78 Front Discs with 74 Rear Drums - Master Cylinder (1 Viewer)

[bamelanc]

So, the PO had a 78 front axle with discs installed...maybe in the 80's. Rear drums remain the same...'74. My question is, is the '74 master cylinder sufficient for a later model calipers? Do I need a master cylinder for a '78? SOR shows the OEM master cylinders to be a different design. Looks to be an aftermarket master...Minaco? Trying to resolve the issue of soft brakes after several brake bleeds... I think the master needs to be replaced and I want to make sure I get the right one.

 

[PEOPLES]

Trying to resolve the issue of soft brakes after several brake bleeds... I think the master needs to be replaced and I want to make sure I get the right one.

I guess the brakes work fine but there is no exact pressure point ?

I have the same with mine (but I have a Bandeirante), with the old Master and Discs on the front. The drums have less volume in the calipers, so with the ols/small Master the brake pedal need more way to start braking and there is almost no pressure point you can fell in the pedal.

Nevertheless, mine truck is breaking great even with that, I just needed to get used to this. I don't have a valve, which distributes the brake pressure for the front/rear axle (like it is normal for modern cars), this was done by the different size of the brake calipers pistons in the brake drums.
Actually mine somehow fit, means I don't have a "overbraked" rear axle.

A bigger Master (for discs only) would mean a better pressure point but more force needed for the rear axle to brake. At least down here in Brazil there is either/or, means only discs with a big Master and only Drums with a small Master.
The fwd disc / rear Drums was never a stock config and therefore no real parts avail.

 

[JohnnyC]

My 74’ has disc front and rear… works just fine

Sounds like you still have air in the rear … or… the rears are not adjusted correctly

 

[Igotmearedone]

I had a similar experience on my 74 but it was much better after I adjusted the rear drum brake cylinders with the tool

 

[JohnnyC]

Btw.. Adjust the rears so you can’t move them and then back off 3 clicks

 

[bamelanc]

Btw.. Adjust the rears so you can’t move them and then back off 3 clicks

I did do this. Tightened until I couldn’t turn the hubs, pressed the brakes a few times, then backed off until they weren’t dragging. 3-5 clicks.

Brake is soft on first press, like, to the floor without stopping, soft. Second press is firm and will chirp the rears, third press slightly firmer. When I release the brakes, about 15-20 seconds later, the are soft again. Repeat.

 

[B y r o n]

If the pedal feel is different with each press then there is air still in the system.

 

[JohnnyC]

only back off 3 .... don't go 5

 

[Living in the Past]

Do not believe the drum brakes on the rear axle changed 74-78. Major brake change was 8/80 to a single self adjusting brake cylinder. I see the booster is still the one used up thru the 75 model for drums on all four wheels. Would hope the master cylinder is for front disc brakes and rear drum brakes.

 

[John McVicker]

Totally agree with @JohnnyC , backing off 5 is a losing proposition. Maybe try this…may sound extreme but I bought my 40 new in ‘75 and this is what I have always done to get decent braking.

I back off only 3 clicks. Then I go for a short test ride in a lightly traveled area. Drive it for 2 miles & then COAST to a stop…DO NOT apply the brakes. Quickly get out and feel your wheels with your hands.

If they are HOT then back off 1 click & do another test run & feel. But if they were warm…not hot…I call it good and leave it at that. They will seat in and you will have good pedal feel. If they were cold, tighten 1 more click & go for another test run. Keep doing your test runs until they are warm to the touch.

This was not my original idea, got it from @pinhead excellent videos on brakes.

 

[Vandal FJ]

Be sure and pull that proportion valve out of the front cylinder on the master. After that mine works great. No problem with 77 disc front in a 72 with rear drums.

 

[3_puppies]

Be sure and pull that residual valve out of the front cylinder on the master. After that mine works great. No problem with 77 disc front in a 72 with rear drums.

fixed it for you