Slant Six Forum :: 1960-1966 Clutch z bars weaker than 1967 newer design?

Gentlemen, the roblem isn't as much the thickness/strength of the materials as it is overcoming the incomplete connection at the torsional junction of the lever and the tube inherent in the factory design. Which design was engineered more for ease (cheapness) of production than for correct engineering. All you need to do is complete the circle of contact the levers want/need around the torque tube to prevent focal points of stress that initiate cracks.

Starting with a stock unit, the simplest way is to add a strip around the "back" of the tube, that connects to the edges of the lever. A "U" shaped piece of 1/4" pencil steel rod (or anything structurally similar) fitted snugly on, and welded all the way around'll accomplish the task. This will more than double the torsional capabilities of the stock unit, to the point that failure will always generate elsewhere.

This is an automatic upgrade on my builds, unless I choose to scratch a better engineered one, with a proper full circle hole in the lever for the torque tube.

Author:	Greg Ondayko [ Mon Aug 17, 2020 7:20 pm ]
Post subject:	1960-1966 Clutch z bars weaker than 1967 newer design?
I had a z bar failure on sunday in my 64 dart. It has recently got a skookum 9.25 mcleod pressure plate installed which is a heavy clutch pedal to push. So I found out that the z bar on the 64 dart was made from thinner material compared to the 69 a body z bar. I am assuming here that the design was redone with extra heft for the 67 model year redesign. So to keep my car running i decided to use the 69 z bar and redo the geometry to match the 64 z bar that has the thinwall tube and broke on my car. Pics: Here is a comparison of the 2 parts.. 64 on right.. notice the id of the tube is the same ... but od is very much smaller on the right side part in the picture. Close up of the metal gauge difference.. Stay off crack.. Taking some angular measurements. Finished product with arms to match offsets, angles and locations of the 64 part. Hope to get it back in the car to test it out soon. Greg

Author:	Dart270 [ Tue Aug 18, 2020 3:29 am ]
Post subject:	Re: 1960-1966 Clutch z bars weaker than 1967 newer design?
Very nice pics and work, Greg. Sorry to hear about the failure. I'm sure you will succeed. I had buddies in high school and college with 4 spd cars and hipo clutches. They were always breaking/bending clutch forks and Z-bars and other linkage stuff. This is one reason (the others being perfect geometry and easy adjustment) why I went straight for the McLeod hydraulic (concentric with input shaft) TOB when I did the T5 in the 64 Dart back in 2002. FYI... Lou

Author:	Greg Ondayko [ Tue Aug 18, 2020 5:17 am ]
Post subject:	Re: 1960-1966 Clutch z bars weaker than 1967 newer design?
I never had a problem until now. All the other Hi Po Stuff I have is a diaphragm style PP. this is really only the 3 Finger PP that I have used so far with heavy springs. I could hear you in the back of my head yapping about the Hyd. TOB. Funds and time just don't make that feasible now. An hour of welding / grinding and some re-engineering have got it solved... test it tonite or tomorrow. I have an AutoX to get to Sunday! Greg

Author:	Dart270 [ Tue Aug 18, 2020 5:37 am ]
Post subject:	Re: 1960-1966 Clutch z bars weaker than 1967 newer design?
Of course, cost is a major factor, and at the time I decided to save up for the hydro. Probably your fix will last a very long time. Lou

Author:	Greg Ondayko [ Tue Aug 18, 2020 6:28 am ]
Post subject:	Re: 1960-1966 Clutch z bars weaker than 1967 newer design?
I can $ave up for it.. just not a priority now.. Rpf01's.... sticky tires and building a proper engine / oil pan are next on the list. Gref

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Author:	Dart270 [ Tue Aug 18, 2020 8:54 am ]
Post subject:	Re: 1960-1966 Clutch z bars weaker than 1967 newer design?
I like your priority list. Lou

Author:	Greg Ondayko [ Tue Aug 18, 2020 9:59 am ]
Post subject:	Re: 1960-1966 Clutch z bars weaker than 1967 newer design?
Quote: I like your priority list. Lou Good! Glad to know it's Dr. Madsen Approved.. that will make my thesis go better. Greg

Author:	Dart270 [ Tue Aug 18, 2020 10:10 am ]
Post subject:	Re: 1960-1966 Clutch z bars weaker than 1967 newer design?
Hah! Nice. I have 3 PhD students getting ready to graduate in the next year or so, so I will be reading/editing hundreds of pages of their theses (thesises) pretty soon. I guess you have written 200+ pages of Slant 6 material already... Lou

Author:	Old6rodder [ Tue Aug 18, 2020 11:39 am ]
Post subject:	Re: 1960-1966 Clutch z bars weaker than 1967 newer design?
Gentlemen, the roblem isn't as much the thickness/strength of the materials as it is overcoming the incomplete connection at the torsional junction of the lever and the tube inherent in the factory design. Which design was engineered more for ease (cheapness) of production than for correct engineering. All you need to do is complete the circle of contact the levers want/need around the torque tube to prevent focal points of stress that initiate cracks. Starting with a stock unit, the simplest way is to add a strip around the "back" of the tube, that connects to the edges of the lever. A "U" shaped piece of 1/4" pencil steel rod (or anything structurally similar) fitted snugly on, and welded all the way around'll accomplish the task. This will more than double the torsional capabilities of the stock unit, to the point that failure will always generate elsewhere. This is an automatic upgrade on my builds, unless I choose to scratch a better engineered one with a proper full circle hole in the lever for the torque tube.

Author:	Greg Ondayko [ Tue Aug 18, 2020 11:41 am ]
Post subject:	Re: 1960-1966 Clutch z bars weaker than 1967 newer design?
Quote: Hah! Nice. I have 3 PhD students getting ready to graduate in the next year or so, so I will be reading/editing hundreds of pages of their theses (thesises) pretty soon. I guess you have written 200+ pages of Slant 6 material already... Lou The forum puts extra needless space and wide margins... so I think not. Greg

Author:	Old6rodder [ Tue Aug 18, 2020 11:48 am ]
Post subject:	Re: 1960-1966 Clutch z bars weaker than 1967 newer design?
1/4" mild pencil rod's on hand at most hardware stores, in 1,2, & 3 foot lengths. I'm fortunate to have an extra few thousand feet of it handy at the float barn. In a pinch, you could sub 5/16" rolled thread stock. Wouldn't be much less strong, and would still be full circle. The stress points at the bottoms of the threads'd likely become the possible failure points of the future, though still significantly better than the stock unit.

Author:	Old6rodder [ Tue Aug 18, 2020 12:26 pm ]
Post subject:	Re: 1960-1966 Clutch z bars weaker than 1967 newer design?
With time as a major element for you, here's a very quick & fairly strong cobble. Run a scrap of whatever you have handy (strap, cap screw, anything that can be cut to fit) to form a straight line from the "front" edge of the lever (the edge that "T"ee's into the tube, not the one that passes by it) to the side of the tube opposite the "passing" edge, and weld it in. This'll form an opposite side to the lever that'll dissipate the stress loading better than nothing. Should be good for around a 40% immediate increase in torsional strength of the unit.

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