Hydroboost brake conversion

[Ford F834]

So much useful information, many thanks for your info Jonathan👍.

If I can source the push rod and parts between the mc and booster I may well go ahead with this conversion. I remember having to alter the pedal pin on my foxbody mustang when I did a cobra brake conversion on that. I can easily fabricate new brake lines with whatever size fittings I need to suit. Will also fit the larger bore later mc and a proportioning valve in to the rear line as I still have rear drum brakes.

Thanks again guys, this forum is great!😁

You are very welcome, if you can manage the brake line fittings then the only part you have to track down is the pedal. Just to clarify, nothing between the master cylinder and the booster needs to change, and the rod between the booster and the pedal should come with the hydroboost unit. The only thing you need to correct is the stud on the pedal arm, or source the correct pedal.

[Gary Lewis]

You are very welcome, if you can manage the brake line fittings then the only part you have to track down is the pedal. Just to clarify, nothing between the master cylinder and the booster needs to change, and the rod between the booster and the pedal should come with the hydroboost unit. The only thing you need to correct is the stud on the pedal arm, or source the correct pedal.

Ok, after a bit of sleuthing here's what I've found, most of which is just to tell me I know what I'm doing because my info matches that of Jonathan:

• My brake pedal, from the '95 F450 with hydroboost that Jim parted out (right, Jim?), is an E7TA-2455-CA, just like the one in Jonathan's pic

• The master cylinder bolt holes are indeed different between the vacuum-boosted F250HD, at 3.2" c/c, and the hydroboosted '95 F450's at 3.45". Said another way, you aren't going to put the F250 M/C on a hydroboost unit.

• The F250's bore size is 1 1/8" while the F450's is 1 5/16"

• But, the line fittings are the same the two M/C's. I measure the one on the rear of the M/C @ 1.0MM pitch, .431" OD and .418" at the root of the threads - as best I can measure with the small threads. That seems to say the little on on the rear is 11-1.0MM. And the bigger one toward the front of the M/C has a 1.5MM pitch and measures .550/.520", which suggests it is a 14-1.5MM. Said another way, the lines from a Bricknose F250HD should work nicely with the bigger M/C.

Now, how 'bout some pics?

Here's a comparison of the F250 M/C in front, and its big brother from the F450 in back:

And here's the F450's hydroboost unit:

And here's the hydrobooster and F450 M/C bolted together: (Where's that competition for most cluttered shop? )

[ArdWrknTrk]

Ok, after a bit of sleuthing here's what I've found, most of which is just to tell me I know what I'm doing because my info matches that of Jonathan:

• My brake pedal, from the '95 F450 with hydroboost that Jim parted out (right, Jim?), is an E7TA-2455-CA, just like the one in Jonathan's pic

• The master cylinder bolt holes are indeed different between the vacuum-boosted F250HD, at 3.2" c/c, and the hydroboosted '95 F450's at 3.45". Said another way, you aren't going to put the F250 M/C on a hydroboost unit.

• The F250's bore size is 1 1/8" while the F450's is 1 5/16"

• But, the line fittings are the same the two M/C's. I measure the one on the rear of the M/C @ 1.0MM pitch, .431" OD and .418" at the root of the threads - as best I can measure with the small threads. That seems to say the little on on the rear is 11-1.0MM. And the bigger one toward the front of the M/C has a 1.5MM pitch and measures .550/.520", which suggests it is a 14-1.5MM. Said another way, the lines from a Bricknose F250HD should work nicely with the bigger M/C.

Now, how 'bout some pics?

Here's a comparison of the F250 M/C in front, and its big brother from the F450 in back:

And here's the F450's hydroboost unit:

And here's the hydrobooster and F450 M/C bolted together: (Where's that competition for most cluttered shop? )

Some people say they slot the master cylinder holes and bolt a 250/350 master to hydrobooster.

The larger bore is because of the massive front and rear *calipers* on the F450's 10 bolt hubs.

Remember, there is no drum e-brake on the 450.

Just the one on the rear of the 4x4

pattern Zf-5

[Gary Lewis]

Some people say they slot the master cylinder holes and bolt a 250/350 master to hydrobooster.

The larger bore is because of the massive front and rear *calipers* on the F450's 10 bolt hubs.

Remember, there is no drum e-brake on the 450.

Just the one on the rear of the 4x4

pattern Zf-5

It would be easy enough to slot the bolt holes .125"/each to mount the smaller master. Especially if you have a mill. But, then you have to do that each time you replace it.

Having said that, my first thought when I looked at the bore sizes was "That's really not that much difference." But, then I put finger to keyboard and found a big difference:

Now, let's go back to Jonathan's post:

Many F250/350 owners opt to use their existing master cylinder which is fine if you have the HD vacuum booster. The stud spacing is the same and they will bolt to the hydroboost. It looks like you are working with a F150. Your master cylinder should therefore be the one for the light duty vacuum booster. The mounting stud spacing is closer together and it will not fit. If you want you can buy and use a F250 HD or F350 master cylinder as they are cheaper and easier to find. I would recommend the 87-96 style with the aluminum body and plastic reservoir vs. the old cast iron type.

