Struggling with front to rear brake balance

[Grover]

I've been gradually trying to diagnose why I have less-than-stellar braking, basically I have very little initial "bite" and it takes a lot of pedal pressure to get strong braking. I say this in contrast to other 2002's I've driven with the same brake set-up, as well as having a couple of knowledgable 2002 folks drive my car and agree that something just isn't right with the system.

Today I went over to see good 'ol JP at A1, and we did a number of emergency stops. In each one, the rears would lock up, but the fronts never did. In essence, it seems to be coming down to not enough hydraulic pressure to the fronts. JP confirmed that all the hard lines are correctly routed. His initial thought was that I should first try a new master cylinder which I am totally willing to do. However, given they're over $200, I thought I'd put the question out if anyone else has dealt with this successfully. Here's what I've got and the tests I've done.

Volvo Girling calipers up front. Metal Master Pads, braided lines. Ferodo pads on 320 drums in the back. ATE 4000 brake fluid recently put in with a power bleeeder, no bubbles to be seen. Checked the brake booster with a vacuum smoke machine and it holds vacuum solidly. Rear drums have been double and triple cheked for correct adjustments. No fluid leaks anywhere that I can see and I lose no fluid over time from the resrvoir.

Any words of wisdom folks?

[02for2]

It's been my experience that these type of issues are almost always the result of improper bleeding, that there is still some air in the system.

Power Bleeders are great, but many people make the mistake of using too much pressure. Rather than force the air through the system, too much pressure will result in the fluid being forced past the air trapped in the system. Try rebleeding with a very low pressure, say 10PSI.

Also, air likes to rise in a fluid rather than be forced downward through it. Try reverse bleeding them from the bleed nipples up to the MC, again at low pressure. You'll need an assistant with turkey baster and catch can to keep the fluid from overflowing the reservoir.

My bet is that if you do this, your issue will be a thing of the past.

Cheers!

[Lee]

I suggest you fit the same pad compound on both axles to beggin with. MetalMasters are crap and won't offer much bite.

Also, what type of rear cylinder are you using?

[Grover]

Thanks for the input Lee, your recommendation to match pad materials is logical. Considering that you don't like the Metal Masters, do you have any brand in particular you'd recommend. My car is a daily driver; it gets maybe 2 track days per year but I'm inclined just to have a spare set of dedicated pads for those days.

In terms of the rear wheel cylinder, in all honesty I don't know the answer to your question. Is there a part number on there that would be visible, or perhaps any sort of visual cue or measurement that could help me figure this out?

Thanks again.

[kbmb02]

Expanding on Lee's second point...

Be aware the rear cylinders come in different diameters, which can impact front to rear brake bias.

[Lee]

In all honesty, I don't have any good advice on pad selection for that 30 year old caliper. If it is a Volvo Girling caliper, maybe a Volvo vendor would have some good offering.

[TobyB]

Yeah, take the metalbastards out and chuck them at passing cars.

THEN you'll see them make cars stop!

With the Volvo front brakes, you should have an inordinate FRONT bias.

Do the pads first- I have used and really like Textars-

http://www.ips-parts.com/ doesn't look like it'll let me link directly,

but you can figure it out. $30. Bed them before repeating the test.

I use about a set every 2 years on the street car, and that includes quite

a few track days... maybe 15x 20- minute sessions, and there's always

some left when I toss new ones on.

If that doesn't make it all better, then yeah, the master could be pooped.

But you NEED real brake pads anyway, so do that first.

Unless you have the 22mm Bav rear cylinders, you're front- biased,

pressure- wise...

hth,

t

[ingraham]

I witnessed grover's brake fluid flush and bleeding, and I am 110% confident it was done correctly. Given the info in this thread and my knowledge of grover's car, I believe the symptoms point to the front brakes not providing enough torque, and I suggest this is due to insufficient front fluid pressure, low friction in the front pads, incorrect piston diameter in any of three places, or excessive rear brake effectiveness.

In panic stops, the rear brakes aren't contributing much due to weight shift, so the rears locking and the fronts not locking suggest the fronts are ineffective.

The pressures are a function of the MC diameter, front caliper piston diameter, rear cylinder diameter, and proportioning valve.

