biffidun

Hi guys, here is my problem. I can drive all day as long as I don't stay in 4th (top gear) for more than say 5-10 minutes. If I stay cruising for too long then a rythmic banging starts to come from the transmission, which progressively gets louder and then the truck starts to hesitate with each bang. All I have to do to fix this (temporarily) is to come to a complete stop and start up again. As I get rolling through first gear there is a clunk and then all is well for another 5 minutes are so.

I have checked and added gear oil to the transmission (not sure how much to put in though) and I have added gear oil to one of the diffs in the rear. I put some Lucas in the transmission thinking it was not getting proper lubrication up at the top on the 3rd 4th gear axle. No significant change, in fact I might say that the problem presents itself sooner with the Lucas in there.

I removed the top plate of the transmission but could not see anything obviously wrong.

Any thoughts?

Adjust the clutch?

Thanks for all the replies. The truck is running great now. I don't get much smoke (parking brake off) and the aneroid valve seems to be doing its thing as you can feel the power build as the valve kicks in with the turbo.

Here is a picture of the old beast. It actually had the cab replaced from a mid 80's truck. Cement truck, so no rust. Trouble is the guys that swapped the cab were hacks and the wiring was a mess. I have most of it fixed now. I just have to tie up anything loose and weld two cracks in the rear cross members. Not big cracks, but it needs to be done properly.

Now if I could just get the reverse lights working...

BTW it is a 1976

Well, this a 237HP 3B family engine. There is no intercooler on it. I opened the back (top) of the injection pump and there was a mechanism in there that appeared to alter fuel rail travel. A couple of the screws had been fudged up, so someone has been monkeying .... I dialed it back a bit and things seem better. I do think the turbo is a bit lazy though, so.... well I don't feel like spending $1000+ for a new turbo so let it be for now. I'll get a more accurate gauge for the turbo and hook up the pyrometer.

Regards.

I can't seem to identify the injection pump on my truck. (I will try to get a picture ASAP). Basically I know it is a Bosch and it has an external puff limiter air piston. The governor seems to be located at the front of the pump (close to front of engine).

I have cleaned and removed all the puff limiter components (I replaced the remote air valve) and all seem to work, but I am still getting loads of smoke. I put a boost gauge in the cab and I can see 15psi boost (not a great gauge so it could be more) BUT the truck has to be under load (driving to see that boost) to get that. Goosing at idle produces no boost.

I still get smoke even when boost registers while driving. I get quite a bit when I shift and then it tails off, but never goes away.

The engine is marked as a 3B family model EN? 576. It starts and idles nicely with little to no blow by.

I would like to dial out the fuel rail, but I don't know what to adjust on this pump for that. I would assume I have to remove a plate at the back, but which screw do I turn to back off fuel delivery?

Any thoughts would be appreciated.

no sign of an electrical connection anywhere. Any ideas? Anyone have a photo or a schematic of this transmission? 5 speed maxitorque.

thanks I'll have a look

Just a basic question. Up here in the great white north (Canada). The feds made everyone raise their pressures in the brakes systems a couple of years ago. Long story short, my "new to me" 1976 DM685S smokes a bit much, well, alot. I yanked the puff limiter valve and cleaned it, but not much change. Here's my question, if the system pressure has been raised, wouldn't the puff limiter be out of spec?

I tried adding two washers to the top of the spring inside the valve, thinking that more pressure would be required to overcome the spring - delaying full rod stroke in the pump. Is my thinking correct or is it reversed?

Hi everyone, I have just picked up my first Mack for around the farm. A 1976 DM685S (I think). Anyway, the previous owner was a hack and has all the wiring messed up. I have been reviving the gauges one at a time. Trouble is, the reverse lights will not activate. Wiring at the lights checks out (amazingly), so I am trying to find the reverse switch in the transmission. It is a 5 speed maxitorque. Any hints?

I also have a question about the pufflimiter, but I'll post that in a different thread.

Regards.