Master cyl piston diameters.....

[mrvette]

When rebuilding the motor home some few years ago, I put in a new master cylinder, one for a large truck, this rig is only a gvw of 8000 lbs according to GM on the door sticker....

I went with a 1 5/16ths diameter master cyl....trick is, even with Hydro Boost on it, the pedal pressure is excessive.....I can do more travel....but the question is....what is the specific difference if going to a say next size down m/c??? thing that is strange is I had a larger/truck m/cyl on the '72 vette when doing the HB converstion, and the thing tossed my nose into the wheel....

so I went with a lesser diameter/stock size m/cyl for the vette, and the brakes have been purrrrrrrrfect since then.....

so question is.....what to do about the MHome excessive pedal pressure....this has to be drivable by a 130 lbs little lady, my wife....which is why the project encompassed tilt wheel, power steering add on, and other tricks.....

 

[SuperBuickGuy]

Trial and error is how I get them - though it normally means I don't need to order a different diameter M/C as I've probably already got one on the shelf.

That said... how's your power steering pump? (belt slipping, worn, etc?) It'd probably be more difficult to do - but you could swap to a smaller diameter pulley

 

[mrvette]

Trial and error is how I get them - though it normally means I don't need to order a different diameter M/C as I've probably already got one on the shelf.

That said... how's your power steering pump? (belt slipping, worn, etc?) It'd probably be more difficult to do - but you could swap to a smaller diameter pulley

P/S pump is a junkyard pull off a similar 350 powered chebby van, and the power steering on the MH is just fine....so I doubt the pump is at fault....

:surrender:

 

[010752]

Smaller dia should give you more stroke and less pedal effort for the same amount of clamp pressure. You can calc the diff if you want.
You can also lower the hole in the pedal arm.

Don't know if this camper came with hydraboost or not, but if it is an add on, be aware there are different boost units for different size trucks and also having the proper 2 port return ps can because you need free flow.
My GMC C3500 (1 ton flatbed) is rated for 12000# has a 1-5/16" master, an 8000# pickup has a 1-1/8" master (big difference).
Your wife could easily drive my 1 ton fully loaded.

Other than booster size, master size, either pump pressure or line restriction are the issue. Check for hose contamination in the steering fluid, same as brake lines.