Tech Q&A - Engine - Clutch and Transmission

CLUTCH CLUNKING NOISE

Question:
You may recall that I spoke to you about a "clunking sound" I was experiencing every time I depressed the clutch on my Model A. I found the problem. The ring gear on the flywheel had slipped forward or, more likely, was driven forward by the engagement of the Bendix gear over a period of many years. The gear was so far forward that it was contacting the back of the engine. I tapped it back into place and center punched (dimpled) the flywheel to tighten the ring. You may want to pass this on to others that may have the same problem.
-- Dave Stoner

Answer:
Thank you so very much for passing on the cause and fix to your problem. I very seldom get this kind of feedback. It helps all of us.
-- Les Andrews, Technical Director


CLUTCH STICKING

Question:
I have a problem with the clutch freezing up on vehicles I put up for the winter. I wonder if anyone knows of a way to prevent it or the best way to loosen a stuck clutch?
-- Rodney Davis

Answer:
The Model A clutch will collect moisture when stored in a humid area for the winter or any long period of time. Storage should be in a dry area. Covering it with a tarp outside makes it worse because it traps the moisture and condensation. The result is the clutch rusts to the Flywheel (there are metal particles in the clutch disk). The only way to get it loose is to pull the engine and remove the pressure plate and clutch. This usually means replacing the clutch plate. Start the car once a week during the winter months and activate the clutch a few times. Spinning the flywheel will eliminate most condensation buildup.
-- Les Andrews, Technical Director


CLUTCH STUCK

Problem:
I have Model A which is not a show car, though I am working on it in pieces and the engine now runs nicely. However, the clutch seems stuck. It won't go into gear when running - grinds if I try. Is there any way to free up the clutch without pulling the engine or rear end? Would loosening the 12 bolts at the inspection hole allow me to free it up?

Solution:
You definitely do not want to loosen the 12 bolts on the pressure plate (through the inspection plate). You would really have a mess then. If the Model A has set for a long period of time in a humid climate, the clutch disk will collect moisture and then rust to the flywheel and never releases. There is not much hope in getting it free without complete disassembly. You will probably need to replace the clutch plate. Your best bet is to pull the engine.
-- Les Andrews, Technical Director


CLUTCH STUCK

I had this problem on a 1939 ford I bought that had sat up for 20 yrs. After I unlocked the engine with marvel mystery oil and a prybar, I found out the clutch was frozen to the flywheel.

I put the rear of the car on jackstands and left the rear wheels free to rotate. I then started the car in 1st gear and ran it a minute or two. I accelerated the car to about 20 mph on the jackstands. Then I depressed the clutch and hit the brake fast and hard. It broke loose!  

I engaged the clutch a few more times on the stands. When I put the car on the ground, the more I drove it the better the clutch worked. I sold the car to a friend of mine who put several thousand miles on the car with no problems.
-- Chip Evans


MULTIPLE DISK CLUTCH

Question:
I have acquired an early 1928 phaeton which I am currently restoring. Of the little material I have read, I get the feeling I shouldn't persist with the original clutch but should get a later single disc model. For the record I like the purist thinking but it is unlikely I will show the car; I would rather drive it. Your thoughts please???

Answer:
If you plan to drive your Model A I would suggest you put the later single disk clutch in. The disadvantage of the multi disk clutch is that oil from the rear main would get into the clutch assembly and mix with dust from the clutch disks and cause the disks to hang up in the flywheel. The clutch would also chatter because of problems with the disks releasing. That's why Ford changed early (about Nov 1928) to the single disk clutch. It can get rather expensive to rebuild a multi disk clutch. More than just the clutch is involved. It will also take some doing to change it out because of major differences.

To change from a multi disk clutch to a single disk clutch you must replace the flywheel, flywheel housing, pressure plate and clutch disk, and transmission. The early transmission for the multi disk clutch had a different front main driver gear and shaft and no throw out bearing. The early transmission case was not tapped for the bolts that hold the front bearing cover, which is a snout (housing) for the throw out bearing slider (hub) to ride on. If you get a later transmission, make sure it has the front retainer which is the slider snout for the throwout bearing, and the throwout bearing hub.
-- Les Andrews, Technical Director


GROWLING GEARS

Question:
I am having a not so unusual problem of a growling transmission. The cluster and both sliders appear to be brand new as do the roller bearings, etc. (The transmission was a gift.) I'm restoring a (hopefully) show car, a February 1928 Sport Coupe. I've changed out clusters and sliders to the point of major frustration, but so far I'm not having success. First and second gear are loud. Third is quiet. My question is, why do gears make noise? What is the physics? That's what I really want to know. Too close tolerances? Too loose tolerances? Obviously, rough, worn and pitted tooth surfaces will do it. But why new gears? I'm pretty sure looseness shouldn't do it, because the drive shaft gear mating with the drive gear on the cluster is a bit sloppy and it's as quiet as can be. The noise with the original new gears is not terribly loud, but unacceptable. Do you know of a source of gears which will not growl? Or am I stuck with the trial and error method?
-- Dick Kilburn, Naperville, IL

Answer:
The Model A transmission has square cut gears vs. helical cut gears in later models. The square cut gear will always be noisier than the helical cut gear. If the square cut gears in the Model A are not kept precisely aligned, more noise will be generated from them. The two slider gears were originally matched fit to the main (spline) drive shaft. This allowed the gears to maintain perfect match up and alignment with the cluster gear. If the slider gears fit too loose on the splined drive shaft, there will be some binding of the slider to cluster gear. Binding creates a growl. Wear in a lot of areas will add up and cause misalignment of gear match and transmit noise. The fit of the end of the main drive shaft into the flywheel pilot bearing must be a snug fit.

