PMB 914-6/GT - Rear Calipers

[Mr Pharmacist]

I agree with Bruce - does look like that bottom nut is wet and not the bleeder

[gridgway]

Certainly of the two phases of 'find the problem' and 'fix it', getting the first sorted makes the second easier.
So double checking where the fluid is actually coming from is the way to go.

In the past on the race car I have had a leak from the banjo bolt through re-using the copper washers that came off. As changing that takes a lot of dismantling, I always use new copper washers every time I have to disconnect the caliper in question (and it comes off quite a lot).

And why is there a bleed nipple at the bottom of the caliper?

Graham

[glovebox]

And why is there a bleed nipple at the bottom of the caliper?

Graham

Good question? One for each piston perhaps??

[914 KEV]

And why is there a bleed nipple at the bottom of the caliper?

Graham

Good question? One for each piston perhaps??

Early 914-4 and 914-6 rear calipers only had one bleed nipple, late 914-4 rear calipers had two.

I think this was just so they only had to machine one outside casting that would fitted both sides.

[gridgway]

You certainly can't bleed air out of the bottom of the caliper!!

[glovebox]

I think I will crack one open and have a look. Plus I want to see why the one calipers spewed out that dirty fluid !

[glovebox]

Well the bolts and spacers and seals were wet!

[Bruce M]

Some nice fresh plump viton o-rings needed in there

[Darren C]

As Bruce says, New seals all round.

I'd also check that the aftermarket calipers haven't had the counterbores machined too deep. The new seal needs to sit proud so it compresses when the halves and spacers are assembled. Worth measuring and comparing with a depth mic between the leaky one and all the others before you re-assemble. Particularly as in your photo of the seal left in the spacer (the one below the bolts) it has definitely been compressed well when assembled, but the others don't seem to show the same compression marks???

[gridgway]

I am still drawn to the action of sending them back. Getting your money back and going elsewhere. Callipers from new that are not sealed is appalling.
Graham

[glovebox]

I am still drawn to the action of sending them back. Getting your money back and going elsewhere. Callipers from new that are not sealed is appalling.
Graham

When you say it like that !! I can't disagree .

So what would be my next rear caliper option ??

[gridgway]

Sorry, don't know what else to suggest, but there has to be more than one option surely?

[tp_reading]

Sorry, don't know what else to suggest, but there has to be more than one option surely?

I have been through all this myself recently. You can fit 911 calipers, but that leaves you with the hand brake issue. The most popular solution involves machining the hub and fitting Boxster handbrake mechs. That's why I would persevere with PMB solution. Is there a specialist near you who you could get to sort it !

[davep]

You certainly can't bleed air out of the bottom of the caliper!!

No, but you cannot drain the fluid out of the top bleeder either. Once you have repaired a few dozen 914 rear calipers you find the amount of rust and exceptionally dirty fluid in the outer piston is very prevalent. This is due to the fact that simply bleeding the calipers when changing fluid does very little to actually changing the fluid within the caliper bores. Simply observing the fluid path from the brake line entrance to the upper bleed nipple shows that no fresh fluid will flow through the outer caliper half. Thus, the only way to change the fluid within the caliper (where the fluid really needs to be changed) is to first drain the caliper, refill, and pressure bleed. I will fill and drain a second time if I do not remove and disassemble the caliper which is my usual practice.

[gridgway]

No, but you cannot drain the fluid out of the top bleeder either. Once you have repaired a few dozen 914 rear calipers you find the amount of rust and exceptionally dirty fluid in the outer piston is very prevalent. This is due to the fact that simply bleeding the calipers when changing fluid does very little to actually changing the fluid within the caliper bores. Simply observing the fluid path from the brake line entrance to the upper bleed nipple shows that no fresh fluid will flow through the outer caliper half. Thus, the only way to change the fluid within the caliper (where the fluid really needs to be changed) is to first drain the caliper, refill, and pressure bleed. I will fill and drain a second time if I do not remove and disassemble the caliper which is my usual practice.

Interesting and good point, looking at the photo again, I can see this. With that arrangement of inlet and outlet on the same side (the inner side), how does air get bled out of the outer side?

And any update on the problem of leaks Mark?

Graham