big master cylinder

[cyrus_the_great]

hi,

i had some problems with rear line pressure , auto part store sent this MS to me but it dosnt fit on the booster and fitting pressure line is unlike to stock one ... bore is 40mm



i think it 's for 90s b bodies ..caprice,impala... i wanna know can i use caprice booster on my GP ? or is there anyway to put this MS on my gp booster?

 

[Bonnewagon]

Hi Cyrus. That MS looks totally different from our cars. You can use any MS that will bolt up and has the same fitting size. I have used a 1980 Firebird cast iron MS as well as B body MS. Sometimes the front/rear reservoirs are reversed and you need to bend the lines to match up. Be carefull of bore size. A smaller bore will reduce pedal effort, but increase pedal travel. A larger bore will increase pedal effort, but decrease pedal travel. I try and use the largest bore I can get, anything one inch or better. That 40mm is huge- too bad it doesn't bolt up. Did you try RockAuto? Big selection like this one. --DORMAN Part # M39376 {#18009816, 18011916, 18013429}
Bore: 24 mm or 36 mm

$31.79 $0.00 $31.79

 

[cyrus_the_great]

Hi Cyrus. That MS looks totally different from our cars. You can use any MS that will bolt up and has the same fitting size. I have used a 1980 Firebird cast iron MS as well as B body MS. Sometimes the front/rear reservoirs are reversed and you need to bend the lines to match up. Be carefull of bore size. A smaller bore will reduce pedal effort, but increase pedal travel. A larger bore will increase pedal effort, but decrease pedal travel. I try and use the largest bore I can get, anything one inch or better. That 40mm is huge- too bad it doesn't bolt up. Did you try RockAuto? Big selection like this one. --DORMAN Part # M39376 {#18009816, 18011916, 18013429}
Bore: 24 mm or 36 mm

$31.79 $0.00 $31.79

hey bonne, i am talking about part store in Iran it 's hard to get parts from rockauto ... part store said i need to have 90s caprice booster to use this MS and that will result better brake power , bolt position is same as our gbody boosters but that center hole of booster is alittle small

anyway i did b body spindle and brake calipers swap before

 

[Bonnewagon]

OK, so are you saying the B body MS doesn't fit the B booster? I know it is a tight fit and has a rubber cup that seals it up. It "should" fit, no? Then will the booster mount to your firewall? If so, great, as a 40mm bore is HUGE for our cars. Are the brake line fittings the same? Or metric? Double flare, or ISO? And remember, a very large bore will result in very little pedal travel, but a big increase in pedal effort. That should not be a problem with a power booster, but a booster has a spring inside to add some "feel" to the pedal. Otherwise the booster would jam the brakes so hard your head would go through the windshield, like the old power boosted drum brake cars did. So even with a booster, using a bigger bore will seem like the pedal needs more effort to apply the brakes because the booster is calibrated for the car it is on. Also-"i had some problems with rear line pressure" that could be the combination proportioning/limiting valve. It limits pressure to the rear brakes and proportions pressure between the front and rear so you get even braking. Did you test pressure at the rear line? Try testing at the MS. A huge difference in pressures may be the valve, which is usually located on the frame just below the firewall.

 

[cyrus_the_great]

first of all i should say problem about my stock master cylinder was weak pressure on rear line +leaking from rear end of master cylinder and i tried to fix it two times and i v replaced MS internal parts and i had the problem yet .. so i decide to replace the MS totally .

in answer to your question i should say
1.my brake booster is stock and mounted on firewall ,yes this 40mm MS can not seat on booster and center hole of booster is small
2.brake line fittings are not metric on new 40mm MS and i can see a code under MS >> B1-TVS

 

[Bonnewagon]

Leaking, understood. Won't bolt to booster, understood. So you must either get the B booster or the proper MS. I'm guessing Iran is under sanctions and no one will ship to you?

 

[cyrus_the_great]

Leaking, understood. Won't bolt to booster, understood. So you must either get the B booster or the proper MS. I'm guessing Iran is under sanctions and no one will ship to you?

i can find these kind of parts in Iran i bought this 40mm MS brand new for 20$ anyway front line fitting is 1/2 and rear 9/16

 

[Bonnewagon]

Yes, those are the normal sizes. $20 is a great price!

 

[cyrus_the_great]

that 's the problem i am talking about ...

 

[Bonnewagon]

The one on the left looks new.