Hydroboost brakes dragging

pcf_mark · Oct 3, 2016

Search simply does not digest "hydroboost" and "brakes" well and you get crazy threads.

Hydroboost install (my second) with canned ham OEM pump with T in the return line with the straight path going from booster to pump. After several stops the brakes begin to drag. After enough stops (10 or so) they drag enough they slow you down. If you park and let it sit engine off for 10 minutes problem goes away for another 5-10 stops.

I thought if it was a too long push rod it would do it from the first time I used them. Do I need a brake return spring to make sure the pedal fully returns?

Thanks guys.

Deano · Oct 3, 2016

There is a adjustment between the hydroboost and master cylinder that need to be shortened about a turn turn and a half and that should cure the problem

ransil · Oct 4, 2016

I used washers between the MC and Booster

englewoodcowboy · Oct 4, 2016

I used a Astro van hydroboost and it has no adjustments so I created them by chance. Instead of using a GM MC, I wanted to keep as much of it Ford as I could. Being the hydro unit is a Bosch and used by most manufacturers I hoped a ford MC would fit. It did not, I had to widen the mounting holes slightly and then discovered that the pushrod on the hydro unit was too short to reach the bottom of the Ford unit. Being it naturally created a captive cavity, I made a "pill" rod to take up the space. I was able to slowly shorten the pill to get the correct play when assembled as the MC needs to return to its static home position if you will, something to do with the internal valving it will hold a position that is not home. That 1/16" play to engagement is critical to that I have found.

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Broncobowsher · Oct 4, 2016

It's a common problem with power brakes in general, not just hydroboost.
Too much initial preload on the master cylinder. the transfer ports are covered. The fluid can't make it back to the reservoir when it starts to expand. It will still bleed fine because of the shape of the cup seal on the retract stroke will allow fluid to bypass.

The problem is on the master cylinder side of the booster, not the pedal side. It is a result of a mix and match of booster and master cylinder. You need to shorten the pushrod coming out of the booster going into the master.

charlie6976 · Oct 4, 2016

Why not plan ahead and start with a hydroboost and master cylinder that work together?
Such as a late 70's big Lincoln/Ford/Mercury. Some came with hydroboost. NAPA has rebuilt ones. Look under 1978 Lincoln Mark V. Or Pick n pull. These cars also came/have the front calipers with the bigger pistons (often referred to as the Thunderbird calipers, they also came on Fords and Mercurys with hydroboost).
Hope this helps someone.

pcf_mark · Oct 4, 2016

I knew you guys would come through! I am going to space my master cylinder forward from the booster by a thick AN washer and see if that cures it. The pedal assembly is perfect I was hoping not to have to make changes there.

Broncobowsher · Oct 4, 2016

charlie6976 said:
Why not plan ahead and start with a hydroboost and master cylinder that work together?
Such as a late 70's big Lincoln/Ford/Mercury. Some came with hydroboost. NAPA has rebuilt ones. Look under 1978 Lincoln Mark V. Or Pick n pull. These cars also came/have the front calipers with the bigger pistons (often referred to as the Thunderbird calipers, they also came on Fords and Mercurys with hydroboost).
Hope this helps someone.

For one, the tuning of the modern boosters is much better, modern boosters are a built with a lot better quality, modern boosters are not parts that are nearly 40 years old. Seals age and parish over time, nothing stops that. The early hydroboost does not have the greatest reputation, but the modern stuff is well known for being good stuff.

pcf_mark · Oct 8, 2016

Thanks again fellas. I spaced the master cylinder forward with one washer under each mouting bolt and no problems.

barronj · Oct 24, 2016

Thanks for the thread. I think this is the next thing I need to fine tune. The bronco jumps a bit sometimes, almost like the engine has to overcome the brakes.

deltabronco · Oct 26, 2016

I had the same problem. Aftermarket brake booster kit and oem disk/ drum brakes. I never could get it right so i ended up replacing the gm mastercylinder with a Ford master. Problem solved.

Hydroboost brakes dragging

pcf_mark

Bronco Guru

Deano

Bronco Guru

ransil

Bronco Guru

englewoodcowboy

Lick Creek Restorations

Broncobowsher

Total hack

charlie6976

Full Member

pcf_mark

Bronco Guru

Broncobowsher

Total hack

pcf_mark

Bronco Guru

barronj

Bronco Guru

deltabronco

Bronco Guru

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