Brake Pedal Feel/Bite with Volvo/VW Rear Disc

[backtrail69]

A few years ago I installed the Volvo "BBK" and a VW rear disc update. I never felt like the braking was to my satisfaction. The pedal feel always felt like it had too much throw and not a lot of bite unless I really mashed on the pedal.  

 

I want to know what the community would think would be the next best steps to improve feel and bite. The things I have thought of but haven't tried is different pads (good recommendation for street pads would be appreciated), New Brake booster and Pedal Rod Adjustments. I also use a motive pressure bleeder and have run tons of fluid through the system making sure there is no air. 

 

Front:

Volvo 240 turbo Girling Calipers

E21 Hubs

77 320i vented rotors

SS Braided Lines

Bosch Ceramic pads

 

Rear:

Mk2 GTI Rear Calipers

VW rabbit front rotors

SS Braided Lines

Bosch Ceramic pads

 

Master Cylinder:

E12 528i

 

Edited June 3, 2020 by backtrail69

[chargin]

I'm running almost the same except a Tii Booster and master cylinder, I'm very happy with the feel and throw as well as stopping power. 

I sourced all of it from Ireland and the installs were relatively painless, the rears took a lot of bleeding to get really good 

 

 

[jireland2002]

I have the same setup on a race car.  Peddle travel before solid engagement is maybe 3/8" to 1/2"

 

Assuming the parking brake is working -- Engage the parking brake and test the brake feel with engine running.  Does it feel different/better?  If so the issue is in the rear.   If not the issue may be the linkage from the peddle box to the booster.

[Son of Marty]

Are you removing the rear calipers when bleeding? If not the bleed port is on the bottom and you'l never get all the air out.

[backtrail69]

4 hours ago, jireland2002 said:

I have the same setup on a race car.  Peddle travel before solid engagement is maybe 3/8" to 1/2"

 

Assuming the parking brake is working -- Engage the parking brake and test the brake feel with engine running.  Does it feel different/better?  If so the issue is in the rear.   If not the issue may be the linkage from the peddle box to the booster.

 

I will have to give that a try. The parking brake does work. 

 

 

3 hours ago, Son of Marty said:

Are you removing the rear calipers when bleeding? If not the bleed port is on the bottom and you'l never get all the air out.

 

Yes, I removed the calipers to bleed. 

[Senna27]

On 6/3/2020 at 10:46 AM, backtrail69 said:

The things I have thought of but haven't tried is different pads (good recommendation for street pads would be appreciated.)

 

 

I've used several types of pads over the years and have never been happy with them. Problems included, squealing, not great pedal feel and dust. I hate the dust. Then I tried Porterfield AP108 R4-S pads. They are nothing short of amazing. Great stopping power, quiet as can be and best of all, virtually dust free. I have tii front struts and brakes up front and drums in the rear. 

www.porterfield-brakes.com

 

This is how dirty my front wheels were after a track day, that included 50-60 laps and an hour's drive to and from the track.

 

Edited June 4, 2020 by Senna27

[Senna27]

23 hours ago, chargin said:

I'm running almost the same except a Tii Booster and master cylinder, I'm very happy with the feel and throw as well as stopping power. 

I sourced all of it from Ireland and the installs were relatively painless, the rears took a lot of bleeding to get really good. 

 

 

 

 

 

FYI. Ireland no longer sells tii boosters. They will still rebuild them if you send them one. That's what I did last month.

[M3M3]

1 hour ago, Senna27 said:

Then I tried Porterfield AP108 R4-S pads

Bingo.  Outstanding choice for a fun street car!!!

[Son of Marty]

The tii booster will not give you anymore braking power than a regular one just more clearance for carbs etc.

Edited June 4, 2020 by Son of Marty

[Senna27]

2 minutes ago, Son of Marty said:

The tii booster will not give you anymore breaking power than a regular one just more clearance for carbs etc.

Which is exactly why I bought one. ?

[kbmb02]

9 minutes ago, Son of Marty said:

The tii booster will not give you anymore breaking power than a regular one just more clearance for carbs etc.

 

You sure about that? (then again, what is "braking power" ...?)

 

I say this because my local brake specialist/rebuilder likes the Tii units, in that they are dual diaphragm (which I believe results in more surface area -> more 'assist power').

 

Anyway, @TobyB will know the facts and theory. And/or will have an opinion.  - because he's like that. -KB

[Senna27]

54 minutes ago, kbmb02 said:

 

You sure about that? (then again, what is "braking power" ...?)

 

I say this because my local brake specialist/rebuilder likes the Tii units, in that they are dual diaphragm (which I believe results in more surface area -> more 'assist power').

 

Anyway, @TobyB will know the facts and theory. And/or will have an opinion.  - because he's like that. -KB

Interesting. I’m swapping out a non-tii booster to a freshly rebuilt tii one to make room for twin 45 DCOE Webers. Other than everything remains the same, so I’ll be able to tell If there’s any difference in pedal feel. 

[Son of Marty]

From the ate literature I've read, and it's not easy or straight forward,  the t 51 on the booster is the amount of  mechanical advantage the unit provides and does not call out the specific booster type, both 02 units and many others in a great number of sizes and shapes all carry a t 51 destination. I could be wrong as I said ate's technical papers makes weber's documentation  look perfectly organised. 

[TobyB]

Quote

Anyway, @TobyB will know the facts and theory. And/or will have an opinion.  - because he's like that. -KB

 

oh, great, nobody told me I was 'that guy', because...

 

...because you never tell 'that guy' he's 'that guy'.

 

I had a tii booster once, and traded it to Bill S for something more fun. 

I forget what, now.

But it was fun.

Never looked at its guts.  

 

As to uninspired pedal, I'd suggest, kinda in order:

 

Brake pads.  Textar are great for the street, moderately dusty, and can even do track days.

 

Bleed it again.  I know, I know...

 

Change brake fluid.  Castrol GTLMA, ATE blue/gold, something like that.

 

Slot the calipers and let them sit lower.  That lip that wears into them causes

a bit of overretraction, and a bit of taper.  Not a lot, but a little.  Getting rid of the

lip helped pedal feel for me.

 

Try the stock 20.6mm master.  I know, that makes no sense, but try it.

Try taking the residual pressure valve out of the back circuit, or gutting it.

 

Rebuild the calipers with name- brand kits.  The seals can over- retract, too.

 

Make sure the brake pedal doesn't exert any pressure on the booster,

and that the booster isn't holding the master slightly forward.

 

...things to try, if you're bored.

 

t

that guy.

 

[kbmb02]

1 hour ago, TobyB said:

oh, great, nobody told me I was 'that guy', because...

...because you never tell 'that guy' he's 'that guy'.

t

that guy.

 

 

It was a compliment to your knowledge, T @TobyB.

 

From a guy who’d walk into his Dad’s shop as a youngster and hear several folks say, “hey, there he is” (what stories they’d heard I did not know). -KB