Mike O'Hara says this about rear brake cylinders: " When you convert to

TII front calipers, you must replace the rear wheel cylinders also to retain

proper brake biasing. 2002's use 15 mm, and TII's use 17 mm wheel cylinders."

I came across the following brake MC part numbers while helping find an alternate MC for a modified Bavaria:

34-31-1-113-656 20.6 mm diameter MC for 2002

34-31-1-120-479 22.2 mm diameter MC for some Bavs

34-31-1-120-478 23.8 mm diameter MC for tii and 2800CS

34-31-1-120-832 23.8 mm diameter MC for some Bavs, E12, and E24

These seem mechanically interchangeable, but some of them require larger grommets for the fluid reservoir hoses. The grommets are 34-31-1-121-911. We used the -832 MC to shorten pedal travel on the Bav.

[TobyB]

I suggest this is due to (1)insufficient front fluid pressure, (2)low friction in the front pads, (3)incorrect piston diameter in any of three places, or (4)excessive rear brake effectiveness.

Just for fun...

1- tied directly, 1:1 with rear pressure. So for this excercise, not a factor.

2- I think we have a winner.

3- you'd have to be way off, but the 22mm rear cylinders WOULD do this.

Masters can't (see 1) and the Volvo caliper only comes one way. It has a

lot of area. I forget how much. It's a LOT.

4- yes, if there were 22's in there (heh) or some fantastic shoe material. I

haven't run across anything with that aggressive a cold bite, but I'm sure

it's out there. Carbotec green worked great IF I kept it cool when I ran

drums on the race car.

Just for fun, of course. I still say start with front pads, then master (if it

lost the front- only cylinder) then attack the rear drums.

t

[Lee]

I would be interested to know the difference in piston size between stock 2002 and Volvo calipers. If the Volvo calipers have smaller pistons, then that explains the bias toward the back. As for the 2002 caliper pistons, my memory seems to remember they are Ø35mm or 36mm. And I am not 100% positive, but I believe the Volvo calipers have bigger 38mm pistons, which should offer more hydraulic pressure to the front pads han a 2002 caliper...

[TobyB]

I have it stuck in my head that they're at least 40mm.

But my notes on that are at home, and I'm at work.

They're quite a bit bigger. And I THINK they're the same

size as the 530 calipers, but again, not swearing this.

t

[Lee]

I have it stuck in my head that they're at least 40mm.

But my notes on that are at home, and I'm at work.

They're quite a bit bigger. And I THINK they're the same

size as the 530 calipers, but again, not swearing this.

t

I believe they are 38mm while the e12 pistons are even bigger at 41mm. The e12 sized pistons require a 23mm MC, while the smaller 35mm 2002 pistons need 21mm MC for proper hydraulic leverage (but hey, everything is a compromise). Anyway, as I mentioned in my first post, start by fitting decent front pads. That will solve your problem.

Lee

[M3M3]

if you have metal master up front and ferrado in the rear, you are automatically shifting bias to the rear with the pads. trash the mm's. try porterfield rs4's up front for street/autox use with the volvo calipers. they actually also make the compound for the 320 and 02 rear drums too. excellent compound! www.porterfield-brakes.com

[Chris_B]

Adding to Curt's excellent post, I believe that E21 320i rear wheel cylinders ~1977 vintage are 19MM (part no. 34211117064) and are a good choice for balancing with tii (and maybe Volvo) calipers. At least, I have the tii front/E21 rear combo on my 02 with no pressure balancing, and the front seem to want to lock up slightly before the rears. BTW, I am running Hawk HPS pads in the front, and they work really well for street applications. Dunno what I have for the rear shoes.

[Grover]

Thanks, as always, folks for the great feedback, this is excellent. As the general consensus seems to be that my current pads stink, I'll at least start there before messing with the MC. I found Textars online, but it doesn't look like there are Porterfield's that are available for the Volvo's Girling calipers. I've heard good things too about the Hawk HPS pads, but these seem like they'd be more track/auto-x focus, no?

If that doesn't fix the problem, I'll give the MC a shot. Either way, I'll report back in the interest of sharing my learning. And again, thanks everyone for the input.