On occasion, my 86 XJ6 S3 (I'm pretty sure its a S3) has a strange issue when starting up facing uphill after sitting all day. It seems and/or sounds like the rear end "disconnects"...the transmission and motor sound normal and it isn't a slip, it is a total loss of power either in the tranny or in the rear end. This is happening (sometimes) when leaving a parking space after being parked uphill for 5 hours or more. The reason I'm thinking the rear end is because 1) When power "reconnects", the clunk seems to come from the rear end area as far as I can tell 2) The disconnect occurs after pulling out at an angle (a car parked in front of me causes me to pull out sharply to the left), as opposed to pulling out going more/less straight ahead (with no car in front of me). It seems the possible difference in spin rate between the two back wheels cause the rear end to pop out somehow. I don't know if it has a Ltd Slip Differential or not. Letting the car come to a stop usually allows things to fix themselves...I don't like to let the engine over-rev as I know it is going to reconnect the power in a second or two and don't want to cause undue stress. The feeling is like the transmission and/or rear end disconnect the physical power to the back wheels, similar to a manual transmission. In this case, the power disconnect is 100%, there is no slipping, only 100 or 0% power.
There are no problems when power comes back online, and shifting is fine as it was before. It doesn't seem to be a problem and doesn't happen too often, but then again, I know when to expect it and it only happens after sitting most of the day, uphill, in a certain parking spot. I've seen my share of gear/transmission problems, but I don't know of anything in the rear end that can interrupt power like that, although that is where I suspect the problem is. The transmission runs well and has no problems, but that is the only place I could imagine the power could be getting lost. Any insights?

Jim - Learning the joys of 86 XJ6 parenthood

 

Mmmmm.

Not aware of an XJ6 having an LSD diff, but I may be wrong. The V12, yes, but the 6 cylinder, not that I know of, BUT, it may have had a diff change in previous life, and an LSD "could" do something like that, but that is also stretching it a tad. The LSD usually give a "chatter" as things do what they do, hence the additive in the oil to reduce that event.

My thought goes to low trans fluid, and that could be by only 1/2 ltr, which will cause fluid starvation, and could also give a "total disconnect" feeling you mention many times.

There are many, many items in the rear suspension/driveline assembly that will be worn etc, but there is simply none I can finger as doing what you describe. Clanking/banging/knocking/whirring/vibrations/etc are kind of normal failure noises in any of these "inboard" brake cars.

 

Torque converter, maybe ?

Trouble with this sort of thing is you only find out when you've stripped things down.

 

Yeah, I agree. Sounds like the trans is momentarily not driving the car and then abruptly engaging. The jolt of engagement creates some clunks and noises in all things aft....which have developed a bit of (perfectly normal) wear and free play over the years.

Check the fuid first, as Grant suggests

As for limited slip it would bery unlikely that a USA-market Ser III XJ6 had it. Technically it wasn't offered on the USA cars. It was optional in other markets.

However, as Grant says, limited slip was standard on V12s of that vintage, and all XJSs. A few of these LSDs may have found their way into 6-cylinder Ser IIIs over the years

Cheers
DD

 

I vote for the transmission as well. Why not try to park the car the other way down the hill next time? Be interesting to see what happens.

Maybe the final answer is "don't do that". Just how steep is this hill? Anyway.

 

With the recent onset of cold air, the problem with the strange slip is increasing slightly. The problem, for whatever reason, only seems to manifest itself after turning in a right (clockwise) direction, such as turning right onto a new road. Going straight or around bends isn't a problem, it only seems to happen when starting from a stop, or near stop with acceleration. To me, the noise sounds like it is coming from the right rear tire...both wheels are driving wheels (I think) as you can feel both tires spinning (as in the recent snow) if you are on snow/ice...posi traction? Once you travel more than a mile, it resolves itself. I have to admit that it sounds like it should be the transmission, but it seems to me (based solely on gut feeling, as well as seat of the pants driving) that the problem is further back. AFAIK, the car hasn't been modded with a new or different rear end, and all tranny fluid levels are OK. The feeling is akin to driving a single drive wheel in a light vehicle (like a van) and giving it too much gas when starting up a hill...the back tire spins easily then gradually engages when you back off the gas a bit...this is an almost identical sensation, except the wheels aren't spinning. If you accelerate in a straight line, no problem. Do it after the car turns right/clockwise and accelerate...loss of power to actual wheel then a fairly sudden re-engage. Otherwise, it purrs like a kitten, usually. Hard to start when down to 15F or less, but eventually can be coaxed to start. With temps forecast to be about 15 below zero F, I'm not even gonna try! Firewood and rum seem like a reasonable idea.

Curious and curiouser.

Jim

 

I am with Grant and Doug. Slip in trans on start up. AKA "morning sickness". Cold fluid in the pan is tougher to pickup than when hot. and, a lot may have oozed out of the convertert and valve bodies making quirky trans action instead of a smooth application of torque.

Decades ago, My Scout II had morning sickness. it was equiopped with the tough as anils MOPAR 727 transmission. I dropped the pan and foud the filter a gelatinous mess. New filter and a self styled flush and all was well for many a moon. My flush was by a disconnect of a coolant line. easy as i had added a supplemtal cooler. Run it and let the fluid go into a pan. Added fluid as I went to make sure the trans was n ot only flushed, but never went dry. Wheh, I was happy with the fluid color, i shut it down, reconnected and checked the level.

Ended up with a mess of ATF in a pan to get rid of!!

Carl