'65 - Pull Away Problems - Action Plan

[geordie]

I posted an earlier message related to pull away problems with my '65.

Car:

Modified '65 Mustang coupe. Engine is 302 cubic inch, .030 inch oversize, heads are high flow 351 Windsor 11:1 compression ratio and cam is Shelby hydraulic. Transmission is Tremec TR-3550 manual 5 speed and rear end is 9 inch Ford.

Car is intended as a daily driver, travelling approx. 15 miles a day to and from work and some mileage at weekends. Car is not raced or driven hard, most mileage done at less than 50 mph.

Problem:

Pulling away from a standing start in first gear is difficult without causing engine to vibrate or judder severely. It is only possible to pull away in first gear very slowly and carefully, concentrating hard on clutch pedal release. Pulling away on an incline is very difficult. Moving slowly and smoothly a line of traffic when coming up to a junction for instance is difficult. It is currently believed that this vibration is clutch chatter.

This first thing I've learned is that the 65's have a bad reputation for clutch chatter. Based on the feedback that I have received to my earlier message, this is my go forward plan. I would welcome comments on this, I've tried to list the actions in the order in which they should be tackled. If anyone has anything more to add, then lets have it all please.

1. Motor Mounts - Determine which motor mounts my '65 has? The '65 motor mounts (the metal frame mounts, not the rubber insulators) were redesigned during the '66 model year, the reason being clutch chatter. The new mounts will move the engine up approximately 0.500". I don't have that much under hood clearance so if I need to change the mounts to the '66 ones then this could be a problem, it may mean that the existing mounts are '66. Replacing the motor mounts to the '66 and later style will be an easy, inexpensive and potential cure.

2. Alignment - First of all the engine/transmission/rear end should be in a perfectly straight line. The home method is to tie a string to the crank pulley and to the rear differential, and see how things line up.

3. Transmission - Inspect the transmission and the bell housing. Apparently, there are two different Tremec gearbox shaft lengths. The big block style has a shorter input shaft and will not engage the pilot bearing properly when installed behind a small block, causing major clutch chatter problems. All other external appearances of the transmissions are the same. The badly worn pilot bushing could be an indication that the input shaft may not be contacting deep enough. There is a taper on the end of the shaft and it must get into the bushing or bearing past the taper or it will let the shaft wobble around and quickly wear out the bushing.

Verify what bell housing is being used with the Tremec transmission. Unless it's one of the aluminum bell housings from Tremec designed for that engine, it needs to be dialed in. What type of pilot bearing performs the best and lasts the longest, roller bearing or stock bushing? Have the pilot bushing / bearing checked for centering. If it is o.k. could the bell housing be out of alignment? Bell housing misalignment could be responsible for the problems.

An improper re-surfacing of the flywheel or misalignment of the bell housing could have caused the uneven clutch disc wear. It may be necessary to have the bell-housing dial indicated to make sure the opening for the transmission is centered properly.

4. Clutch Assembly - Inspect and assess the condition of the clutch. Check to ensure that there is no oil leaking from either the engine or the transmission on to the clutch.

Consider replacing it with a heavy-duty street three-finger type pressure plate-clutch set up with organic linings, correctly resurface the flywheel (not using a brake lathe), and replace the throwout bearing and the pilot bearing.

There are horror stories around about not getting clutches perfectly aligned axially with the driveline, the clutch should be concentric with the flywheel to within something like 0.005". That's not a whole lot of tolerance to be playing with.

If the previous garage found it necessary to limit pedal travel, it sounds like an incorrect pressure plate. The original clutch is a three finger borg and beck design. If a new style diaphragm clutch is used, there is too much clearance between the throwout bearing and the fingers. If the linkage is adjusted for a Borg and dech style, and then if it is adjusted to meet the fingers, there can be too much travel and cause the disc to over center. The clutch pedal can stick down also because the new style disc travel isn't enough to push the pedal back against the assist spring in the pedal assembly.

Inspect and assess the condition of the existing clutch linkage. Consider replacing the entire clutch linkage, new z-bar, new clutch pedal bushings, new pedal to z-bar rod, new clutch pedal bushings, new pedal to z-bar rod, new z-bar and clutch rod, all new bushings etc. The clutch pedal bushings can become elongated and cause a big problem.

5. Motor - A poorly tuned engine will exacerbate clutch chatter problems.