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MG TD TF 1500 - dual circuit master cyl bolt-on

Jim Merz,
You expressed interest in the dual circuit master cylinder for safety sake. I, too, had a yearning for the dual circuit simply for the safety aspect- one ride with my wife and you'd understand that she doesn't know what safe stopping distance means.
I got lucky and hit the trifecta,
a dual circuit master cylinder,
and can be modified to bolt on.
Better yet, the brake system now is engineered to incorporate the MGB front discs since I also installed a proportioning valve, which you really won't need keeping all four drums brakes.
I started with a NewOldStock Chevette master cylinder off of ebay for $25 including shipping. Currently, the same seller has continued offering them at the same price. I wanted to make sure the reservoi was cast into the unit, rather than an addon plastic reservoir since I went to remote reservoir filler.
more photos coming....

Jim Northrup

I cut off the two bolt flanges in the band saw, then chucked the MC in the lathe. It had the hint of being centerdrilled in at the small end; that got centerdrilled deeper and a live center held all perfectly in place. I machine that 2 bolt flange end down and also machined off the end port. Then an 1/8" drill bit buzzed a hole through that centerdrilled hole for one of the brake ports.
After the lathe, I used an electric discharge machine to burn a hole through the irregular casting by the flange, to accept the 1/2" steel tube for the bolt. A mill could drill that hole using and end mill, but a drillpress and drill would a bit of a challenge.
A hole was drilled through the reservoir to accept another chunk of 1/2" tubing.
An 1/8th inch NPT hole was drilled/tapped for the fitting to the reservoir sightglass.
A 1/4" JIC male fitting was cut off and braze onto the end of the mastercyl for the back brake circuit and the remnants of the original side port was brazed closed. The 1/2" steel tube were brazed on for the mounting bolts.

Jim Northrup

Note the brazed joint at the front for the #4 JIC male thread, and also the hint of the original hole for the side port were it was ground out to clear the crossmember. The 1/4" SAE brass long nut looks nice in keeping with a bunch others used elsewhere and works perfctly.
The top where the cover originally snapped on, was ground down on a slight pitch and then a sheet steel cover was brazed on.

Jim Northrup

frame-side view

Jim Northrup

...painted and ready to install.
I found a square ring that stretched over the end and slapped the original TD MC rubber bellows over the rod.
The only real modification to original TD parts was shortening the brake rod. The amount of lash can be pretty critical since the rod doesn't extend deep into the MC piston, one does not want that rod dropping down disengaging the piston!!! Only with tremendous slop cold that happen, though.

Jim Northrup

Bolt-on dual circuit master cylinder! I've completed installation with proportioning valve and bled it all.
This MC has a 3/4" bore, whereas the original was 7/8". This setup will have more pressure for superior stopping and also better pedal feel. Of course it takes a bit more pedal movement- imagining the pedal range from 8 o'clock through 2 o'clock position (before bleediing), this hits the wall at about 12 o'clock or a touch past.

If there was a great deal of interest, I'd considered doing a batch for the MI NEMGTR for auction at GOF Central.

Last but not least, the reservoir sightglass is coming...

Jim Northrup

1915 De Laval drip oiler ($15 off of ebay)asssigned to a new life as the brake fluid reservoir sightglass. It has to be a sight"glass" since brakefluid wasted a couple made of clear plastic. What brakefluid does to paint, also, isn't very pretty! Checking level and topping up will be a whole lot more convenient, and it has been interesting observing the fall and rise of fluid under different circumstances.
1/4" stainless line is flared, secured by another 1/4" SAE brass long nut to a bulkhead 1/4" JIC fitting bolted into a small stainless bracket.
Our old plastic honey dispenser will be retired in favor of a hypo to top up the sightglass.

Jim Northrup

Jim your successful project is WAAAAYYYYYY beyond my capabilities and I would not/could not attempt such a fete. GREAT JOB!!!
I have found some possible tandem master cyliinders that are narrow in width with vertical mounting holes. One might be installed with a reinforced "L" shaped adapter bracket using the original m/c frame mounting holes. The bore would be at or near the stock m/c. The stroke might be kept near the same by the L shaped bracket design and frame mounting hole location.
I could pick a drum/disc m/c and figure that the port for the rear drum brake would be a direct connection realizing that there are different thread/brake pipe sizes to be addressed. The disc side of the m/c is the unknown part. I think the disc half of the m/c puts out more pressure and greater volume. So the big question in my mind is how could this pressure/volume output be reduced so as not blow the seals out of the front brake cylinders?
I would try to keep the fluid reservoir at or near its current location under the floorboard.
I invite any and all thoughts on my "too much time on my hands" project.
Jim Merz

John Crowley used one from a Vega on a TF, nearly identical. He cut the box and fastened a bracket to hold the casting. Lid would be removed from below to check the level from floorboard hole. You could email John for his pics.

