Brake Master Cylinder

[kd7kmp]

The only thing that is not new in my '90 Burban's braking system are the hard lines (it's a V1500). My issue is that the brake pedal is sooooooooooooooo mushy and I can't get adequate braking performance. I have noticed that the master cylinder squirts a "geyser" of fluid upward upon application of the brake pedal. This is from the rearward portion of the resevior--it feed the front brakes. Before anyone asks, yes, the system is completely purged of air...there is no doubt there.

My thought for fixing this problem is a different master cylinder. I have looked at several GM trucks of the same year and they all exhibit the same problem. I have a 1977 G30 van that doesn't exhibit this "geyser" phenomenon. The brake pedal is rock solid and braking is great. Any ideas on a different master cylinder? Thanks for the help.

Kevin

 

[k20]

goin out on a limb, as i have never dealt with one, but maybe has something to do w/ the anti-lock brakes? Thats the only thing that I can think of.

 

[divorced]

I put a new (rebuilt) master cylinder on my K20 and it still shot fluid out of it; I had to leave the cap on it while bleeding to avoid a big mess.

 

[kd7kmp]

K20,

I thought of that. I actually bent up some hard line and bypassed the ABS. Braking was the same. Thanks for the thought.

Kevin

 

[kd7kmp]

Divorced,

This is the exact problem I am talking about. I think it is a poor design to bleed off pressure that would otherwise be put to use in stopping the truck.

Kevin

 

[ZZ4x4]

Not sure if there is a difference between hydroboost MCs and the regular kind, but most MCs I've bled eject fluid when you hit the pedal. In fact the instructions for bleeding brakes that I have says to watch for it as a sign things are working correctly. Hope it helps.

 

[kd7kmp]

ZZ4x4,

Thanks for letting me know. This is the first time I've heard this. I will look into it.

Kevin

 

[clarkjw24]

Did you bench bleed it before installing. There is a difference in hydro and vac master cylinders but not in fuctionallity.

 

[kd7kmp]

I did bench bleed it. Thanks for the info.

Kevin

 

[crawford]

A lot of times the geyser means that air is still in the lines. It gets compressed when you step on the brake pedal. As soon as you let off the pedal the air in the line expands again shooting fluid back up the lines and making a geyser.

 

[socalblazer]

The geyser is normal for many types of MC's. How did you bleed the system? I've experienced problems with manually (Pedal pumping) bleeding some systems, mainly hydro-boost. I've had to vacuum bleed these system to get a solid pedal and even at that it's not great, but it's better then the dreaded smooshy pedal. When you figure it out post up so we know. Good luck.

 

[imiceman44]

The only thing that is not new in my '90 Burban's braking system are the hard lines (it's a V1500). My issue is that the brake pedal is sooooooooooooooo mushy and I can't get adequate braking performance. I have noticed that the master cylinder squirts a "geyser" of fluid upward upon application of the brake pedal. This is from the rearward portion of the resevior--it feed the front brakes. Before anyone asks, yes, the system is completely purged of air...there is no doubt there.

My thought for fixing this problem is a different master cylinder. I have looked at several GM trucks of the same year and they all exhibit the same problem. I have a 1977 G30 van that doesn't exhibit this "geyser" phenomenon. The brake pedal is rock solid and braking is great. Any ideas on a different master cylinder? Thanks for the help.

Kevin

The geyzer you see is normal on the newer style plastic reservoir MC.
The earlier style cast iron tanks, you should always keep the cap on, it's the only thing pressurizing between the front and rear tanks if you don't have the cap on when you pump it the fluid will go the path of least resistance from the rear to the front reservoir. Bad design but that's how it works.