Transmission "clunk" when going into reverse?
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Senior User
Joined: Apr 2015
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Transmission "clunk" when going into reverse?
Since I've had this truck, every time I put it into reverse, the whole truck sits back on it's suspension and I get a little "clunk" from the transmission.
Does anyone know what could be causing this? And how do I sort it out? It's a C6 (I think?) coupled to a 390 on a '76 F250 Extended cab/bed.
Also, slightly related, but does anyone know of an easy swap transmission that can be put in instead of the C6 I currently have installed? I'd like to improve the MPG (like a lot of people I'd guess) but keep the get up and go the truck currently has. American Power Train advertises "we make transmissions for ALL trucks" but there's nothing for the older F series... If anyone has done a replacement let me know what you used (in stupid terms... this is my first project truck...)
Does anyone know what could be causing this? And how do I sort it out? It's a C6 (I think?) coupled to a 390 on a '76 F250 Extended cab/bed.
Also, slightly related, but does anyone know of an easy swap transmission that can be put in instead of the C6 I currently have installed? I'd like to improve the MPG (like a lot of people I'd guess) but keep the get up and go the truck currently has. American Power Train advertises "we make transmissions for ALL trucks" but there's nothing for the older F series... If anyone has done a replacement let me know what you used (in stupid terms... this is my first project truck...)
Fleet Mechanic
Joined: Jun 2013
Posts: 1,895
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You need someone to sit in the truck and cycle the gears while you watch to see what's making the noise.. With a truck this old it could be the transmission, leafspring, leaf spring perch, ubolts, universal joints ect ect.. Please be careful and look at the truck peering in out from under the truck, don't wanna get squished!
It is a C6 if the motor is a 390.. You can definitely lower those rpms drastically by changing the gear ratio and its much easier than swapping the transmission but I wouldn't expect too much north of 13-15 MPG(I'm sure someone can give you exact numbers)
It is a C6 if the motor is a 390.. You can definitely lower those rpms drastically by changing the gear ratio and its much easier than swapping the transmission but I wouldn't expect too much north of 13-15 MPG(I'm sure someone can give you exact numbers)
Lead Driver
Joined: Nov 2006
Posts: 5,217
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From: Pa.
The clunk is more than likely slop in the driveline .. To isolate the issue first test the U-joints .. With engine off and tires blocked put the transmission in neutral .. Crawl under the vehicle and at every U-joint place a hand on each side of the U-joint on the drive shaft .. Twist the shaft in opposite directions looking for slop .. No slop is the only acceptable result .. On the U-joints at the transmission and the differential place your hand/hands on the drive shaft down stream from the U-joint and rock it back and forth looking for slop .. No slop is the only acceptable result ..
While your inspecting each U-joint make sure the U-bolts are secure and no nuts are missing and if the U-joints have a grease cert lubricate while your there ..
While your inspecting each U-joint make sure the U-bolts are secure and no nuts are missing and if the U-joints have a grease cert lubricate while your there ..
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