Transmission additives(slipping under load), share your experiences, please help.

The auto trans in my 91 Supra (90,000miles) has developed a slipping issue. It revs a little between up shifts, and completely slips while downshifting under heavy load. The fluid has always been clean/regularly changed with the proper grade ATF since it's been under my ownership. Rebuilding is out of the question financially right now so I'm looking for an additive that you have experienced positive results from. I'm not expecting miracles, but a noticeable change for the better would be nice.

Has anyone tried Lucas Transmission Fix, or TransX?

Thanks!

sounds like u have a toyota....

the upshifts are called 'flares' and the downshifts are simple an open clutch...since you have felt it long enuf to post, the plates are most likely gone and no additive will replace material.

it could be a sliver of stuff got into a clutch pack seal - no additive will fix that. could be clutch material and or bakelite has gummed up any shift valves....but only a teardown/cleaning will fix that.

what you can try to do is manually shift it, if that helps then I would suspect line pressures not rising from the throttle valve.

I appreciate the reality check. I understand the trans will need physical help in the long term, but it's not an option at the moment. A band-aid fix is about the only thing in my budget right now. Sharing any benifical experiences with additives or quick tricks would be greatly appreciated.

Cheers and thanks.

2 bottles of Lucas trans fix and the car is fine, for now :)

Lucas thickens trans fluid. If it works, it sounds as if you have an intenal fluid leak due to wea or damage.
Try just a tiny splash of brake fluid (not DOT 5 fluid) it will swell the O rings and seals in the clutch packs and can help, if those seals are leaking.
It has worked for me.

Yeah, brake fluid worked for my '85 Caprice. Every time I would put it in reverse, it would take about 2-3 seconds to engage. Step-dad told me about this trick and told me not to beat on it for about a week, then to change the fluid.
It's been fine ever since....