Problem with clutch disengaging

[Clarke]

I have a '62 3/4 ton with a 305D and SM420. The guy I bought it from said the orig clutch fell apart so he replaced the pressure plate and clutch disk. He also said he flipped the starter ring gear over because it was grinding. I don't think he ever fixed or replaced the starter, because when I bought the truck the starter was grinding again.

I put up with it for several years... A year or two ago I replaced all the brake and clutch hydraulic components, except for the clutch line because I couldn't find a replacement. I noticed there was no slack in the clutch petal or clutch fork, so I added the recommended slack. As a result, the clutch would not disengage. So I took all the slack back out and the clutch would disengage, but barley.

Over the winter, I decided to install a new ring gear. Pressure plate and clutch disk looked good, but I wasn't sure about the pilot and release bearings, so I took them into NAPA and bought new. I compared/measured old with new and they matched. While I was at it, I had a new clutch line made to replace the original. After putting all back together, I couldn't get the clutch to disengage, even after taking all the slack out. I bled the line multiple ways, replaced master and slave cylinders, reinstalled the original line, bled the line multiple ways again and again with no luck.

Fed up, took the truck to the dealer, they quickly told me I had good travel, but I had the wrong release bearing. They said there is a short and long, I had the short and I needed the long. Fed up, I let them do the work. I picked it up the next day and it was driving fine.

Approx 100 miles later on my way home I'm not able to shift; clutch is not disengaging again... I have to stop the engine, shift into gear, restart, drive, repeat... I rolled under the truck tonight, hoping to find slack in the clutch fork, readjust and be back on the road. I noticed the adjustment nut was approx in the middle of the adjustment rod (with the longer release bearing vs. towards the end with the short release bearing), but after I released the clutch fork spring I found there was no slack. I readjusted it several times (both directions), bled the system several times and no luck!

Any suggestions??? I'll be calling the shop tomorrow, but I'd like to pass on any suggestions the group may have to minimize the drama.

Thank you in advance.

David

[FetchMeAPepsi]

I havent dug into clutch stuff yet but are you sure he put the right plate and disk in? They dont have the right disks anymore from what I have heard. You have to have the old one resurfaced because the springs are on the wrong side and it makes it too big or somesuch.

I know that doesn't help much, but maybe someone with knowledge of the borg-warner clutch disks (discs?) will reply and clear it up some. It has something to do with the diaphrams.

[David R Leifheit]

The last time I had to deal with a clutch the discs were still available, but had to be ordered. Now I understand you can't get them..

I have a clutch disc in my office, I am pretty sure it is a GMC since I don't actually have any Chevrolet... And the spring pack and "nose" are on the same side of the disc, which means on the Chevrolet disc they are on opposite sides. There isn't enough clearance for it to work with the Chevrolet disc. The recess in the flywheel is just enough for the bolt heads.

There are two different release or throwout bearings, a long and a short so the shop was correct on that. I found out the hard way... An important part to look at when working with the clutch is the input shaft bearing cover. It doesn't just cover the bearing but also the input shaft and the throwout bearing "rides" on this. With the wrong bearing or improperly adjusted bearing, this can break off. My first 4-speed didn't have this and it took me quite a while to find a cover that was intact.

The clutch adjustment rod should have two nuts on it, so once adjusted it doesn't change. I had mine back out on a lonely stretch of road. -funny story, when it did that and I got the truck stopped, there was a nut of the same size and thread on the shoulder of the road-

As of late I haven't been the most active or the "best" source of information. But if you have questions and need to look at manuals, http://www.oeltd.net/doc/6066.htm is the site for my trucks and there is a link at the top to my manuals. Some of the manuals have had sections scanned in, so take a look and see if I have scanned in what you need. If not, email me and I will try to scan in whatever information you are looking for.

[Andice]

Having learned from previous "experts" concerning clutches and pressure plates I have my old parts rebuilt now. It may cost a little more up front but I've been happier in the end.

[Funky61]

David R Leifheit Re: Problem with clutch disengaging

The last time I had to deal with a clutch the discs were still available, but had to be ordered. Now I understand you can't get them..

I have a clutch disc in my office, I am pretty sure it is a GMC since I don't actually have any Chevrolet... And the spring pack and "nose" are on the same side of the disc, which means on the Chevrolet disc they are on opposite sides. There isn't enough clearance for it to work with the Chevrolet disc. The recess in the flywheel is just enough for the bolt heads.

Here is a photo

[Clarke]

Update:

My local dealership has decided they are not going to trouble shoot the issue, so I guess I'm stuck trying again myself...

To clarify, I did not change the clutch disk or pressure plate when replacing my starter ring gear, so these are the same parts.

I believe it's a hydraulic issue... When reviewing the service manual, appears I'm supposed to have a "fluid damper valve" installed between the slave cylinder and clutch line (1500 Series with SM420)? Does anyone else have this on their truck? Is it possible this can be the issue, or add to it?

I'm going to remove the master cylinder and bench bleed it to verify it's good.

[raycow]

Are you saying that this "fluid damper valve" is a separate external component which is installed in the line between the master cylinder and slave cylinder? If yes, I don't have one and I have never heard of such a thing before now.

Ray

[David R Leifheit]

Originally Posted by Clarke

Update:

I believe it's a hydraulic issue... When reviewing the service manual, appears I'm supposed to have a "fluid damper valve" installed between the slave cylinder and clutch line (1500 Series with SM420)? Does anyone else have this on their truck? Is it possible this can be the issue, or add to it?

Just curious, what service manual are you using?
You should have the X-6223 manual.
1000-5000 series trucks.

http://www.oeltd.net/doc/GMC_Manuals...6223-5-299.jpg
through
http://www.oeltd.net/doc/GMC_Manuals...6223-5-309.jpg
Are scans of the clutch section of the manual.
Or you can just go here:
http://www.oeltd.net/doc/GMC_Manuals/X-6223/
To see which sections I already scanned in out of the manual.

Each scan is numbered by the manual-section-page

http://www.oeltd.net/doc/manual.htm
The manuals list, ones I own and as well as an overview of all the manuals for the 60-66 trucks. Any that I have scanned in any pages for will have a link. For clarity purposes, any manuals listed in italics are ones I do _not_ own but have found referenced in other manuals or have seen for sale.

[Clarke]

Yes, I'm using X-6223; the fluid damper valve is noted in Section 5, Page 302. It is also noted on Page 301. I'm curious to know if anyone has this installed on their truck...

[David R Leifheit]

Originally Posted by Clarke

Yes, I'm using X-6223; the fluid damper valve is noted in Section 5, Page 302. It is also noted on Page 301. I'm curious to know if anyone has this installed on their truck...

Now I am going to have to go and crawl under my trucks. I have never noticed this before, and I have changed the transmission on my '61 and have pulled and put back in the trans/clutch lines on a couple others.

I don't think I have seen this valve... or even knew it was a valve.

After all these years and I still learn something...