part number on one tone master cylinder??

[colonel mustard]

good morning all

my master cylinder on my 81 k5 is shot. I have a 14 bolt rear with jb6 rear disk conversion and 3/4 ton 10 bolt front. I'm thinking I would like to upgrade to a 1 ton MC.

1. does anyone have the part number

2. is it truly a direct swap?

3. any tips?

thanks in advance

 

[Keith Seymore]

My '81 brake chart is at home; I've got the 85 part numbers in front me.

85 K10 w JB5 = 18013434. JB6 is the same.

85 K30 w JB8 = 14066425.

I hate to be Debbie Downer but probably not a direct swap. The light duty master cylinders are the aluminum base with the plastic reservoir; the one tons are cast iron.

That doesn't sound like much but the aluminum ones probably have the "quick take up" feature, which means the diameter where they fit to the booster will be different (ie, larger). Also - the rear port of the aluminum cylinder may be the port connected to the front system, whereas on the cast unit the front port might be the one that goes to the front system. Again - not a show stopper but just something to be on the lookout for.

There are a million ways for a master cylinder to "not" fit: internal bore diameter, external bore diameter, QTU vs non QTU; inboard outlets vs outboard outlets, English threads vs ISO threads to name a few. Back when I was a brake development engineer I decided I wanted to try an alum/plastic m/c to replace the cast iron unit on my Chevelle. I couldn't come up with one I liked, even with all of GM at my disposal. I finally went back to the production cast iron unit.

Bottom line: you are really not going to know for sure till you try it, particularly relative to pedal "feel" (travel vs force, initial onset of braking).

K

 

[CSFJ]

How common were the one ton trucks without hydroboost?

 

[colonel mustard]

My '81 brake chart is at home; I've got the 85 part numbers in front me.

85 K10 w JB5 = 18013434. JB6 is the same.

85 K30 w JB8 = 14066425.

I hate to be Debbie Downer but probably not a direct swap. The light duty master cylinders are the aluminum base with the plastic reservoir; the one tons are cast iron.

That doesn't sound like much but the aluminum ones probably have the "quick take up" feature, which means the diameter where they fit to the booster will be different (ie, larger). Also - the rear port of the aluminum cylinder may be the port connected to the front system, whereas on the cast unit the front port might be the one that goes to the front system. Again - not a show stopper but just something to be on the lookout for.

There are a million ways for a master cylinder to "not" fit: internal bore diameter, external bore diameter, QTU vs non QTU; inboard outlets vs outboard outlets, English threads vs ISO threads to name a few. Back when I was a brake development engineer I decided I wanted to try an alum/plastic m/c to replace the cast iron unit on my Chevelle. I couldn't come up with one I liked, even with all of GM at my disposal. I finally went back to the production cast iron unit.

Bottom line: you are really not going to know for sure till you try it, particularly relative to pedal "feel" (travel vs force, initial onset of braking).

K

thanks...everything I have rear is that it is a direct bolt on upgrade. will be trying this week

 

[Keith Seymore]

How common were the one ton trucks without hydroboost?

None common.

All one tons were hydraboost in this timeframe, but the code remains JB8.

'87 brake release chart shown for reference:

You must be registered for see images attach

 

[Keith Seymore]

thanks...everything I have rear is that it is a direct bolt on upgrade. will be trying this week

Yep - the parts will probably bolt right up. That doesn't necessarily mean it is "tuned" for what you are trying to do.

K

 

[CSFJ]

None common.

All one tons were hydraboost in this timeframe, but the code remains JB8.

'87 brake release chart shown for reference:

You must be registered for see images attach

Yeah, I was trying to recall if I'd ever run across one, but kept coming up blank.

 

[Dougnsalem]

How common were the one ton trucks without hydroboost?

Yeah, I was trying to recall if I'd ever run across one, but kept coming up blank.

Good question. I don't really recall seeing one without the hydroboost either. Got me wondering though....

 

[Frankenchevy]

Yeah, I was trying to recall if I'd ever run across one, but kept coming up blank.

I believe @Craig 85 ’s truck is vac booster

 

[nvrenuf]

I used a master cylinder from a '99 C3500, this is supposed to be a vacuum disc/disc application. Worked great on my '91 vacuum booster.

 

[Termite_Delight]

good morning all

my master cylinder on my 81 k5 is shot. I have a 14 bolt rear with jb6 rear disk conversion and 3/4 ton 10 bolt front. I'm thinking I would like to upgrade to a 1 ton MC.

1. does anyone have the part number

2. is it truly a direct swap?

3. any tips?

thanks in advance

When you upgraded to disk on the 14 bolt did you add a residual check valve ?
I think it's 2lb for disk and 10lb for drums.

 

[colonel mustard]

When you upgraded to disk on the 14 bolt did you add a residual check valve ?
I think it's 2lb for disk and 10lb for drums.

no I sure didn't. I have actually never heard of these...reading about them now. does anyone have at real world experience with them?

 

[Craig 85]

I believe @Craig 85 ’s truck is vac booster

My truck is hydro boost. You may be thinking of my last truck I did the axle swap on. Inline tube may be able to help on this topic.

https://www.inlinetube.com/

 

[Keith Seymore]

Good question. I don't really recall seeing one without the hydroboost either. Got me wondering though....

None common.

All one tons were hydraboost in this timeframe, but the code remains JB8.

'87 brake release chart shown for reference:

You must be registered for see images attach

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