VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Cause of 'Clunk' in reverse gear and hum (low roar) at 35-45 mph

OK people, the problemm is stated in the "Subject" heading.

I just replaced the 4 motor mounts and the transmission mount, but the problem is un-diminished. I suspect the Universal Joint, which is a ----- to replace, but I also suspect I may be wrong. A problem with the transmission bearings (front or back)?, differential?, or something else entirely?

I did replace the clutch (throwout bearing, etc.) about 4 months ago, and it worked fine after that, but was always a bit rough in reverse, but nothing like this.

Any help would be appreciated before I invest $150 + shippimg, in a new U Joint.

DocB

Is the hum worse when you let off the gas and start to coast or worse when you are accelerating? Have you eliminated the differential and rear axles and prop shaft from this equation? You may want to reconsider....since the noise will travel up the prop shaft and torque tube to the front of the driveline.

Possible cause of problem - but difficult to tell without driving the car.

!# suspect would be the U joint-Believe they can be purchased cheaper at NAPA-or if you have time on Ebay.

#2-transmission-would require inspection

#3-differential-spider gears or???

MrMack,

Seems to be there all the time, between 35-45, accelerating or not. That's just a minor annoyance, but I think it's symptomatic of somthing more serious. It's the heavy "clunk" in reverse that worries me and told me 'U-Joint'.

And no, I haven't eliminated the rear axles, differential and prop shaft from the equation, 'cause it's been 45 years since I've really worked on this 'beast'. I think it's time to take my fellow local club member up on his offer to "give" me the torque tube, axle and everything else from the 40 Master 85 (differential ratio 3.7? to 1)he is planning to "Rod".

Appreciate your help and any further diagnoses will be appreciated.

BTW, is Commanche County anywhere near Austin? Spent 2 years, in the mid-60's, in Austin at UT. Love Texas and miss it.

DocB

Doc, We are about 150 miles North and a little West of Austin. One reason I was interested in your problem is I developed one in my 53 with standard tranny. It surges in reverse kinda jerks when the clutch is let out, no clunk and it also has a click in 1st gear about one click every rev of the tires. I have the tranny out and haven't found a problem with the u joint or the front drive shaft bushing, and the differential seems to have about the right amount of slack between forward and reverse. The car has a large clutch that the pressure plate will barely fit inside the flywheel,it may be from a truck since I believe the 235 engine is off a pickup, and it looks ok except it looks like the throwout bearing has been riding on the clutch diaphram springs (the clutch link from the fork to the peddle is an inch shorter than the parts book calls for and an inch shorter than the one I have from a 54 car). I am going to pull the clutch today and look at the pressure plate, pilot bushing and flywheel .

:confused:
Anyone want to speculate what the cause of the surgeing in reverse is?

DOC
The noise and clunk are both most likely U-joint.
If the ring gear and pinion (3:7?) is in good shape you should put in the rear end and U-joint.
I put a 3:55 R and P from a 54 powerglide and a new U=joint in my "41 . Best move I have made in years. The change is tremendous. Even if this does not correct your problem you will not regret the change. Chevgene walked me through my change. He would be glad to help you.
Good Luck JIM