VT Brake upgrade - Long and Spongy Pedal

[hq-racing]

My car is parked just around the corner from you at Old Noarlunga. It has the VT M/C & booster upgrade - your welcome to come have a squizz if you like.

haha yea right, small world!! yea 2morro would be cool, what time would be cool for you?

[HamaTime™]

Double checked a few things, Calipers are definately on correctly, with bleed nipple at top and hose connected at the bottom. I'm going to wear the pads and rotors in for another couple of 100 k's before I start asking the mechanic, probably one of the only people I reallly trust to do a good job.

So I'm still thinking the problem will be up near the booster/Master Cylinder, somehow related to the pushrod of the VS Booster/the shaft.

Anyone have anything to say????

There are plenty of people on the forum who have done exactly the same upgrade as me....surely someone has a fair idea of where the spongy pedal is being caused and how to fix it or diagnose the real probkem is.

[Commydoor]

they make a 1" master cylinder for VR/VS that bolt straight on so you dont have to change boosters...if you cant solve it just fit up the old booster and bang one of those on...

[HamaTime™]

I've heard about them, but I bought the spacer plate that goes between the Master and Booster from Race Brakes Sydney which solves that problem.....I've still got the stock VS Booster on....and probably going to try and fit up the VT Booster once I get a bracket for it.

[Not_An_Abba_Fan]

When you apply the brakes, does the pedal travel a fair way down first then the brakes seem to grab really hard at the last minute?

[IBLOWN]

Bah ive done the upgrade years ago an never did the master cylinder. The front brakes lock up before the pedal hits the floor. Only thing is because the pedal goes down further the rears would harder than normal. Little bit sketchy slowing down at the drags from 160 or so lol but who does that on the street?

[HamaTime™]

When you apply the brakes, does the pedal travel a fair way down first then the brakes seem to grab really hard at the last minute?

Yep, first 40% of the pedal has no affect. Then they grab but aren't responsive, with the pedal left, it's either just rubbing and barely slowing or almost locking up, but I'm guessing thats to do with the brand new pads and rotors, not even worn in yet. Point being that they aren't responsive, which is what I'm looking for. Not to mention wanting to have brakes right at the top of the pedal.

Bah ive done the upgrade years ago an never did the master cylinder. The front brakes lock up before the pedal hits the floor. Only thing is because the pedal goes down further the rears would harder than normal. Little bit sketchy slowing down at the drags from 160 or so lol but who does that on the street?

So you just did the calipers and kept the VS Booster/Master?

[88GreenVN]

I'm still thinking the booster is not working for you.

[88GreenVN]

haha yea right, small world!! yea 2morro would be cool, what time would be cool for you?

Sorry for the late reply - got side tracked last night. I'm here Monday to Thursday 10 to 4 and every second weekend.

[HamaTime™]

I'm still thinking the booster is not working for you.

Yeah that's what I'm thinking. Did a fair bit of driving on them today. They really are just not performing very well, So I'm going to replace the Booster with the VT one, rather than trouble shoot the VS one...

Just got to get my hands on that bracket from Mark.

[Commydoor]

im like IBLOWN have had my bigger brakes on for a while now and has only 1/2 pedal but it still stops way better than it did and it had quality brakes on it back then...ive only just got a 1" master for it and its still sitting on the bench lol...way things are panning out it sounds like your booster is the next target...

[HamaTime™]

im like IBLOWN have had my bigger brakes on for a while now and has only 1/2 pedal but it still stops way better than it did and it had quality brakes on it back then...ive only just got a 1" master for it and its still sitting on the bench lol...way things are panning out it sounds like your booster is the next target...

So you and IBLOWN just run the larger VT Calipers off the stock VS Booster/Master? The funny thing is though, I've got the VT Master on there at the moment, and it's basically stopping just as bad as it was with the stock VS Single piston calipers on it, with a much smaller pedal threshhold....

This whole thing is just weird!!!!!

So yeah, the VT booster will definately be next target.

[Commydoor]

i got a kit off ebay...330mm front 315mm rear both ventilated discs with PBR twins front and PBR single rear...their VT style but i dont think they are actually VT...am running stock master and booster but ive got ABS too...the pedals 1/2 travel but thats cause the master is 15/16 and why i now have a 1" to go on...if its the same with either booster they are either both crook or thats not your prob...go over it again to be certain...check your hoses aint twisted, rebleed them, check the slides aint rusty and are lubed, make sure the pads are siting in the the clips are sitting properly, were they s/hand calipers?...is one seized in the piston?...what about the hoses themselves if they are soft they might be expanding under pressure...


DOH just reread your post its the master you changed not the booster so disregard my last post...

[HamaTime™]

Well I thought about staying with the VS Booster/Master but I was recommended to use the larger VT/VX Master due to the larger volume of fluid needed to push out the bigger pistons on the VT calipers compared to the VS HSV twin piston brakes (which used the same booster/master, but had smaller pistons, which is why the VE upgrade is now popular because of the smaller pistons you don't have to replace the Booster/Master)...

