Clunking noise when putting PG into gear
OK trying to get all the bugs worked off the shakedown list. When shifting the Powerglide trans into reverse or back into drive there is a clunking noise which sounds like it is in the rear differential. It is a non-posi unit. Trans was rebuilt, all U-joints were replaced in drive and half-shafts. Trailing arms and bearings are new. I think that I had the differential checked out when the car was dis-assembled back in 93, but I'm not 100% sure (I do know I had to fill it with fluid prior to starting the car, so I think it was checked). ANYWAY, how is the best way to isolate the clunking noise if it is in the rear of the car? Hope this is not a dumb question. Al
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Re: Clunking noise when putting PG into gear
The 2 speed cast iron PG in my 1960 has always made a clunking noise and a slight jolt in the car frame every time I shift to D or R; more so in one than the other. There was no difference in the degree of clunking before or after I had the PG rebuilt over 3 years ago. The re-builder told me that it is normal to feel the jolt. I have wondered if a "PG technician" went through all of the adjustment steps that are shown in the 1961 Passenger Car Shop Manual, and there are many, many adjustments with special tools, the PG might perform better and the clunking noise and jolt would be less. -
Re: Clunking noise when putting PG into gear
Joe, it does have more of a jolt or clunk going into reverse than driveComment
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Re: Clunking noise when putting PG into gear
I would say that is accurate for my car as well. I have never driven or ridden in another Vette with PG to experience or not experience the same clunk/jolt.Comment
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Re: Clunking noise when putting PG into gear
Any PG owners out there to offer their opinions or info on clunks?Comment
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Re: Clunking noise when putting PG into gear
Al, most clunking noises are generally something to do with things like the snubber bushing, U-joints, rear diff. back lash not set properly, and lastly the internals of transmission, most transmissions use a wave plate in the clutch packs to soften the blow on engagement. the best way to approach this is have someone engage transmission while watching for any possible movement anywhere. trailing arm bushing and bolts should also be tighten to stop any sort of movement. Al also check the idle speed the lower you can adjust it may lessen the engagement.New England chapter member, 63 Convert. 327/340- Chapter/Regional/national Top Flight, 72 coupe- chapter and regional Top Flight.Comment
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Re: Clunking noise when putting PG into gear
Al,
That is why the PG's got the nick-name of "clunkers"! They lived up to the name!
JRComment
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Re: Clunking noise when putting PG into gear
With any slush box idle speed is critical. Make sure you are slow enough. Another harsh engagement cause can be line pressure. Make sure that engine vacuum is up to where it should be and is registering that same figure at the modulator valve on the trans. The mod regulates line pressure which, in addition to altering shift points, alters apply pressures. If the vac is low the trans thinks the engine is working hard and raises apply pressures to the clutches and servos. If line pressure is already boosted when you shift into gear it will engage harshly. Reverse is more evident because line pressure is boosted by50 to 100% (can't remember specifics on a pg) for reverse application vs elements applied for forward movement. Ultimately you can use the test port and measure line pressure at idle and compare to spec if you have suspicions. Fluid type and condition is also very important.
Slop in the drive line, rubber mounts, snubbers etc are also important, of course. But the next most likely place is the diff. It is seldom backlash. The play you feel when you rock the driveshaft (trans in neutral, wheels not turning) is mostly the play between the spider gears, the pin they ride on and the axle gears. If you pay very close attention as you rock the drive shaft and just move it a very little you will feel the pinion rocking against the crown.This is like .006" in an ideal. Even at twice the backlash specified, it's a pretty small amount. As you continue to rotate the driveshaft without the wheels turning the rest of this play is in the differential portion of the component. In a non posi, hold the driveshaft and one wheel still while you turn the other wheel and look at how much slop you have. Spider gears loose on the pin, pin loose in the carrier, spiders worn into the carrier are all probable/possible causes if you have excess play in the dif. More common on non posi axles. The dif was designed to allow one wheel to turn slightly faster than the other to round a corner. They were never intended to allow one wheel to sit still while the other spun madly. Spider and axles gears turning much faster and harder than they were ever intended to. PG cars aren't as likely to have seen that abuse, but who knows.
Just a couple more suggestions to throw into the mix.
Steve
Edit. Line pressure is internally adjustable. Some modulators are adjustable with an allen wrench through the vac hose port.Comment
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Re: Clunking noise when putting PG into gear
Hey guys, thanks for the comments and tips. I know the vacuum is a little lower than it should be. Don't remember exactly what it is. I probably have it in an earlier post from last summer. So, this could be part or all of it. I will check all suggested items hopefully this weekend if time permitsComment
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Re: Clunking noise when putting PG into gear
I have a 63 with a PG . I have owned it from 1970 and it always clunked when putting it in drive or reverse.Comment
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Re: Clunking noise when putting PG into gear
I have a 66 PG and a 73 turbohydramatic 400 and they both clunk when putting them into gear. I have had the 73 since new and it has always clunked at least some.Comment
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Re: Clunking noise when putting PG into gear
I have a 65 with a fresh Turbo 350 in it and it clunks even at a very slow idle speed.Comment
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Re: Clunking noise when putting PG into gear
I would like to know your idle speed and vacuum in Drive. In neutral at 500 RPM on a manual it should be about 18-19" Hg assuming the OE cam or something with the same effective overlap.
Go through the idle speed/mixture adjustement procedure in Drive, and shoot for 450-500 RPM, the lower the better. Measure vacuum. Then put it in neutral and measure idle speed and vacuum.
Request you post the data - speed/vacuum in Drive and speed/vacuum in neutral after you have it dialed in.
You should also verify that the VAC is functioning properly. OE is a "355 16" (or a B20 or B26 replacment) should provide 16 deg @ 12". and the initial timing should be in the range of 6-8 deg.
Idle vacuum needs to be a little higher than the maximum vacuum required to pull the VAC to the limit or the idle could be unstable.
DukeComment
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Re: Clunking noise when putting PG into gear
Duke, it will probably be the end of next week before I get a chance to check the vacuum. I had company come over and I leave AT 6 tomorrow for TN. I will post later.Comment
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