Like most folks that have had their transmissions rebuilt, its pretty common for the shops to install an adjustable vaccum modulator.


When I bought the car it was set to about 80% to the firmness side. The trans shop said the firmer the shifts, the longer the transmission would last...according to the previous owner.



I was wondering, if the trans shifts harder and faster, that must put more wear on some part of the trans.

I was under the impression that a common failure on the 4t60-hd trannies was either the 1st or 2nd gear clutches, forget at the moment.


The main question I have is what are the advantages and disadvantages of having the transmission set on a very firm setting, vs the softer setting

according to my dad and the knowledge i have learned from this site, its actually the other way around.. the harder the shift, the quicker the shift, which puts less wear time on the clutch gears

in the 60 HD, quicker shifts means less clutch wear
The tighter u dial in that modulator, the harder the car will engage into all gears, as in, Park to D or R.
The harder it slams into R from Park, the more wear you put on the Reverse Reactor shell, a common 60 failure.

And the more stress on the diff. It'* a tradeoff.

Firmer shifts are better for performance, and reduce clutch wear. For the 60, the second gear clutches, for the 65, the 4th gear clutches. But it does put more stress on the hard parts with the abrupt shift.

But it feels soooo right lol

With slicks next summer on the Zilla, I'll probably back the Modulator all the way soft. Save the diff. I still have the shift kit.

If you have your modulator set up right, the R and D engagement is about as smooth as stock modulator. However the shifts driving firm up much more. I have no idea how many turns mine is, but it'* not that insanely firm backed all the way in. I did have a reverse engagement shudder with the stock non-adjustable modulator [that was tested and worked fine], that went away with the adjustable.

The adjustable modulator on max in addition to my shift kit is brutal in second gear. Breaks 'em loose every time.

Is there a such thing as a happy medium?

Depends on how much power you're making at the shift, and how strong your trans is. Also how big your budget is for later.