Problems After Paj Master Cyl Install

[caibs]

so i have a ke38, sr20, just put a r31 diff that i had cut down with new brakes. put in the paj master cylinder at the same time as the diff.

 

the pedal feels very hard and the brakes don't seem to work as well as before.

the rears lock up first when the brakes are stomped on and after a long drive tonight it smells a little like burning.

the front rotors are warm/hot and the rear rotors are very hot.

 

possibly master cyl is cactus ? rears getting boosted alot more than the fronts?

[Jono.C]

What front brakes do you have? Could be rear wheel cylinders

[B.L.Z.BUB]

What brakes up front?

[caibs]

stock ke30 brakes up front. new pads and rotors.

 

stock r31 skyline brakes in the rear (discs) new pads, rotors and calipers.

 

 

i just read this thread on toymods:

http://www.toymods.org.au/forums/tech-conversions/25511-diy-pajero-brake-master-cylinder-upgrade.html

 

i used that exact master cylinder, but used a blanking plug for one of those ports for the front brakes, instead of the telstar banjo fitting. wonder if thats got anything to do with it. wouldnt have thought so.

[LittleRedSpirit]

Fittings and what type will have little impact. Sounds like you failed to reconnect the vac line to the booster, and maybe that you might need to rid the car of the pressure limiting valve in the rear brake system as discs need not have it, but drums would. It would cause locking of the rears. Did you just switch from drum to disc through all this?

[caibs]

Yeah it was drum rear before. Booster VAC line hasn't been touched but it does feel like its unboosted. Where's this valve located ?

[altezzaclub]

You will have to make sure the m'cyl is coming all the way off. The pintle in the front of the booster is usually ajustable to set the 'stop' point of the m'cyl pistons moving back. If they stay a couple of mm too far forward the brakes will go on but not release correctly. Hence the burning smell and hot brakes... the other explanation would be dirty pistons/calipers in the front so the pistons jam forward. Were all these components stripped and cleaned before use?

 

What are the ratios of the front disc piston area, the rear disc pistons and the m'cyl diameter like?? This will set the brake bias initially and if you have a mish-mash of different vehicles you have probably upset it. Pick one vehicle and match those three parameters. Pad area is also a factor but I don't think it is as important.

 

If you can't get the piston areas right then you can fit a brake force limiter in either front or rear line. It sounds like the one in the rear line (if there is one) is incorrect and letting too much force onto the rear pistons so they lock up. They used to be a separate unit down the back, but modern cars have them built into the junction box on the firewall. We used to drill and tap one end of the unit to fit a bolt that held the spring back and gave us adjustable limiting.

[oh what a nissan feeling!]

You need to upgrade the front brakes, the bias will be way off. Small front cylinders and big rear.

 

You also need to check the depth of the factory cylinder where the rod goes in from the booster and compare that to the pajero one. The depth needs to be the same for the booster to work propery.

 

[altezzaclub]

Small front cylinders and big rear

 

Now, I assume that is what is on the car, right?? So it needs larger front pistons or smaller rear, or a limiter to stop pressure building up in the rear.

 

Fronts do 70-80% of the braking so they need to be that much bigger without a limiter.

[LittleRedSpirit]

Is there a one way valve in the vac line to the booster? It is important to trap the vacuum in the booster properly or you goet less assisitance.

 

There is a small piece in the rear brake line on the firewall it may or may not be related to the problem. Disc cars don't have them drum cars do, you can probably just remove it or pull it out and make sure it has no spring and needle valve thats doing odd things to your pressures at the rear.

 

What do they have in an r31? You may need that part installed if there is anything special about the rear brakes on the 31. I'm pretty confident you just remove the mechanism if its there.

[Banjo]

Interesting discussion, as I just fitted a Pajero master cylinder to my KE30 this week, after upgrading the front rotors & calipers to Cressida. I used the same Pajero MC to move more fluid into the larger front caliper pistons. Was your Pajero MC a new one, or a salvaged one ? They are only $ 61.00 on ebay + postage, so a very good idea to use a new one. I did notice, as mentioned in the Toymods link, that there are several different Pajero MCs, with all the same dimensions. The only difference is the out line ports position & style. (Models JB1712, JB1762, JB6069)

 

Here's one with both outlets on the same side.

