the give away 412 has a problem

vwfye · Post by **vwfye** » Thu Dec 29, 2005 6:19 pm

the 73 412 that i am giving away has finally arrived at its last mechanical correction tonight... and that is where i need help. we did a complete brake bleed of the system and though we have good pedal, we still have huge drag on the right front caliper. why? the inner side plunger is frozen in place. this is where i need some help. does anyone have a extra caliper that they would be willing to donate for a charitable cause? this is not for the 74 412 i am selling. i am receiving no compensation for the car, so please don't think you would be donating to a profitable venture.

so, if you have one that you know is good, please email me at vwfye@charter.net and let me know if you can help. once this is fixed, the young family will have a car! thanks everyone!!!

raygreenwood · Post by **raygreenwood** » Fri Dec 30, 2005 3:13 pm

Dissassemble teh caliper...cle3an teh rust ridge away..and smooth the inside with 200 grit paper. Its about an hour. Then clean in alcohol...re-assemble with brake fluid and you will be good to go. Ray

ubercrap · Post by **ubercrap** » Fri Dec 30, 2005 5:03 pm

Should that read 2000 grit

vwfye · Post by **vwfye** » Fri Dec 30, 2005 6:50 pm

the piston refuses go leave the caliper! any ideas?

vwbill · Post by **vwbill** » Fri Dec 30, 2005 8:03 pm

So did you try popping it out with it still attached to the brake system? You could use a clamp on one and pump up the pedal to pop the one side then put it back in and hold with a clamp and pop the other side. You could try compressed air and wd40 inside the bleeders and use a clamp to hold the other one? I think I had to try to rotate the piston in the caliper to get it to break the rust?? bill
p.s. Hey were our calipers on the 411/412 used on alot of vehicles? Autozone has rebuilts for 33 bucks with a core change of 17.

raygreenwood · Post by **raygreenwood** » Sat Dec 31, 2005 5:37 am

Yes....that is 2000 grit...not 200. I start with 400-600 to get most of the rust away, then polish to near mirror polish with 1500-2000 grit. Rust pits on the cylinder wall are not important...as long as the pits do not span across teh edge of teh groove where the seal goes.

In reality, the cylinder walls of the caliper can have honing marks...but its best not to hone these. You want to remove as little tolerance as possible.

The really critical part is the piston. It must be polished with 600-800 starting and polish with 2000 and xxx steel wool. In brake cylinders...you want 0 honing marks. This is not a cast iron ringed cylinder. You do not want to "break in" teh seals. You want a perfect seal on teh wall.

But...since the seals in calipers are staionary in teh grroves....the piston slides back and forth through them. It must be a mirror smooth polish.

As noted...pull off the caliper....put on some goggles, clamp teh good piston into the bottom of its bore with a Cclamp...mount in a vise.....put some pentrating oil around the edge of the stuck piston. then tap it back into its bore to get it moving. Add more penetrating oil...maybe a little heat with a torch....about 300F. Then grab the air hose....put a thin block of wood between the pistons...watch your fingers......use high pressure air to blow teh piston out of its bore. It may take several workings back and forth to to this. Ray

vwfye · Post by **vwfye** » Wed Jan 11, 2006 3:39 pm

alright... the piston absolutely refuses to let go in the caliper for disassembly. so the hunt is on for a cheap caliper! the car is sooooo close to being given away. i just did the final tune up on the engine, got the fan for the stocker heater working and just need to get that caliper done!