The tranny was brand new when I got the truck. It is securely bolted to the cross member. I wonder if the cross member is loose?

The guy said he was going to "check that everything was tight" as it had been a week since the new tranny was added.

I need to get this thing on a lift. Something has to be loose.

 

So the shift linkage is a rod that goes from the column to the trans.

I pull down from park to drive. The rod goes down & the tranny is in drive.

When I hit the gas the shifter on the column pulls down from drive into 2nd. & the tranny goes from 1st to 2nd @ the same time.

It's almost like the tranny is pushing forward while the hard shift rod is staying put forcing the trans to shift down into 2nd.

I know the *** squats big time & the engine is tight.

I wish my pics had saved.

The cross member has to be moving.

The rear end is hard mounted to a welded in cross member. I can't see that flexing under torque & the yolk has about 2 inches of play if it did.

 

I think I'll take it to my local tranny shop for a diagnosis

 

Take pics when you have it up in the air -- also double check the motor mounts

 

The rear end squat on hard launches is a design characteristic of the Jag IRS. It was designed for high speed cornering, not drag racing. If your intent is/was to do drag launches this was the wrong rear suspension choice, you would have been better served by a solid axle with 4 link, or ladder bars.

 

That is a whole other can of worms. I need to add anti - sway bars on both front & rear.

This truck has some serious body roll in the corners.

 

My cousin had a 70 f100 that would shell a rear u joint everytime he nailed it.After much frustration,we pulled the rear springs..They were so worn they would flatten completely just by standing on them.New springs solved the problem.

 

I think the rear squatting is probably not the cause just a quirk of the hot rod rear end.

I'm now leaning toward a loose trans crossmember. If the trans is climbing off the mount an inch, maybe less, it would be enough to down shift.

When it goes into 2nd I lose torque & the tranny drops back in place pulling the shift lever from drive to 2.

That would sure explain it

 

Probably not,just throwing that out there,i never would of thought tbat it could have been the problem with his,but sometimes we got to think outside of the normal.A loose crossmember may be your gremlin.Good luck on finding it.

 

Yup. Thanks.

I think I'll have the shop replace the u joints & torque everything down & check the linkage.

 

A fix for the squatting and the body roll on cornering you may want to change your coilover or springs

 

A lot of the suggestions being thrown around keep missing the fact that Brassmonkey is running a JAG IRS not a solid axle or leaf springs. Changing the coilovers would just make the ride harsher not make the geometry behave any differently. The Jag IRS is not designed for drag launches, the geometry makes it squat.
BM, you shouldn't be using IFS, IRS with out sway bars! Put the SJ6/12 stock sway bar on the rear and a front bar the diameter of the Jag front that fits on the front. But sway bars alone won't stop body roll. That's the function of the shocks entering and exiting a corner, the sway bar doesn't affect the roll until mid corner.
The truck is always going to have a lot of roll, both actual and perceived. Actual because by nature it has a high roll center, and perceived because you are sitting higher than that roll center, like sitting on an upper deck of a boat in a rough sea it will feel like you are rolling more than if you were sitting low.

 

Just a question and comment. Did the fan contact radiator high or low? If it is the trans. mount I would expect it to contact high.
Good luck in your quest

 

AxeRacer has a clue as to what he's talking about.
And, unless you want serious repair bills, you shouldn't ever try to "launch" with that rear end.

 

Man you guys are bumming me out!

Great advice though & I really appreciate it.

I happened to come across an old rusty Ford Bronco (91) I will take a look @ the sway bar setup on it & see what I need to do.