Upgraded brakes, now I have issues. :(

[shelldrake]

Hey Guys,

So, here's the deal -

I was running the "$250 brake upgrade" - mx62 calipers, ra60 discs for the fronts. Standard t-series drum brake rear end, with a 1" Camry master cylinder. Standard ta22 brake booster. Standard fixed bias valve.

It was a pretty good setup - The bias was definitely towards the front brakes, but otherwise was a nice firm pedal feel.

6 months later after a few changes I have now got an r31 disc brake rear end. A wilwood adjustable bias valve, the same mx62 fronts. When bleeding the system we pushed through a fair bit of fluid to flush the system (It was looking a bit dirty). The pedal feel seems to fade on the first push(Firms at the very bottom). If you pump the pedal, the second pump feels firmer(and how I would expect it to feel).

There are no visible leaks near connections or calipers... I thought it may have been a master cylinder issue so I bought another camry master cylinder from a wrecker, bled it indivually, then the system but it felt the same as the first...

It feels like there is air in the system, but there's no bubbles from the nipples when bleeding...

I should also mention when I set up the rear calipers on the diff it was more convenient, and appeared correct, to mount them upside down (opposite to how they were originally setup), I'm not 100 % certain that this is not the issue - But I would have expected any air to be forced out by now...

Any help much appreciated...

[thechuckster]

do the rear calipers have the bleed valve at the top (e.g. above the pressure line)? if not, then you'll never bleed them.

[frostyadonis]

ed,
why cant you swap calipers left to right.

[lexsmaz]

Air will go to the highest point in the calliper which means it will be trapped in the top section of the upside down callipers & as has been said there is no way you will ever get all the air out ..

Also did you change the M/cyl to a rear disc M/cyl set up when you changed it ? as a drum rear end M/cyl will have a restricter in the outlet line to keep slight residual pressure in the line to keep tension / pressure on the cylinder cups etc & if you dont take out the restricter or change the m/cyl the rear brakes will drag on when hot ..

[Hen]

You can't mount calipers upside-down (generally). As chuck says, this puts the bleed nipple at the bottom of the caliper and so an air pocket can form in behind the piston which you will never get out.

Incidentally when I made this mistake I had the exact same syptoms you've described.

[pandaah]

ive never had a problem at work with bleeders up the top, and i just let them drip bleed...

sounds like your master cylinder is on the way out...

try this before hand, open up all the bleeders with a tray underneath EACH bleeder where it drips fluid.. and let the fluid drip for long enough to put a bottle through the reservior... tighten them all up, see if the pedal feels better... if not sounds like the seals in your master cylinder have failed from you bleeding the brakes and pressing the pedal all the way to the floor... (really you should only let it go down an inch or two when the bleeder is cracked)

[thechuckster]

pandaah: you'll always have an air-pocket, it'll compress unlike the fluid, the moisture in it combined with the absorbed water in the brake fluid will encourage corrosion, and your calipers will never work effectively.

You can buy a simple pump-thru bleeder from most auto parts store - they're just a one-way valve in a tube.

shelldrake: which order did you bleed the brakes? you should always start at the caliper furthest from the master cyl.

[shelldrake]

Hey Guys,

Appreciate the responses. When I bled the brakes I went rear p/s, then d/s, front p/s then d/s. I was using a one man bleeder kit.

if not sounds like the seals in your master cylinder have failed from you bleeding the brakes and pressing the pedal all the way to the floor... (really you should only let it go down an inch or two when the bleeder is cracked)

I suspect this may be the case. Someone explained the logic to me that with a master cylinder that's getting on a bit, perhaps pushing the piston in all the way when bleeding an empty system may compromise the seal by sliding the piston into a previously not used portion. (Most likely crusty)

If you look at the pics below you'll see the position of the bleeder. I was also thinking of removing the calipers(jamming some wood where the disc should be), then try to bleed again. (You'll see the nipple is actually at the higher side of the caliper)

[pandaah]

yeh your right bout the crustly portion of the master cylinder bore...

like i said, try drip bleed it.. if that doesnt work master cylinder = fail.. like i said mate, ive NEVER had a problem with an upwards facing bleed nipple at work, NEVER

[twentyEight]

You can buy a simple pump-thru bleeder from most auto parts store - they're just a one-way valve in a tube.

Ed should already have one of these lying around, as I gave him one...

Ed, have you gotten rid of all your old brake fluid in the system? That is to say, since taking it out on track, have you given it a full fluid flush? I'm probably not giving you any new information, but brake fluid will go off if taken past the boiling point, and will be almost as useless as water if not replaced in it's entirety.

[Hen]

ive NEVER had a problem with an upwards facing bleed nipple

That's exactly it. The bleed nipple has to be at the top of the caliper. You get problems if the bleeder is low in the caliper.

It's hard to tell from those pictures, but if you can post a bigger shot of the bleed nipple and calipers while mounted in the car it'd help.

[twentyEight]

It's hard to tell from those pictures, but if you can post a bigger shot of the bleed nipple and calipers while mounted in the car it'd help.

I completely agree Ben, it's hard to tell, but it does look like the bleed nipples (whilst facing upwards) are on the lower half of the caliper from those pics.

[shelldrake]

Fair call. Some good points to look at. Thanks guys.

[fade-e]

mate looking at that diff pic, when it is placed correctly the nipple is definitely facing downwards... as mentioned before, swap the calipers over and that should solve that issue easily. then bleed and should be all good

cheers

["Z" UTE]

Tweety suffered a similar problem after a Wakefield track day. Problem was traced to balooning rubber hoses on the front brakes. Replaced with braided line and all came good.

Removing the caliper, to position the bleed nipple at highest point, and blocking piston movement with a piece of wood clamped in position is the way to go, if you can not swap them over. Not ideal, but will solve the bleeding problem in the iterim until you sort out the correct mounting.

cheers Chuck.