[Mk2] [Turbo] Big brake caliper upgrade, whos done it? im having problems..

[RyanRs]

Just wondering whos upgraded there front calipers and if they have ran into issues with a very spongy pedal, perhaps Master cylinder issues etc?

What i have done is fitted some nissan 300zx alloy 4-pots to the front using some adapters, i replaced all the banjos and washers on the flexi hoses and bled the living life out of them to ensure there is no air (hopefully) in the system, the calipers are in good condition and show no signs of leaking etc. The problem i am having is that the pedal will travel almost all the way to the floor! but upon pumping the pedal it will stiffen up to how it should feel and the brakes will 'appear' to operate as they should (this is what i can tell from driving up and down my street at a slow pace), however it only takes a few seconds of non appliance for the pedal to loose its pump and travel down to the floor again.

When the engine is off, i can pump the pedal up till its solid and it will stay solid, i have also pumped it up (engine on and off) and held pressure on the pedal to see if it gradually looses pressure (MC) but it stays put.

I think the issue might be down to MC vs slave piston ratios? From what i have read on the internet, the piston diameter on the nissan 4-pots is 41.3mm per piston. if my maths are correct then thats a total area of 10720mm (8 pistons,4per side) however im not sure how to work out the stock 2-pot slide calipers as the pistons obv move twice as far for the slide mechanism...?

Has anyone come across this problem before? could they shed some light on whats wrong and what needs to be done?

Btw, does it matter if i bleed the brakes with the car facing uphill? i did it on a bit of a slope tbh, using the traditional method of 2-people 'nipple open, pedal down, nipple shut, pedal up' routine..

Thanks

[raptor95GTS]

there are a few folks using the 300zx calipers and none have reported your issues. The fact the brakes pump up then fade through non use is a worry. Does the level of brake fluid in the system get lower and have you checked for vacuum leaks in the assist mechanism?

Why did you change the calipers, what issues did you have before? I dont think uphill or downhill matters when bleeding brakes though obv for checking levels it's far more accurate if the car is on level ground

[slipping clutch]

I dont know if this will help you or not BUT here goes - when I changed my rev 1 front brakes over to hispec four pots after bleeding everything numerous times I still had a spongy brake pedal. I swopped over to a rev 3 master cylinder AND balance valve a the problem was cured - if you do a search some where on here I did a basic write up. Hope this helps a little.

[RyanRs]

The brake fluid level does not drop as if there is a leak, however whether it moves whilst pumping the pedal i will have to check. I did try bleeding the brakes with a large 100ml syringe to start with and i did discover that if i was to fill the syringe with fluid then inject it back through the calliper nipple, i could get the fluid reservoir to fill up bottom first.. Is this supposed to happen?? I don't think there is anything wrong with the servo system as the pedal will pump stiff on any car with the engine off.

Slipping Clutch - I just read through prob all your brake upgrade related posts that i could find and it seems i am subject to the same problem that you was having! The brakes do work but the pedal travel is just far too long! However, I could not find your write up anywhere? Also, my car is already a Rev3 so the rev3 brakes and MC are my OEM parts for me. I guess if i was to upgrade the MC i would need a 1" 4-runner MC, however if there are people running nissan 4-pots on rev2~3 MC's without any problem, then obv i want to be sure i dont have a fault anywhere.

[raptor95GTS]

the pedal should work the same way every time, my point was yours appears not to behave the same way on each pedal push. IE you pump up the pedal with the engine running and thenn if you dont use the brakes the pedal falls away. I use Porsche callipers up front on mine though their 36/40mm pistons and my pedal travels same distance everytime and certainly doesn't go to the floor

[tarmac terrorist]

I run 8 pots on my Ryan solid pedal & it's a rev2 if you have no leaks sounds more like air in the system

[RyanRs]

Might be so nick, we did bleed them for a hell of a long time tho! the fluid coming out of the nipple was clearly the new stuff that we was putting in the reservoir!

