Brake pump - ZR-1 Net Registry Forums

max76 · 03-24-2021

Hi guys,
my 90 zr1 have a strange problem.
The brake oil level in the reservoir on the brake pump is the same from front and rear....After few miles one is higher....its seems that the oil pass from one to the other reservoir...Has anyone happened? what can it be?

Paul Workman · 03-24-2021

Is in fact the level in one reservoir actually increasing or is one decreasing and it appears to be doing as you say - (essentially) swapping fluid, one side to the other?

Assuming your assumption, i.e., fluid is swapping, it would most certainly be an issue in the master cylinder (I'd bet).

The seals do wear out, especially if water gets in the fluid (turns the brake fluid black). Replacing the master cylinder is cheap enough and considering the age (by now) if it hasn't been changed by now, it wouldn't be wrong to routinely change it anyway - and the problem will (most likely) go away.

Rock Auto, or NAPPA is where to get the new master. Or, some have had them rebuilt, in a "pinch". But, depending on how the rebuild is done and the parts used will determine how long the rebuilt part lasts. And, the cost of a new one is likely cheaper than a properly rebuilt one, unless you DIY. Also, the brake lines should be bled while you're at it.

----------------

FWIW, I bought my master and slave from Rock Auto and am very happy with the new parts (cast iron too, BTW).

Mitivac (from Summit) makes a nice reservoir bottle and vacuum pump kit for flushing both the brakes & the clutch.

DOT-3 fluid for the brakes and the clutch is what was used initially, and what I use too. Some use DOT-4, but I'll let them speak to that.

max76 · 03-24-2021

Hi Paul,
yes, i think change the master cylinder is the right thing. The car is all original and has low miles. Rockauto have 4 kind of master cylinder...can you suggest me whats the best?
https://www.rockauto.com/en/catalog/...+cylinder,1836

There's a website for NAPA?
I cant find only the parts to rebuilt...is there a proper kit?

Young1 · 03-24-2021

The fluid reservoir for the front brakes will decrease in level at a higher rate than the rear because the front brakes have a higher capacity to replace as the pads wear. The reservoirs are not connected. One decreases in level more rapidly than the other. Normal.

max76 · 03-24-2021

I know that is normal an oil decrease during use...but I say that happen after few kilometres...if I replace the correct level in the next 50 miles the oil level change...I think that is not normal, but I'll try to check the thickness of the brake pad...thanks

secondchance · 03-24-2021

This is suppose to be OEM for 90. Compare carefully with your current master. Description does not indicate standard C4 and ZR-1.

max76 · 03-26-2021

Quote:

Originally Posted by secondchance

This is suppose to be OEM for 90. Compare carefully with your current master. Description does not indicate standard C4 and ZR-1.

Zr1 have different master than stock 1990 base coupe?

max76 · 03-26-2021

Quote:

Originally Posted by secondchance

This is suppose to be OEM for 90. Compare carefully with your current master. Description does not indicate standard C4 and ZR-1.

I'll check the master of a 1990 l98 of my friend...thanks for the idea... ;-)

Marc Haibeck · 03-27-2021

Hi,

I have seen this several times. The master cylinder can transfer fluid from the front reservoir to the rear reservoir when there is an internal leak in the cylinder.

For replacement we use Dorman PN MC39716.

03-24-2021	#1
max76 Join Date: Apr 2009 Location: ITALY Posts: 264	Brake pump Hi guys, my 90 zr1 have a strange problem. The brake oil level in the reservoir on the brake pump is the same from front and rear....After few miles one is higher....its seems that the oil pass from one to the other reservoir...Has anyone happened? what can it be?

03-24-2021	#2
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Re: Brake pump Is in fact the level in one reservoir actually increasing or is one decreasing and it appears to be doing as you say - (essentially) swapping fluid, one side to the other? Assuming your assumption, i.e., fluid is swapping, it would most certainly be an issue in the master cylinder (I'd bet). The seals do wear out, especially if water gets in the fluid (turns the brake fluid black). Replacing the master cylinder is cheap enough and considering the age (by now) if it hasn't been changed by now, it wouldn't be wrong to routinely change it anyway - and the problem will (most likely) go away. Rock Auto, or NAPPA is where to get the new master. Or, some have had them rebuilt, in a "pinch". But, depending on how the rebuild is done and the parts used will determine how long the rebuilt part lasts. And, the cost of a new one is likely cheaper than a properly rebuilt one, unless you DIY. Also, the brake lines should be bled while you're at it. ---------------- FWIW, I bought my master and slave from Rock Auto and am very happy with the new parts (cast iron too, BTW). Mitivac (from Summit) makes a nice reservoir bottle and vacuum pump kit for flushing both the brakes & the clutch. DOT-3 fluid for the brakes and the clutch is what was used initially, and what I use too. Some use DOT-4, but I'll let them speak to that. __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry

03-24-2021	#3
max76 Join Date: Apr 2009 Location: ITALY Posts: 264	Re: Brake pump Hi Paul, yes, i think change the master cylinder is the right thing. The car is all original and has low miles. Rockauto have 4 kind of master cylinder...can you suggest me whats the best? https://www.rockauto.com/en/catalog/...+cylinder,1836 There's a website for NAPA? I cant find only the parts to rebuilt...is there a proper kit?

03-24-2021	#4
Young1 Join Date: Sep 2016 Location: Ocala, FL Posts: 900	Re: Brake pump The fluid reservoir for the front brakes will decrease in level at a higher rate than the rear because the front brakes have a higher capacity to replace as the pads wear. The reservoirs are not connected. One decreases in level more rapidly than the other. Normal. __________________ Steve Young 1991 ZR-1 Quasar Blue Metallic/Black #729 Second Owner 1991 ZR-1 Dark Red Metallic/Black #2040 SOLD 1990 ZR-1 Dark Red Metallic/Saddle #1670 SOLD Double your happiness.....complain half as much.

03-24-2021	#5
max76 Join Date: Apr 2009 Location: ITALY Posts: 264	Re: Brake pump I know that is normal an oil decrease during use...but I say that happen after few kilometres...if I replace the correct level in the next 50 miles the oil level change...I think that is not normal, but I'll try to check the thickness of the brake pad...thanks

03-24-2021	#6
secondchance Join Date: Aug 2006 Location: McLean, VA Posts: 3,723	Re: Brake pump This is suppose to be OEM for 90. Compare carefully with your current master. Description does not indicate standard C4 and ZR-1.

03-27-2021	#9
Marc Haibeck Join Date: May 2007 Location: Addison IL Posts: 250	Re: Brake pump Hi, I have seen this several times. The master cylinder can transfer fluid from the front reservoir to the rear reservoir when there is an internal leak in the cylinder. For replacement we use Dorman PN MC39716.