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Master/Slave Cylinder Compatibility - M5OD


voodoochylde

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I nearly have my '86 BII back up and running. I junked the dead A4LD, bought a '92 Exploder donor, and swapped in an M5OD. Everything was going well until....

My new master cylinder that I bought to replace the old, leaky Ford part is acting funny. I cannot get enough stroke to disengage the clutch. The system is bled and both hydraulic components (master and slave) are brand new and working.



I have searched a TON but am having trouble finding a definitive answer. Do I need to buy a clutch master cylinder for a BII? Will it work with an M5OD slave?

I got my clutch kit here. It included the slave.

Not sure if it matters but I got my clutch/brake pedal from the Exploder. Cut the rod to length and it swapped into my stock BII pedal bracket with no problems. There's no difference in the pushrod mounting point on the two different clutch pedals, right?

I'm going nuts! Any help would be a godsend!
 


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alwaysFlOoReD

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I have no help but can the cylinder bore size be different sizes than original or did you replace all as a kit from the same manufacturer; master,line, and slave?
Did you bench bleed the master?
Richard
 

voodoochylde

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I bench bled the master and am fairly sure there's no air in the system. The bore very well could be different as the old master *seems* to have a slightly smaller diameter than the current master. It went in easier than the new Advance Auto/Perfection M.C. In fact, I had to grind the mounting hole in the firewall by about 2 or 3 mm to get it to fit at all.

The slave came with the new Gripforce clutch kit. No idea what size bore it has - never thought about the possibility of different bores/strokes between the different years/models/engineer's moods.
 

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It takes a lot to bleed the system.
 

voodoochylde

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It very well could be a bleed issue. However, I crawled underneath the truck and watched the throwout bearing/slave actuate while my girlfriend's father actuated the clutch pedal. I was only getting 3/4" to 1" of travel. The clutch pedal was bottoming out on the floor.

While that sounds like the typical "air in the system" problem, there's something a bit different here. Total travel of the Master Cylinder push-rod was only about.....3/4" to 1".

I disconnected the pushrod and used a screwdriver through the eyelet to actuate the master cylinder by hand and VOILA! The clutch disengaged! I could turn the tranny output shaft by hand.

I took a measuring tape to the BII and the Exploder last night and the dimensions from the MC hole in the firewall to the pedal rod mount (vertical measurement) in the brackets of both are the same. There also appears to be the same distance outward from the firewall to the pedal rod mount.

Is there a difference in the pushrod pivot point location between the BII pedal and the Exploder pedal? If there's not, then I'm starting to suspect a mismatch between the master and slave cylinders...

Dangit.
 

cocoasranger

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When I switched from an A4LD to a Mazda 5 speed the stroke was too short to allow shifting; just like you are experiencing. There ARE different bore sizes in different year clutch masters, the larger bores allow much more travel with the same pedal travel.

I cheated and welded a quarter inch extension on the push :icon_cheers:rod, but a larger bore clutch cylinder would have been a better fix.
 

alwaysFlOoReD

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Can any one give info on larger bore sizes; what years, etc. I have a '85 b-II w/'91ish 4.0 and 5-spd and have suspected this is the problem. I just haven't had time to look into it in depth since I've started my race truck.
Richard
 

voodoochylde

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I don't know the bore of the slave. The description on Advance Auto's website lists the master cylinder's bore as 3/4". The old one seems to be 3/4" as well...

AFAIK, the only larger RBV master cylinder is the 7/8" MC which only yields an advantage of 1.16667:1 assuming the slave also has a 3/4" bore.

I dunno, getting frustrated.

cocoasranger, you say you welded a 1/4" extension onto your pushrod? More details?
 
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cocoasranger

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I checked out the clutchcityonline.com site and it appears there are different masters for the 2.9L, probably more if you count the 4.0L. If you call them and explain your problem they can suggest which master you need.
Their number is (866) 762-5141.

Regarding the push rod: I just cut it in the middle and added a short length of rod and welded it back together.This allowed for slightly more fluid to flow; just enough to completely disengage the friction disc. If you want to get tricky, you could cut the rod, thread the two ends and fit them into a threaded sleeve (like a turnbuckle) so you could adjust the rod length when it's on the truck.

Note that once the rod is snapped into the master, it's almost impossible to get back off. I filed the sharp edge a little on the push rod end where it is grooved which allows it to be snapped off and on at will with some effort.

Your best bet is to get the larger bore master.:icon_cheers:
 

voodoochylde

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Thanks for the suggestion. I called Clutch City Online and they didn't have much experience with my particular problem (using explorer pedals in a BII *without* swapping the bracket).

I'm heading to the junkyard after work today to see if I can find a BII with a clutch pedal. Hopefully, I'll find a difference. If I can't discern a difference, my next suspect is the slave cylinder...which I don't wanna mess with as I have to drop the tranny again.

I'll update if I figure out anything...

Maybe cocoas idea will give me something else to fall back on.
 

voodoochylde

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Tentative update: Made it to the JY yesterday and forgot how fun they are to snoop around in. Several BII's, mostly '85. Some had standards. The clutch pedal is noticeably different so I asked the owner to pull it for me. Should have it by this afternoon and have it in tomorrow. I'll update next week with failure or success.
 

alwaysFlOoReD

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I'm interested in seeing what happens. Keep us updated.
Richard
 

voodoochylde

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OK...the BII clutch pedal (out of an '85 XLT) WAS rather different from the exploder. It gave about 2 inches of stroke...while it was in the '85 BII. It only gave me about an inch on mine with the '92 Exploder clutch master cylider.


So I cheated...I cut the pushrod, welded a 2 inch section of all-thread on one end (after a 1 inch piece of the pushrod broke off during my attempt to thread it) and welded a 5/16-18 coupling on the other end. Everything seems fine.

Playing with different master cylinders may have given me different results. I dunno. If I can think about it tomorrow, I'll pull the pushrod and get a total length measurement. Maybe some others can do the same and we can compare dimensions.

In any case....IT LIVES! Drove it up and down the driveway and put 2 miles on it yesterday!
 

alwaysFlOoReD

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Good job :icon_thumby:, this gives me hope for mine.
So, did you also install the 'new' clutch pedal or JUST do the pushrod?
Richard
 

voodoochylde

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Using the junkyard clutch pedal from an '85 bronco ii **AND** modified the clutch MC pushrod.

I forgot to mention this earlier so you may wanna think about this one:

My clutch pedal now sits almost even with the park brake pedal...since I've NEVER driven a standard, I have nothing to compare it to so it's not bothering me.

YMMV.
 


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