I was reading this thread

Spongy Brake Pedal after VT Brake Upgrade

And NAAF was giving some advice to a problem which sounds similar to mine, yet this guy hadn't fit a VT master...I have, so that only points to the fact that I must have something wrong with my Booster....or is my 11pm over tired logic playing games on me?

[50LTRv8]

Well I thought about staying with the VS Booster/Master but I was recommended to use the larger VT/VX Master due to the larger volume of fluid needed to push out the bigger pistons on the VT calipers compared to the VS HSV twin piston brakes (which used the same booster/master, but had smaller pistons, which is why the VE upgrade is now popular because of the smaller pistons you don't have to replace the Booster/Master)...

I was reading this thread

Spongy Brake Pedal after VT Brake Upgrade

And NAAF was giving some advice to a problem which sounds similar to mine, yet this guy hadn't fit a VT master...I have, so that only points to the fact that I must have something wrong with my Booster....or is my 11pm over tired logic playing games on me?

Been following this, I think your logic is sound, it is the only thing you havn't changed

[HamaTime™]

Been following this, I think your logic is sound, it is the only thing you havn't changed

Yeah, and considering most other people have had alot of success with this conversion (i.e. using VT Master on VS Booster) so yeah, booster must have basically shit itself, might have been one of the reasons my VS single piston brakes were so shit over the last few months. I'll get my nice shiny new twin diaphragm VX Booster on as soon as I get the bracket

[IBLOWN]

Yep. Just the calipers. The booster and master is stock VS.

[Not_An_Abba_Fan]

Back to my original question about when the brakes react. I think it may be the reaction disk between the pedal and the booster.

[HamaTime™]

Back to my original question about when the brakes react. I think it may be the reaction disk between the pedal and the booster.

Reaction disc? thats the plate in the middle/back of the Booster unit itself isn't it? So what do you think about it? Could be faulty/i.e. Booster is dead?

[HamaTime™]

Ok so I've done a booster check following the guide on this handbook

http://www.autoshop101.com/forms/brake05.pdf

With the motor off, I depress the pedal and it will eventually get higher after about 3 or 4 pushes, i.e. locked right at the top, so you can't push it anywhere. I.e. the pedal reserve distance

I turn the car on and the pedal sinks, i.e. to normal operating levels, still with the same 40-50% 'free' threshold which has no affect i.e. 'long' pedal.

So according to these checks, the booster is fine?????????????

ARGHGHHHHHHHH!!!!!!!!

Well I'm getting the bracket sometime next week I think, so I'll get it put on and we'll see how we go.

[88GreenVN]

Ok so I've done a booster check following the guide on this handbook

http://www.autoshop101.com/forms/brake05.pdf

With the motor off, I depress the pedal and it will eventually get higher after about 3 or 4 pushes, i.e. locked right at the top, so you can't push it anywhere. I.e. the pedal reserve distance

I turn the car on and the pedal sinks, i.e. to normal operating levels, still with the same 40-50% 'free' threshold which has no affect i.e. 'long' pedal.

So according to these checks, the booster is fine?????????????

ARGHGHHHHHHHH!!!!!!!!

Well I'm getting the bracket sometime next week I think, so I'll get it put on and we'll see how we go.

It must be how it's assembled then - all 3 of my upgrade kits went in without issue (from markovr). But if your going to pull it apart (such a pain) may as well fit the VX booster and see if that fixes the issue.

You should have the best peddle feel ever - my VN really does feel better than the VZ........ and the VZ has new pads - same type as in the VN.

[HamaTime™]

Yeah, that is definately the next step. Fit the VX Booster, get the brakes re-bled etc etc. Maybe test the master whilst I'm there. Actually it probably wouldn't be a master issue would it? I don't see how a 'dead' top half of a pedal can be caused by the master....

still has to be related to the booster/pushrod/pedal - somewhere in there..

arghhhhh, I've checked, researched, made calls, posted stuff!!! BRAKES JUST WORK DAMNIT!!!!!! haha

[Not_An_Abba_Fan]

The reaction disc is a small rubber disc that sits between the pedal push rod and the diaphram. If the booster has been removed at all, this can fall off and give the exact symptoms you have.

[HamaTime™]

I'll check that....thanks NAAF

[HamaTime™]

Well Booster bracket is on it's way, so I'll get that installed ASAP!

Also just found out that the Resevoir isn't actually the VS one, it's still the VX one that came with the M/C, so it's sitting on a slight angle. Mechanic said this was because the VS one doesn't bolt straight up....it doesn't...hmm

I'm pretty sure someone told me that Holden make a specified one that will sit flat for a VS onto a VX M/C...Am I correct?

Also, had a look at my VX Booster, how far down should I redrill the hole for the pedal??? anyone got a pic or some rough estimate etc etc...