I've been trying to find a good source for a Trac-Lok rebuild kit. I'm a bit cautious about buying the one I found on everyone's favorite auction site.

Also, while I'm here, would the 79 Broncos have had a 2-pinion, or 4-pinion differential?

And if there is a lot of free play in the differential, do I need to get new side and pinion gears while I'm at it? The ring/pinion backlash is tight, as observed through the fill-plug hole, but there is still about 1/8 turn or more of the driveshaft before the differential slop is taken up. I know it needs clutches because the wheels turn easily in opposite directions, but will that also fix the excessive play in the differential? I'm thinking if the clutches are that worn, then it allows the side gears to separate more and cause the extra clearance.

 

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Now as far as your lash problem, The loose pinion gear would indicate that either the pre-load on the pinion has gone bad or that you have a problem in the diff itself. Worn internal gears / clutches will not cause this loose condition.
You mention that when viewed through the fill hole, you can see that the lash is tight??? You must have a very accurate eye. Just a few thousandths can cause this loose condition, and I trust that the old calibrated eye might still not be able to detect this.
I might add that even worn clutches should turn both tires in the same direction if the tires are off of the ground.
Sure you have a LS unit back there?

 

The Ford TL unit uses 4 pinions & 3 shafts. They have nothing to do with ring & pinion lash. You can buy a pinion kit but I don't know about the side gears. If they can't be found new, the right side, side gear will interchange with a open differential rear. For the left I took a open diff gear, ground the shoulder down close as I could & took it to a local machine shop to have it surface ground the rest of the way, put it in and it worked fine.

 

Post the AXLE code from the 2nd line of the Warranty Plate, which is located on the left door face below the latch.

If the AXLE code begins with a letter, it does have Limited Slip (Trac-Lok).

If the AXLE code begins with a number = No Limited Slip (Trac-Lok).

 

I think there's some misunderstanding.

Looking through the filler hole, the 5/8 head, recessed ring gear bolts that are characteristic of the Trac-Lok can be seen.

Through this hole, it can also be seen that with the driveshaft turned CW or CCW as far as it will go, the ring gear begins turning immediately when the driveshaft is turned in the opposite direction. Sure there's some unmeasurable-with-the-human-eye backlash, but it can be seen that the pinion is turning the ring gear immediately. The driveshaft turns a little over 1/8 of a turn, turning the ring gear and differential the whole time, before all slack and free-play is taken up. That's what I meant by the ring/pinion being tight. They turn together, but there is still a lot of free rotation in the driveshaft. This can only indicate that the over 1/8 turn at the driveshaft is because of slack in the differential.

I may have been misleading by making the initial ring/pinion statement in the middle of talk about the differential and its components. The pinion, as in ring/pinion, seems ok, as there's no lateral or axial play in the yoke, just rotational.

Only one wheel turns when they are both off the ground and the driveshaft is turned. This is also where turning one wheel turns the other in the opposite direction, and very easily.

Now, hopefully it is clearer, and I'll ask again if just the clutches can cause this much looseness in the differential's side gears and pinion gears. Logic would say that is is possible because the clutches are what take up the space between side gear and case. So if they are worn badly, or even gone, then it would allow the diff's internals to be loose. The reason for asking is to find out if it's more likely that the internal gears are also worn and I need to buy new ones to fix the problem.

It's funny. I thought I had seen the parts at JBG a long time ago, so that's the first place I looked, but I couldn't fing them. Guess I had a stupid moment.

Additionally, this all stemmed from a heavy clunk or bang when puting it in R. I knew the U-joints were very questionable, and subsequently found that the driveshaft splines were also shot. So I got a new driveshaft and still had the clunk, though greatly reduced. Further investigation found what I've explained. Now it's time to order parts to fix it. I want to do it while I'm replacing the axle bearings that have about 1/8" of end play.

 

....To back up and confirm the Trac-Lok:

78/79 Broncos had them as standard equipment, along with 31 spline axles.

The axle code is H2.

and the rear axle tag indicates a 3L50 ratio.

The visual inspection and the above 3 indicators all say the same thing. Trac-Lok.

My only question about these units themselves is if the 78/79 Bronco came with a 2- or 4- pinion unit. I saw Mark A. state that the TL unit uses 4 pinions and 3 shafts, but I believe there is also a 2-pinion unit.

Maybe I'm wrong and they are all 4-pinion units.

 

did I say something wrong?

 

Not all 1978/79 Bronco's had Trac Lok, and there's more than one ratio that did come with it.

1978/79 Bronco Warranty Plate AXLE Codes

With Limited Slip (Trac-Lok) 3750 lb. Rear Axle Capacity

1978/79: H2 = 3.50-1

1979: H3 = 2.75-1

1978/79: H4 = 3.25-1

1978/79: H9 = 4.11-1
----------------------
Without Limited Slip (Trac-Lok) 3750 lb. Rear Axle Capacity

1979: 12 = 4.11-1

1978/79: 13 = 2.75-1

1978/79: 14 = 3.00-1

1978/79: 15 = 3.25-1

1978/79: 16 = 3.50-1

Info source: 1973/79 Ford Passenger Car Parts Catalog / Bronco Warranty Plate Rear Axle Ratio Codes / General Info Section / Page 41.

Bronco parts & general info are listed in the car parts catalogs 1966/79.

 

Good information. I remebered incorrectly. It was just the 31 spline axles that were standard.

Nonetheless, I do have the Trac-Lok, based on the other information and observations.

 

Randy's Ring & Pinion

 

Pull the pumpkin and tear into it. I'm going with spent spiders and side gears or worse something broken. I have a 9" T4 Trac-Loc that is cracked all the way around the ring gear bolts from repeated abuse in a 4-speed '67 mustang.