 

 

The JB1712 model, doesn't need the "banjo" adaptor for the front brake line. I was able to use the existing lines by just bending them around a little, as seen in these before & after pics.

 

Before:

 

 

After:

 

 

I did notice, as Altezzaclub mentioned, that the actuator pin/rod coming out of the booster was adjustable. I used the rear depth guage on a vernier to measure accurately the depth of the MC actuator pin/rod socket to the mounting face of the MC. I then adjusted the actuator pin/rod, so that it stuck out proud of the booster MC mounting face by exactly the same distance. Very important, when you are mixing & matching MCs and boosters.

 

I believe the pressure limiting device on the rear line, is the one on the firewall as in the pic below. The darker slightly bigger one at the bottom.

 

 

I think I'd be getting rid of that, as I believe it is only needed for combo systems where you have disks in the front & drums at the rear. I've retained my rear drums, but am upgrading to the larger 9" KE55 ones, when I fit my BW diff in.

 

It sounds like your car has too much rear braking, with original disks on the front. Like the others have advised, the caliper piston cross sectional areas are probably all wrong.

 

You could try an adjustable pressure limiter on the rear line, and if that doesn't work, upgrade the front brakes to something bigger, so the MC is pumping approximately equal amounts of fluid into front & rear caliper pistons.

 

Let us know how you go.

 

Cheers Banjo

Edited August 8, 2014 by Banjo

[caibs]

these are all some excellent tips. greatly appreciated. some points to note:

 

- mc was a used unit, i didnt realise you could get them new off ebay for so cheap. i will order one now to rule that out.

- i will adjust the booster rod and see how that goes this weekend.

- i have ordered rx7 4 pot calipers on ae86 coilovers which were meant to arrive this week after a month of waiting, i found out yesterday it'll be another fortnight until i see them. not very happy with either communication or service by AJPS so far.

 

i wonder if i should fit my stock MC and see how it goes compared to the pajero one while i wait for it to arrive?

[Banjo]

If you've got the time, it wouldn't hurt. The original MC will be suited to the front, and the rear will get what fluid it gets, which will probably not be enough, but that's what you need, as the rears are so big, compared to the front.

 

If you want to "buzz" off the limiter for the rear end, get a 3 way line adaptor off the front of a KE30-55. The "goldie" coloured one in the photo above, and put a blanking plug in one port.

 

Let us know what effect it has. At least you'll be very good at bleeding after all this is finished !

 

Cheers Banjo

[caibs]

ahaha thanks once again guys.

 

today i cleaned the stock master cyl, it was full of mud and rust, and put it back in with a bit of a bleed.

when i went to bleed the rears, we noticed that the brakes were dragging even without any pressure in the system. turns out the handbrake mechanism had been over adjusted on the new calipers. whether or not it has anything to do with the paj MC being cactus i'm not sure. but it looks like there were a couple of issues at hand.

 

the burning smell turned out to be diff oil leaking from one axle, combined with the rears dragging so hopefully ive remedied that as well, i'm taking it to final drive tomorrow to hopefully sort out the vibration & whine that it has. if its still leaking tomorrow i'll get new seals put on the axle.

 

but once bled, even with the stock MC and the much larger r31 rear discs, it brakes better than it ever has. surprisingly well infact. i can't imagine what it'll be like with the rx7 calipers and new paj MC.

[chestikoph1]

Caibs, the r31 handbrake mechanism is notoriously crap, it's a shit design.

Useless for any comp work.

Most skyline guys upgrade to a commodore caliper instead and run a hydro set up for the handbrake.

Just a heads up though, the hydro will slowly bleed away over prolonged parking and the car will roll away.

I am running Rx7 fronts with 2 sets of caliper on the rears, skyline for foot brake and stock hand brake and commodore for hydro handbrake, with a commodore MC.

With a decent set of pads you will love it.

On a side note stay on to Dave,s back about your gear otherwise it may take another 2 months.

The guy gave me the run around as well.