Installing John's car quarterbreed kit and THM700 (edited)Any advice?

And so it is finally happening.
Many years ago, I acquired a quarterbreed kit + THM700 (edited) transmission + a whole bunch of other bits from a XJ6 being wrecked.
I got the transmission and torque converter rebuilt at my local shop (who found that the casing was cracked and replaced it…).
Today, finally, I mated all the parts for a trial fit. I dont have the installation instructions but so far it has just been like a little game of Lego. I suspect there are surprises ahead…
If any one has advice and guidance, I’d happily listen :slight_smile:

Main plate and cranshaft adaptor in place, ready for the flex plate

Reconditionned torque converter. I also got loads of bolts and nuts but I am missing one of the 3 bolts to fit to the flex plate :frowning:

Once mated it makes a hefty piece of mechanics…

Does anyone know what this is and where it goes?

The cooling lines need some adjusting… and the BW bracket has to go to make room for the starte motor

Very interesting! I’ll follow this with interest. Good luck.

Jeff H.

The plate that has “John’s Cars” and “Dallas, TX” stamped on it is the rear transmission mount which goes across/under the tunnel. It replaces the Jaguar assembly entirely. There should also be a standard GM-type transmission mount with two lugs that goes into the holes. I also have John’s Quarterbreed kit in my Series 2 XJ that mates the v12 with a 700R-4. I hope this helps.

Cedric Chew


And how and where does the starter go?

The apparent lack of starter pinion access to the ring gear does seem strange. I cannot recall the pattern of the adaptor plate in my kit as it’s been so many years since being installed, but it must’ve had that area cut out. I do recall though that on my Quarterbreed kit the transmission housing needed a slot or hole cut into it so the starter mounting bolt hole could be accessed. The starter location on the V12 is on the same side of the engine as the XK.

The starter motor fits where the BW bracket is on the photo. Of course the bracket has to go. So it is positioned much lower that the original Jaguar set up, by the sump.
The starter motor is from a Camaro.
I will show photos as I go.

Ah… got it!

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I now have to educate myself on things such as lockup systems, TV cable, etc. Bliss…

Here is the starter motor. Probably from a Camaro, early 80’s.
Just got it tested, runs like a champ. Needs a little cleaning and paint.

Be careful fitting the motor. You may have to shim it to get correct mesh or risk the teeth skidding over the flex plate ring gear, or the alloy pinion housing breaking, which is a common failure mode according the the fitting instructions that come with those motors.

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Is there a technique to verify that the Bendix pinion gets where it is supposed to?

Ah well, Google delivered this:

This one is good too.

Ah, yes the classic big AC Delco used in many GM cars.

There are smaller and lighter gear reduction units.

My LT1 uses one. I tried the big AC Delco as well. when I had my “starter wars”. Now resolved, thank greatness!!! Several went in! I have a spare now, a Malaysian new from scratch.

I was lucky, each meshed just right. No shim needed.

Mine inluded a bit to hold the bolts in the hoe while the starter was hefted up into place. Tricky, hold with one hand and drive the bolts with the other. Much easier with the GR, a lot lighter!!!

Knock on wood, not getting out much, but it cranks just fine…

Pete’s Brontosaurus uses these.


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Check TV cable geometry specs on the Bowtie Overdrives site and notice that the throttle lever and cable attach pin on the jag TB is no where near in spec with gm measurements. I couldn’t get mine to shift right until I got this sorted, which entailed a spare TB mounted on a jig with lots of measuring, several hours time, trial and error etc… I made a C shaped adapter for the throttle lever to put the Pin in the correct orientation and it shifted as designed, but I ended up changing governor springs to fine tune and you’ll need to add a vacuum switch for the TC. But it will make a huge transformation in your XJ, it will drive like it should have when new. Lower first gear makes it a decent car in town rather than a slug, OD makes it cruise great on the road. You’ll need to fit the driveshaft… And I would put a TC override switch on the console with an led idiot light for when the TC is engaged.
Seems like there were bits for the valve body that came with the kit that needed to be swapped too.

Thank you for all this.
However, I struggle to make sense of it all as I am not used to the vocabulary.
My understanding is that I have a 4 speed THM700 box with Torque Converter lock-up.

I get TV cable : Throttle Valve cable
TC : Torque Converter
But TB : ?

My car is 1975 with 2 HIF7 carburetors.


Not sure, but, it seems that the reference is TB for throttle body.


Ok, then what is a “Throttle Body” on a carburated car?

The throttle body is sort of generic expression for the source of the vacuum for the gearbox, Eric. The box needs manifold vacuum for proper operation - sourced from the manifold itself or the carb…

xj6 85 Sov Europe (UK/NZ)


The throttle body is in carburetor as the throttle (if you lift the piston you can see it).
Any throttle takes away air from the engine, so the engine can’t breathe freely, can’t burn as much, so it produces less power, and this suffering produces vacuum between the throttle and the combustion chambers.

On any transmission with a mechanical throttle valve the throttle position (0-100%) is taken from the throttle or linkage. If you change the throttle unit the transmission is attached to, the signal is altered, so you have to somehow emulate the throttle the transmission was designed for. At the least, you want the same travel 0-100%, I don’t know if a different torque curve changes things that much.

Normally a transmission with a TV cable needs no vacuum to function, unless it is for the kickdown. It does need the TV cable to be adjusted and behave properly so it’s not harsh or wearing quickly, and so that the shift points are acceptable.

A transmission with a vacuum port senses the load on the engine (no vacuum is full load, regardless of rpm or throttle position etc., change into lowest acceptable gear; high vacuum means find the highest gear for the speeds involved).

A TV cable one finds these differently, but it also has input, output and demand inputs. And the demand input needs to be about right, which can be a little adventure it seems, but shouldn’t be too hard if you take time…