PEX is rated to hold 80 PSI of water at 200 degrees. This isn't holding pressure so it would have to be very hot to physically deform. How hot? I don't know but it took forever to heat up enough with my heat gun so that it became soft enough to bend to shape. Plus I covered it in heat resistant fiberglass sheathing for extra precaution.

 

So, the TV (throttle valve) cable on the 2004R and 700R4 transmissions does the work of the vacuum and electric kick down systems on the Borg Warner and TH400 transmissions. The cable, when attached to the throttle, swings a lever that pushes the throttle valve in. The reason that you hear horror stories about these is that GM made all of their throttle brackets and levers so they mate with the stock TV cable on specific cars. But as soon as people started putting these transmissions in other cars, with their own throttle brackets and geometry, the precision of GM's work became apparent—and transmissions failed (I killed a 700R4 on a ‘55 Chevy I restored because I didn’t understand the importance of the TV cable being tight but I was 23 and didn’t know anything).

The stock XJ12 (and XJS) throttle linkage disc (can’t recall the technical term) turns about 90 degrees from idle to full throttle. And so the TV cable needs to be installed so that there is a tiny bit of pressure on the throttle valve at idle and then at full throttle, needs to be fully depressed.

I couldn’t understand the instructions provided in the Quarterbreed kit and there aren’t pictures in the booklet to explain how to install it, so I just experimented. And got it right the first time. Jk, I drilled a bunch of holes in the disc trying to find a position where the cable end could mount and didn’t interfere with anything during its swing.

Here is the TV Cable at the throttle, note the copper washers (in red circle), that’s where the ball stud mounts on the bottom side of the throttle disc, the ball stud attaches to the end of the cable with the black plastic clip (barely visible)

Here you can see the throttle valve bracket and how it’s screwed into the stock mounting post of the throttle disc.

This is the throttle valve (round shaft in red circle) , viewed with the transmission pan off. This is at the idle position, the lever is putting a small amount of pressure on the throttle valve and depressing it slightly. At full throttle, the throttle valve is fully depressed and becomes invisible.

 

Success!

I drove the car yesterday and transmission shifted smoothly and at the correct speeds. I didn't get above 35 MPH or so on the test drive but then disaster--but not transmission disaster. One of the rear calipers is seized...

This car sat for decades and while I rebuilt the front calipers I took a chance that rears would work after bleeding the brakes (Ironically, the rear discs and pads look "new" and were probably replaced not long before car left the road). Well, they did work until that caliper seized. The car felt jerky and grabby as I coasted to a stop sign and once home I could smell overheated pads.

So, now I'm going to drop the rear subframe and rebuild those calipers and maybe switch the shocks, as well as subframe mounts (they're decent with only small cracks but I can't abide putting them back in).

FYI, I previously restored an XJS and used aftermarket suspension bushings but never again. Every bushing I've bought (including the just purchased rear subframe mounts) has been OEM metalastic (As much as can be guaranteed in these times of aftermarket parts).

 

Andy, replace the flexible too. Congrats on the gearbox success.

 

Copy that Greg.

Rear cage back in with new calipers, shocks and brake line. Also cleaned and greased everything.

after the rear cage was back in I took a test drive again and it drove great except for the stiffness of the throttle due to how I mounted the TV cable. so changed how it’s mounted...


mounted it to the passenger carb linkage, again had to experiment with different mounting points for the pin that the cable clips to, the Throttle valve inside tranny needs to be slightly depressed at idle and then fully depressed at full throttle. The best way to check this is with the tranny pan off

 

Well, more work needed. I've got a driveline vibration that I'm trying to sort out. Rotated the driveshaft and then altered the height of the transmission mount to try and sort but no joy.

I'm thinking about modifying the original driveshaft and reusing it. Of course, the way that Jaguar made the 2-piece driveshaft is insane, in particular the center bearing mount but that seems like an effort to absorb vibes.

Anybody got any insight about a 1 piece versus 2-piece driveshaft and the effect on vibrations?

 

Andy
The two-piece driveshaft is there to ensure the angle the U joints are asked to work at is not greater than they can accept, a one piece prop will not work reliably and will also show nasty symptoms. The centre-bearing arrangement is used by many makers. Have you renewed that bearing, as that is the usual cause of the driveline vibration?

 

Just an aside to Greg's post, some members have had interference problems with 1-piece drive shafts. Usually lumps with more oomph than the stock engine, on hard acceleration the cage is forced forward and up slightly and the drive shaft hits the tunnel. I haven't had that problem with the 2-piece. Side-to-side adjustment of the center bearing can be used to fine tune slight misalignment if necessary. Have a reputable gear/drive line shop balance the whole thing and make sure all the u-joints/center bearing are in good shape.

Dave

 

700r4, one piece shaft, monster torque, no vibration, slight brushing on stock insulation at the rear of the tunnel. John's Car's drive shaft & trans mount.

 

Mine had a vibration at 80mph with my one piece, that I didn’t have until I swapped gears from 2:88-3:73, so I took it and had it balanced all
good now!! And I also had rub that Dave mentioned, new rear end mounts seemed to have taken care of that issue!

