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Joe K · 10-09-2020, 09:51 AM

I started a hydraulic brake conversion. Bought the "adapter kit" with the rings, bought the used backing plates and drums, even bought the entire front and rear axles from a 1940 Ford (in 1978 it was perhaps $40 for both from a scrapyard in Maine)

The kit was set up around using the later backing plates against the Model A spindles and rear trumpets. To do this you had to "slot" the bolt holes in the backing plates AND use the spacer ring. The fit was not great as I didn't want to modify the Model A parts.

And putting a slot in the rear backing plates for the rear spring perch kind of got me to questioning - is this the way I want to go? (I have since learned that some "rotate" the backing plate but that leaves the hose visible and available to get hung up on roadside brush and torn off.)

Some conversation with a local semi-professional restorer brought me to the thought of "what tires are you going to be using with this?" For me the answer was "Model A 28-29 21" wheels like original." And his reply "Do you think this is going to stop you any better?" He says this like there was some question?

And there is question for a number of reasons. The conversion kit is not by itself questionable, but definitely not "engineered" well - all that material removed from a backing plate including the bolt hole slots MUST compromise it's strength. Strength that you count on to resist the torque of stopping. And - using original tires - the limitation on stopping is the point when the tires skid - and you only have about a 2" x 4" patch of rubber keeping you from a skid. AND you have a juice brake system designed for a car about 1.5 the weight of a Model A, and designed for a 4" x 8" patch of rubber with wider tires. Or we can go into the "dynamics" of braking and how the later juice brakes are SUPPOSED to be self adjusting - a big rationalizer for going juice - but the earlier pre-WWII juice versions like the ones I bought were not.

I threw off the 39-48 conversion as a poor idea. Fortunately, at the time I only had about $64 into the project - and a car trip up to Rockland, ME to get it. Ultimately all those parts and the axle were scrapped in "expedient disposal." Well, I was a college student at the time.

But you do as you will. The street rod crowd have available now some "seriously engineered" disk brake systems - with a serious price tag attached. Some of these are done so well they are held within the original brake drums and are seen only through the connecting hoses. MANY have done what they consider reasonable conversions - but like the few who buy a Cadillac (or a Volkswagen - heh!) there is no finer driving experience.

I could go on about the experiential hours I spent under my 2003 VW TDI Golf including removing the engine mount bolts to change a timing belt (IIRC 275ft-lbs on a $27 each stretch bolt.) Fine-ness is in the eye of the owner most certainly.

The computerized self-timing feature of the TDI Bosch injection pump was pleasant...

Unless you want to upgrade to the later Ford Mid-30s wire wheels, I would keep it stock.

Joe K

10-09-2020, 09:51 AM	#5
Joe K Senior Member Join Date: Jul 2010 Location: Cow Hampshire Posts: 4,188	Re: Juice brakes I started a hydraulic brake conversion. Bought the "adapter kit" with the rings, bought the used backing plates and drums, even bought the entire front and rear axles from a 1940 Ford (in 1978 it was perhaps $40 for both from a scrapyard in Maine) The kit was set up around using the later backing plates against the Model A spindles and rear trumpets. To do this you had to "slot" the bolt holes in the backing plates AND use the spacer ring. The fit was not great as I didn't want to modify the Model A parts. And putting a slot in the rear backing plates for the rear spring perch kind of got me to questioning - is this the way I want to go? (I have since learned that some "rotate" the backing plate but that leaves the hose visible and available to get hung up on roadside brush and torn off.) Some conversation with a local semi-professional restorer brought me to the thought of "what tires are you going to be using with this?" For me the answer was "Model A 28-29 21" wheels like original." And his reply "Do you think this is going to stop you any better?" He says this like there was some question? And there is question for a number of reasons. The conversion kit is not by itself questionable, but definitely not "engineered" well - all that material removed from a backing plate including the bolt hole slots MUST compromise it's strength. Strength that you count on to resist the torque of stopping. And - using original tires - the limitation on stopping is the point when the tires skid - and you only have about a 2" x 4" patch of rubber keeping you from a skid. AND you have a juice brake system designed for a car about 1.5 the weight of a Model A, and designed for a 4" x 8" patch of rubber with wider tires. Or we can go into the "dynamics" of braking and how the later juice brakes are SUPPOSED to be self adjusting - a big rationalizer for going juice - but the earlier pre-WWII juice versions like the ones I bought were not. I threw off the 39-48 conversion as a poor idea. Fortunately, at the time I only had about $64 into the project - and a car trip up to Rockland, ME to get it. Ultimately all those parts and the axle were scrapped in "expedient disposal." Well, I was a college student at the time. But you do as you will. The street rod crowd have available now some "seriously engineered" disk brake systems - with a serious price tag attached. Some of these are done so well they are held within the original brake drums and are seen only through the connecting hoses. MANY have done what they consider reasonable conversions - but like the few who buy a Cadillac (or a Volkswagen - heh!) there is no finer driving experience. I could go on about the experiential hours I spent under my 2003 VW TDI Golf including removing the engine mount bolts to change a timing belt (IIRC 275ft-lbs on a $27 each stretch bolt.) Fine-ness is in the eye of the owner most certainly. The computerized self-timing feature of the TDI Bosch injection pump was pleasant... Unless you want to upgrade to the later Ford Mid-30s wire wheels, I would keep it stock. Joe K __________________ Shudda kept the horse.