1967 Jetaway "Clunks" on downshift

Dapapadon · 02-24-2008, 06:29 PM

I drove my 67 Cutlass Supreme project car to the Community College yesterday for some lower windshield channel rust repair. A mile or so into the trip I noticed a "clunking" when I slowed down. Finally figured out it was the transmission when it downshifted. Hard braking to slow down & I get a hard "clunk" and if I coast & lightly brake it's minor, hardly noticeable.

I did a Google search and the only thing I found was on a Buick forum. Same ST300 trans. a guy was having the same trouble with. Basically the reply was live with it. OK, I don't have a problem with that if it will last a while. I've got a TH350 I plan to install later. But if anyone is familiar with this problem I'd appreciate the input. With my "To Do" & Priority lists on the project it will be a while before I swap to the TH350.

Does the governor control downshifts when you slow down? If so, would pulling it and cleaning it possibly help the problem? And 'No' I haven't changed the fluid & filter. But the fluids looks good. And I don't plan to drive it more than a 200 miles at most before I swap it out.

For anyone interested this was the only problem I had and it's 20 miles or so each way! This was the first time I drove the car any distance. Up till yesterday it was only short road tests. She cruised down the freeway with no problems.

On the rust repair I got the lower channel replaced. The aftermarket channel doesn't line up right with the A pillars, but I can deal with that later. And I still need to replace the lower two inches or so of the dash next time. Bad news is I cracked the windshield

(several times) and will need to replace it (again

) when I'm done with the repairs.

Thanks for any input, Don

88 coupe · 02-25-2008, 03:07 AM

Quote:

Originally Posted by Dapapadon

........ it was the transmission when it downshifted ........

Make sure it's in "proper tune" and the warm idle is 500 (or 550 with AC) RPM.

Norm

Dapapadon · 02-25-2008, 08:55 PM

Thanks for the reply Norm. The parts are new, I'll double check everything. I'm sure the idle is a little high. I wouldn't thought of that.

Don

Giftman23 · 02-26-2008, 01:37 AM

I have had this problem with numerous '67's that I have owned. Apparently, there was a factory service bulletin issued sometime in '67 to address this. If I recall, it required re-routing some vacuum lines (and more.) I had a copy faxed to me by one of the OCA's '67 model year advisors. Maybe someone here can help further.

02-24-2008, 06:29 PM	#1 (permalink)
Dapapadon Senior Member Join Date: Jan 2007 Location: Portland, OR Posts: 311	1967 Jetaway "Clunks" on downshift I drove my 67 Cutlass Supreme project car to the Community College yesterday for some lower windshield channel rust repair. A mile or so into the trip I noticed a "clunking" when I slowed down. Finally figured out it was the transmission when it downshifted. Hard braking to slow down & I get a hard "clunk" and if I coast & lightly brake it's minor, hardly noticeable. I did a Google search and the only thing I found was on a Buick forum. Same ST300 trans. a guy was having the same trouble with. Basically the reply was live with it. OK, I don't have a problem with that if it will last a while. I've got a TH350 I plan to install later. But if anyone is familiar with this problem I'd appreciate the input. With my "To Do" & Priority lists on the project it will be a while before I swap to the TH350. Does the governor control downshifts when you slow down? If so, would pulling it and cleaning it possibly help the problem? And 'No' I haven't changed the fluid & filter. But the fluids looks good. And I don't plan to drive it more than a 200 miles at most before I swap it out. For anyone interested this was the only problem I had and it's 20 miles or so each way! This was the first time I drove the car any distance. Up till yesterday it was only short road tests. She cruised down the freeway with no problems. On the rust repair I got the lower channel replaced. The aftermarket channel doesn't line up right with the A pillars, but I can deal with that later. And I still need to replace the lower two inches or so of the dash next time. Bad news is I cracked the windshield (several times) and will need to replace it (again) when I'm done with the repairs. Thanks for any input, Don

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02-25-2008, 08:55 PM	#3 (permalink)
Dapapadon Senior Member Join Date: Jan 2007 Location: Portland, OR Posts: 311	Thanks for the reply Norm. The parts are new, I'll double check everything. I'm sure the idle is a little high. I wouldn't thought of that. Don

02-26-2008, 01:37 AM	#4 (permalink)
Giftman23 Junior Member Join Date: Mar 2006 Posts: 4	I have had this problem with numerous '67's that I have owned. Apparently, there was a factory service bulletin issued sometime in '67 to address this. If I recall, it required re-routing some vacuum lines (and more.) I had a copy faxed to me by one of the OCA's '67 model year advisors. Maybe someone here can help further.