Replaced mod valve shifted great for a week,punch it, down shift and shifted out fine.
Today noticed normal driving will not shift into 3rd till 50 mph, then I punched it later on highway it down shifted into 2nd but would not shift into 3rd and when slowing down stays in 2nd. The only way to get it to shift into 3rd is snap the accelerator.
If you barely give it gas when going from stop and I mean barely it shifts fine all gears but if you punch it stays in 2nd.
Can anyone help me out ?
Thank you.

 

Model year?

 

The tranny is a Chevy 400, most local shops can fix them cheap. I took mine out in an hour and took to shop, rebuilt in a day $400, bought my own modulator and installed in an hour. Make sure to tell shop for Jag, so they can install correct parts, still was not expensive as dealer said $5k for in out and rebuild.

 

1990 xjs

 

New modulator is Chevy. Are the Modulators adjustable, the older ones you could adjust with screwdriver, if I remember correctly.

 

Duplicated "send" again, sorry guys.

 

OK, out on a limb here, but here goes.

Remove the modulator, catch the dribbles of fluid, place you "little finger" in the hole, HAHAHA, and feel the modulator plunger is sliding freely in the valve body, as they can jam up.

NOW, some I have dealt with have a spring behind that plunger, so it moves outward as the modulator is removed, some have NO spring, which I firmly believe is WRONG.

One of mine had no spring, and a mongrel at times getting to shift nicely. Inserted a spring, all good.

Many schools of thought about that spring, claiming fluid pressure replaces it, mmmm, not convinced.

That plunger on your little finger should have a nice smooth travel in the bore.

Reading your post a few times, and the fact it changes on light pedal pressure points me to the modulator, or the valve I mentioned.

Anyway, we are flying out to Las Vegas in a few hours, so I will be AWOL for a couple of weeks, good luck.

 

If you have not left yet. If no spring where would I get one?
Have a Great and safe vacation and thank you for all the past and present help.

 

Any tranny shop.

Being a tight a%#e, I went rummaging thru all my junk (I throw NOTHING away), and found a spring that gave me the warm and fuzzy feeling, good as.

It is not a heavy spring, just something to keep the plunger up against the modulator pin.

That was in 1998, so I really cannot picture its specs anymore. Still works fine today.

Thanks, FUN will be had. A one legged oldy in Vegas, HAHA, but I always claim I will dead for a loooooong time, so get on with it.