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MG MGB GT V8 Factory Originals Technical - Clutch slave help

Guy I need help!! I was going to use a Stock MGB M/C and slave setup to run my ford Clutch. I have had a heck of a time getting the system bled as is common. I now have 1/2" travel, but it is not disengaging the clutch. What is normal clutch arm travel for a stock B?

After read Paul Hunt's site I am now thinking about using a MGB V8 (factory) slave cylinder with my stock B master Cyl. Has anyone done this or seen it done?

Any help, PLEASE!?? I am using a stock Ford bellhousing and T5 with my 302. This is the LAST thing keeping her pff the road! ARGHHH!!
Larry Embrey

Larry, The stock cyl isn't going to cut it with american clutch geometry as you've discovered. On my 1st setup I cut down the clutch fork an inch or two and used a smaller cylinder. I tried three sizes or more before getting something that worked well enough.
What I ended up with was a 3/4" bore slave, 3/4" bore master. This drove an arm with a ratio of 6.75" to 3", effectively cutting the movement in half. As I recall the MG clutch fork had the pivot on the opposite side of the case and a much smaller ratio, but that was a very long time ago. Sorry I don't have the part numbers for you. I do have a number for a NAPA 37398 which has a 13/16" bore.

If you use the fork at the stock length, I would suggest an 11/16" slave to start with. If it is too small you can then go to a 11/16" master without fabricating up new mounts, since unless you are able to use racing or custom slaves the mounts will all be different.
Jim Blackwood

Yeah I was thinking of the MGB V8 slave since it is smaller bore than the stock MGB one. Should make it throw more when coupled to the stock MGB master cyl.

MGB and V8 M/C and slave bore sizes differ as follows:
MGB M/C: 19mm
MGB slave: 32mm
V8 M/C: 17.8mm
V8 slave: 25.4mm

I drove a firneds V8 with the McLeod HTOB and did not like it at all, have to break your leg to work clutch..
Larry Embrey

Normal clutch slave travel, on both the standard B and the factory V8, is about 1/2".
Paul Hunt

Larry, I think you will need to do a little measuring and calculating. Here's where I'm coming from: Under the dash, measure the distance the clutch pedal moves the pivot for the clutch MC rod. That should be your available stroke. Now you need to know how far the clutch fork needs to move to disengage the clutch--for this you will probably have to find a V8 Mustang (or something) with the same bell housing/fork arrangement and measure the movement at the place on the fork where you would attach your slave cylinder. With this and the diameters of the MC and slave cylinders, you should be able to determine how much the pedal movement will extend the slave (volume displaced is volume received). The hard part (I think) is determining how much movement you need at the slave cylinder.

Wayne Pearson

Playing with this a little more:

[(Clutch master cylinder dia)/2]sq X pi X available stroke = [(slave cylinder dia)/2]sq X pi X resultant stroke


(Clutch master cylinder dia)squared X available stroke = (slave cylinder dia)squared X resultant stroke

Shouldn't be too hard to plug in known values and solve.

Wayne Pearson

Wayne thanks for the info. I knew there had to be a "straighforward" formula fo figuring this. The HARD part is finding a mustang in a wrecker that has not already been torn apart for parts. most yard now adays pull the mustang motor and tranny before they will release it to the public.

I threw that formula into excel. Now I just ned to measure my master cylinder throw and can start looking at it more.

Larry Embrey

Anyone here know the diam of the MGC slave cylinder?
Larry Embrey

Well using the formula and lots of searching I came to the realization that the stock unit just plain can't cut it, nor will most any normal slave cylinder given the Ford clutch arm set-up. I found on a mustang site that Mcleod now makes a HTOB for Ford T5's, I called Mcleod for a local dealer and found one. Called them and they wanted an arm and a leg for the unit $329 and he did not know if he had one, it could be up to a week to get! I then called Fast Cars for one, they relayed me to D&D. Sure enough Dan had one in stock waiting for me. After adding one of his custom braided lines AND next day shipping I was within a couple bucks of what the local guy would have charged me after tax!!!


I now have on the way a HTBO, braided line that goes from master cyl to HTOB, and they have all been tested with a MGB master Cyl!!

Time to pull the motor, which needed to happen anyway since the tranny is leaking fluid badly. Should be a fun weekend.
Larry Embrey

Using figures above I calculated the following.

equals 12.7 mm

MGB slave has 2524.0576 square mm and with 12.7 mm slave travel that means the displaced volume is 32055.53152 cubic mm.
MGB master has 889.8289 square mm so the distance the clutch lever must push the master cylinder to displace the required 32055.53152 cubic mm is 36.0 mm or about 1.4 inches.
The V8 slave has 1590.254884 square mm so the 32055.53152 cubic mm volume displaced by the standard MGB master would extend the V8 slave 20 mm or about .787 inch or over .
The V8 master has 780.978916 square mm and if the clutch lever pushes it 36 mm then it displaces 28115.240976 cubic mm.
The V8 slave should move 17.7 mm when the V8 master pushes 28115.240976 cubic mm or about .69685 inch or under .

This assumes the standard MGB slave moves one half inch (it did every time I measured it) and that the factory V8 used the same clutch pedal as the standard MGB. I seem to recall Paul Kyle said the factory V8 used the slave from the midget. If all these figures are correct, we can conclude the factory needed more than of slave travel to operate the V8 clutch, but didnt need over and so didnt use the standard master cylinder because that combination would needlessly increase pedal effort, may over extend the slave cylinder or was simply cheaper.
George Champion

I think you'll be happier with that solution. I bought a HTOB from Dan last winter, and with an 11/16 master the pedal feels right. I never was entirely happy with the external slave either in terms of feel or travel.

I have heard there's a HTOB available for $150 but since I now have one I didn't pay much attention.

Jim Blackwood

The $150 one I got is from Howe, purchased through requires a 3/4" MC being installed this weekend. I will post results next week.

Well, I purchased the unit Dan @ D&D sells. It is a weber/Mcleod unit. came with a spacer as well to match my ford T5. Dropped right on, and bled in about 2 minutes. Works like a charm. The pedal feel is a bit stiff than I am used to but not bad. I just used to the soft pedals of these japanese cars..
Larry Embrey

This may not help anybody, but then it might too.
The late 1984 jeep cherokee 4 cyl (perhaps other years too) came from the factory with the T4 or T5 transmisions. It used Girling hydraulics and an external slave cylinder. I think this may be the ticket for an inexpensive and effective way to keep costs down and use readily available parts. They are matched, and should fit in an MG. I have over 200,000 miles on a jeep with this setup. Works well and is relatively easy to service.

This thread was discussed between 25/04/2002 and 30/04/2002

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