I need some 620 help

[cptrucks.com]

I have a customer with a 620 truck "I think" that has an issue I am unfamiliar with.

 

I know nothing about these trucks.

 

Does anyone have a good shop that I can call or talk to about this truck?

 

Here is the truck in question...

 

Thanks in advance for any help.

 

[KlassicMotion]

What's your question?  That's what all of us are here for.  Just ask your question and post some pics of the issue.  There is more than a lifetime of knowledge here, between all the members.

[cptrucks.com]

When you lock the rear in and the front out at highway speeds the truck for lack of better terms "buck s" and "jumps" I have no idea where to start.

 

When you lock the front in and the rear out the front grinds and pops like no tomorrow.

[Guest Rick-rat]

This looks a lot like the truck I saw in Williams, if it is the only thing Datsun about this truck is the body, You should contact the shop that built this truck for him and maybe they can give you some assistance. It is the first time I ever saw a locking hubs on the rear 

[datzenmike]

First I think the rear is always IN. Never seen a 4x4 where you could disconnect the rear end, only the front.

 

I would find out if both front and rear differentials are the same ratio.

[Guest Rick-rat]

If that is the truck from Texas that I saw at Williams, it does have locking hubs on the front and rear and was built somewhere in the Las Vegas area

[dr.feltersnatch]

does it have a welded diffs? they sound like fun until you actually have to drive the damn thing. also if it does have locking hubs in the rear i would assume its a front end put in the rear, i am not sure if they are designed to run in reverse at highway speed, especially if its some sort of limited slip.  

[Hooligan]

Both statements above - if the front and rear axle are running different ratios, this would cause a reaction like you are explaining. If its during corners I would swing towards a welded diff or locker of the sort

[ohmrchristopher]

I have a welded diff, there is no indication or commotion until you are turning sharply at slow speeds. Then its like living in a ShakeWeight.

 

City and Highway driving are perfectly fine...

 

except!! When on a wet surface, on a corner, at which point you will reach the threshold limit of the tires trying to turn at the same speed and a slight "slip" or "kick-out" of the rear will happen. Normally not noticed on the dry roads, because that is when the tire just "skids" and excessive wear begins.

[Guest Rick-rat]

I have E-mailed the owner of the truck, lets see if he responds with more info

[cptrucks.com]

Rick-Rat:

 

You are correct the truck is owned by a fellow in Texas our shop is in Texas. It was put together from someone in Cali and Vegas.

 

It was restored for a Doctor and then sold to a Museum. Our customer bought it from Ebay last year.

Im not sure who built it. But so far this is been helpful info. I have since found out that there never was a 620 4wd.

 

datzenmike:

 

It definitely has locking hubs in the rear just like in the front. I've never thought about the gear ratios. That shouldn't matter though with either of them unlocked.

 

Hooligan:

 

It would explain the bucking if both the front and rear were locked at the same time.

[dr.feltersnatch]

 

Im not sure who built it. But so far this is been helpful info. I have since found out that there never was a 620 4wd.

 

they were converted at dealerships

[datzenmike]

Actually the dealerships would send them away to a regional conversion center for the swap. Had nothing to do with Nissan. I doubt that one was one of these conversions and was probably just a custom job. The locking rear certainly wasn't part of the dealership conversions and I don't know why someone would have locking hubs in the rear anyway other than to show it could be done or if they planned rear wheel steering.

[cptrucks.com]

Any more ideas?

[denmarkboy]

Yeah , time for the tear down ! Front grinds and pops when you engage ?

1 st Front end needs to be torn down so you can see what has failed . Great time to double check ratios, and transfer case info : what type ? Pics of the axles or any tags or stamps ?

 

I would pull the front drive line and drive it , depending on how that goes , tear into that front end .

[jvb5577]

I bet this truck was built more for a show truck and not a functional truck.  Rear lockers?  Thats just crazy.

 

Sure the only thing datsun is the body..

 

I would do what is mentioned above and open up the front diff if that is where you are having problems.

[Wylder1324]

This is in fact the truck from Williams and is in our collection.  As for the rear locking hubs it was done quite simply for towing the truck behind another vehicle….not really THAT uncommon.  This allows it to freewheel.  It has Dana 44 in the rear and Dana 30 up front.  As for the issues its been having it can definitely be narrowed down to when the rear is locked in.  (This is prior to the front having issues of its own now) Anyway, when the rears are locked in it does it's "bucking" routine which also seems to feel as though its slipping in and out of gear….I think this simply by because it gives the sensation of being in neutral or pressing clutch and getting the rapid rise in RPMs without any of that power going to the wheels….all of this only seems to start at speeds of 40mph and above.  While trying different things to see what we could eliminate as a problem we tried unlocking the rears and locking in the fronts dropping into 4 wheel high effectively turning it into a front wheel drive and all of those symptoms vanished.