Topic: Dual T-Case Grinding Noise (Help, Marlin!!)

[calitaco]

I recently got this 89 shortbed pickup with dual t-cases using a Marlin MC08 adapter.  There's a loud grinding noise during hard deceleration without depressing the clutch pedal (like engine braking) and after you depress it but it stops when you start to accelerate again.  It does this in almost every gear except 1st (guess I wasn't going fast enough).  I thought it was the tranny, so I replaced it with a W56.  Still does it so the only thing left are the t-cases.  Does anybody ever had this problem?

I currently have the crawler sitting on my workbench with the crawler box torn apart (not the rear t-case).  I have no idea what to look for.  Any help would be appreciated.

Thanks,
Pete

[bluetoy84]

It's your driveshaft vibrating. This is a very common problem on a short wheelbase truck with dual t-cases and over 3" of lift. The driveshaft will vibrate and make a lot of noise when you let off the gas , but will quit when you get back on the gas. It sucks that you've already swapped transmissions and tore your t-cases apart. I'm 100% sure it's just your driveshaft. My '89 does exactly the same thing. Almost every standard cab that I've seen with dual t-cases has the same issue. 

The most common way to fix this is to run a CV driveshaft , but on my '89 to run a CV joint I would have to cut the horse collar cross member. I barely have enough clearance for a standard u-joint. I've been driving mine for over a year like this, I've just learned to live with the noise.

[calitaco [OP]]

Really?   Yours does it too?  We are talking about a loud grinding noise, like a starter not engaging all the way kind of grinding noise, right?  I'm just curious as to what would cause that noise from the driveshaft.  I guess I'll reassemble the crawler and see if I can find a CV driveshaft.  Thanks for the reply.

[Hottrod81]

Make sure with the CV driveshaft you point the pinion to the T/C.  If that doesn't work, you might have a broken front left motormount.  Got this information from Marlin myself and that's how I fixed mine.

[bluetoy84]

Really?   Yours does it too?  We are talking about a loud grinding noise, like a starter not engaging all the way kind of grinding noise, right?  I'm just curious as to what would cause that noise from the driveshaft. 

It sounds really bad. I wouldn't have thought that the driveshaft would make a noise like that either. But, I know it's the driveshaft. It only does it when your coasting. It has no noise or vibration when your accelerating or cruising down the road, but soon as you let off the gas to slow down it sounds terrible. Mine is not the only one I've seen do this, it seems to only be a problem on a short wheelbase. My '84 xtra cab had about the same lift with dual cases and it was fine. The problem is the driveshaft angle due to lift springs and a shorter shaft with the dual cases.

When I first put my dual t-case in this truck I had about 4" of lift , it didn't make any noise before the dual cases, after the dual cases it had the noise. I ran it for a while like that, then I lowered the rear suspension about 2" and the noise went away.Then later I raised it back up and the noise came back. How much lift is on your truck?

You could also cut and turn the spring perches to correct the driveshaft angle. I think this might be my best option because a CV will hit my crossmember.

[calitaco [OP]]

Wow, it seems like a common problem with the standard cab with dual t-cases.  My truck has 63" Chevy's in the back and 44044's in the front.  Sits kinda high though.  I have 33" and the bottom of the cab is the height of the tires.  Thanks for the info.  I'll start reassemble it tonight.  Where's a good place to get CV driveshafts?

Hottrod81, I'll check the front motor mounts.  I'll try and eliminate all possible causes.  I've already done the tranny 

[bluetoy84]

Use an IFS front shaft to make your rear CV driveshaft. You'll need to redrill your rear output flange or buy a triple drilled flange from marlin, because the CV has a different bolt pattern than a standard u-joint yoke. You could just use the front output flange from a donor t-case, but it's better to have a double drilled flange so you can use either a CV or standard yoke. This way you can keep your old shaft as a trail spare and it will still bolt up.

Good luck, and let us know how it works.