Front V8 Caliper Piston Insertion

amcdonald

amcdonald

Active Member
Hello

I poked around on the forum and surprisingly did not find any info on my particular challenge. I had to remove the three pistons, which was okay. Well, not really in the bigger picture but I got them out. Then on the rebuild I was able to insert the dust seal in the figure-8 side but the big piston side was a bit loose. Now, the issue is the dust seal just interferes with the piston when you try to push it through, and it basically won't go through and also the seal gets disturbed. I see how the ID of the seal needs to match the diameter of the groove on the piston so it obviously needs to be (quite a bit) smaller than the piston.

What am I missing here? In the manual they just magically go in.

Adrian
 
It is a bit fingery / fumbly to get them to go in.
Firstly, the groove in the caliper FOR THE DUST SEAL can get very rusty and can reduce in diameter, this grove needs to be cleaned out with a scraper back to original size. If not the piston will be a very tight fit, and the fitting will be hard, and the brake may bind.
Once the dust seal is fitted, lube with red brake grease, and lube the piston as well.
The trick is to offer up the piston to the dust seal and get the piston started through the dust seal only, drag the dust seal up the piston a little, then seat the piston in the caliper up to the main seal ( which you previously lubed ) and push squarely in.
Finally make sure the dust seal is fitted into the groove in the piston nicely.

On some calipers the main seal is profiled and has to go in a certain way round, IIRC the P6 seals are square and can go in any way round.
 
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Hi

thanks a lot; all makes sense. I removed all the crud so it’s all clean. Maybe the “new” dust seals are a little harder than when properly new and it doesn’t help that one is too loose in the piston groove so it will be difficult to pull up the seal onto the piston as it will probably just come out. I will give it a try but maybe I will need to order a new rebuild kit.

curiously the piston main seals were slightly too big in this kit of unknown provenance but fortunately the original ones are good.

Adrian
 
Okay so I miraculously found another seal kit. And it was the same - the big seal was harder and a bit small but the figure-8 one was softer and a snug fit. So the figure-8 pistons could be installed by installing the seal into the groove and then pulling the seal skirt up the piston prior to pushing them in. On the big piston, it had to happen the other way around. The skirt was installed on the piston first with the seal out of the caliper and then when pushing the piston in, the seal could be pressed into the groove then the caliper eventually after much wiggling pushed through. Unfortunately that was not the end of the story....
 
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