 

My lump has a one piece drive shafr. works just fne under all conditions.

SAnd, my lump has a Gm trnsmission mount. Very simple, unlike the jaguar unit.

Carl

 

Update:

I took my original 2 piece shaft to a local shop and had new u joints installed and and the front shaft shortened and a 2004R yoke welded on and shaft balanced.

I reinstalled this 2-piece shaft with new rubber mounts on the center bearing but I did not change the original center bearing because it felt smooth. Test drive revealed 90% of vibration at highway speed gone but I then developed a nasty thump on acceleration. Soooo, back to the forums and discovered procedure for aligning driveshaft.

I made my own version of the JD46 tool to align the driveshaft and discovered that due to all the changes I made in how there transmission mounted that the driveshaft was not straight front to back. The center support bearing requires shimming so that the front and rear shafts look/act like a 1-piece shaft. A picture is worth a thousand words, but I don't have one, so another way to think about it is to imagine firing a rifle shot through the back of the drive shaft, it should travel straight through without hitting top or bottom of shaft.

I also straightened it side to side, again rifle shot analogy, fired from back it should travel straight through without hitting either SIDE of the driveshaft.

So, with it straight looking from top and side I took a test drive. The thump on acceleration was gone. There seemed to be a slight vibration that seemed driveshaft in origin and so decided to change the center bearing did some more research.

So, I initially made the driveshaft straight in terms of side to side but just noticed that in the manual it calls for a 2.38mm distance in the middle dimension (see below).

I installed a new center bearing and I'm gonna readjust the driveshaft to have that 2.38mm gap in middle section and see what difference that makes but would be curious if ya'll have any insight into why that distance might be there (instead of straight)?

 

Andy
All I know is that the two-piece shaft was needed so that not too great an angle change between the gearbox output shaft and the differential input shaft (looking at each from the side view) has to be accomodated by the UJs at each end. In effect the middle UJ reduces the angle that each UJ has to resolve.
So just maybe that middle UJ needs a touch of "misalignment" to prevent unwanted harmonics or some such effect that occurs if they are dead straight?

 

Greg is correct, UJ's should never be setup dead straight. A slight misalignment is needed to prevent vibrations.

Dave

 

Yes. When I was in college, there was a guy who thought he was all that and a bag of chips; bragged about the car he was "restoring" from the ground up (wasn't in Any automotive classes, met him in the SUB), who Insisted that all his drive train be in a **Totally** **Straight** **Line!**
No deviation from laser straight was allowed.

He was weird in other ways too (crooked as a dog's hind leg). He was an Electrical Engineer who worked at the radar base. We all figured his brain got fried.
(';')

 

Ahhhhh, those explanations make sense about u-joints not being straight.

I re-adjusted the driveshaft so that it now has the necessary clearance on the side. Wasn't able to drive it to test just yet.

Looking back on it, i'm not sure why I didn't just listen the engineers who wrote the repair manual, because of course they knew what they were doing. It's probably because after taking apart the center bearing and replacing those rubber bits and being amazed at how complicated that set up is (later cars have a more traditional center bearing set-up, my '74 doesn't) my faith in Jaguar wobbled. As it did when I changed the original tranny mount. 🤣

 

Well folks, the 2004R install was a success, I was able to realign the driveshaft and it was vibration free to 95 MPH, which I determined was “enough.” But…

While I thought an original ‘74 XJ12 with 2 fuel pumps, two switch-over valves and 4 carbs was cool, the reality is that there is a reason Jaguar began installing fuel injection on cars manufactured mere weeks after my car. Carbs suck.

And then a derelict ‘95 XJ12 showed up on Facebook marketplace and my gears started turning. Rust free Fern grey ‘74 with a 6.0 liter and 4l80e from the ‘95? Now we’re talkin’…

so, I’m starting a new thread about that engine swap. And also announcing that my 2004R, conversion kit and all accessories is for sale for someone considering switching to an overdrive tranny. Original 5.3 engine will also be available, 4 rebuilt Stromberg carbs, rebuilt distributor with new mechanical curve and vacuum advance

 

That will be a great conversion! Will the 4L80 fit in the body, or will it need modification? I ask because the 4L80 is both longer and wider than the original transmission.

Regarding driveshafts, another reason for the 2 piece is to increase the critical speed. A shorter driveshaft can rotate faster than a longer one before it starts to whip and rotate off it's centreline. As the original XJ12's were capable of 150 mph, I expect a one piece couldn't go that fast. Similarly, police versions of the Ford Crown Victoria have a shorter driveshaft than regular cars, and a longer transmission tailshaft to allow higher speeds. The driveshaft is also aluminum vs steel to reduce mass.

2 piece shafts can also be made from smaller diameter tubing than a single piece, and that lowers the rotating mass - again reducing vibration and increasing refinement. The center bearing allows adjustment of the U joint angle to fine tune the shaft to the car to ensure the compound angles (taking into account both horizontal and vertical planes to arrive at an overall angle) are equal across the 3 joints. This can't be done with a single piece shaft.

 

Wanted to give a heads up that I've got this kit for sale in classifieds (finally).