Brake Booster Response Time comparison and remedy/modification

K

kreibach

Veteran Member
Joined
Feb 18, 2005
Location
Wichita, KS
TDI
sold my 03 :-(
My Jetta brakes work great. They're in stock config. no issues. My desire is to get my 2003 suburban to work like that. Specifically the time between when you slam on the brakes and when they are at max braking is short in the Jetta and Looong in the chevy. Love this forum for my Jetta. I wish there was one like if for chevy. I've replaced the booster with no change. I haven't replaced anything else yet. But they've always worked like that along with most Chevy's I've known.

Online research is unfruitful on this topic perhaps due to the complexity or liability involved. It appears to be an OEM specialty that only they will touch.

I find this from section 5.2.1 of Brake Design and Safety (3rd Edition) ISBN 978-0-7680-3438-7:
The booster response time should be less than 0.1 second to reach the saturation point in the event of a rapid brake application with pedal travel rates at 1 m/s (3 ft/s).

The Jetta seems like it achieves that. The Chevy takes a painfully long time. In emergency braking I'm doing a leg press on the pedal while the pedal takes it's sweet time to go down to max braking no matter how hard I press.

Any pointers to anything anywhere?
 
USMCFieldMP

USMCFieldMP

Veteran Member
Joined
Jun 30, 2011
Location
Fort Worth, TX
TDI
2014 Jetta TDI
I don't think this is a brake booster problem, but have you checked to make sure the brake booster vacuum line is flowing well and sealed properly? What pads are you using and have you changed the pads previously? Are the slider pins on the calipers properly lubricated? When was the last time that the fluid was flushed?

I had a similar problem when I first got my MK6 TDI and again now on my S5, although not nearly as bad. On the TDI, it felt like I had to stand on the brake pedal to get the thing to stop in an emergency. The TDI's problem was cured when I swapped the rotors (ECS blanks), put in more aggressive pads (Hawk HPS 5.0's), and flushed the fluid (ATE Typ 200). I seem to recall installing TyrolSport's caliper stiffening kit at the same time. Braked fantastically after that - good enough for me to trust it late braking at a track day (got a point-by from a Spec Miata and rode the ass through the corners of a newer 3-series on sub-200TW tires), along with multiple autocross events, again beating much sportier/faster cars.

Also, I find it hard to believe that you can't find a good Chevy forum. I know there are good truck forums out there; maybe not Suburban specific, but there's a ton of GM forums out there.
 
K

kreibach

Veteran Member
Joined
Feb 18, 2005
Location
Wichita, KS
TDI
sold my 03 :-(
Yea, there are chevy forums, but none as amazing as this for TDI's. They just don't feel like home. And I was curious about other TDI/chevy owners thoughts.

So many Chevy's I've driven over the years have a similar bad pedal feel and thus I assumed it was design differences. But, you are right, it could be a problem in a different component and i'm not thru troubleshooting them all. In my mind I'm contemplating what would contribute to the slow response time.

Here's what I've done:
- vacuum tests good. New booster didn't respond significantly faster than the original so it probably wasn't bad and follows the OEM design (which I wonder about and don't want to open up a chevy and VW booster to investigate. Too expensive and risky. But I wish someone would do this).

- I installed new pads (Raybestos ceramic) and rotors (Raybestos cheap rotors) in 2011. I didn't affect the response time. It's time for new pads and rotors. Caliper sliders probably haven't been touched since 2011 but it's low miles, garaged, and no indication of a problem. I'll definitely service them when I do new pads/rotors, or I'll get new calipers.

- Fluid replacement has been neglected so I sucked new fluid into the front calipers last week. I broke off the siezed bleeders from both the aluminum alloy rear calipers, so I need new rear calipers.

- Hoses are OEM. They could need replacement, but I'd expect them to go bad not all 4 corners at once and there's no sign of an imbalance. Perhaps I should replace them anyway.

- Master cyl is original.

There is an upgrade talked about to install 07 tahoe front rotors (and calipers) because they are 13" dia instead of 12" dia. But I'd need to buy 17" wheels instead of my 16". That addresses stopping power (and is expensive), but not response time.
 
Last edited:
Vince Waldon

Vince Waldon

Top Post Dawg
Joined
Apr 25, 2009
Location
Edmonton AB Canada
TDI
2001 ALH Jetta, 2003 ALH Wagon, 2005 BEW Wagon
One thought, for someone who seems to take the thoughtful approach: have you done a back-of-the-envelope comparison between the two systems in terms of chassis weight vs. available "brake-feet" (just made that up)... by this I mean surface area of the pads X the distance of the pads to the center of the wheel.

I'm thinking of this 'cause as I understand it you have a butt-braking-dyno feeling that your Jetta stops faster than your Chevy... might be interested to postulate how apples-to-oranges the comparison is, from the broad strokes of the two configurations.

If one system is much heavier than the other, or has much more (brake pad surface area X leverage ) perhaps it's too apples-to-oranges to be instructive.
 
