Brake master cylinder Q.

[Hobbz]

Are GQ and GU brake master cylinders interchangeable ?

The problem is that the pedal keeps sinking, it dosent get really firm, so maybe a shot master cylinder ? and i have a spare GQ lying around ...

[jcclures]

I am running a GU master cylinder on my MK Nissan.

[MyGQ]

does it give you better braking? i am thinking of swapping out to a GU master cylinder. if not time to upgrade brakes to GU

[jcclures]

No, I think it is worse than standard. The bigger master cylinder has given me more pedal height but less stopping power, I am going to try to fit the GU power booster this should fix it as they have a double diaphragm booster this will put more power to the brakes.

[nick bj40]

can i ask wat size master these gu items are plz and which model are they from and if they are hard to fit or is it easyer to get booster and m/cylinder??

thx and sorry for heaps of questions

[jcclures]

The mq master cylinder is smaller in bore, than some of the gq master cylinders, the easiest way is to measure is to measure the outside. The mq is 32mm and the larger gq is 36mm, from memory the bore is 4 mm larger.

MQ master cylinder



I am going to try to fit a gq power booster as they have a double diaphragm, I should know in a few weeks if they will fit. They are the same diameter but longer in depth.

GQ power booster.

[Mark2]

Dont forget that GQ drum rear m/c's are internally different to disc rear m/c's

[jcclures]

Neither the MK or GQ have a valve to hold pressure on the drum brakes, like some other master cylinders do, the only difference you see visually when you strip the two master cylinders down is the bore size, so I don’t think there should be a problem there.

[CWBYUP]

Dont forget that GQ drum rear m/c's are internally different to disc rear m/c's

How much differance does this make to braking capablity ?

I'm currently doing a Disk rear Swap and wanted to hang out on changing the M/C until I sort out the new body.

Thanks Nick

[jcclures]

I am currently doing a disk swap on the rear as well, this is why I have been trying the different master cylinder, and I would think you need the bigger booster to get the affect of more feel to the brakes.

On its own I have got more pedal but I have to stand on it harder to stop the Nissan. This is the nature of hydraulics the bigger the master cylinder the less leverage you have, the only other option is a longer brake pedal which is not practical.

[Mark2]

Dont forget that GQ drum rear m/c's are internally different to disc rear m/c's

How much differance does this make to braking capablity ?

I'm currently doing a Disk rear Swap and wanted to hang out on changing the M/C until I sort out the new body.

Thanks Nick

I dont know how much difference it makes in practice. They are listed as separate part numbers - I've heard the drum master puts pressure to the rear a little faster to take up slack in the shoes, not sure about this however.