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Hello everyone. I think I may have a problem with my brake booster. I replaced it with a Tuff Stuff Chrome Power Brake, but the brake pedal is very stiff and doesn't brake properly unless I press it hard, even with the engine running. The pedal never touches the floor. I'd appreciate any advice. Thank you.
You bought just the booster?
Or bought booster / master cyl matching combo?
This issue you are having is exactly why some of us stick with the Delco design.
The marriage of both of the above parts is critical. More importantly, the booster rod (end) gap and the master cyl piston has to be precise.
Something tells me your new booster is at a bad angle on the firewall perhaps. Something is binding.
You bought just the booster?
Or bought booster / master cyl matching combo?
This issue you are having is exactly why some of us stick with the Delco design.
The marriage of both of the above parts is critical. More importantly, the booster rod (end) gap and the master cyl piston has to be precise.
Something tells me your new booster is at a bad angle on the firewall perhaps. Something is binding.
I bought this Booster Master matching combo at JEGS. I didn't have the rod tool, so I'm not sure if the length is correct.
Amazon also sells that gap tool, which may be a quicker and less expensive route to Japan.
Are you saying that the pedal feels as if the power brake booster isn't providing the boost -- similar to when the engine is shut off and the vacuum to the brakes is lost? Have you checked the vacuum suckage at the booster hose? When you first start the car with your foot on the brake, does the pedal lower/soften when the engine fires? (BTW, your goal is not to have the pedal touch the floor.)
ブレーキペダルアセンブリには、ダッシュボード下のブースターロッド用の取り付け穴が 2種類ありますか？
ある年もあれば、ない年もありました。[/QUOTE
]
There are two holes for the booster rod on the pedal. It's hard to see, but I took a photo. The booster rod is attached to the lower hole.
Ok. Good job on the photo.
You have two options for brake pedal / booster rod travel distance.
I do not know which hole is needed for your 1971.
One hole may be for std manual brakes.
The other hole for P.B.
Maybe somebody else will chime in to help.
But regardless, you are not using original equipment. That may or may not be a factor.
Another thing, is the Tuff Stuff booster rod adjustable? You can not see if the rod has threads on it unless you remove the master cyl.
Does the instruction book mention adjustable booster rod?
Last edited by HeadsU.P.; Sep 21, 2025 at 10:09 AM.
There are two master cylinder bore sizes
1.0" for manual brakes and 1.25" for power brakes.
There are two height mounting options for the booster rod on the brake pedal under the dash.
The high position is for manual brakes, it gives you more leverage, but also more pedal travel.
The lower position is for the power brakes, it is very stiff unless the booster works.
Your too firm comment sounds to me like no booster function.
Pull the hose from the booster, after the engine was run, and sat a few minutes.
It should still be holding vacuum, or the booster is bad/leaking.
Check the engine vacuum at idle, it needs to be 12"HG or higher for the booster to work well.
If all that seems ok, I would pull the master, and measure the rod depth into the booster.
Something like .010" clearance is the spec.
A lot more and you get no booster / brake action.
Pull the hose on & off, with the engine running, and try the brakes both ways, while stopped, you should feel a big difference.
それから、Tuff Stuffのブースターロッドは調整可能でしょうか？マスターシリンダーを取り外さな い限り、ロッドにネジ山があるかどうかは分かりません。
取扱説明書には調整可能なブースターロッドについて記載されていますか？[/QUOTE
]
I removed the master cylinder and measured it. The rod is not adjustable, can I adjust it on the pedal side?
Sorry, I don't know if there is a threaded adjustment under the dash. Not likely, but just two-hole options to attach the rod.
I know nothing about Tuff Stuff boosters / masters.
I am far from a purist on my C3. In fact, hardly anything left is GM stock.
However, I am a firm believer in Delco parts for the original style brake system.
Buying / installing aftermarket brake system seems to be nothing but a pain in the ***.
They seldom mate-up correctly and seldom bleed properly.
That's true, there are a lot of problems. The booster rod is only a little long, but is it okay to cut or grind it down to adjust it? Sorry for asking so many questions.
That's true, there are a lot of problems. The booster rod is only a little long, but is it okay to cut or grind it down to adjust it? Sorry for asking so many questions.
I still say something is binding. You can grind off some of booster rod length but that is not going to fix the problem.
The reason for the booster rod gap is to make sure the master cyl piston can return to its neutral position (pedal all the way up)
If that gap is too wide, the pedal will travel a bit too far BEFORE engaging the master.
If that gap is too small, the master piston will not allow the calipers / pads to release in their respect bores.
This will result in constant brake pad drag. The pads will never release the rotor.
You will smell them.
You will feel them.
You will wear them out soon.
I prefer a booster rod gap of 1/16 of an inch or less. That is nothing to the pedal but makes a huge difference to the master piston retracting.
I would not grind on that booster rod. Something else is the issue.
If you do grind on the end it must be rounded-off to fit the back of the master cyl perfect. The master piston is concaved.
With the master cyl removed, how does the brake pedal operate? Smooth or stiff?
Have a helper push on the pedal while you observe the rod end at the booster. Is it sticking?
Braking is ineffective
