Brakes Not Working

[Guest Ian & Carole]

Did you try nipping all the flexi pipes like I suggested ???

[Dave Ed]

Yeah I did that. It made no difference to the brake pedal and I still get travel when I start the engine

[Guest 2b cruising]

If your pedal is solid when not running, this is correct.

If still solid after running and pumping a few times to empty the vacuum, there is nothing wrong.

Only if your pedal stays soft after switching off and pumping a good few times, is there something wrong.

The servo could be overpowered. 3:1 is considered powerful. The size of the Sierra vacuum chamber seems lots more than 3:1.

The older Jags and other large powerful cars used to run on 4:1

You need someone with the tech info to find the power ratio of the standard Sierra servo.

As long as your pedal stays stiff after standing, on the first pump, and no leaks on the system, the only fault I can bring to mind would be a week flexi pipe swelling under full pressure with the servo.

I doubt this and sugest that you have someone else that is used to the system on there own cars, to compare it with there own.

Is there nobody lives near enough to you from the club.

Also my own pedal is very soft when running and I know I have absolutely no faults with my own system. I have been right through it from end to end replacing needed parts, and replacing all the fluid to higher spec stuff.

[Guest Barry Knowles]

have you bleed forthist away from master to nearest

[Dave Ed]

Barry, I've bled front then back as described in the Haynes manual.

 

2B, I've thought about bulging hoses so will have to get the wife involved again.

I work shifts including weekends so getting a second opinion or a house call isn't easy.

 

The mot tester said due to the travel on the pedal it would be a fail and wasn't worth starting the retest.

I think I'll look at a different brand of fluid and see what happens.

[Guest 2b cruising]

If your pedal is stiff and hard without vacuum, disconnect the vac feed to your servo and block it off.

How much travel on your pedal with no vacuum?

If only an inch or two, that is good.

If more but pedal hard when it bites, that is definately adjustment. If this is the cause it can be proved by pumping your pedal quickly.

If the pedal travel gets less, but pedal solid, that's your proof.

If it is bleeding, there is no way that your pedal can possibly be hard. Pump up to a higher bite point yes, but solid no.

Is your mechanical link between pedal and m/cyl adjustable, some are, some aren't.

If pedal Two stages can be felt when taking up free travel, you have room for adjusting the travel. It means your link rod is moving too much without contacting the piston.

In no situation do you want the rod putting pressure on the piston before the brake is pressed, this would give you brake bind.

As I say just disconnect it for test, or take elsewhere.

Show the examiner the lack of travel without vacuum, and that the travel is purely due to the vacuum assist.

My pedal like yours has loads of travel when engine running.

Ps. Fluid brand should not make any difference to pedal travel.

No matter how thin or thick, no fluid is compressible. Hence soggy pedal when air in the system. Only reason for different fluids is boiling point. That's to stop air getting in when boiling, not in your case.

These are physical facts. Same as solid pedal when air free under normal pressure.

Just had a quick blimp. Are your drums ok. If week they can stretch out of shape or when cracked.

Did you wind up the drum self adjusters. This is also a must.

If your drums have a lip stopping your drum coming off.

If so, just grind the lip only off. Then expand your shoes by the self adjuster, easy done but take care not to overdo.

After adjustment and with drum Bach on, pump your pedal a few times to centralise the shoes then go through the same adjustment again. The less air gap between shoe and drum the less free travel.

Most importantly test your drums for cracks or stretching out of shape when brakes applied when engine running.

Edited July 21, 2015 by 2b cruising

[Guest 2b cruising]

Sorry for pestering but if drums and all else ok, a bigger bore m/cyl will do the job.

If you are on multi piston discs, this leads to greater area to fill with your m/cyl also. Same cure required.

[Dave Ed]

OK cheers 2B, i will start from the top and work down, thanks for all your input

Dave

[Longboarder]

Having re-read the thread I think you have covered almost all the possible faults.

You are sure the callipers are on the correct sides with the bleed nipples at the highest point of the calliper? Can you post a picture of one side?

 

The only other thing I can think of is have you been supplied with the wrong callipers for your set-up? You have 1.6 solid disc donor. Most sierras had vented front discs and those callipers are different although they will bolt on just fine but could give a long pedal and won't work properly. I hope you still have the part numbers so you can do some research online or with your local supplier to check you do have 1.6 solid disc callipers.

 

In your first post you commented 'I can see the front callipers flexing as the pedal is applied so I know there is pressure there'. What bit flexed? I don't think I see any movement when I press the pedal on mine. This is another possible hint that you have the wrong callipers and their alignment is out. I may be barking up the wrong tree however but worth checking.

 

Nigel

Edited July 22, 2015 by Longboarder

[Guest 2b cruising]

Longboards is right. There should be no calipers movement.

If they are not mounted correctly, the calipers mounts will flex to bring the calipers to the same flat plane as the discs are running.

Should have re read the article myself.

Any flexing will give more travel under servo power. You are actually bending metal.

Same effect as damaged drums.

Edited July 22, 2015 by 2b cruising

[Guest 2b cruising]

If only you weren't so far away.

[agent_zed]

As longboarder said the only factor that has changed since perfect brakes is the changing to recon front calipers. So swapping fluid or adjusting rears shouldn't really be part of the solution i would guess. That's not to say it's not worth checking but unless something got disturbed i'd put money on it being an issue with the calipers / airlock. Switching to a new m/c again doesn't seem worth it just yet as your system worked before the caliper change. First double check you have the correct calipers for solid discs.

 

I remember having a stubborn caliper when bleeding which took ages to clear the airlock. I can't quite remember which way round i did it but i either pushed the piston all the way in and then bled them or allowed the piston out a bit further (put something in there to stop it coming out completely).

 

If you have the big sierra pressure reducing valve (the one that cuts the force to the back under heavy braking) on the system then you could have a bit of trapped air in there.

 

I think my flexi hoses move slightly when i put the brakes on but i think that is normal. They aren't bulging just a slight twitch under pressure.

 

Worth bleeding the entire system though as already said. How is the rear split? is it single pipe to rear with a splitter? if so is the splitter level?

 

hth

[Dave Ed]

I'll post some pictures tonight hopefully but it will probably be a couple of days before i can get on it properly.

Cheers guys for all your input so far

Dave

[stevedohc2b]

I think What was the last thing changed /done can only point to wrong calpers supplied.

Richard had problems with so called re con calipers on his sons carfor iva.

 

Stephen

[Dave Ed]

The calipers were CA401's

as far as I can work out they are correct for solid disks for a 1.6