The dual circuit master cylinders generate equal pressure at the two ports, but the volumes are independent so you won't have any problem using one, and you won't need the proportioning valve. It really won't be any different than the single circuit except the added safety for separation of the two circuits in case of a leak.

Only issue to watch out for would be going way over on the bore of the new one... larger area, less pressure to the brake cylinders.

The idea of using an MG twin master cylinder (clutch/brakes) and using a Y shaped brake rod has been tossed out for discussion before. That would lead to problems where shoe adjustment would be super critical to equalize braking front/rear, too dangerous. The Y shaped rod would have to pivot.

Archives have discussed VW MC used successfully.

If anyone has been driving and had the brake pedal go to the floor, they'd think seriously about dual circuit brakes. Numerous trucks of mine have dual circuit brakes and have still let me down at very inopportune moments!
Jim Northrup

Jim N, are you saying that if I use a disc/drum m/c on my TD, all I have to be concerned with it adapting thread sizes for the disc half and connecting to the front drum brakes? If thats the case, I have been concerned needlessly about pressure and volume! WOW
Jim Merz

Jim Merz,
You should be good to go, or stop. For your 4 stock drum brakes, the simple dual circuit master cylinders should work without the proportioning valve. They have two pistons inline separated by some brake fluid. Pushing the one exerts the same force on the second one, equal pressure. Both lines are free to emit whatever volumes are needed.

I'm pretty sure the stock TD mc is 7/8" bore. Going much larger reduces the line pressure to where extra exertion is going to be required. I lucked out and got 3/4" which will yield more pressure/exertion, give better feel, but it will take a touch longer movement.

A proportioning valve should be added if going to front discs/rear drums, to avoid spinouts.

I can email John Crowley's conversion pictures if you're intersted... just needs carving up the pedal box and a simple bracket.

Jim Northrup

Jim (N.), any chance that you could send John Crowley's images to me so that I could put them on the Ttalk website? Thanks, Bud
Bud Krueger (TD10855)

Of course you won't find these in a junk yard or on sale at the local auto supply, but it's designed for side mounting or front mounting. Quite unique if your not on a budget. Here's their web site. PJ

P Jennings

Bud, et al.
John has offered his email in a previous discussion. It is his work and he was kind enough to forward it to me.

Mr. Jennings,
It would be wise to determine the length of the above aftermarket mastercylinder. I had to machine the 2-bolt flange down in order to insert the Chevy unit in farther to just barely clear the crossmember. Since they have the throughbolt holes, one could likewise machine the flange down on the aluminum ones, too. With the Philips screws holding the cover, it would either require pulling the whole footwell (if there is one) or adding a remote reservoir. That would assume the cap & gasket would hold brake fluid with a litle head pressure. That's why I brazed an airtight steel cover on mine.
Jim Northrup

I never gave it a thought about the length. Your right, it looks a little long to fit where the original goes. I like the remote reservoir idea if your not into original correctness. PJ
P Jennings

Jim, I'm like PJ in that I forgot about the length of a replacement cylinder. I only thought about width and port locations for my RHD TD. Gotta go downstairs and get under to check it all out more thoroughly. Thanks for that reminder,
Jim Merz

The aluminium* (*alumiium for a British car) master cylinder could work!?

Like I mentioned, my 2 bolt flange was turned off on the lathe so it could be stuck into the pedal box about a half an inch to clear the cross member. I first lopped off the ears on my vertical band saw before spinning it in the lathe; a hack saw could knock off the flanges, too, but I think it would still be too large to slip into the pedal box without taking somemore off around the whole flange.

Also, I expected that after adding an elevated remote filler, that cover gasket might allow brake fluid to seep out over time. That's why I brazed a steel lid on, but you won't have that option with an aluminum master cylinder. Maybe you'd have more confidence in the seal or some additional sealant, than me. I'm just sure my brazed joint will never leak nor need attention.

You could always drill & tap 2 plug holes in the side at the top to inject brake fluid from underneath in each reservoir periodically to make sure they're full. Or maybe make a hole in the lid and add rubber plug to peer through under the floorboard.

As my layout has only one hole for the remote filler, I had to grind down some of the partition separating the two sides, so the fluid would run over into the other chamber.

I'd say the extra money and time invested in a dual circuit master cylinder is cheap insurance! How many of you have had brakes go out when you needed them, raise your hands.... I've got both my hands raised! There are others out there that had their brakes go out and didn't live to tell about it! Just the thoughts of replacing a TD radiator and fenders sends chills down my spine.
Jim Northrup

See for John Crawley's information --- Bud
Bud Krueger (TD10855)

This thread was discussed between 04/02/2011 and 23/02/2011

MG TD TF 1500 index

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