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MG TD TF 1500 - Tapping Intake Manifold for Servo

Some of you may recall that, along with converting from DOT4 to DOT5 I'm installing a servo. Take a look at http://www.ttalk.info/TinkerServo.htm for a look at how David Tinker did it. I've run into a problem. I think David is using separate air cleaners on his carburetors (2nd image below). I'm sticking with the stock oil-bath system (first image below). The problem is in how to tap the manifold for the vacuum. The servo kit comes with a 5/8 UNF adaptor (shown below). There isn't room between the intake maifild and the air intake tube for such a device. The vacuum hose to the servo seems to have about 3/8" i.d. Any suggestions? Tnx. Bud


Bud Krueger

You've got lots of options. I don't have an engine with that intake to look at right now, but look at drill/tapping into that balance tube and installing a street elbow & hose barb fitting just off to the side a touch, if looks don't matter. You might shoot horizontally right out the back (again, I can't study one right now) or shoot a pair of smaller hoses straight out along side of the carbs. You don't need to use a single large hose. Maybe look at dropping a couple of steel lines down just off the manifold flanges, room permitting.

You can tap right into the carbs by the flanges, but there'll probably be a backlash from critics on this suggestion. Just ignore them.

I made up a four-runner intake adapting motorcycle carbs to a Honda car engine, welding four 1/4" stainless tubes onto the flamecut steel flange for the brake booster.

Use your imagination and then surprise us with your creation.

My wife needs all the braking power money can buy for her TD!!! I installed the MGB discs up front with a dual circuit small bore master cylinder and proportioning valve.
JIM NORTHRUP SR

You can also tap the core plugs on the manifold. The photo shows it plugged.
Regards
Declan


Declan Burns

Bud,

the position of the vacuum port for the remote servo is not critical at all.
I tried different positions on B-series engines of my MGB's without any difference in operation of the brake booster or in engine operation conditions.
Be careful with the center position though, as some manifolds have a flow limiter inset just in this position.
I like Declan's solution.

Ralph
R.S. Ralph Siebenhaar

Danke, and thanks Jim. I'd be concerned that tapping in at the end of the manifold might affect the flow at the carburetors. I think I'll try some of Jim's creativity and consider tapping the section of the manifold that can be seen in the image, just to the left of the air intake tube.
I don't want to use the adapter that came with the set. The 5/8-18 thread is huge. Jim, what do you mean by "street elbow"?

I understand that there are such things as electrical automotive vacuum pumps. Anybody know anything about them? TIA. Bud
Bud Krueger

Street elbow is fitting (45, 90 or any angle elbow) with one female thread and one male thread, so you can thread it into the casting without using an extra nipple. More compact and cleaner look.

I don't think you'll notice any power transients by coming straight back out the end. Booster is sucked out in a heartbeat and just sets until brakes are applied. That would probably make the best looking installation, depending on where you install your booster. And if you install it offcenter on the top, as you mentioned, you'll still be sucking mainly off one side because of that flow limiter. Maybe tap a pair of smaller hoses, one off each side.

A lot of diesel vehicles have small vacuum pump on the back of the alternator, for what that's worth.
JIM NORTHRUP SR

Thanks, Jim. I'm really beginning to give serious thought to Declan's idea of tapping the end plug of the manifold. Access through the carburetor flange will allow me to minimize the protrusion of the adapter into the air stream. I'l have to take a close look at the proximity of the exhaust port. Thanks again. Bud
Bud Krueger

I actually tapped both ends of the the manifold and connected them on a temporary basis with silicon hose as a balance pipe so as not to upset the carbs. I remade the core plugs in 3mm brass so they can be tapped. I also fitted a temporary vacuum gauge which reads -700mbar at idle. A cigarette butt end as a damper in the pipe to the gauge stops the gauge needle fluctuating and trying to disintegrate and shows a constant reading. Experimentation is ongoing.
Regards
Declan
Declan Burns

This thread was discussed between 21/07/2013 and 22/07/2013

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.