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As some of you may know, we have had a 75 XJ6C here as a project for many years (a recent pic attached- this was our first LS powered Jag- the prototype for the kits and parts we offer now). It's been a runner/driver for long while now, and gets worked on/upgraded occasionally during lulls in other projects, but has not been a top priority. However, as we've seen interest in these cars go up in the last few years, I got a little itch to get this one down off the lift and do a few things. In the last year we did a lot of work on my 88 XJSC, reconverting it with an LS1 and 6 speed manual trans, adding a late XJS outboard brake rear suspension with 3,.54 posi, full front suspension rebuild with ZF steering rack upgrade, and more. Since the 2 cars share essentially the same platform, I decided to do some of those same upgrades on the XJ6C, and first one was swapping out the old inboard rear suspension for a modern outboard unit.
We located a nice complete late XJS rear suspension assembly and basically went about the process. It was expected that this would be a bolt in for the most part but what was a surprise was that it was even easier on the older car than the later one. There wasn't even the need to do any brake line flaring- with a few left over (inboard) brake pipes and parts, everything pretty much snapped together, including even the parking brake cable. Since that car already had one of our rear sway bar kits, the trailing arms of the new suspension were perfect as well (they come with the needed brackets for the sway bar links). On the brake line side, we had upgraded to braided steel hoses, and the rear (single unit) was retained, going to a hard pipe that led up to the original Jag brass tee up high in the middle. From there, another spare pipe on each side ( from the parts bin) led down to the edge of the suspension cage. At that point, the stock (late XJS) brake hoses could be brought to that same cage section (and through a drilled hole) anchored to the cage and then connected to the left and right pipes. Then our hydraulic supplier made up a set of braided hoses using the stock late XJS pieces as patterns- they were a prefect fit. The original later XJS cross body brake line wasn't even needed, nor were any additional brackets on the body. It was a snap. See the pics below to make sense of everything above- feel free to Email or PM for more info should you have questions....
More info coming soon- we're redoing the exhaust in the car now with a new better flowing, full dual, X-pipe equipped, 2 1/2" system- pics coming....
Thanks
Andrew Jaguar Specialties You get the basic idea- it's not close to stock (The body kit came on the car.....)
Nice clean good used assembly. Early OB model with solid rear rotors- may switch to vented in the future....
Left side rear feed brake pipe from master cylinder- joins to older style braided brake hose (note- the bracket seen here was originally on the right side of the body- this car uses a complete XJ6 Series 3 brake master and pipes and really the only difference between original and Series 3 is what side of the car the brake pipe runs on. This upgrade could be done the same way-feeding from the right instead- on a stock XJ6C)
Stock main feed pipe comes from the old style main brake hose up to the stock Jaguar brass tee.
Left side branch from brass tee down to the braided hose to caliper
Right side branch from brass tee down to the braided hose to caliper
Our hydraulic supplier took the old outboard rubber hoses as a pattern and made new braided units for us. Identical in fit.
Great job! But I'm confused as to the year of the XJ6C you have pictured. I have a 1975 XJ6C also and it's a Series II. Your '75 looks like a Series I ??
The car is a 75 (Series 2). But it has a Series 1 (73) hood on it. Since that picture was taken it also now has a Series 1 front bumper.....
Originally Posted by yachtmanbuttson
Great job! But I'm confused as to the year of the XJ6C you have pictured. I have a 1975 XJ6C also and it's a Series II. Your '75 looks like a Series I ??
yes! one of the points of XJ/XJS is the inboard rear brakes, it always makes great show talk!
Lets be realistic if the brakes are completley rebuilt at time of car build , nobody is ever gonna have to deal with them again,in this life time!
performance wise a toss up , both perform great, and i like the idea of less unsprung weight, designed for a smooth ride, more than anything else!
ron
pic of my 1975 XJ12C , with Spline Drive wire wheels, two ear Knockers, Manual shift with V12, 3.58 gears ,LSD.
somebody put a lot of money into the swap?
yes! one of the points of XJ/XJS is the inboard rear brakes, it always makes great show talk!
Lets be realistic if the brakes are completley rebuilt at time of car build , nobody is ever gonna have to deal with them again,in this life time!
performance wise a toss up , both perform great, and i like the idea of less unsprung weight, designed for a smooth ride, more than anything else!
ron
Im my experince pushing these car to their limits, inboard brakes are useless. For an everyday as built daily driver that stays inside the speed limits inboards are fine and safe becasue they dont do much which heavily forward biases the brake system and helps reduce the chance of a spin. . Once you start upping the power inboards become a liability. The most important thing on a car is balance, once you upgrade the engine, the suspension, brakes front and rear are next.
There are two type of outboard boards than can be transfered from an XJS, vented and sold rotor. The vented are large and the caliper is substantial. The sold rotor are much smaller and the caliper piston area is about the same as the inboards.
I would caution anyone upgrading the rears to outboard vented, they will tend to lock early. With out ABS the car will be be very loose out back especially under heavy braking and that can cause a loss of control. Jaguar used a rising rate pressure control valve on the rear circuit with both late XJS inboard and outboard vented brakes which decreased the rate of pressure increase as weight shifts forward. Jaguar refered to this device as a PRV. They are different PRV for each brake design. The PRV was discussed in this thread too https://www.jaguarforums.com/forum/x...nector-222430/
The "unsprung" weight thing is a bit mis-understood... on a street car, especially at the rear it isn't all that important since F=MA. Yes the mass has increase but the acceleration from a road impact is very small so the resultant change in force is also small. The rear suspension travel is only a few inches and with 4 shocks the acceleration delta and resultant force is small.
Case study... I recently upgraded my D2 Audi A8 to D3 brakes from a later model year Audi. Both the caliper and rotors are considerably larger and heavier. I thought there would be a noticeable decrease in ride quality and thumping over road impacts. I changed one side at a time to test it. Initially I could detect ZERO difference in ride quality. I drive around for 40 minutes hitting every bump I could with one side of the car and then the other side to compare. After a while I think there was a slight change but nothing all that noticeable in ride and impact quality unless you were really paying attention. However the brake performance increase from the larger calipers and rotors was nothing short of amazing. So as a trade off... far better braking is worth an almost nondetectible change in ride quality.
Besides the easier service and the option for vented rotors, the outboard brakes offer one other great benefit over inboard- oil leakage. My experience has been that the heat generated by the inboard brakes never did great things for the differential side seals over time. The quality of that seal material didn't hold up well vs the heat not to mention that British rubber products were never world class to begin with. Interestingly, the later XJS diffs (as in at least 93 1/2 and up, that were part of outboard brake rear axles) all used different, improved, differential side seals that are non interchangeable with the earlier seals. Those newer seals were of an improved material as well (my machinist thought they were Viton) so leaks were a thing of the past. That change was interesting as heat source nearby (the inboard brakes) weren't there any more. What probably actually happened is that the change was implemented in the 1992 or so models (beginning of facelift, maybe to help with leaks?) and then carried forward past where the brakes went outboard. Also, many XJ40 design detail/improvements made their way into the XJS as well, and later seals may be similar if not the same as XJ40 diff pieces....
Regardless, the days of those inboard headaches are over for me....
I have this very same setup (except with vented rotors) on my 88 XJSC LS1/6 speed manual car and the performance is perfect. Perhaps the XJS is more balanced front-rear than an XJS as I've seen no premature rear lockup on this car. We'll see how the XJ6C is when it's back on the road.
Getting motivated on our XJ6C.......