This confuses me. I found today that Huck, the Bricknose F250, had different mounting hole spacing on the M/C than the F450 does. And Huck had a GVWR of ~8600 lbs, same as Big Blue. And, both have the 8-lug hubs, full-floating rear, etc. Doesn't that make then heavy duty F250's?

Here's a snippet from the catalog, which seems to say that in 1984-86 the break between LD and HD was at 8500 GVWR, but that in 1987 it changed to 7000.

Huck was a '90 F250 w/an 8600 GVWR and yet his M/C's mounting holes are closer together than the F450's. So, how can the HD F250's M/C's bolt to the hydroboost?

I'm missing something obvious, I'm sure.

 

[ArdWrknTrk]

It would be easy enough to slot the bolt holes .125"/each to mount the smaller master. Especially if you have a mill. But, then you have to do that each time you replace it.

Having said that, my first thought when I looked at the bore sizes was "That's really not that much difference." But, then I put finger to keyboard and found a big difference:

Now, let's go back to Jonathan's post:

Many F250/350 owners opt to use their existing master cylinder which is fine if you have the HD vacuum booster. The stud spacing is the same and they will bolt to the hydroboost. It looks like you are working with a F150. Your master cylinder should therefore be the one for the light duty vacuum booster. The mounting stud spacing is closer together and it will not fit. If you want you can buy and use a F250 HD or F350 master cylinder as they are cheaper and easier to find. I would recommend the 87-96 style with the aluminum body and plastic reservoir vs. the old cast iron type.

This confuses me. I found today that Huck, the Bricknose F250, had different mounting hole spacing on the M/C than the F450 does. And Huck had a GVWR of ~8600 lbs, same as Big Blue. And, both have the 8-lug hubs, full-floating rear, etc. Doesn't that make then heavy duty F250's?

Here's a snippet from the catalog, which seems to say that in 1984-86 the break between LD and HD was at 8500 GVWR, but that in 1987 it changed to 7000.

Huck was a '90 F250 w/an 8600 GVWR and yet his M/C's mounting holes are closer together than the F450's. So, how can the HD F250's M/C's bolt to the hydroboost?

I'm missing something obvious, I'm sure.

Gary,

The cutoff for HD is 8,500 gvw. Always has been, always will.

150's (and maybe 250 ld) have a 15/16 (or 1"? CRS)

250's and 350's have 1 1/8" bore.

The 450 is a different animal, and with HD discs all around, needs to move more fluid.

Usually if you went to a bigger master the brakes would be heavy and feel wooden.

But because of the relocated pivot and higher pressure boost they don't.

If anything you have to get used to them quickly, before they put you through the windshield.

Edit: to me this suggests that a/o December 1987 Ford started using the bigger calipers on trucks as light as 7k gvw.

Not that the cutoff for what was considered HD moved.

[ArdWrknTrk]

Ok, Where's that competition for most cluttered shop? )

It looks like Matthew is making an attempt to keep up (but failing miserably)

He does have a much prettier red benchtop though!

[Dorsai]

It looks like Matthew is making an attempt to keep up (but failing miserably)

He does have a much prettier red benchtop though!

That red benchtop is the finest in mover-grade cheap red protective carpet. When we bought this house five years ago the movers left three big rolls of the stuff (they put it down to protect the floor from their handtrucks) behind when they were done. I replaced what was on my workbench (it protects my plywood) when I cleaned the other day; at the rate I'm going, I'll be out of the stuff by 2060.

And now that finals are over, I can start cluttering things up again!

 

[ArdWrknTrk]

It looks like Matthew is making an attempt to keep up (but failing miserably)

He does have a much prettier red benchtop though!

That red benchtop is the finest in mover-grade cheap red protective carpet. When we bought this house five years ago the movers left three big rolls of the stuff (they put it down to protect the floor from their handtrucks) behind when they were done. I replaced what was on my workbench (it protects my plywood) when I cleaned the other day; at the rate I'm going, I'll be out of the stuff by 2060.

And now that finals are over, I can start cluttering things up again!

This is way off topic, but would you mind telling what you're studying for?

[Dorsai]

This is way off topic, but would you mind telling what you're studying for?

I'm working on a masters degree in analytics. I still have about 15 years to go before retirement, and I don't think my current role at AT&T is going to be around that long...so I need to upgrade.

[Gary Lewis]

This is way off topic, but would you mind telling what you're studying for?

I'm working on a masters degree in analytics. I still have about 15 years to go before retirement, and I don't think my current role at AT&T is going to be around that long...so I need to upgrade.

What type of analytics? (I assume there are different types, like statistics?)