I can usually make the change with the valve body simply swung out of the way with the parking rod still engaged. It will take several tries to get it as good as possible due to all the variables involved.