Hi All - Long time, no post (by me, of course!)... It's good to be back. At any rate, I'm in the process of rebuilding the LR caliper on my GT4. I have the caliper off and the 2 halves separated. Following the tutorial on Birdman's website, I'm at the stage where I'm removing the piston from the cylinder from the rear half. I've advanced it out as far as it will go by turning the gear on the opposite side, and according to the tutorial, I have to pull it the rest of the way out by hand. The problem is, this thing won't budge. I spent an honest hour today on just that step...pulling and twisting, trying everything possible, and it just won't move even a hair. Obviously, any drastic (usual) measures that would involve metal tools and some variant of a prying motion are contraindicated for this procedure, as damaging the piston OR the cylinder wall are bad news. Anybody have some "been there, seen that, know-the-solution" wisdom? Any advice is greatly appreciated!
perserverance furthers. i used a plastic drift and penetrating oil to wrestle mine out. another less agressive method is the grease gun. replace the bleeder valve with a grease fitting and pump grease into the caliper. the grease will force the piston out. quite messy but civilised.
Aaron, if your GT4 caliper is the same as 308 (basically, with the built-in/internal hand brake mechanism) then you might find that the piston is still partially threaded on to the adjustment stud. You can wind the piston itself out further (if it is indeed still on the threads) by carefully using a broad mouth set of plyer on the outside face of the lip for the dust boot. Obviously, you don't want to use plyers on the piston surface or go digging around looking for leverage on the bore side either. I suggest dripping some brake fluid around the edge of the (partially exposed/removed piston) to ensure that the piston seal is lubricated as best as possible, but it's OK if the seal gets damaged because you're going to be replacing it anyway. If you try to use air pressure, or grease pumped into the caliper, while the piston is still threaded onto the stud then you're not going to get anywhere. As I recall from rebuilding the rear calipers recently on my 308, the piston was still partially threaded onto the stud even after turning out the adjustmentment screw as much as I possible, and I therefore had to wind out the piston itself using the above method. Good luck!
Interesting that many of us have worked on the LR just to get a working handbrake. Besides the great writeup on Birdmans, also read the Porche writeup as it's the same mechanicals. http://www.pelicanparts.com/techarticles/914_caliper_rebuild/914_caliper_rebuild.htm I recall minor difficulty getting the piston out and recall trying air pressure (ineffective) and gently rotating with protected jaw pliers. One thing I found helpful was to use my drill press when putting it back together occasions when 3 hands and force was needed.
I'm working on my RR as I type. Fun isn't it ? I've tried to carefully pry engaging the edge for the dust boot. I've had some success, and I've also seen one edge chip. I wouldn't call it a contraindication, Just look it it as an off-label procedure Seriously, just be patient. Maybe try and move it back in the bore. One thing I was thinking of is trying a syringe without a locking luer filled with brake fluid. A 5cc should generate a bunch of hydraulic pressue. Please post your success story.
This was the solution to the problem! The piston was indeed still threaded on about 1/4 - 1/2 of a turn. I put a rag over the piston and *gently* gripped it (as gentle as possible without slippage) to turn counterclockwise. Almost immediately, I felt the piston move in the cylinder, and with another reposition of the pliers and 1 more twist, it came free. Thank you to all who responded!
