Change T-350 shift points

billyjack

billyjack

Master Mechanic
Mar 27, 2009
449
4
18
Western PA
#11
Mr. Sony is correct.
Essentially, the governor affects only low vacuum (WOT) shift points, while the modulator influences light to mid-throttle shift points.
Make sure your modulator is plumbed directly to manifold vacuum, not ported vacuum. Is the trans dead stock or has it had any mods, such as a shift kit or raised line pressure? If so, you may have to reverse the mods. I'd try the adjustable modulator first, as it's easy to change.

Bill
 
vanrah

vanrah

G-Body Guru
Apr 16, 2013
723
753
93
Near Afton, Wisconsin
#12
Mr. Bonnewagon & all; Even though your modulator isn't leaking tranny fluid doesn't necessarily mean it is working properly! The diaphragm still could be hard & crisp, junk but just not leaking YET. And I'm guessin, but adjustable now days are just as available as non adjustable? Since GM didn't engineer your combo a OE non adjustable may prove NOT to be your friend? Just sayin' if it's adjustable it could be beneficial? And when ya take apart the governor use a med-big box (white) with 2 to 4 inch sides. The LIttle E-clips like to escape, Ole' Bob.
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,946
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113
Queens, NY
#14
OK thanks for those links. " If the shifts are too late, you need stiffer springs, or possibly heavier weights " Still doesn't say if the heavier weights or springs come in a kit. They all seem geared to raise the shift point- I want to lower it. Every single T-350 I've had shifted at very low speed. I guess what I need is a set of stock springs and weights for one of those models. AFAIK this is a stock trans but for the W-72 301.
 
TURNA

TURNA

Geezer
Jul 24, 2009
6,591
8,474
113
Socialist NY
#15
What is the engine originally from?
 
Last edited:
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,946
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113
Queens, NY
#16
I don't know. It is a standard 4 barrel 1978 YA engine which could have been from a Firebird or a station wagon. The trans code is MJ which is a non- turbo 301 trans. We "were told" it was from a 1980 Trans Am and if that is so then it is a special trans to go with the W72 301 engine. We assumed that is why it shifted so late but maybe there are other issues. All this is jammed into a 1985 Grand Prix and the engine works surprisingly well. A 3:08 rear makes for decent highway manners. We just want it to shift more normally because the 400 has no need to rev.
 
TURNA

TURNA

Geezer
Jul 24, 2009
6,591
8,474
113
Socialist NY
#17
I would just get a governor from a car that had a 400/TH360 in it then

Try one from a 77 TA
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,946
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Queens, NY
#18
That makes sense. A quick check shows RockAuto does not offer that so I hopefully a site like TCI does. EDIT: PATC has it- $100.
 
pontiacgp

pontiacgp

Canadian Prime Minister
Mar 31, 2006
24,191
9,405
113
Kitchener, Ontario
#19
I helped rebuild a powerglide and it didn't make it around 1 lap so I'll just keep reading the posts thank you.......:popcorn:
 
Bonnewagon

Bonnewagon

Geezer
Sep 18, 2009
5,946
2,069
113
Queens, NY
#20
One more thing. He has these super small tires on the rear. Aluminum slotted 14" wheels and very wide yet very low profile tires. Compared to my 27" high tires they looked to be about 23" or 24". That would change the 3:08 rear ratio to something far different. Might that confuse the governor shift point? And would that not cause it to shift too early? Instead I am shifting far too late.
 

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