Front Drive Control issues

[middlecalf]

Howdy mudders. Been a while for this boy scout to hang out here but still plugging along with the '65 FJ40. No major issues over the last year or so, but now I'm having one. Front drive control (vacuum system) engages and disengages on demand, but when engaged it now is intermittently disengaging very briefly (with audible noise and light going out) and reengages quickly (light comes on - so I know the diaphragm push rod is moving to initiate the switch and light). And the intermittency is intermittent (e.g. no consistency to help in determining issue). One thing, with 4wd engaged but the hubs turned out (so no load) if doesn't disengage intermittently, only with the hubs turned in (loaded). So I guess I either have mechanical issues (linkage, pins, fork, etc.) or vacuum (hoses, diaphragm, etc.). I've searched and absorbed what I can from others who've dealt with this/related issues. But I'm seeking ideas on tests to help determine cause short of dismantling sub-units. I'm thinking of switching the vacuum lines, and if the drive control unit behaves then I guess that would tell me leak or change valve issue. The load/unloaded test I've run makes me wonder about mechanical issues. If all else fails when it warms up enough I'll pull the diaphragm sub-unit and check things out related to mechanical issues. (FYI - my rigs a '65 but the entire transfer case front drive control unit looks just like that in the 69-71 Landcruiser FJ40 Repair Manual I got from Specter Off-road, Part IV pages 3-31 to 3-35).

 

[middlecalf]

Well, kind of quiet around here. Let me try this:
it looks like from the Land Cruiser FJ40 Repair Manual that removing the front drive extension housing is straight forward: drop front drive shaft, unbolt housing and it pops off the transfer case (along with diaphragm chamber which I need to get to check out innards, especially the diaphragm itself). Is this correct or are there any special details with removing that I need to pay attention to? I would be doing this with transmission and transfer case still installed in vehicle. Thanks.

 

[65swb45]

Leave the driveshaft in place. Just remove the front drive control box from the front extension housing by means of the four bolts that hold it on. Intermittent popping under load is a fair indicator of a worn shift fork.

I just harvested 3 good ones of those from early vacuum shifters on Tuesday. You can call me at the shop if it turns out you need one. No PMs please.

 

[fjc-man]

Mark, would you PM me some pics of that 79 aisin carb you mentioned ?

 

[middlecalf]

I tried to remove the control box but there isn't room. I have an SBC so maybe that's changed clearance with frame compared to stock. What would make the diaphragm push rod move so that the indicator light goes out?

 

[65swb45]

SBC! For sure undoing the motor mounts for the necessary wiggle room is still easier than a front nose cone. That said, how much wiggle does the front output flange have where the driveshaft connects? A collapsed needle bearing on the output shaft could also be causing the front drive to disengage.

 

[middlecalf]

No wiggle (or not any detectable). I'll drop the right SBC exhaust pipe, that might get me enough room to wiggle out the control box. Possibly the front drive shaft as well. Done both before. Any specs on what the front shift fork should be to be "acceptable?"