Sunday, June 7, 2009

Q & A clutch assembly

Q: I bought one of the aftermarket clutch forks for my SCRambler and it doesn't fit properly. Installed, it drags on the bottom of the bellhousing slot! The fork is for a 67-70 amc bellhousing and T-10. Have you heard of this before?

A: I've since talked to Jeff Kennedy and he tells me that AMC issued a replacement fork around 1975 and it was not made correctly. All of todays reproduction forks, sold by all the vendors are stamped copies of the incorrect 1975 fork.

They all ride on the bottom of the bellhousing slot! Solution: find and use original OEM forks!!

The problem I've having with the reproduction fork, is wear and tear on the release bearing. It presses unevenly on the pressure plate tines (diaphram plate), causing the ballbearings to heat up due to the added rolling friction.
The bearing wears quickley and the grease is spun out all around the inside of the bellhousing.

When I press in the clutch pedal to the floor, I get an awful grinding sound and a vibration right up the clutch pedal. Three bearings now in 9000 miles. (three summers) . I shall take out the trans next week and put in my OEM fork along with a new bearing and see how things work.

Here is a write up on this subject by Jim McKee:

Hi Bob,

Replacing the Borg and Beck pressure plate with a diaphragm pressure plate is a good move. I have reinforced so many of the clutch linkage bellcranks bent from trying to overcome the locking action of Borg and Beck pressure plates I have lost count. The B & B pressure plates have rollers that jam the plate into the clutch disc increasing pressure as the rpm goes up. This is what bends the bellcrank trying to overcome this roller action.

It is the primary reason AMC T-10s are hard to shift at upper rpms with this style clutch.
I recommend the Hays Street/Strip diaphragm #40-111 and disc #33-610.
These bolt onto the stock flywheel with a 10 1/2" disc with 1 1/8" x 10 splines.

Be careful using Hay's supplied bolts, because I have had problems with the bolt's shoulder not allowing the diaphragm pressure plate to pull up tight to the stock flywheels, because most stock flywheel holes are not counterbored.

Hays tells me these clutches are good for up to 600 HP and 7000 rpm. Buy an AMC clutch alignment tool and use it. The plastic ones are $ 4.00 at Advance Auto Parts last time I bought one. Good price on this clutch at Summit. Read the Hay's directions.

The correct throwout bearing for diaphragm pressure plates has a rounded outside edge that contacts the diaphragm fingers. The flat face throwout bearings tend to dig into the diaphragm fingers.
I also find the throwout bearing collar that holds the bearing needs to be shortened some, usually about .15" to .20" to allow freeplay adjustment as the disc wears.

Use a carbide bit on a lathe, because the thing is hardened. The throwout fork end that the bellcrank to fork rod presses against needs to be forward of the mid-point of the boot opening.

Most times this rod length needs to be adjusted shorter. I take this opportunity to use a 3/8" bolt and a spherical bearing at the bellcrank end by grinding off the welded stud in the bellcrank that accepts the clutch adjustment rod.
There is usually just a tack weld on the back of the stud. Both ends of the new rod need to be 3/8" x 24 thread to use the stock AMC adjuster hex and nut.

As Gerry has discovered, throwout bearings need to contact the pressure plate fingers evenly or vibration , accelerated wear, and/or binding occur.

I believe Jeff Kennedy about the later year throwout forks being incorrect, but I have no experience with this issue.

When you go to the diaphragm clutch, I also recommend changing the front and rear transmission seals and using synthetic gear lubricant. There is no warm up period with this fluid and I have had good luck with all of the synthetic gearbox lubes. I don't use synthetic lube in the AMC positraction rear ends and recommend Valvoline 75-90WHigh performance lube for them. Regards, Jim

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