Can anyone tell me if this is the correct 1" master cylinder that i need?

http://www.ebay.co.uk/itm/brake-master- ... 41606ad709

[raptor95GTS]

thats a non abs model and I'm sure the pipes come out the other side by I could be wrong

[RyanRs]

Mines non ABS... so im guessing its correct? the seller has emailed me with 1" bore and the bolt spacing on the 4 bolts that attach to the servo are 75mm horiz and 45mm vert.

[raptor95GTS]

best get your ruler out and measure your own Looks ok going by other mr2 units I seen (non ABS)

[RyanRs]

Ok, update. I've upgraded to a 1" MC off a Hilux, had 3 of us bleeding the system through (one on the brake pedal, one tapping and topping up the reservoir & me on the nipples ) I now have brakes again!! however it seems i don't have much of a 'bite', ie i cant really feel the pads contact the disc through the pedal, instead it feels almost like a mega excessive case of MC flex!
I also find the front wheels are bloomin easy to lock up now! i can hold my left foot on the brake while my right is on the throttle and drive down the road with the front wheels locked!

I have noticed two things tho that could be contributing to the lack of bite feel. There is quite a lot of firewall / MC flex which i know can be fixed with a brace and the second is that if i remove the front wheels and get someone to step on the brake with some force, i have noticed that the calipers 'Flex' ?! i dont know if this is normal or what but its prob not helping the situation. Are ally calipers known to flex?

[raptor95GTS]

i doubt you'll be seeing the caliper flex, sure two piece calipers will flex more than monoblocs but in the real world of road driving I doubt it makes a difference far less be able to see it. If you could see it flex then I'd imagine the seals in the calipers would be leaking all over the place. Again can you really see the firewall flexing? Are you sure all the bracket bolts are done up properly and biting ok?

The lack of feel is I think because the bigger the MC the more force required to move it the same distance however more fluid being move means shorter pedal travel and you'll likely need to adjust your foots sensitivity to get it working smoothly.

[djpkins]

if you open the bonnet and stand on the brakes you'll see that the firewall bends like it's made from paper...I developed a brake cylinder stopper which cured this and fitted as a bolt on to an existing location...but no-one showed an interest, so I sacked the idea...I and a couple of mates have them, and they'te pukka, really effective...I believe you can buy a similar product now on ebay for around £35, looks like a load of pipes but it doesn't really take much to stop it from flexing...doesn't affect the abs or owt either.

[RyanRs]

djpkins - thats exactly the flex im talking about with the firewall, the flex has always been there but because i had a good feel and bite on the pedal i never see it as a priority item to sort out.

The calipers however i am 100% sure i can see flexing! infact, it was one of my friends that was helping with the bleeding process that noticed it. however, its quite hard to judge how its flexing as it almost seems like its moving on the hub mountings but i cannot get my head in there to see for sure...

[djpkins]

I know 2 people who have used the nissan 4 pots...gazrev1tubby on here has them and I have some ready to stick on aswell...the only thing I can suggest is that the brackets may be at fault...this seems like a "sucking eggs" question but...are you sure that the right size and thread bolts were used to attach the calipers?

[Leakie Tbar]

The fact that the pedal creeps when engine is off is normal ,

I answered you thread on the OC you need a hilux master cylinder

[djpkins]

I had a wilwood kit...that didn't need any different master cylinder...nor did my mate who had the Hi-spec kit.

[RyanRs]

Leakie - i have a 1" hilux MC on there now, fitted it on sat, 2 posts ago!

the bracket i am using is one of gazrev1tubby's items and it seems to fit / line up perfectly. The caliper falls bang in the middle of the disc and its not crooked in either horiz or vert axis. Even the pads align perfectly with the wear line outer inner edge on the disc that was made by the rev3 calipers.

someone on the usa OC has suggested i check the caliper bridge bolts are tight so i shall do that, and i think the brake MC flex stopper is prob going to be a must.

[djpkins]

yep...there's nowt wrong with gaz's car...one of my special stoppers on it's way to you old chap.

[Driftlimits Performance]

Go through your bleeding technique for us, that may be where you fault lies!