Brake balancing

[ecurb.renots]

I have got involved, as you do, with a neighbours R4 1983 GTL which has recently been CT tested in France and had brake results of

Front left 169
Front right 127
Rear left 139
Rear right 106

Overall efficiency 71% and handbrake 25%

We have changed discs and pads at the front and freed off a sticky caliper so expect that the front will now be okay. The back brakes appear good with wheel cylinders free, not leaking and good linings so i am assuming the difference must be down to adjustment. It is fitted with Bendix brakes. However i had expected that the auto adjusters whould adjust them evenly in which case what would explain the 139 to 106 difference.

Also does the difference front to back look about right. Sorry to ask if it was my car i would just fiddle until i was happy but with someone else car i feel under more pressure to know its right and to get it so first time.

Thanks, Bruce

 

[jcarruthers2]

Hi Bruce

Sometimes the auto adjusters don't work and it is a case of manually adjusting them.

Best Regards

 

[angel]

Adjusting the brake shoes does nothing more than decrease brake pedal travel, so if the rest of the system is OK and one or both rear brakes slightly out of ajustment, you won't expect to see any difference in braking performance.
Brake imbalance comes from a number of reasons, like air in one wheel cylinder, lining glazing or oil contamination on one side, differences in drum and/or shoe lining wear, partially seized wheel cylinders, new brake shoes not bedded in (they take a lot of time) etc. Without checking components one by one it's hard to tell, because, for example, what shows like a " set of brake shoes in perfect condition" coud be a mixed set of brake shoes fitted at some point of the vehicle's life.

 

[ecurb.renots]

Adjusting the brake shoes does nothing more than decrease brake pedal travel, so if the rest of the system is OK and one or both rear brakes slightly out of ajustment, you won't expect to see any difference in braking performance.
Brake imbalance comes from a number of reasons, like air in one wheel cylinder, lining glazing or oil contamination on one side, differences in drum and/or shoe lining wear, partially seized wheel cylinders, new brake shoes not bedded in (they take a lot of time) etc. Without checking components one by one it's hard to tell, because, for example, what shows like a " set of brake shoes in perfect condition" coud be a mixed set of brake shoes fitted at some point of the vehicle's life.

That is always the problem of playing with someone elses toy, not knowing any past history or wanting to suggest swapping too many components. As you suggest i just need to work thorough them all until the problem is located. I will admit to having not considered a mixed set of brake shoes.

 

[mr-reno-139]

R4 rears can use different bore size cylinders which look externally identical
Had this before on parts suppied by customer

 

[orsome]

Hi Guys,
Had problem with brake lights, took off master brake cylinder switch, it was dead , succeeded to order new one and put it in.
I added some new brake fluid and tried to bleed all corners many times.Did not manage to get the pedal as hard as earlier on.
I got new brake shoes all around and in two corners also new slave cylinders.I guess the shoes are quite right adjusted because brake housing wheel gives some resistance when rotated with wrench.
so what to do, is there some special trick you must do when changing a new switch?? at least now the brake lights lighten up easily.

 

[orsome]

i took a look at old queries;

I have been using a vacuum bleeder for some years and it beats the pressure bleeder that I had been using (eezibleed) everywhere. I coat the threads of each nipple with PTFE tape before commencing bleeding. It works wonders, no vacuum leak from the threads.
Mojo, try to find an assistant and bleed the following way: tell him/her to pump the pedal three or four times then hold it depressed. Then open the nipple just for a second, close it, then tell the assistant to release the pedal. Do this 2-3 times at each wheel,starting with the front ones, then the rear ones, then the master cylinder nipple.
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.. i think i do not have this in my R4 from 1977 master?
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and the following;
This bleed nipple is to bleed the pressure drop indicator circuit (a separate small piston). Without doing this you will never get rid of all the air. You have to first bleed the four wheels just like you did, then bleed this circuit, then possibly go over the system once again, but always ending with this nipple.
There is no point "bench bleeding" the master cylinder, as air will enter the lines again when putting the master cylinder back on the car. Plus, with a full master cylinder and fluid leaking all over the place, it will be a hassle to connect back all four brake lines.
If you don't have an assistant pressure or even better vacuum bleeding works great when you have to fill the whole system from dry.
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does this mean that i have to open/close (like bleeding the slave cylinders) the indicator screw (because there is no separate bleeding screw) to get rid of any air there might be left after the switch change???

 

[angel]

All of the above apply for the later dual circuit master cylinder, as your car has an hydraulic brake switch it's the earlier type, so don't look for a fifth bleed nipple.
You are right, there must be air trapped at the end of the master cylinder. I would try what you have thought about using the switch as a bleed nipple. To avoid drawing more air in the circuit, have an assistant press the brake pedal firmly, loosen brake switch 1/4 to 1/2 turn - no more - until pedal goes to floor, tighten switch THEN release pedal. No more than two tries should be necessary, if not, try bleeding the system from the wheels once again.
It's quite normal for this switch to bleed itself, either after leaving the car for 2-3 days, or after a short drive.

 

[orsome]

Hi Angel,

as you mention it seem to have some kind of self bleeding feature, leaving not even for overnight but for few hours only and pedal get somewhat harder, i'll enclose a photo of my cylinder hereto. Certainly i will try to bleed the head cylinder with loosing some the switch, i asked yesterday help from my 20y son but he was all evening busy with his computer play

 

[orsome]

Hi Angel,

as you mention it seem to have some kind of self bleeding feature, leaving not even for overnight but for few hours only and pedal get somewhat harder, i'll enclose a photo of my cylinder hereto. Certainly i will try to bleed the head cylinder with loosing some the switch, i asked yesterday help from my 20y son but he was all evening busy with his computer play

**bleeding of the switch did not help any(did twice)

 

[mr-reno-139]

If you can't now Bleed It using conventional or possibly a gunson pressure bleed then you've got to start thinking about either clamping off each flexible hose in turn to see if you can locate a problem or accept the master cylinder may have not like to being disturbed by being bled as if the internal bore of the cylinder is rusty the rubber seals would never normally get disturbed by pushing the pedal that far down so a new cylinder may be the best solution