P38 brake fluid leak from reservoir

feyniriel · Jul 1, 2025

Hi guys, my P38 brake fluid reservoir is wet all around and the fluid level goes up and down. I recently fitted new front disks and pads, after which the brakes were spongy. After driving the car, upon opening the brake fluid reservoir, air rushed in and brake fluid dropped to normal level. Brakes feel fine now. Then a week later, brakes were spongy again, brake fluid reservoir was wet and it looked as if it was sucked in. Again upon opening air rushed in and it leveled and brakes turned hard again. The brake fluid is brown in colour, which we will fix as soon as we can.
Any ideas what could be causing this? Thanks.

Datatek · Jul 1, 2025

feyniriel said:
Hi guys, my P38 brake fluid reservoir is wet all around and the fluid level goes up and down. I recently fitted new front disks and pads, after which the brakes were spongy. After driving the car, upon opening the brake fluid reservoir, air rushed in and brake fluid dropped to normal level. Brakes feel fine now. Then a week later, brakes were spongy again, brake fluid reservoir was wet and it looked as if it was sucked in. Again upon opening air rushed in and it leveled and brakes turned hard again. The brake fluid is brown in colour, which we will fix as soon as we can.
Any ideas what could be causing this? Thanks.

Over filled? The level should be correct with the engine running. It will rise with the engine stopped. I do not think the cap should be airtight.

Grrrrrr · Jul 1, 2025

feyniriel said:
Hi guys, my P38 brake fluid reservoir is wet all around and the fluid level goes up and down. I recently fitted new front disks and pads, after which the brakes were spongy. After driving the car, upon opening the brake fluid reservoir, air rushed in and brake fluid dropped to normal level. Brakes feel fine now. Then a week later, brakes were spongy again, brake fluid reservoir was wet and it looked as if it was sucked in. Again upon opening air rushed in and it leveled and brakes turned hard again. The brake fluid is brown in colour, which we will fix as soon as we can.
Any ideas what could be causing this? Thanks.

Cheapest fix and first job with brakes is to follow the bleed procedure as per RAVE. Don't rush it and pump plenty of fresh fluid through.

How many presses of the brake pedal before the ABS pump kicks in? If the accumulator membrane is shot it might leak fluid into that.

Also, check the brake lines where they go over the chassis by the fuel tank at the rear. If they haven't been replaced they need replacing.

kermit_rr · Jul 1, 2025

I think it's air tight otherwise moisture will get in? I can't remember, don't the caps have a diaphragm seal like bikes?

FEI · Jul 1, 2025

+1 on doing the brake bleed procedure as per Rave.
If you think youve got all the air out on a step give it another 5 pumps and more air will come out.

kermit_rr · Jul 1, 2025

FEI said:
+1 on doing the brake bleed procedure as per Rave.
If you think youve got all the air out on a step give it another 5 pumps and more air will come out.

All 3 nipples!! Not just the 2 you can see

Datatek · Jul 2, 2025

kermit_rr said:
I think it's air tight otherwise moisture will get in? I can't remember, don't the caps have a diaphragm seal like bikes?

Given the amount of rise and fall of the fluid, an airtight cap is unlikely IMO.

kermit_rr · Jul 2, 2025

Datatek said:
Given the amount of rise and fall of the fluid, an airtight cap is unlikely IMO.

Good point. Even more reason to keep on top of regular fluid changes

kermit_rr · Jul 2, 2025

Datatek said:
Given the amount of rise and fall of the fluid, an airtight cap is unlikely IMO.

Perhaps it is airtight in this case then and that's the problem?

Datatek · Jul 2, 2025

kermit_rr said:
Perhaps it is airtight in this case then and that's the problem?

Could be, I'll take a close look at mine later. Edit, I can confirm that the cap has an air hole best viewed from the inside of the cap. A partial vacuum in the reservoir is likely to affect braking.

P38 brake fluid leak from reservoir

feyniriel

Active Member

Datatek

Well-Known Member

Grrrrrr

Technician, Bodgit & Scarper Ltd

kermit_rr

Very

FEI

Well-Known Member

kermit_rr

Very

Datatek

Well-Known Member

kermit_rr

Very

kermit_rr

Very

Datatek

Well-Known Member

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