bad brake pedal, help with diagnosis please

[Toby_Goodmk]

I have a factory hydroboost original to the car. My latest condition has a very strange pedal. Ill try to describe best as possible with a listing of what I have done trying to make it better

The brake pedal tends to activate the HB. Normally the pedal is firm, and doesnt move hardly at all. My pedal goes down an inch or more and braking doesnt fully lock until I mash it. Tires let loose at about 2k rpm with a 3k stall converter 0 boost.

My system makes a ton of noise. It whines like crazy. It foams badly. I converted to 87 so I am using a remote reservoir. I have all new lines, on my second pump. I am using lucas power steering oil with conditioner. I am also running an in line filter to the return to reservoir. No leaks at all. I even converted my lines to AN-6 lines. My steering gear is only a year old. I pulled vacuum on the reservoir and it held 15" till I let it loose...i know the system is leak free.

I bled the brakes to hell and back. I bled the master cylinder to make sure no air...there was none. I bled the lines, all of them. I even bled the proportioning valve. I have fluid that comes from all 4 corners at a steady rate no air.

Here is another symptom. Turning the wheel while applying light pressure on the brake pedal you can feel feedback from the steering, almost like the pedal is fighting back the pressure I am applying.

I am thinking the HB is toast.

Thoughts???

 

[DR BOOST]

please take a picture of how the low pressure return hoses are plumbed.

 

[Toby_Goodmk]

please take a picture of how the low pressure return hoses are plumbed.

I wish I could take a good picture, but the lines for the AC, Vacuum and others are impeding a good picture.

I have a T in the return line which comes off the gear box about 6" then proceeds to both the reservoir about 12" and then onto the HB factory line which is about 24." The return line goes into the side of a round canister from a astro van (i believe) on top, the feed is a 5/8 line below the return.

 

[Nick Micale]

Not sure about your "second pump", but if you have a 1986-7 pump, check to see if you have an issue with the belt slipping on the original PS pump as it was not designed for the additional load of a HB?

 

[Toby_Goodmk]

Nick,

THis is an issue that surfaced recently. But I will change the belt out to see if there is a difference.

 

[Toby_Goodmk]

Spent some time with Jim from Hydratech on the phone today. Recommends replacement of the master cylinder. So we will go that route first.

Another interesting tid bit. As for the whining and foaming at the reservoir....this is possibly due to higher that normal volume in the pump which is creating aeration inside the reservoir. Decreasing the orifice size at the pressure side of the pump to this. http://www.purechoicemotorsports.co...ct_id=412/category_id=-1/mode=prod/prd412.htm will hopefully reduce the foam and whine. It makes sense because the system is extremely quiet until I have some run time and the fluid circulates for a couple minutes. Slowing the rate will keep aeration to a min. Also the reservoir needs vented. Parts on order!

 

[Toby_Goodmk]

Hot damn!!! It's fixed with an 18$ part!!! The whining is gone no onto the master cylinder replacement

 

[1KWIKSIX]

Toby,
Which unit did you go for?
1" Hex or 7/8" Hex?
Or does it really make any difference?

 

[Toby_Goodmk]

I went with the 7/8" because that is what Jim told me to use, and it worked and was the same size as orig.

 

[Toby_Goodmk]

ok...update. Replaced master cylinder, bought a motive power bleeder. Did two cycles of RR, LR, RF, LF bleed sequence. Got some air out, and acquired a good pedal. Started the car up.....pedal goes down like before after a couple pedal pushes. Shut the car off, got decent pedal again. I am thinking hydroboost definitely now. Thoughts? Experiences like this anyone??

 

[Jerryl]

Fighting the exact same issue.
Already replaced the MC with an new ACDELCO unit. Bled 4 times and went through 4 quarts of fluid.

My thoughts are MC because the assist is just that: An assist. Don't know . . . stumped. One thing I do know: Should have kept the PM.

Sent from my SM-N910H using Tapatalk

 

[Toby_Goodmk]

Fighting the exact same issue.
Already replaced the MC with an new ACDELCO unit. Bled 4 times and went through 4 quarts of fluid.

My thoughts are MC because the assist is just that: An assist. Don't know . . . stumped. One thing I do know: Should have kept the PM.

Sent from my SM-N910H using Tapatalk

Do you have a good pedal while the engine is not running?

 

[DR BOOST]

Based on the advice from another member on here, I plumbed in the T with the horizontal legs going to the gearbo and reservoir and the vertical leg going to the hydroboost. When I had the vertical leg going to the reservoir, my pedal would sag. It was mentioned that the fluid returning from the gearbox could cause back pressure in the hydro boost if they are attached to the t aiming directly at each other . I hope this makes sense and works for you

 

[Toby_Goodmk]

that is worth noting, but also note that I cannot bring the car to a stop....3 mph... at all unless I stomp on the pedal with all kinds of leg...and even after this point it is not even enough to lock up the wheels.

 

[Jerryl]

Do you have a good pedal while the engine is not running?

Yes . . . than no. Have not driven enough to narrow it down but do know this: brakes work than pedal drops to the floor. Bench bleed, no leaks . . [emoji35] [emoji35]

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[Toby_Goodmk]

Yes . . . than no. Have not driven enough to narrow it down but do know this: brakes work than pedal drops to the floor. Bench bleed, no leaks . . [emoji35] [emoji35]

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spoke to Jim from Hydratech again this am..... Man what a nice fella. Jerryl, here is what he told me to do. Take the return hose coming from the HB and disconnect it from the "T." Plug off the open "T" and place the disconnected end of the return hose in the steering reservoir. Start car, push on brake pedal. If steering fluid comes out of the return hose....bingo....issue with hydroboost. I am traveling to Nashville this week so cannot perform the task till Sat.

 

[Jerryl]

Awesome. Will have to try that. Thanks for sharing. Will update when i test.

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[Toby_Goodmk]

Awesome. Will have to try that. Thanks for sharing. Will update when i test.

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you have a chance yet? I am going to perform later this eve or definitely tomorrow.

 

[Jerryl]

Sorry, not yet. The car is down for another 2 weeks. Working on a few other things.

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[TexasT]

So, are both of y'all using a factory hb unit? What master cylinder? Powermaster pedal?

I'm not sure how the reservoir has bubbles if air isn't being introduced. Something is causing the fluid to be agitated. I do see the thought about the fluid running into itself and being agitated.