Many times the end of this shaft is badly worn from spinning inside the pilot bearing instead of the bearing doing the spinning. This wear and loose fit causes lateral movement of the shaft, thereby placing a tilt and misalignment of the transmission drive shaft. Also the flywheel housing should be true with the flywheel and crank with no more than .006" variance. I have seen flywheel housings warped to more than .020" variance. This causes a real stress and misalignment of the drive line. I do not know if the new cluster gears are machined correctly for correct fit and clearance of gear teeth contact. There must be adequate (about .005 to .008 ) clearance (backlash) of the gear mesh. A quiet transmission requires a straight alignment of the drive line, a precise fit of the two slider gears on the splined drive shaft, a snug fit of the drive shaft in the pilot bearing on the flywheel, and no more than .006" variation of flywheel to flywheel housing. I hope this gives you a little better understanding of what causes a noisy transmission. It doesn't take much wear in the wrong place to cause a square cut gear transmission to get noisy. That's why they went to a helical cut gear, in addition to the synchromesh.

A side note: A correct fit slider gear to splined drive gear: apply 600W oil on the splined shaft and set the shaft upright. Place a slider gear on the shaft and the gear should slide down the shaft with some resistance, i.e., take about 1.5 seconds to fall. If it drops straight down on the shaft with no drag or resistance, its an inadequate fit.
-- Les Andrews, Technical Director


GEAR OIL AND SHIFTING

Question:
My transmission works fine with the 600W oil until it warms up, but then it begins to grind a little when shifting between gears. My question is can I either use all STP or a half and half mixture to slow down the shaft since it appears that once the shaft speed is reduced I get no grinding or will double clutching help the situation or both.
-- Rich Greenwood

Answer:
The Model A does not have syncromesh gears and therefore requires double clutching between gears. I have found that anything from 50/50 STP /600W to straight STP works well in the transmission. It allows much smoother shifting (still should double clutch until you get use to the correct rpm for smooth shifting).
-- Les Andrews, Technical Director


GRINDING GEARS

Question :
I have a 1930 Deluxe Coupe. The transmission grinds when you go from 2nd gear to 3rd gear. Also you can not down shift from 3rd in to 2nd gear. Is this a sign that the clutch is going or not properly engaging?
-- Graham Family

Answer:
I don't know what your driving experience is with the Model A, but are you aware that the Model A does not have synchromesh gears ?? You must double clutch when going between gears. Down shifting in a Model A is extremely difficult if you are not use to it. Because you do not have synchronized gears, to down shift you must double clutch, while doubling the engine RPM while in the neutral state before dropping into the lower gear. It takes lots of practice and familiarity with your car. I suggest you not attempt to down shift your Model A. Try adding STP oil additive to your transmission. It will help give you a smoother shift of gears. With proper double clutching, you should get a smooth shifting of gears. You may also need to adjust the trunion nut arm on the bottom of the clutch pedal. If you can't get a good release of the clutch then you may need to replace the clutch disk.
-- Les Andrews, Technical Director


PITTED TRANSMISSION CASE

Question:
I have an early 1930 AA truck. The 4 speed transmission case has been badly pitted by rust. I was wondering if I could use a body filler to fill the pits and then texture it with a sponge so it looked like the original casting?

Answer:
It should work fine. Be sure to fill in small amounts. It will hold up better if you build it up in thin layers rather than all in one step.
-- Les Andrews, Technical Director


SLIPPING OUT OF GEAR

Question:
I have recently purchased a 28 Phaeton model A, I have trouble with it slipping out of third gear going back into neutral occasionally, any suggestions to what the problem might be and how it could be rectified? Would greatly appreciate your advice.
-- Glen Williams, South Australia

Answer:
There are several things that cause the transmission to slip out of gear. The main cause is due to a car that is 70 years old and has worn parts. The front main drive shaft on the transmission fits in the flywheel pilot bearing. When the end of this shaft gets excessively worn (and many do) it causes too much lateral movement of the main shaft and misalignment of the drive line and gears, causing the gear to disengage under load. If the flywheel housing is out of alignment with the flywheel or with the crank by more than .006" variance, this will also misalign the transmission drive line and cause the transmission to disengage. Badly worn shifting tower forks and weak tower springs will also aid in disengaging transmission.

1. Rebuild transmission, making sure the front drive shaft is not worn where it enters the pilot bearing.
2. Replace pilot bearing in flywheel and all transmission bearings.
3. Check flywheel housing variation (no more than .006" variation.)
4. Reverse the shifting tower forks (swap them front to back) to eliminate wear side.

-- Les Andrews, Technical Director


Last Updated: 04/01/2012
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