109 or 88 dual master cylinder?

[busboy]

Fixed it. There are both double flares and DIN flares on a Rover. The DIN flare looks like a mushroom.

I don't remember the master cylinder lines having din flares but it might have and I just didn't pay attention it's close to two years ago and I was in a rush at the time, lol.

[o2batsea]

Honestly I can't recall either whether some of the older MCs have 45 flares as some had adapters. I think it may be that the remote reservoir MCs that have the tin can use 45 double flare at the reservoir fitting and a DIN flare on the MC. It's always best to just go by what is on your truck as it is difficult to make sweeping statement like I did.

[TeriAnn]

I recently had to replace the master cylinder on my 71 2a 88 but couldn't get one in time for a show so I managed to get a new 109, not only did bolt straight in but it works exactly the same as the one I had which was original.

88 dual master cylinders are the same diameter front and rear. 109s had twice the number of front wheel cylinders so the diameter of the master cylinder is larger for the front brake circuit and the same diameter for the rear brake circuit which has the same number of wheel cylinders as the 88.

SO yes a 109 master cylinder will pump plenty for an 88. But the 88 master cylinder will not pump enough volume for the four 109 front wheel cylinders. First pump usually goes to the floor & you need a second or third pump to get brakes on a 109 using an 88 dual master cylinder.

[busboy]

88 dual master cylinders are the same diameter front and rear. 109s had twice the number of front wheel cylinders so the diameter of the master cylinder is larger for the front brake circuit and the same diameter for the rear brake circuit which has the same number of wheel cylinders as the 88.

SO yes a 109 master cylinder will pump plenty for an 88. But the 88 master cylinder will not pump enough volume for the four 109 front wheel cylinders. First pump usually goes to the floor & you need a second or third pump to get brakes on a 109 using an 88 dual master cylinder.

Interesting to note, you would think they would have made one part that would do for all, no wonder they couldn't make money, lol. I just know that a 109 works on my 88.

[SafeAirOne]

Interesting to note, you would think they would have made one part that would do for all, no wonder they couldn't make money, lol. I just know that a 109 works on my 88.

If the bore on the front circuit portion of the 109 MC is a larger diameter than the bore on the rear circuit section, you will be moving more fluid to the front wheel cylinders than the rear cylinders for the same amount of pedal travel, actuating the front brakes before the rear, causing the front shoes to do more of the braking work than the rear.

I'm not saying that's a problem--but I am saying that it's probably happening on your 88 if the MC bores are different. Presuming you don't have the fronts adjusted way out, that is...

[busboy]

If the bore on the front circuit portion of the 109 MC is a larger diameter than the bore on the rear circuit section, you will be moving more fluid to the front wheel cylinders than the rear cylinders for the same amount of pedal travel, actuating the front brakes before the rear, causing the front shoes to do more of the braking work than the rear.

I'm not saying that's a problem--but I am saying that it's probably happening on your 88 if the MC bores are different. Presuming you don't have the fronts adjusted way out, that is...

Yeh I could see it being a problem if it was the rear brakes getting the extra fluid but I think the front can take it. My brakes are like new and adjusted right up, I don't use it very much at hi-way speeds anymore so with no heavy braking they pretty well stay in good adjustment. Sitting thinking about it I did know that the front portion would produce more fluid when I installed it so I remember taking it extremely easy to see how it responded. Memory is not so good anymore.

[o2batsea]

If your brake shoes are adjusted properly, the amount of travel is a matter of a hundredths or even thousandths of an inch. The amount of fluid required to push the wheel cylinders open this much is very small. That's the very definition of a firm pedal. So, assuming that the drums, shoes and wheel cylinders are in good condition and adjusted properly, an 88 MC would be perfectly fine and serviceable on a 109.
Also, the MC has a shuttle piston, so no, the fronts don't come on before the rears. All operate under equal pressure simultaneously. What happens when you brake is a weight shift from back to front, so that most of the actual stopping is done by the front wheels ( and why you don't jab the rear brake only when on a motorcycle). That's why you want them too be more stout. Rear wheels will lose braking traction and lock up before the front because there is less force acting on them. ABS works primarily on the rear axle for this very reason.

[TeriAnn]

So, assuming that the drums, shoes and wheel cylinders are in good condition and adjusted properly, an 88 MC would be perfectly fine and serviceable on a 109.

I beg to differ on that one. When I converted to power bakes I was accidentally shipped an 88 master cylinder. Not knowing the difference I installed it. No brakes or absolute minimum brakes the first pump. That was with all shoes adjusted one click down from full lock and dragging on the drum. Out 2 clicks from lock I needed 2 pumps to get any brakes.

[o2batsea]

I beg to differ on that one. When I converted to power bakes I was accidentally shipped an 88 master cylinder. Not knowing the difference I installed it. No brakes or absolute minimum brakes the first pump. That was with all shoes adjusted one click down from full lock and dragging on the drum. Out 2 clicks from lock I needed 2 pumps to get any brakes.

our experiences differ indeed.

[greenrover]

I took a look at your pictures. None of them are a eye level profile of the body but it looks to me like you are installing an 88 master cylinder. If you look at the master cylinder pictures I have about half way down the web page you can see the differences. The 88 brake cylinder body is a constant diameter when viewed from profile. The 109 master cylinder when viewed from the side is taller for the half of the cylinder body closest to the servo unit then about half way down its length steps down. This is the diagnostic visible difference between the two types. Look at my pictures then look at your master cylinder. It should become obvious.

TeriAnn
Thanks for the response.

I took another look from the side and the casting does change in diameter (see pic) and consistent with their pics the diameter of the rear port is larger (~7/16") than that of the front port (~3/8") so it seems it is a 109MC. So I think I got the right MC for my conversion. However when I was looking at the series III shop manual on how to run the lines I noticed the manual contradicts your web site as to what axle goes to what port. The manual says on a 109 dual MC the rear port goes to the rear wheels and the front port goes to the front wheels and that it is the opposite on the 88 MC. Understand your logic about needing more volume for the front brakes but could it be possible that the fitting diameter does not correlate to bore volume displacement?
Can anyone tell me how the fluid flows inside the MC bore when it is stroked?SIII WS manual Brakes.pdf