K

KrashDH

Top Post Dawg
Joined
Dec 22, 2013
Location
Washington
TDI
2002 Golf
kreibach said:
Yea, there are chevy forums, but none as amazing as this for TDI's. They just don't feel like home. And I was curious about other TDI/chevy owners thoughts.

So many Chevy's I've driven over the years have a similar bad pedal feel and thus I assumed it was design differences. But, you are right, it could be a problem in a different component and i'm not thru troubleshooting them all. In my mind I'm contemplating what would contribute to the slow response time.

Here's what I've done:
- vacuum tests good. New booster didn't respond significantly faster than the original so it probably wasn't bad and follows the OEM design (which I wonder about and don't want to open up a chevy and VW booster to investigate. Too expensive and risky. But I wish someone would do this).

- I installed new pads (Raybestos ceramic) and rotors (Raybestos cheap rotors) in 2011. I didn't affect the response time. It's time for new pads and rotors. Caliper sliders probably haven't been touched since 2011 but it's low miles, garaged, and no indication of a problem. I'll definitely service them when I do new pads/rotors, or I'll get new calipers.

- Fluid replacement has been neglected so I sucked new fluid into the front calipers last week. I broke off the siezed bleeders from both the aluminum alloy rear calipers, so I need new rear calipers.

- Hoses are OEM. They could need replacement, but I'd expect them to go bad not all 4 corners at once and there's no sign of an imbalance. Perhaps I should replace them anyway.

- Master cyl is original.

There is an upgrade talked about to install 07 tahoe front rotors (and calipers) because they are 13" dia instead of 12" dia. But I'd need to buy 17" wheels instead of my 16". That addresses stopping power (and is expensive), but not response time.
Click to expand...
Slide pins are good to check but if there isn't any uneven wear, they're probably ok. You'll know right away if they are working correctly or not as you should be able to move the caliper by hand on the slide pins.

Fluid FLUSH would be a must. All 4 corners, all new fluid. Fluid collects moisture, moisture ruins internal components, causes rusting which can seize pistons, which leads to uneven wear also.

When the calipers are off check the pistons for good actuation. They should easily pump out with the pedal (don't go too far) and a C clamp or piston tool should press them back in without much grief. If they're really hard to push back in, then it's time for a caliper rebuild, or if you don't want to do that, new calipers.

Rubber components (hoses) over time deteriorate and start to "bulge" basically. This can give you a soft pedal feel.

Finally, properly bedding in your brakes is critical when you get new brakes and rotors. Fail to do this and the braking system will never feel good.

I usually start with a few 45mph-->15mph brisk slow downs, but ensure to never come to a complete stop (roll out of the 15mph zone). Then I'll do a few HARD stops (Ie as fast as you can safely) from about 55-60--->10mph or so, but like above, make sure that you are still rolling. Don't come to a complete stop while bedding. The goal is to "deposit" the pad material onto the rotor. It also helps to wet sand the pad before you install it. I use isopropyl alcohol for the "wet".

I have a 2500 Cummins and I use the same procedures for both for bedding in the brakes. I actually think the brakes on my truck feel more "grabby" then the ones on my Golf. Both are good systems though.
 
K

kreibach

Veteran Member
Joined
Feb 18, 2005
Location
Wichita, KS
TDI
sold my 03 :-(
Calculating sounds fun (nerd glasses on). But this era of chevy brakes have a reputation for being inadequate so I'm sure without calculating anything that the braking performance is subpar. It can be remedied by larger rotors and/or higher friction pads, which I would like to do at some level. But the response time? That's a different problem dealing with flow rates and restrictions of the air in the booster and hydraulic fluids through the whole system.
 
B

befarrer

Well-known member
Joined
Apr 17, 2020
Location
Edmonton, AB
TDI
05 Golf
I had a 04 Tahoe, same problem, crap brakes, slow response, long pedal travel. Our Tahoe had the Hydroboost brakes, not the vacuum booster. I tried everything to make them work better. One large change was to get the brake booster pushrod freeplay set. The pushrod was not adjustable, and measuring it out, the booster kept the master cylinder from fully returning, I added some thin washers to space the master cylinder away from the booster, and it firmed up the pedal, but did not help with feel. I ended up accepting that its a badly designed brake system. Around town, my rear rotors were always alot hotter than the fronts, but on the highway, I could coast to a stop, and all 4 rotors are ambient temperature, so no brakes are dragging, rear calipers were new too. This tells me the rear brakes are doing most of the stopping around town. Doing a panic stop on the highway, the front brakes ended up getting hotter than the rear. I read about lots of people online with this platform having to replace the rear pads 2-3X more often than the fronts, which also adds to my hypothesis, so I put it up that the GM's from that era had brake bias more to the rear on normal driving, which would reduce nose diving when stopping I guess.
 
K

kreibach

Veteran Member
Joined
Feb 18, 2005
Location
Wichita, KS
TDI
sold my 03 :-(
Instead of trying to tinker with it, I gave up on it and converted my suburban to hydroboost. Night and day difference. Instant and powerful. problems solved.
 
You must log in or register to reply here.
Top