VH SLX, Would a V8 master cylinder fit on a 6 cylinder braking system

[vc commodore]

I think your problem was caused by the booster having too much pushrod length and after a few applications it was not allowing the cups in the master cylinder to come back far enough to expose ports for the fluid to return to the reservoir...so it sort of like driving with your foot on the brake pedal.
I have found when a booster fails it can cause excessive travel but also then it can also make the brakes slam on right at the floor depending on wear dimensions and tolerances but the problem wont disappear when you try to bleed the master cylinder like you have.

One thing I didn't mention in the original thread was the original booster actually gave me a hard pedal on start up, hence the change to the one in the thread and the insuing problem.

That being said, yes I do understand what you are saying and I actually did some further enquiring about booster interchanging inbetween models, as the one in the thread didn't have an adjuster....So I wasn't limited to a couple of model commodores for another booster and was able to get another to fix the problem....

So I can make the assumption, a failing booster can cause both issues...Both hard and soft pedals?....

 

[vc commodore]

I got the bracket from the wrecker when I got the booster.

I think the different flares on the brake pipes was more due to a change is design, I think series 2 VP? So pre that would be fine?
Someone mentioned the different rod length. That jogged my memory. I can't remember if I was able to adjust the length or if there was something I did by putting something down the hole of the booster?

This goes back 20 years ago, so I'm rusty on the details. I liked the end result. A few years before I sold the car I put VZ brakes on too.

Overall, the job was straight forward to do, not too time consuming and @OP should go for it.

This is true.....Trying to remember back 20 years is difficult....I have trouble remembering back 20 minutes ....I only posted up about my experiences with them, as it was only 12 months or so I went through it all

 

[griezy]

Thanks guys, with all the info, in short if you change the M/C it’s best to change the booster to suit otherwise you have a larger travel in the pedal and feel it’s harder to stop

I’m actually happy with the braking power I already got, I cruise the wagon, it no bat out of hell machine, I just thought to ask if I upgraded it would eliminate the failure each year, (to many close calls) I’m thinking of sticking to what I have now, but what is the better make, (I’ve found four different makes, PBR(but can not find a new one) there’s also protecx and Bosch and IBS which one is the better make?

 

[losh1971]

PBR is the best but it is becoming increasingly hard to find. A mate found me one of the last two remaining PBR MCs for my VR. Once the last one sells there will be only cheap Protex available.

 

[griezy]

Ok, apart from PBR, which I can not find new for the VH, which of the three left are better Bosch - Protex or IBS, which of these three brands are better makes, last three brands i can find new in the standard Master cylinder

Protex: https://www.ebay.com.au/itm/PROTEX-...epid=0&hash=item4b3c5f43f3:g:twwAAOSwbgpase6I

IBS: https://www.ebay.com.au/itm/IBS-Bra...273526?hash=item3a84cf2e76:g:fYIAAOSwsTxXjudX

BOSCH: https://www.ebay.com.au/itm/BOSCH-B...475835&hash=item4655bd7f83:g:SGAAAOSw~2xcfyHe

 

[Vin999]

Really anyone of them will do depending on your budget, they look ok with body, you never know with copies, they probably made at the same chinese factory, hopefully all of them at least use the same pbr important internal seals, chances are they dont make the seals, just the body.

See if your old/new 1 was pbr, if not, don't get that brand you have if it's 1 of the 3.

 

[Vin999]

Happy to be corrected but how can it vary much? I would think the same principle applies? If the MC was identical except bore diam how can a smaller diam one not be higher pressure like it is on a bike? Are the car ones operating in some different way, asides from the booster?

To much info to type about differences BUT just on pressure,
example is when you use say 12mm irrigation pipe on 2 sprinklers you have good pressure and flow, when you add further sprinklers on the line the pressure is the same but can’t deliver enough flow/volume for all the sprinklers to operate properly. So you upscale to 19mm pipe and the pressure is the same as 12mm but you have more volume to add more sprinklers for a bigger area.

Basically same principle on brake conversion. When you add more pots/calipers plus bigger pad/disk area you need bigger volume master cylinder than standard size to handle/fill the load for brakes to work properly. Using a smaller m/c won’t deliver the larger volume needed regardless of pressure that’s why if you go bigger brake system you upscale the m/c and any large enough brake booster is just the feel you add that force of pressure, that’s why you can use the single diaphragm with larger brake conversions over the double diaphragm, just has different pedal feel assist and start of brakes working,

Thats why when people upgrade to VT 4 pot callipers and bigger 298mm disks over the stock early gen 1 car 15/16” m/cyl with standard 2 pot 268mm disks ... they also use the VT 1” m/cyl with the fast fill option to cater for the larger area of pistons, pads n disks, and then use the VS single plastic booster as it fits to VT m/c and to car firewall/pedal without having to modify the metal VT double diaphragm booster brackets or pedal slot.

If they used the smaller m/c (with the vt combo) like your example of the bike m/c there would be issues.

 

[Fu Manchu]

Back in the day, I used to overhaul my own master cylinders with new seals etc and bench bleed them. It’s just what we did. Didn’t go buy new units. Maybe that’s something we have to do to keep the pbr master cylinders?

 

[vc commodore]

Thanks guys, with all the info, in short if you change the M/C it’s best to change the booster to suit otherwise you have a larger travel in the pedal and feel it’s harder to stop

I’m actually happy with the braking power I already got, I cruise the wagon, it no bat out of hell machine, I just thought to ask if I upgraded it would eliminate the failure each year, (to many close calls) I’m thinking of sticking to what I have now, but what is the better make, (I’ve found four different makes, PBR(but can not find a new one) there’s also protecx and Bosch and IBS which one is the better make?

Just change M/C and perhaps get another one recoed properly....ie that is have it resleeved which is done with a stainless steel insert. Yes, gettting it done that way maybe a little more expense than you might have anticipated but if you are keeping the old girl, it's worthwhile

 

[Skylarking]

Back in the day, I used to overhaul my own master cylinders with new seals etc and bench bleed them. It’s just what we did. Didn’t go buy new units. Maybe that’s something we have to do to keep the pbr master cylinders?

And back then there were lots of places that would machine them and insert standard ID stainless steel sleeves into the bore so rust pitting was no longer an issue. Chuck in new seals and all was well again.

But who does such these days (rhetorical)?

(vc commodore posted before I finished typing some posts..)