Overdrive or drive
Melting Slicks
Joined: Feb 2003
Posts: 2,677
Likes: 812
From: Saskatoon Sask.
1st gear - Application of forward clutches - no shift timing.
2nd gear - Application of band - no shift timing.
3rd gear - release of band and application of 3-4 clutches - must be timed in that order to prevent improper gear change.
4th gear - application of band - no shift timing.
The service bulletin mentions the conical spring and a modified exhaust port in the separator plate. By this, I can only surmise they are trying to delay the application of the band(by using more spring) and quickening the release of the 3-4 clutches(larger exhaust port) during the 3-2 downshift. Without this modification, you are in fact momentarily attaining a 4th gear condition.(3-4 clutches applied and band applied). It is probably important to verify what condition one actually has before proceeding.
Melting Slicks
Joined: May 2019
Posts: 3,243
Likes: 1,403
From: Mid-Atlantic
2025 C4 of the Year Finalist - Unmodified
2023 C4 of the Year Finalist - Unmodified
2022 C4 of the Year Finalist - Unmodified
2021 C4 of the Year - Unmodified Finalist
Upon reading the service bulletin further and digesting it, the following may be of note to some. Natty, you mention in your first post that the "clunk" happens during the 2-1 downshift. If this is indeed the case, then you may go to the expense and the work and not achieve any results. The service bulletin is for correction of a 3-2 downshift clunk. Two entirely different conditions. The 2-3 and the 3-2 shifts are the only two conditions in the 4L60 that require shift timing. For those unfamiliar, I will explain.
1st gear - Application of forward clutches - no shift timing.
2nd gear - Application of band - no shift timing.
3rd gear - release of band and application of 3-4 clutches - must be timed in that order to prevent improper gear change.
4th gear - application of band - no shift timing.
The service bulletin mentions the conical spring and a modified exhaust port in the separator plate. By this, I can only surmise they are trying to delay the application of the band(by using more spring) and quickening the release of the 3-4 clutches(larger exhaust port) during the 3-2 downshift. Without this modification, you are in fact momentarily attaining a 4th gear condition.(3-4 clutches applied and band applied). It is probably important to verify what condition one actually has before proceeding.
1st gear - Application of forward clutches - no shift timing.
2nd gear - Application of band - no shift timing.
3rd gear - release of band and application of 3-4 clutches - must be timed in that order to prevent improper gear change.
4th gear - application of band - no shift timing.
The service bulletin mentions the conical spring and a modified exhaust port in the separator plate. By this, I can only surmise they are trying to delay the application of the band(by using more spring) and quickening the release of the 3-4 clutches(larger exhaust port) during the 3-2 downshift. Without this modification, you are in fact momentarily attaining a 4th gear condition.(3-4 clutches applied and band applied). It is probably important to verify what condition one actually has before proceeding.
I actually just got back from a Sunday afternoon cruise through the winding back roads. It's driving really well, too. I don't even turn the radio on, that's how good it sounds cruising down the road. No squeaks. No ratttles. It's just running so darned smoothly. Really enjoyed running it around over the weekend, now that the weather is good.
Safety Car
Joined: Dec 2009
Posts: 4,363
Likes: 429
From: Birmingham Al
Over drive
Had my 93-trans rebuilt, with custom governor goes into OD at 59 mph, drive around in drive in traffic get on interstate bam OD best both worlds .. Before I had it rebuilt it went into OD at 43 mph it was back and forth in drive in OD drove me nuts not just right . Just saying ..
