front brakes locked

My 89xj had rust issues and it was time to part ways.. I stripped and scrapped it and bought a 94xj to build. I finished today and took it for a test drive. Didn't work out well. Made it about 1/8th of a mile got it up to highway speeds and hit the brakes. When I hit the brakes some of the worst death wobble I have ever experienced reared it's ugly head. Drove another 1/4 mile fighting the dw before I could turn around. Got back to the shop and my front brakes were smoking. Now the set up.



94xj mid 90s D30 with 1t otk steering and track bar, stock calipers pads, yj brake lines, stock proportioning valve, 99xj booster and master cylinder. everything in good working order before the swap. Brakes bled twice with a power bleeder.

What would cause both front brakes to lock up at these time and not unlock?





Parakeet

I'm pretty sure the 97" boosters are different. Sounds like your master cylinder is not releasing the pressure completely and it "builds" up. As for the DW, is everything good? Knuckles use inserts, or are they reamed concentrically?

Now that you think about it I don't think I bench bled the master cylinder. as far as the dw I need to make sure everything is tightened. I may have missed something


Parakeet

It's not that, if you have fluid at the calipers it's bled. The problem is compatibility between your pedal, pedal bracket, booster and master cylinder. The 95-96 booster is bolt in. Not so sure about the 97+.

That booster and mc worked just fine in the 89 for a long time before this swap. I don't see it not working because the pedal is different.


Parakeet

Compare the pedals, something is wrong. This usually happens when the MC can't return all the way and slowly builds up pressure.

Just for grins, you can take the front wheels off and crack a bleeder screw. If you get a squirt of fluid and the rotor can then be turned by hand (remember, it's spinning the front differential so it will have some resistance) then your problem is in the hydraulic system - between pedal and line.
If you don't get fluid squirting (squirt, not dribble) then you probably have rusted / seized calipers. Also, I've never heard of worn knuckles causing an issue as bad as this, but your knuckles may be worn where the brake pad rides on them. Can cause real funky stuff.
If your back brakes were / are fine, it makes me think the MC might also be fine - but this is far from gospel.

Mark the more I ponder on this the more it makes sense. I'm going to space the booster out a little more from the fire wall and see if that fixes it before I put new pads and rotors on.

Before it goes back on the road I'll go through the front end to see what I missed when I reassembled the front end. I'll let you know how it plays out


Parakeet