700r4 question

[nbrown2500]

I have a 90 blazer with a 350tbi, 700r4, and 35in tires with 3.73 gears. The PO had the trans rebuilt and a small shift kit installed locally. When in the "D" position there is a noticeable firmness between first and second. The firmness varies as to how much throttle I give it. I am assuming that is the shift kit. When in the "D" position downshifting is smooth through all the gears.
When in the "3" position there is also a firm shift between first and second but the downshift between first and second also has a noticeable shift and a sudden drop in rpm. What causes that kind of downshifting in "3" but not "D"?

 

[6872xtc]

I should be the fact that there is a bump in pressure when in 3rd, compared to overdrive. I believe that it is how the trans is designed, but then is more noticeable when some modifications are made.

 

[diesel4me]

It may be "programmed" into the valve body--I know on TH350 and TH400 transmissions,if you leave them in drive,the upshifting is more rapid and softer,than if you put the selector in "2",or upshift manually from 1st gear to 2nd gear,in that position the transmission slightly delays the upshift and it goes in much more firmly than in the "drive" position.,it has to do with how the fluid is routed through the various valve body passages according to a service manual I have..

 

[nbrown2500]

It may be "programmed" into the valve body--I know on TH350 and TH400 transmissions,if you leave them in drive,the upshifting is more rapid and softer,than if you put the selector in "2",or upshift manually from 1st gear to 2nd gear,in that position the transmission slightly delays the upshift and it goes in much more firmly than in the "drive" position.,it has to do with how the fluid is routed through the various valve body passages according to a service manual I have..

This was also what I was thinking. I must confess, I have not yet explored the transmission section of my service manuals.

 

[nbrown2500]

I should be the fact that there is a bump in pressure when in 3rd, compared to overdrive. I believe that it is how the trans is designed, but then is more noticeable when some modifications are made.

I can agree with that, I searched more after creating this thread and found another thread about this same topic. Everyone mostly agreed it was "normal" and just the functioning of a 700r4.

 

[6872xtc]

It was the early form of tow/haul mode, since you aren't supposed to tow in overdrive.

My wife doesn't like the shifts of my big block truck in 3rd.... but we did a lot to that trans to make it holds up to a fat block.

 

[6.2Blazer]

The firmness varies as to how much throttle I give it. I am assuming that is the shift kit.

The firmness of the shifts should always increase under heavier throttle, that is normal for even a completely stock 700r4. That is what the throttle valve cable (TV cable) does.

I've never noticed a difference in my '90 between having the shifter in 3 vs. D for up or down shifts.

 

[Blue85]

A 700 has a clunk in 2-1 due to the servo bottoming out. I can't remember why it only happens in D, not OD. It was resolved sometime in the late 80's. You can fix it by modifying your servo: https://ck5.com/forums/threads/hard-downshift-any-idea-why.304181/#post-3222981

 

[nbrown2500]

Thank you guys for all the replies. You all have answered my questions. I am so glad I joined this site after I bought my Blazer. There is so much great information of this site and everyone is awesome, thanks.