Turbo 400 experts please step in....

ss3011 · 10-24-2018, 03:24 PM

The basic differences between the modulators is a spring force , and the size of the diaphragm . It works by vacuum acting on the diaphragm area to back off the load on the spring . If no vacuum (WOT) then just the full load of the spring acts against the modulator valve which regulates a pressure that makes line pressure and also works on the shift valvetrains . This is max modulator pressure . When you have high vacuum (closed throttle) ,then the diaphragm works against the spring , reducing it to zero . This means zero modulator pressure which gets you minimum line pressure , usually 60 psi , and minimum shift points . So all these different modulators are just combinations of spring loads , and Diaphragm areas . The problem in this thread is sounding like the diaphragm area is too big so under medium engine load it backs off the modulator pressure and gives an early shift . It would be nice to have a chart of different modulator part numbers with spring load , diaphragm area , and ID stripes . Also note that the adjustment screw is usually adjusted at the factory to get a certain load at a certain vacuum , back when these were more common there was not a screw , but the adjustment was done by dimpling the top of the housing .

joespanova · 10-24-2018, 06:59 PM

OK guys , thanks again........
I'll conclude with this:
I have the "hard" line that has a "necked down" area at each end , but I'm having a hard time understanding how that would effect the 1-2 shift?
I'll replace the full length rubber hose it has now BUT , it seems to me those reduced areas joining at modulator or nipple on manifold top of runner , the only point of that feature was to locate the tube securely on the production line ( slipping inside the mating device ) and the short rubber hose at each end just kept it all together ?

Mark Ugrich · 10-24-2018, 08:03 PM

You are partly correct. The tube was necked down to locate it to the fittings. This allowed for just a straight short piece of rubber vacuum line to seal the connection. If you look closely into the opening of the tube, you will most likely see a restriction on the end by the modulator. I would open up the ends of the metal line with a drill of appropriate size.It’s possible you may have to change the 1-2 shift valve spring in the valve body to get the trans to shift where you want it to.

joespanova · 10-24-2018, 09:03 PM

Quote:

Originally Posted by Mark Ugrich

You are partly correct. The tube was necked down to locate it to the fittings. This allowed for just a straight short piece of rubber vacuum line to seal the connection. If you look closely into the opening of the tube, you will most likely see a restriction on the end by the modulator. I would open up the ends of the metal line with a drill of appropriate size.It’s possible you may have to change the 1-2 shift valve spring in the valve body to get the trans to shift where you want it to.

Thanks.

10-24-2018, 03:24 PM	#1
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 909 Likes: 70 Liked 239 Times in 114 Posts	Re: Turbo 400 experts please step in.... The basic differences between the modulators is a spring force , and the size of the diaphragm . It works by vacuum acting on the diaphragm area to back off the load on the spring . If no vacuum (WOT) then just the full load of the spring acts against the modulator valve which regulates a pressure that makes line pressure and also works on the shift valvetrains . This is max modulator pressure . When you have high vacuum (closed throttle) ,then the diaphragm works against the spring , reducing it to zero . This means zero modulator pressure which gets you minimum line pressure , usually 60 psi , and minimum shift points . So all these different modulators are just combinations of spring loads , and Diaphragm areas . The problem in this thread is sounding like the diaphragm area is too big so under medium engine load it backs off the modulator pressure and gives an early shift . It would be nice to have a chart of different modulator part numbers with spring load , diaphragm area , and ID stripes . Also note that the adjustment screw is usually adjusted at the factory to get a certain load at a certain vacuum , back when these were more common there was not a screw , but the adjustment was done by dimpling the top of the housing .

10-24-2018, 06:59 PM	#2
joespanova Senior Member Join Date: Jun 2011 Location: Ga. Posts: 521 Likes: 7 Liked 13 Times in 11 Posts	Re: Turbo 400 experts please step in.... OK guys , thanks again........ I'll conclude with this: I have the "hard" line that has a "necked down" area at each end , but I'm having a hard time understanding how that would effect the 1-2 shift? I'll replace the full length rubber hose it has now BUT , it seems to me those reduced areas joining at modulator or nipple on manifold top of runner , the only point of that feature was to locate the tube securely on the production line ( slipping inside the mating device ) and the short rubber hose at each end just kept it all together ?

10-24-2018, 08:03 PM	#3
Mark Ugrich Member Join Date: May 2011 Location: Auburndale,Florida Posts: 220 Likes: 29 Liked 71 Times in 38 Posts	Re: Turbo 400 experts please step in.... You are partly correct. The tube was necked down to locate it to the fittings. This allowed for just a straight short piece of rubber vacuum line to seal the connection. If you look closely into the opening of the tube, you will most likely see a restriction on the end by the modulator. I would open up the ends of the metal line with a drill of appropriate size.It’s possible you may have to change the 1-2 shift valve spring in the valve body to get the trans to shift where you want it to.