As the title suggests I've got a new to me '77 FXE with a front brake issue. It requires a lot of hand force, but the performance is horrible.

I'm running the original front master cylinder, but the caliper is an '84-'99 unit. I believe the bore on my '77 stock master cylinder is 3/4", while the one for an '84-99 single caliper should 9/16". The caliper is mounted to Pro-1 wide glide legs.

Am I correct in thinking that the bore size of my master cylinder may be my problem? If so, is there a smaller bore master cylinder available that looks like my '77 OEM unit? I'd like to keep my switches and controls stock appearing.

 

your correct the diam of the master has to match the caliper and the early evo caliper single is 5/8 not 9/16 < 1996 on - also the shovel used dot 3 fluid and the evo used dot 5 and dot 5 is aerated almost like selzer - used in the wrong system you will never get the correct feel in the brake, and in most cases the lever travel is to the bar before it stops the machine

in road racing we can change the line inside diam to help a rider with what they call road feel at 170MPH in turns - not my cup of tea but I use a brake bleeder pressure gauge to get exact what they want

 

Thanks, I thought I was on the right track, though I believe the caliper is a late Evo. It looks just like the one on my '99 Dyna FXD. Looks like I'm going to be replacing my hand controls.

If I flush and clean the the entire brake system completely, can I go to DOT 4 fluid?

 

the seals are the issue dot 5 is silicone

Dot 3 - 4 and 5.1 is not and will remove paint if spilled

its the rubber that is used that is at issue

 

John... this is the first time ever I heard that shovels used DOT5... my understanding is that HD always used DOT5 for brakes
I think my 79 Electra glide had a sticker on the handlebar saying DOT5?

 

1973 dot 5 was not invented yet - dot 3 and disc brakes came along with the newly badged AMF Harley in 1973 before that from 1958 with hydraulic rear drum brakes were dot 3 . it was when ***** D took Harley back from AMF that all the vision of modernization came along with that - around 1981 the papers were signed but his influence was from around 1977 when the shovel was changing

all brake fluid was dot 3 in the USA back then, Europe started using a DOT 4 Castrol sort of in the 70s but it was late 70s /80s before DOT 5 came along available in parts stores don't remember exactly

he the OP has a blend of parts that do not match fluids and mechanical advantage, master verses caliper sizing, happens with rear brake wheel cylinders as well, all Harley brake lines are zero 3 in size internally but today kits are available to adjust feel and lever / pedal travel using zero 1 and 2 sizing as well -- don't go to that its mathematical verses pressures verses travel distances stick with what is in spec for the machine you have and what your doing

 

Kinda sounds like what I'm going through on my rear upgraded PM caliper.... Very hard pedal with very little breaking..... Gonna flush it out with DOT 3 first....