6.5 Master Cylinder 7200# VS 8600#?

[pgguru]

Does any one know the
difference
between these two master cylinders and if its worth an upgrade. I have changed my calipers to 8600# and they looked Identical.
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[Burning oil]

Might be a rear disc brake MC. I would stick with the MC that matches the type brakes you have. The size of the piston in the MC would be different for disc vs drum brakes

 

[THEFERMANATOR]

What brake code do you have? JD? The brakes are sized according to there own code, not according to GVWR. If you have a hydro-boost, then it should be the same one IIRC anyways.

 

[nobby]

Brakes are sized by their own RPO code however this is then based on GVWR.

JD5 - 6400#
JD6 - 7200#
JD7 - 8400#

Vin codes 5 digit
E 6001# - 7000#
F 7001# - 8000#
G 8001# - 9000#

As I understand it the calipers are the same body with different bore diameters. Funnily enough in my experience the generics supply the same caliper part number for both only Delco does the 3400 in a 75mm and 80mm. I have know idea what bore size the generics went with.

One thing you do have to be careful with as I discovered on mine is that the pads are sized differently as the rotors are a smaller diameter for the JD6 (11.57" x 1.25") spec however the smaller JD6 pad will fit on the JD7 (12.5" x 1.26") rotor still but you will not be using the full radius amount of the rotor. When I did my pads the ones I was supplied were bigger than I what I was taking off. Further investigation at the parts store lead me to the above explanation.

As to the Master Cylinder question my GM manual does not discuss any differences other than the fact that Diesels are Hydroboost. So I do not know if they are different in bore size etc.

Oh yeah if you are looking for better braking then I highly recommend the TSB that changes the combination valve for suburbans made the world of difference to mine. As far as I am concerned my rears were not doing diddly squat for braking before the change.
TSB# 99-05-24-001A
http://www.dieselplace.com/forum/showthread.php?t=231646&highlight=brake+tsb

Cheers
Nobby

 

[OregonHorseTug]

Might be a rear disc brake MC. I would stick with the MC that matches the type brakes you have. The size of the piston in the MC would be different for disc vs drum brakes

I've got 8600 GVW and drums on the rear (RPO code: JD7 8400# brakes); 11" drums I think.

 

[SnowDrift]

I'm not sure you would stand to gain anything by installing a larger master cylinder. Your system will only draw so much fluid, anyhow.

 

[just a number]

I think it' more of a concern of not having enough to do the job. larger bores require more fluid.

 

[pgguru]

That is what I was thinking. I lager Boar would mean less peddle travel...?

I had a 2.2 Turbo Daytona with a Master Cylinder from a Caravan and you had to clench your teeth to keep your fillings in when you hit the brakes.

 

[just a number]

you might get the same amount of pedal travel, but not the same amount of fluid going to the brakes.

 

[bk95td]

Brake hydraulica are a deicate balance of displacement and pressure.I wouldn't mess with it. If you want better brakes upgrade the pads/shoes and rotors.