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1940 Buick grinding when down shifting into second


kingrudy
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My 1940 Buick Super has started to grind a bit when down shifting from third to second. I have tried to be very conscientious about putting my foot to the floor when down shifting, but no help. I have tried double clutching, but no help.  The car shifts through the gears first, second and third fine, but here in Asheville there is no such thing as a flat surface, so there are times when downshifting is necessary going up a hill. 

Any suggestions would be greatly appreciated.

 

Thanks,

Mike

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My suggestions:

 

1) Most importantly make sure the clutch is disengaging completely. First adjust the clutch per the manual, to make sure that part is OK. Then, with the engine idling on flat ground, disengage the clutch, put the transmission in second or third to stop the gears. Then put the transmission in first. Never let up the clutch pedal. Then take it out of first gear carefully, going only to neutral. Do not let up the clutch pedal. Count 5 seconds and try to put it back in first. If it grinds, the clutch is dragging for some reason. and you will have to investigate further. There could be oil on the clutch disc, or there could be some worn out linkage parts, or another mechanical problem.

 

2) If it went right back in first gear, or went with just the tiniest bit of a thunk, and did not grind, your second gear synchronizer is not working. It might be shot. My second suggestion, on the off chance there is some super-slippery hypoid gear oil in there, is to change the oil to some real synchromesh oil, like Redline MT-90, or Redline 75w140NS, or GM Synchromesh, or something similar. and see if it helps. It might not, but it is easier than taking the transmission apart.

 

If the clutch does not drag, you should be able to bypass a bad synchronizer by double clutching.

 

Edited by Bloo (see edit history)
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Whenever I downshift from 3rd to 2nd (whether a non-synchro Model "A" or my Buick), I've found that slightly "goosing" the accelerator between gears really helps the downshift slide easier.

The quick increase in engine RPM's seems to help the gears mesh much easier.

 

Clutch in, slide gearshift out of third, release clutch, quick "goose" the accelerator, clutch in, slide up into second, on your way

 

I have a hill by my house and this is a daily event so I have mastered this maneuver.  

 

Maybe it'll help to try it.

 

Gary

 

***  Edited the technique.  Yes, "goose" it with the clutch released to match the gear RPM's, then depress the clutch and downshift into second.  ***

Edited by Gary W
Downshift sequence was wrong (see edit history)
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1 minute ago, Gary W said:

Whenever I downshift from 3rd to 2nd (whether a non-synchro Model "A" or my Buick), I've found that slightly "goosing" the accelerator between gears really helps the downshift slide easier.

The quick increase in engine RPM's seems to help the gears mesh much easier.

 

Clutch in, slide gearshift out of third, quick "goose" the accelerator, (clutch still in), slide up into second.  

 

I have a hill by my house and this is a daily event so I have mastered this maneuver.  

 

Maybe it'll help to try it.

 

Gary

Thanks Gary, I have a hill by my house also and this will be common event. 

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The goosing is an ESSENTIAL part of double clutching when downshifting. The whole point is to match gear speeds.

 

Disengage clutch, pull out of gear, re-engage clutch, goose engine, disengage clutch, pull into gear.

 

Timing is everything, and will have to be worked out by trial and error.

 

The truth about what is happening is a bit complicated, but the way oversimplified version goes something like this: The engine would be turning faster if the car was already in second gear, so you must "match" that speed with the disengaged gear. You first disengage the clutch and pull the transmission out of gear. Then you reengage the clutch. This reconnects the spinning parts of the transmission to the engine. You then goose the engine to increase the speed of those parts. You need to go a little bit too high. Then you disengage the clutch a second time. When you disengage the clutch for the second time, the spinning transmission parts will instantly begin to slow down. You then shift to second.

 

The trick is to spin the transmission parts fast enough that when you disengage the clutch the second time, and their speed falls, their RPM matches second gear at the same instant you shift to second.

 

Give the engine some gas as you re-engage the clutch for the second time. The gears may have matched when you shifted to second, but they are still slowing down, and the engine has slowed down probably even more, and you don't want the car to lurch slower when you re-engage the clutch.

 

If the engine speed matches what it should for the current speed in second gear, the re-engagement will be smooth, but a bit too much engine speed is way better than too little.

 

Note: you could probably eliminate the FIRST clutch pedal disengagement when you pull the transmission out of gear, as in Gary W's post above, because the point is to spin the transmission parts up to a higher speed. The clutch must be engaged to spin those parts up when you goose the engine. You might even need to eliminate that first disengagement for timing reasons. It depends on the car, the hill, etc. etc.

 

Edited by Bloo (see edit history)
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6 hours ago, Bloo said:

Note: you could probably eliminate the FIRST clutch pedal disengagement when you pull the transmission out of gear, as in Gary W's post above, because the point is to spin the transmission parts up to a higher speed. The clutch must be engaged to spin those parts up when you goose the engine. You might even need to eliminate that first disengagement for timing reasons. It depends on the car, the hill, etc. etc.

 

Okay, please bear with me because I'm trying to learn something here, even though my Super does not have this problem (yet, anyway).

