C3500 Almost No Brake Pedal.

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

1ton-o-fun

Automotive Durability Tester
Joined
Aug 30, 2020
Messages
1,602
Reaction score
4,496
Location
Louisville, Kentucky
My '93 C3500. Master cylinder fluid level is fine. No visible leaks anywhere there, or the wheels, or on the ground. It's been hot and sunny this month, so I've been driving it daily. Last week, I noticed I have about half the brake pedal (no resistance for about half of the pedal travel before brake activation). This week there's almost no pedal at all (about an inch and a half from the floor). Now it's parked until I get it fixed.
Normally I would suspect the master cylinder. But this is my first experience with hydroboost. Any thoughts?
 

Pinger

I'm Awesome
Joined
Mar 10, 2020
Messages
3,013
Reaction score
5,935
Location
Scotland.
Things I have done on my C2500 to get a proper 'pedal'.

Replaced rear wheel cylinders. They hide their leaks well but consensus is as well as leaking outwards they'll draw air in leading to mushy pedal.
Adjusted rear shoes - big difference. Everything said about 'long pedals' being solved by adjusting the rears is true.
Freed up the sliding of the calipers.
New flexible hoses - no difference to pedal but didn't hurt to replace them.
New master cylinder.
New PAS (thus HydroBoost) fluid.
Bleeding associated with above work - unavoidable.

I'd focus on the first three of the above. Changing master cylinder and fretting about the HydroBoost changed nothing for the better on mine.
 

HotrodZ06

GMT400 Collector
Supporting Member
Joined
Apr 30, 2016
Messages
172
Reaction score
217
Location
Lake Texoma
My first thought would be the abs unit being master cylinder seems fine. Usually can verify by by blocking lines starting at the master cyl and working towards the wheels to see where the pedal starts getting soft.
 

Frank Enstein

Best. Day. EVER!
Joined
Jul 15, 2018
Messages
2,005
Reaction score
3,431
Location
Canton, Ohio
Things I have done on my C2500 to get a proper 'pedal'.

Replaced rear wheel cylinders. They hide their leaks well but consensus is as well as leaking outwards they'll draw air in leading to mushy pedal.
Adjusted rear shoes - big difference. Everything said about 'long pedals' being solved by adjusting the rears is true.
Freed up the sliding of the calipers.
New flexible hoses - no difference to pedal but didn't hurt to replace them.
New master cylinder.
New PAS (thus HydroBoost) fluid.
Bleeding associated with above work - unavoidable.

I'd focus on the first three of the above. Changing master cylinder and fretting about the HydroBoost changed nothing for the better on mine.
^^^^^^ What he said.

The rear drum self adjusters rarely work properly. As far as adjusting the brakes this is how I do it;
1) Adjust the rears until you feel drag.
2) Depress the brake pedal firmly a few times (this centers the shoes).
3) Repeat steps 1 and 2 until there is a slight drag when you spin the rear tires.
4) Loosen the adjusters until there is no drag.
This will require you to push the self adjuster lever away from the star wheel while turning the adjusters.

In my opinion this is the first thing I would do because it's fast, easy, free, and the most likely reason for your truck's symptoms.

Using Earl's Solo Bleed bleeder screws and braided flexible brake hoses are the first brake upgrade I do.
 

HotWheelsBurban

Gotta have 4 doors..... Rawhide, TOTY 2023!
Joined
Sep 18, 2019
Messages
9,685
Reaction score
17,568
Location
Houston, Texas
Have you checked the power steering fluid level? If that is low, and there's no leaks around the lines or fittings, the internal seals may be going. There's a weep hole at the base of the hydro boost unit, and when the seals go bad, it'll be freshly wet under there. But also look at the master cylinder and wheel cylinders, they could be bad too.
 
Top