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Fast Shifting and Free wheeling Hubs

Don Ho

Don Ho

Stock 85
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Mar 23, 2017
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I just bought a 1985 Blazer 350 - Automatic . The tranny shifts fast and I want to spread it out . Will an adjustable vacuum advance Help ? 2 - Can I install the free wheeling hubs on this Blazer without any additional issues ? Any Help would be Great , Thanks Don
 
Don Ho said:
I just bought a 1985 Blazer 350 - Automatic . The tranny shifts fast and I want to spread it out . Will an adjustable vacuum advance Help ? 2 - Can I install the free wheeling hubs on this Blazer without any additional issues ? Any Help would be Great , Thanks Don
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My *experience* which is not the end all, is that the vacuum modulator made at most a 5MPH difference in shifting connected/disconnected. I thought it's main purpose was to modulate line pressure so that it shifted harder under load, and softer when not, but I've heard otherwise, and that it may make more of a difference in some applications than I experienced.

Are you saying that it shifts at a pretty low RPM,1-2-3? If so, that's the governor, and they make kits to modify it to change shift points.
 
dyeager535 said:
My *experience* which is not the end all, is that the vacuum modulator made at most a 5MPH difference in shifting connected/disconnected. I thought it's main purpose was to modulate line pressure so that it shifted harder under load, and softer when not, but I've heard otherwise, and that it may make more of a difference in some applications than I experienced.

Are you saying that it shifts at a pretty low RPM,1-2-3? If so, that's the governor, and they make kits to modify it to change shift points.
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Yes , at low RPM it shifts very quickly . I'll look on EBay for the kits thanks ( Do you know who offers the governors ? Thanks Don
 
Don Ho said:
Yes , at low RPM it shifts very quickly . I'll look on EBay for the kits thanks ( Do you know who offers the governors ? Thanks Don
Click to expand...

If you check summitracing you'll probably find kits to modify your governor. Since it's RPM based, there can't be a one size fits all solution.
 
Before you start buying stuff, make sure what you have is set up correctly.

Is the vacuum modulator hooked up? (Vacuum hose from the back corner of trans to the manifold or carb) this isn't likely the issue.

Is the tv/kickdown cable hooked up and adjusted properly?

Does it shift early under part throttle only, or under full throttle too?
 
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Oh and on question 2... yes. You can remove the auto-locking hubs and install manual locking hubs without issues. You'll just have to remember to lock the hubs before heading off road.
 
It sounds to me like the TV cable isn't set correctly. When they are not set right you can get what is called "stacked" shifts. The shift quality is soft, and it shifts way to early.

My 90 Blazer was like this when I bought it. The seller thought the trans was junk. I reset the TV cable, and presto...firm shifts at the correct times.
 
I'm confused...a 4-speed O/D TH700R4 (the normal factory tranny for your truck) would not have a vacuum modulator or a kickdown cable, it would have had only the TV cable mentioned previously. The vacuum modulator would have been used on the 3-speed 3/4-ton TH400 tranny.

Make sure we're all on the same page before you go spending dollars...
 
campfire said:
I'm confused...a 4-speed O/D TH700R4 (the normal factory tranny for your truck) would not have a vacuum modulator or a kickdown cable, it would have had only the TV cable mentioned previously. The vacuum modulator would have been used on the 3-speed 3/4-ton TH400 tranny.

Make sure we're all on the same page before you go spending dollars...
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I was under the impression that a th350 as well as a th700 were options in 85. Was I mistaken?

Edit......just checked the specs page here and it says a th350 was available in 85
 
ChrisPerry said:
Oh and on question 2... yes. You can remove the auto-locking hubs and install manual locking hubs without issues. You'll just have to remember to lock the hubs before heading off road.
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Chris , I'll check that cable adj first . Thanks Don
 
ChrisPerry said:
Before you start buying stuff, make sure what you have is set up correctly.

Is the vacuum modulator hooked up? (Vacuum hose from the back corner of trans to the manifold or carb) this isn't likely the issue.

Is the tv/kickdown cable hooked up and adjusted properly?

Does it shift early under part throttle only, or under full throttle too?
Click to expand...
Where Can I find the TV cable adjustment info ?
 
ChrisPerry said:
I was under the impression that a th350 as well as a th700 were options in 85. Was I mistaken?

Edit......just checked the specs page here and it says a th350 was available in 85
Click to expand...

Alright, I had thought the TH350 was phased out by then. That only underscores the importance of figuring out what we're talking about!
 
ChrisPerry said:
Oh and on question 2... yes. You can remove the auto-locking hubs and install manual locking hubs without issues. You'll just have to remember to lock the hubs before heading off road.
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Is it worth changing over ?
 
Don Ho said:
I'm checking . . thx
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This is always handy.

stock-transmission-pans.png
 
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