C4 Grinding or Scraping Noise Shifting Into 2nd

[kb5ynf]

I've searched the forums and haven't found mention of this particular problem yet so I wanted to see if anyone can help diagnose this problem.

In the last few days, my '77 (302 with C4) has started making an odd noise when it shifts from 1st to 2nd gear. I heard it intermittently a few weeks ago but it only did it once and then again a few days later. At the time, I wasn't sure what I was hearing. Both times I was turning a corner and I thought the sound was something sliding across the bed in the back of the truck (there are a few things loose back there; so it made sense).

I didn't hear the sound again until a couple of days ago and now it has started recurring regularly. It actually sounds like a scraping noise, not overly loud but easily heard and very short, maybe one second in length. It sounds very similar to something sliding across a floor, maybe a dresser being slid away from a wall on a hard floor; something like that.

Also, it only happens when accelerating and the truck shifts from first to second gear; and only when increasing at a slow rate. When I drive it slightly more aggressively from takeoff (normal for me), I don't hear the noise but there is a hard kick when it shifts into second. Second to third is extremely smooth; so much so that you have to listen for it or you won't even notice the shift.

Lastly, when I shift the truck manually, the noise isn't produced. And other than the noise I'm hearing the truck is driving fine. I have checked the fluid levels and they are good. Any ideas what I might be looking at here; things to check?

Thanks,

Jack

 

[BUCKNBRONK]

If its shifting fin and not slipping check ur u-joints and cv on the drive shaft 1st before tearing into the tranny. also could be rear or front axle bearings jack it up & check for play. then if all that checks out drop the pan and look for metal or friction material in the pan.

 

[Viperwolf1]

The intermediate band (2nd gear) may be slipping a little too much at the shift. Try to adjust that band.

You will need a 3/4" wrench and a 5/16" wrench. 5 minute job.

1) Bust the locknut loose.
2) Turn the adjuster in (CW) until you can tell it seats good. This tightens the band around the drum.
3) Now turn the adjuster out 1 1/2 turns. This provides proper band to drum clearance.
4) Hold the adjuster still and tighten the locknut to about 30 ft-lbs.

That is for the intermediate band (front) adjustment. The low/reverse band (rear) gets 3 turns out. If you turn the adjusters out too far you could drop the struts between the band and adjusters. That would require removal of the valve body to put it back together.

 

[kb5ynf]

Thanks for suggestions fellas. I'm going to be out of town for a few days but will check the items you've mentioned and see what I can find out when I return. I appreciate the help.

Regards,

Jack

 

[Rugby73]

Thanks for suggestions fellas. I'm going to be out of town for a few days but will check the items you've mentioned and see what I can find out when I return. I appreciate the help.

Regards,

Jack

An easier and cheaper fix that surprisingly might work is to replace the vacuum modulator on the back of the C4. Screws in out and takes 5min. I've seen weird acting transmission that were fixed by this simple change.

 

[Viperwolf1]

An easier and cheaper fix that surprisingly might work is to replace the vacuum modulator on the back of the C4. Screws in out and takes 5min. I've seen weird acting transmission that were fixed by this simple change.

This isn't a modulator issue. There is nothing to gain by swapping it.

 

[kb5ynf]

Well, I adjusted the bands with no improvement. But the tranny is getting worse. I haven't been driving it but I've been trying different stuff and testing it for improvements. Now reverse is the only gear that's still working properly. In drive it acts like it's in neutral; just spins. Shifting manually works for 1st and 2nd, but it slips in both now; and drive just doesn't engage at all. You guys have any more suggestions?

Thanks,

Jack

Sent from my Nexus 7 using Tapatalk 2

 

[Viperwolf1]

Sounds like the forward clutch is pretty well done. There is no cure in a bottle. A rebuild is needed.

 

[kb5ynf]

That's what I suspected... Thanks.

Sent from my Nexus 7 using Tapatalk 2

 

[Viperwolf1]

I got back just 2 hrs ago from looking at a Bronco with those same symptoms. That transmission is probably almost on the floor by now. Its no big deal, they wear out.

 

[kb5ynf]

Yes sir. Many thanks for your help in diagnosing the problem. I guess I better get started fixing this one; I need it to be my primary driver once my son starts back to school next month.

Sent from my Nexus 7 using Tapatalk 2

 

[kb5ynf]

Just as an update, I work slowly on projects like this because I always over-research and because I'm out of town a lot and don't always have the time I need to dedicate to such things. So, I finally got my tranny out of the truck back around the first week of September. I tore it down and found that the forward clutch pack did have a lot of wear on the fibers. Also, the forward planet had a lot of wear on the end of it and the thrust washer it rides against did as well. Apparently that planet/washer wear is pretty common on C4's. I checked the endplay before tearing into the transmission and the play was at 0.065. I just got around to reassembling the transmission last night and re-checked the endplay; it's now at 0.012. I'm pretty happy with how it all turned out. I used the video from Bad Shoe Productions as my main resource, along with tons of internet searches and referencing threads here. I hope to get it back in the bronco this weekend but I probably still won't get it on the road for a few more weeks. I hope it all works correctly once I'm finished.

 

[kb5ynf]

Well, I'm back on the road finally. Looking forward to daily driving again.

 

[wheelsblank27]

Read your thread, I'm installing a c4 in my 68' bronco that I took a np435 4spd out , I am like you i research the whole deal as much as I can before I dive in. Thx WWW. did you install any mods to your c4? I'm rebuilding the one I bought that had been in a car so I had to buy a adapter from a cb member and since the trans is used I'm rebuilding. It also came with some n spare parts ( c5 forward clutch pack I think gives it lockup in 3rd) and a v8 valve body (previous car had a v6) also a new front pump. I am gonna install a shift kit and a master rebuild kit from oregonperformancetransmission.com . Also I want to buy the servo for a Shelby mustang.I also have to collect a few more parts for the conversion like floor shifter, cable, trans cooler. I'm gonna watch that video you used and hopefully it all works out. I'm hopin I can run the trans on my schools tranny dyno before install.

 

[kb5ynf]

The only mod I did was a shift kit. I did install a new forward planet as well; that's not a mod though. That video is very helpful and includes step by step tear down and assembly instructions. My rebuild turned out great. I hope yours does as well. Good luck!

Oh, internally, I didn't do any mods; but, I did mod the cooling system. I installed an external stacked plate cooler with fan and a screw on filter as well as a drain plug and temperature gauge.