M1008 Master cylinder / hydroboost verification

[blueblaze]

So I noticed a couple days ago that my master cylinder was leaking from the cover. I was just going to replace the gasket but I figured its 30 years old, time for a new one. Anyways my new master shows up and I notice it's much larger then the one that's on the the truck. After more digging and looking at past pictures of trucks I used to own, I came to the conclusion that I have a totally different master cylinder then my other M1008/M1028 trucks. Then I look at a picture of a Blazer I used to own and it looks identical to the one I have on my current M1008. So as far as I can tell, some one in the services replaced my M1008 master cylinder with one from a Blazer. Also I noticed my K30 cucvs all had "CM" on the hydroboost assembly and this one has "FY" on it. Can someone confirm that all the blazer hydro boost units were of the "FY" variety? If that's the case, then the entire assembly is wrong, not just the master.

 

[porkysplace]

If they are different there should be different part numbers in the parts TM.

 

[joshuak]

 

[blueblaze]

I know the part numbers are different but I can't find the numbers on the booster to verify as such. The only identifier I can find is the "CM" and "FY" stickers on the booster. And I can't find those in any of the TMs to relate too. Hence I'd like to know if everyone with a M1009 has the "FY" setup.

 

[cucvrus]

That is on the attachment plate. I order the boosters for a K5, K10, K20,K30, C10, C20, C30. All the same. I installed many. The remanufactured ones do not come with the mounting plate. And I have used the m1008, M1028 on M1009's in the past with out any adverse conditions. I seen that comic in the PM years ago. I removed one looked it over and switched them on the plow trucks as they died and never NEVER had any issues. I hope that helps. I know there are doubters but if you order one look it over and it does not come with the push rod or sprag spring washer.

 

[blueblaze]

The brakes seem to work fine with how it is. I still can't believe I've been driving this truck for years and years and never noticed this especially when I had 5 of these trucks at one time. I found a couple pictures of M1009 boosters since I posted and they all have the "FY" sticker on the plate so I'm satisfied that someone in the services swapped the whole thing from a Blazer. Luckily the push rod and plate carry the same part numbers for all the cucvs.

 

[Dave Kay]

Can't recall the research I did at the time but I tend to believe that FY are M1009 and CM are M1008; replaced mine (on my M1008 which came marked as FY with a Mil-surplus CM and it gave my brakes a new feel, like less pedal pressure netted better braking feel than before. Seems there is an internal valving difference in these two types. Think about it; 1-ton M1008 weighs 5900lbs and Blazer weighs... 4500 w/6.2. My $.0. ALSO suggest when doing a brake job on these old trucks, replace your rubber brake hoses with braided stainless and you'll feel a marked improvement in braking. Hope that helped.