 

I think I understand all of Bloo's explanation, except for the extra paragraph I have quoted above.  As I read Gary's post, he never says that he is goosing the engine with the clutch engaged.  Gary says "Clutch in, slide gearshift out of third, quick "goose" the accelerator, (clutch still in), slide up into second."  So I'm confused by what Bloo means when he says that you could probably eliminate the FIRST clutch pedal disengagement when you pull the transmission out of gear "as in Gary W's post above."  I also don't understand how Gary's method accomplishes the desired purpose of spinning up the transmission parts to a higher speed since he is not engaging the clutch with the transmission in neutral when he is goosing the engine.  I'm sure I'm missing something, but I don't see how Gary's post can be reconciled with Bloo's.  Any help would be most appreciated.

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OH!

 

I think I need to edit that. Traditional double clutching, as you might imagine, involves pushing the clutch down twice. But, the clutch has to be engaged to spin the gears up.

 

I may have COMPLETELY misinterpreted what Gary said. I think I am going to wait until he comments before I edit. I thought Gary just eliminated the first push, pulled the car out of gear without using the clutch, and went straight to spinning the gears up. Then he disengaged the clutch to make the shift. There's nothing wrong with that. Reading it now, I am not so sure that is what he meant.

 

There is another similar technique called "floating a gear" that works well on pure crashboxes like a model A, and especially on big truck transmissions with real sliding gears. It does not work nearly so well on a worn out synchromesh transmission, or at least it is a lot tougher for me. It goes like this. You don't use the clutch at all. You pull the transmission out of gear, goose it, but shoot for a really close RPM match, don't go over significantly like you would to double clutch, then you lightly, with a finger or 2 on the lever "feel" the lower gear. If you matched the RPM right it goes "tha-tha-thunk!" and right in.

 

Edited by Bloo (see edit history)
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11 hours ago, Bloo said:

The goosing is an ESSENTIAL part of double clutching when downshifting. The whole point is to match gear speeds.

 

Disengage clutch, pull out of gear, re-engage clutch, goose engine, disengage clutch, pull into gear.

 

Timing is everything, and will have to be worked out by trial and error.

 

The truth about what is happening is a bit complicated, but the way oversimplified version goes something like this: The engine would be turning faster if the car was already in second gear, so you must "match" that speed with the disengaged gear. You first disengage the clutch and pull the transmission out of gear. Then you reengage the clutch. This reconnects the spinning parts of the transmission to the engine. You then goose the engine to increase the speed of those parts. You need to go a little bit too high. Then you disengage the clutch a second time. When you disengage the clutch for the second time, the spinning transmission parts will instantly begin to slow down. You then shift to second.

 

The trick is to spin the transmission parts fast enough that when you disengage the clutch the second time, and their speed falls, their RPM matches second gear at the same instant you shift to second.

 

Give the engine some gas as you re-engage the clutch for the second time. The gears may have matched when you shifted to second, but they are still slowing down, and the engine has slowed down probably even more, and you don't want the car to lurch slower when you re-engage the clutch.

 

If the engine speed matches what it should for the current speed in second gear, the re-engagement will be smooth, but a bit too much engine speed is way better than too little.

 

Note: you could probably eliminate the FIRST clutch pedal disengagement when you pull the transmission out of gear, as in Gary W's post above, because the point is to spin the transmission parts up to a higher speed. The clutch must be engaged to spin those parts up when you goose the engine. You might even need to eliminate that first disengagement for timing reasons. It depends on the car, the hill, etc. etc.

 

Bloo, thanks for the great information! I will take the car out on Friday for some practice.

 

Mike 

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Sorry for any confusion...  I edited my original post so the proper downshift technique is up top.  

 

But the "goose" between gears makes the downshift effortless.

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On 7/19/2021 at 12:00 PM, Bloo said:

My second suggestion, on the off chance there is some super-slippery hypoid gear oil in there, is to change the oil to some real synchromesh oil, like Redline MT-90

 

I'll second the suggestion for Redline MT oil.  I put that into my GP (has a B-W T10) and it shifts 'like butter'...  ;)

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On 7/20/2021 at 10:33 AM, Gary W said:

I've found that slightly "goosing" the accelerator between gears really helps the downshift slide easier.

The quick increase in engine RPM's seems to help the gears mesh much easier.

 

Clutch in, slide gearshift out of third, release clutch, quick "goose" the accelerator, clutch in, slide up into second, on your way

 

AKA double clutching!😉

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Thank you everyone for all of the feedback. I took the car out for a long drive today and practiced downshifting. I did this on some gently rolling hills and steeper ones. Great success, though I did goof up a little and forgot to goose it when shifting down into second. I plan on more practice tomorrow. I will also change the trans fluid soon. 

 

Thanks,

 

Mike 

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Modern term of “goosing the accelerator” when downshifting is called “Rev Matching”and is a common technique when downshifting modern manual trans cars too.  Some new cars and motorcycles have what is called an “Auto Blipper” that does this same thing…..helping to rev-match for easier downshifts!  

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