Brake pump

[max76]

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]

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.

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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]

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]

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]

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]

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

[max76]

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]

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]

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.