TheSamba.com :: View topic - Rear brakes are stronger than front brakes.

Thu Apr 12, 2012 3:56 pm

I've been noticing that my rear brake are stronger than the front. If I slam on the brake it will lock up the back tires. Is there an adjustment to even the pressure between front and back?
I've got drum brakes BTW

Thu Apr 12, 2012 4:16 pm

The only way that could be is if you have larger than stock wheel cylinders in back (which is a good thing), or you have a problem like like internally collapsed flex hoses or contaminated brake linings.

Double check all your brakes are functioning then figure out what size wheel cylinders you have. If you have large wheel cylinders in back (like 22.8 mm front Super Beetle) then you could also increase the size of the front wheel cylinders to balance the braking force.

Thu Apr 12, 2012 4:18 pm

on a lite-weight car like a fiberglass buggy, you WANT the rear brakes to lock-up first....if you lock-up the fronts you loose steering control.....what you have is a GOOD thing..!!!

Thu Apr 12, 2012 4:39 pm

I wouldn't recommend that any rear heavy street car be set up so that the back brakes lock first. Your tail lights can pass you in a hurry. It can be difficult to correct fast enough once the spin starts.

VW Beetle brake balance is set by choosing the wheel cylinder sizes. There is no adjustment aside from changing wheel cylinders, though I suppose a proportioning valve could be added. It is common to do something to increase rear braking force with beach buggies. They tend to lock the front wheel way to early.

Thu Apr 12, 2012 5:06 pm

Check your shoe adjustment front and rear. You can fudge the bias a bit with that. Loosen the rear one or two clicks and tighten the fornt the same. You can play around till you get them close. I did this for years autocrossing. Once you put big sticky slicks on both ends of a car it becomes even worse, but I got close. You could also install a bias valve on the rear brake line to reduce some of the brake pressure. Mount it by the shifter and play wiht it somewhere safe till you get a good balance.

brad

Thu Apr 12, 2012 6:32 pm

the rears are stronger on vws because they are rear engined, they have more weight over the rear tires than the fronts. Most cars have alot of the weight over the front there fore the bias up front is stronger

Thu Apr 12, 2012 10:06 pm

I might be the only one who does this, but here's a quick tip for anyone who puts 100 pounds of camping gear on your buggy's roof rack - make sure you leave the wheel cylinders in their stock locations. The front brakes will lock up slightly sooner than the rears under hard braking with the buggy empty, but the bias quickly shifts to the front when you have that much weight up top and it will stop just fine.

Personally, I plan to eventually switch to discs at all four corners and do the bias valve thing Brad mentioned. One setting is for empty, the other for loaded. Another benefit of discs will be I won't have to clean all the dust out of the brakes every few trips!

Lee

EDIT: Although the pan for my Manx is a '72, I converted to Wide 5 brakes so the bias is less than it would be with the stock '72 brakes. That might be why it works pretty well full or empty.

Thu Apr 12, 2012 10:07 pm

clay ford wrote: the rears are stronger on vws

No they're not. Most bugs had 19mm wheel cylinders in front and 17mm in back. Elfrink says the early (circa 1960) Bugs had a 43/57 F/R weight distribution. But with a driver and passenger they'd be closer to 50/50. Put on the brakes and the weight shifts forward more.

Fiberglass bodies are a lot lighter with a lower c.g. so the weight shift under braking is less. With the bigger tires typically used on buggies they need larger rear wheel cylinders than stock bugs.

Thu Apr 12, 2012 10:57 pm

My understanding... (someone will correct me if I'm wrong)

The front wheel cylinders are 22mm in diameter from '58-'77 (USA.) There are 2 different cylinders, '58-'64 and '65-'77. The front brakes for all of these years is 40mm wide.

The rear wheel cylinders are 19mm in diameter from '58-'67 and 17mm from '68-'79 (USA.) There are 3 different wheel cylinders, '58-'64, '65-'67, and '68-'79. There are 2 different width rear brakes, 30mm wide from '58-'67 and 40mm wide from '68-'79.

Wheel cylinders for 30mm brakes will not fit on 40mm brakes, or the other way around. With a '68 up Beetle is should be possible to run 4 front or 4 rear wheel cylinders, instead of 2 of each, to make the brake balance 50/50. 4 rears would result in a shorter than stock pedal movement and more pedal force while 4 fronts would increase pedal travel and decrease pedal effort. It is important to make sure that the pedal doesn't hit the floor with 1 bleeder valve open, because that would defeat the safety enhancement duel circuit braking offers.

Thu Apr 12, 2012 11:08 pm

EVfun, thanks for pointing out the differences in years. I edited my original post above because it does make a difference.

Fri Apr 13, 2012 12:12 am

Thank you so much for all the replies! I'm going to check tomorrow, but I only replaced the rear brake cylinders. Could it be a possibility that the fronts or smaller than the rears, or got the wrong ones?

Fri Apr 13, 2012 5:24 am

If the brakes are 1968 or newer it is possible that you are running rear wheel cylinders up front and front wheel cylinders in back. That would dramatically shift brake balance to the rear. It may cause the rear to lock first, even in a buggy where the rear tires are much larger than the front.

Fri Apr 13, 2012 9:51 am

I would guess this is what needs to be done. slalombuggy wrote: Check your shoe adjustment front and rear. You can fudge the bias a bit with that. Loosen the rear one or two clicks and tighten the fornt the same. You can play around till you get them close..

brad

Fri Apr 13, 2012 10:50 am

EVfun wrote: My understanding... (someone will correct me if I'm wrong)

The front wheel cylinders are 22mm in diameter from '58-'77 (USA.) There are 2 different cylinders, '58-'64 and '65-'77.

The rear wheel cylinders are 19mm in diameter from '58-'67 and 17mm from '68-'79 (USA.) There are 3 different wheel cylinders, '58-'64, '65-'67, and '68-'79. There are 2 different width rear brakes, 30mm wide from '58-'67 and 40mm wide from '68-'79.

Those are just the sizes being substituted/sold by CIP, they aren't the original sizes.

The 22mm fronts and 19mm rear started with the Super Beetle.

First thing Sockles needs to do is check his brakes are all working correctly(bled, no collapsed brake hoses or contaminated shoes.) Then he should check the bore size of his wheel cylinders (it might be cast on the outside, but it might require pulling off a rubber boot and pushing a piston in until he can measure the bore)

To effectively bleed a front brake you sometimes need to unbolt the backing plate and rotate the wheel cylinder to 12 o'clock then with the drum over the shoes, bleed it.