Which Wildwood Master Cylinder Model Number for Fiero (Page 2/3)
fieroguru SEP 26, 07:09 AM
It is apparent I need to further explain what a Quick take up master does...

The Fiero masters have a stepped bore (two separate bore sizes) where the larger bore is only used to move the caliper pads to the rotors.
Once the pads make contact there is a pressure bypass on the large bore and the smaller bore takes over for actual braking pressure.
The smaller bore is then the source for all brake pressure through the system - not the larger one.
This was done to allow the pads to retract further from the rotors for fuel economy.
You can use a quick take up master with almost any caliper.
However, using a standard bore master on calipers designed for the quick take up master will have more dead pedal as the smaller master bore will be the only thing moving the pads to the rotor and it will take more travel than the larger bore would.

So if you have an 84-87 and looking for a non-stepped master from another supplier, you would need the 1" diameter one.
However, doing this will result in more dead pedal travel as you will eliminate the quick take up feature.
Going to a larger bore would reduce the dead pedal travel some, but at the expense of brake line pressure and result in less braking force, making the conversion a brake downgrade.

fierogt28 SEP 26, 07:27 AM
The 84-87 Raybestos bore diameter size is 26.400mm.

But the Centric brand MC says the bore is 25.4mm = 1”.

I can’t confirm because I never measured these 2 MC to actually see it.

These measurements are listed on RockAuto website.

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fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.

Dennis LaGrua SEP 26, 08:25 AM
Hard to figure out. I got that new piston assembly out of a Raybestos box and the measurements are shown here in this thread.. The last MC that I replaced was AC Delco. marked USA but who knows? Have had good luck with Chinese Centric products so may go with that next time. All the major brands are Chinese made. Its just strange that a large US company like Wilwood cannot recommend a direct replacement. If the replacement had a 1.43" bore it may work OK. With the S-10 brake booster you would probably not notice much difference in pedal feel.

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olejoedad SEP 26, 09:28 AM
While I appreciate the effort to buy American made products where possible, in this case it seems like one would be better of buying a quality rebuilt master cylinder that is designed for the car.
Signupacct SEP 26, 01:11 PM
Yes I wish I could change the wording on this thread becuase I am becoming less enthusiastic on the Wilwood simply becuase they will not issue out a parts compatibility recommendation on the fiero.

Well as for remans I been to that rodeo and got the t shirt. In another post I mentioned that if the cars were just 5 or 7 or even 10 years old then a reman unit is likely not entirely worn and a rebuilding can make more sense. But over time as the units are used the surfaces wear and then rebuiding takes even more to smooth out and thus less likely to be a reliable option. Especially now that some oem units are almost 40 years old. And the core charge attracts all kinds of candidate for the reman process and the reman factory is more oriented to GET ANOTHER UNIT OUT THE DOOR kind of thing.

SOOOO! then what is the highest on the pecking order for new units. Made in the USA OEM specs. Ok let's go there. First Made in the USA: not a guarantee that any NEW unit will be made in USA and so then next down from there is Mexico and then from there China. Why USA is likely best choice, because they are more likely to appreciate what the product promises to be, an OEM replacement and likely to have the OEM specs and not have a language barrier to interpreting it. Then why Mexico over China, well some just over the border manuafacturing still has US oversight, more so then China with a language barrier.Everything is a crap shoot these days but these are my thoughts so far.

[This message has been edited by Signupacct (edited 09-26-2024).]

Signupacct SEP 26, 01:35 PM
fierogt28 you are on my Christmas card list.

I finally can see at least what the specs are for the bore size on the RockAuto website. Though I have not been able to find any OEM documentation that specifies that OEM is 1 inch.

But the preponderance of the evidence in that most of the units listed at Rock Auto are 1.0

Raybestos, AC Delco and Centric all list as 1.0 inch

the NM1988 which is Duralast which I have here is 1.4 inch. It goes back to Autozone.

It is listed as NM1988 by FVP and DFC and Quality Built are all listing at Rock Auto as 1.4 inch

I would like to make a post of this in a titled thread since this seems to be the best answer to the this question.

thanks again

BTW i reached out to Rock Auto by email with these question related to this and got the brush off.

But that's ok because at least their website lists the diameter and others that I have seen do not.

Joe k

[This message has been edited by Signupacct (edited 09-26-2024).]

Signupacct SEP 27, 11:58 AM

quote
Originally posted by fieroguru:

It is apparent I need to further explain what a Quick take up master does...

The Fiero masters have a stepped bore (two separate bore sizes) where the larger bore is only used to move the caliper pads to the rotors.
Once the pads make contact there is a pressure bypass on the large bore and the smaller bore takes over for actual braking pressure.
The smaller bore is then the source for all brake pressure through the system - not the larger one.
This was done to allow the pads to retract further from the rotors for fuel economy.
You can use a quick take up master with almost any caliper.
However, using a standard bore master on calipers designed for the quick take up master will have more dead pedal as the smaller master bore will be the only thing moving the pads to the rotor and it will take more travel than the larger bore would.

So if you have an 84-87 and looking for a non-stepped master from another supplier, you would need the 1" diameter one.
However, doing this will result in more dead pedal travel as you will eliminate the quick take up feature.
Going to a larger bore would reduce the dead pedal travel some, but at the expense of brake line pressure and result in less braking force, making the conversion a brake downgrade.




dont know why my browser is just now showing your post and that's ok

thank you for your explanation.

So after reviewing the specs on the Rock Auto site as I noted which say 1.0 for some units and which say 1.4 for other units and noting the Raybestos cited 1.0 in the description I received my Raybestos and when I opened it I noted that the diameter of the unit is 1.4 mm

So Im guessing that 1.4 is the measurement at the top of the piston and then further into the unit it is 1.0 and that is what counts ?

I am now figuring out how to get to ogre's cave to find data there.


Joe k

[This message has been edited by Signupacct (edited 09-27-2024).]

fieroguru SEP 27, 05:38 PM

quote
Originally posted by Signupacct:

So Im guessing that 1.4 is the measurement at the top of the piston and then further into the unit it is 1.0 and that is what counts ?




All Fiero masters have 2 bore diameters.
The 36mm (or 1.4") is the diameter of the quick take up bore and this has nothing to do with brake pressure, it is for pad movement only.
https://fierocave.shorturl.com/index.htm

For the 84-87, the smaller bore is 1" and this what what actually provides the brake pressure. This is confirmed with the chart on this page:
https://fierocave.shorturl.com/index.htm

On the 88 Fieros this smaller bore is 15/16".

Wilwood does not offer any master cylinders with the quick take-up stepped bore setup, so they can't offer a stock replacement for the Fiero without it having some type of negative performance (more dead pedal travel or less overall braking force).

If I needed one for an 84-87, I would buy this one:
https://www.summitracing.co...odel/fiero/year/1987

[This message has been edited by fieroguru (edited 09-27-2024).]

pmbrunelle SEP 27, 05:59 PM

quote
Originally posted by fieroguru:
calipers designed for the quick take up master



According to my understanding, basically all calipers use square seals.

Would a low-drag caliper have a seal with a larger square section?
fieroguru SEP 27, 06:35 PM

quote
Originally posted by pmbrunelle:


According to my understanding, basically all calipers use square seals.

Would a low-drag caliper have a seal with a larger square section?



My understanding is that the seal surface on the piston is the same, but the seal surface within the caliper is more of a wedge shape with a little more clearance along the sides.
http://www.remaninc.com/pdfs/lowdragcalipers.pdf