(hydroboost) brakes locking up at idle

[BoostedSUV]

Just finally fired up my truck after a 6 month build and when I start the truck the hydroboost is applying the brakes. When the truck is off it rolls and there is very little drag on the brakes as normal. With the engine is running the truck won't even move in gear. I Unbolted the master cylinder and started the truck and the brake rod presses out hard against the master. I couldn't even hold it back and The brake pedal sucks to the floor. All the plumbing is brand new flex line, I replaced the hydroboost unit and the powersteering pump .

Any ideas? Also running c5 vette brakes and zq8 steering box.

 

[BoostedSUV]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

Forgot to mention that I'm using Mike's (TYTILIDIE) brake pedal adapter as well.

 

[blackty]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

There is no vacuum pulling? Not familiar with hydroboost, but sounds like engine vacuum??

 

[BoostedSUV]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

Hydroboost brakes work off the powersteering pump. There isn't any vacuum conection. I'm wondering if I have the lines reversed or a bad hydroboost unit?

 

[MRKING]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

If you disconnect the rod , are the brakes still applied ?

 

[BoostedSUV]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

If you disconnect the rod , are the brakes still applied ?

I didn't try to disconnect the rod with it running but with the engine off (no pump pressure) the brakes are released and there isn't any drag. With truck running the pedal is still in the same position but the pump pressure is applying the brakes. I didn't dig into too deeply yet but I was seeing if it was something I missed.

 

[Windedv6]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

Recheck your plumbing. Also check to see if your rod is engaging by being to long. There should not be any tension on the rod at he peddal.

John

 

[Quickstop [UK]]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

Plumbing, not rod. Is this a new install?

 

[BoostedSUV]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

Recheck your plumbing. Also check to see if your rod is engaging by being to long. There should not be any tension on the rod at he peddal.

John

John the rod isn't engaged at all with the truck off, I took off the master cylinder and the rod wasn't pressing against the bore. When I started the truck the rod pressed out against the bore and applied the brakes.

Plumbing, not rod. Is this a new install?

Yeah it's a new install and I'm new to hydroboost setups. I made the lines for high pressure feed, return, and used 3/8 hose for the low pressure and T-ed into the p/s cooler. I'm also using TYTILDIE's adapter plate and pedal adapter. I'm thinking its a plumbing issue since with the truck not running the brakes operate as they should. When I turn the truck on its like I have a 4 wheel line lock and the pedal is hard as a rock

 

[BoostedSUV]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

Is it possible I have the lines reversed? Will there be any risk of swapping them and trying it?

 

[warmpancakes]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

if lines are swapped it will do exactally what you are experiencing

 

[BoostedSUV]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

if lines are swapped it will do exactally what you are experiencing

Thanks Ken, that was the simple solution I was hoping for. I didn't have time to swap them last night and try it again. I followed the write-up MRKING did when I did the install except I used the o-ring fittings (after I realized the others didn't feel right).

I'll try swapping them and see if that works. I'm anal and I didn't like how the criss-crossed at the booster anyway :lol:

 

[BoostedSUV]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

according to this write up I have everything plumbed correctly :
http://www.syty.net/forums/showthread.php?t=38220



Here's my setup...

 

[BoostedSUV]

Re: brakes locked at idle (hydroboost)

Re: brakes locked at idle (hydroboost)

plumbed like this:

 

[neildemo]

Re: (hydroboost) brakes locking up at idle

Dam that Ty Is clean! looks like it rolled off the factory floor, no better.

 

[BoostedSUV]

Re: (hydroboost) brakes locking up at idle

Dam that Ty Is clean! looks like it rolled off the factory floor, no better.

thanks, spent a lot of time cleaning, painting, and powdercoating. I will start a thread showing the stages of the build shortly... stay tuned.

 

[MRKING]

Re: (hydroboost) brakes locking up at idle

Looking over your setup and how i did mine , i would say it appears to be correct . The 2nd to last pic of your engine bay seems to not have the low pressure return line connected , although i assume that was just your progress point in the install and is connected now .

I never did find the exact year and model of my unit , so it could be possible the fluid travel is reversed . Id say that or the rod is just longer than needed . When the unit pressurizes initially at start up your saying the brakes apply ?

I didnt have any brake issues other than the brake light switch needing to be adjusted . Try swapping the lines and see if the problems still there . If not , id say grinding/cutting the end of the brake rod may solve it .

x2 on the clean engine bay , looking real good .

 

[BoostedSUV]

Re: (hydroboost) brakes locking up at idle

I bought this truck as a roller and it was somebody elses project that never happened. The hydroboost unit came with the truck but wasn't installed, just mounted to the firewall. I don't know where it came from either. From every diagram I see on the web it is plumbed properly. I'm wondering if there's some air in the system because I didn't really give it much attention. I started the engine for the first time so I was looking for leaks, setting the timing etc...

The low pressure wasn't hooked up the time of the pics, it is now. I will fire it up again and try to pump the brakes and see if I can get them to function properly. The rod doesn't feel like the problem because the pedal feels good and the rod isn't pressing against the master when the truck is off. All I had to do was adjust the brake switches... Everything was fairly easy. I will look at it with more attention now that the rest of the truck is good.

 

[TYTILIDIE]

Re: (hydroboost) brakes locking up at idle

For the sake of taking my kit out of the equation, can you disconnect the shaft/adapter, fire it up and see if you still have the same problem? Also, I sold those with requiring the use of the 94 Astro hydraboost unit, see if you can't verify what you are using somehow.

 

[BoostedSUV]

Re: (hydroboost) brakes locking up at idle

For the sake of taking my kit out of the equation, can you disconnect the shaft/adapter, fire it up and see if you still have the same problem? Also, I sold those with requiring the use of the 94 Astro hydraboost unit, see if you can't verify what you are using somehow.

I'm going to try that mike. I didn't get too deep into trouble shooting yet. I just posted on my way out the door hopeing somebody had a similar issue.