V12 manual bellhousing - converting for hydraulic throwout bearing

Hi everyone,
I have an early (1969) S1 XJ6 MOD gearbox that I wanna use with a V12 but as you probably know those early boxes don’t have mounting bosses for the V12 slave cylinder. I’d like to use a hydraulic throwout bearing instead of modifying the gearbox case to accept the OEM slave cylinder.

Can anyone who’s done that before tell me which throwout bearing you used and how you wound up mounting it inside the original V12 bell? I’m sure I could figure something out but it would be easier if I had a starting point… Or maybe point me at an existing thread… Pics would be great too!


You’re a far braver man than me. I’ve heard little but one horror story after another from people who’ve tried to install hydraulic throwouts in Jags, Triumphs, and others. One guy I know sold hundreds of 5-speed transmission conversions for Triumphs, and used hydraulic throw-outs. He had horrible quality problems with the available cylinders. And removing the tranny in a TR-3 is about 100X easier than in an E-Type.

It’s a bit inconvenient when the normal, external slave cylinder fails. When the hydraulic throwout fails, you are completely screwed. Out comes the engine…

Ray L.


Interesting Ray - I hadn’t heard that they were so troublesome. Indeed recent cars seem to use that style of throwout exclusively.

Really my reason for wanting to do this was more about not having to completely disassemble a well functioning box to spotface and drill the case. I also had thought about making a bracket that would use 2 of the top cover bolts and a mounting flange bolt to avoid drilling the case…

I might just hafta bite the bullet and pull the box apart.


Just to be clear, are you talking about installing a concentric slave cylinder? Like one of these?

Because there are also hydraulic slave cylinders that mount outside the bell housing and operate through a fork.

Whatever, these concentric things can’t be too bad if Chevy uses them OEM.

I’ve never understood how you’re supposed to bleed those things. I think if I were installing one I’d find a way to extend that bleed port out the top of the bellhousing to where I could get at it.

BTW, waaaaay back in the day when I was trying to shoehorn a 5-speed into my XJ-S, I considered looking at the hydraulic clutch system that was used in the Firebird/Camaro that the 5-speed BW NWC came out of. Come to find out that the master cylinder, the line, and the slave cylinder were all a single piece of plastic that came pre-filled with hydraulic fluid. Weird. I opted to go another route, as I couldn’t figure out how to use that thing anyway.

1 Like

The internal hydraulic throwout is fine, IF you can easily remove the transmission should the throwout fail. R&R’ing the gearbox on most cars takes no more than 3-4 hours, many are much less. R&R’ing the gearbox on an E-type takes two DAYS, IF you’re proficient. In most cases, doing it at home, it’ll be more like 3-4 days.

Ray L.


Excellent point. But do you really expect one of these things to fail anytime soon? And even if it doesn’t, there are other things in there that can go wrong. Does the OEM setup use that carbon-faced throwout bearing? How reliable is that thing compared to the roller bearing used on the concentric hydraulic unit?

Like I said, every, single person that I have EVER talked to that has installed a hydraulic throwout in a non-OEM installation, has had problems. I’m not saying it can’t work, but I am saying, on an E-type, if you don’t get it right the very first time, or you get a faulty part, or you suffer an “infant mortality”, it is a massive PITA to fix it.

Any installation on an E-type would HAVE to ensure the TO was properly located, and/or provided some means of dealing with any mis-location. There are several ways to accomplish that, and NONE of the good ways involve a carbon block.

Ray L.

What choice does the OP have? Is there a way he can install an external lever-type throwout on the bellhousing he has? Or does he have to go find a different bellhousing?

I assume he has the fork, throwout and arm from the “donor” application, which I’m assuming had a mechanical release mechanism? From his description, it sounds like the only missing piece is the bosses to mount a slave cylinder. That sounds to me like a little simple fabrication and/or welding, and he’d have something functionally equivalent to a stock E-type clutch system.

Ray L.

1 Like

A little real-world experience:
Regarding the aftermarket hydraulic TO bearings: I’ve had multiple failures with the McCleod product. I’ve had multiple successes with the RAM product, most notably in our SIII eType.

It does not mount to the bell housing, it sits on the nose of the trans. There is ususally an anti-rotation pin that goes in place in one of the studs on the front bearing retainer (on a T5.) Not sure about your application, but you’ll need an anti-rotation solution.

I am not sure what your gearbox looks like… If the bellhousing is integral you are in for an adventure because it will be very difficult to test fit and set depth…EDIT: Actually maybe not. Would need to build a device to measure depth from block mating surface to clutch fingers, then measure from bellhousing mating surface to TO bearing face… doable now that I think about it. Knowing those dimensions is how you set the bearing distance out from the nose of the trans so it almost touches the clutch fingers.

Get the remote bleeder kit to go with it, it’s a simple braided line. Bleeding is a non-event.

Make sure you understand the bore and stroke of your clutch master cylinder, and compare it to what the TO bearing manufacturer calls for.

Fuel line is not hydraulic line. Use hydraulic line. Like from the remote reservoir to the clutch MC.

All the usual suspects (Speedway, Jegs, Summit) sell a depth tool that will help you properly space the bearing out from the front of the trans so that it is the right distance from the clutch fingers. Get one, understand it, use it.

If you go with a stock clutch MC, you’ll have a bit of drama finding adapters to the normal US-spec pressure line on the TO bearing. I don’t recall the details, it’s been 10 years, but we finally found one.

Some manufacturers (RAM) say that the clutch release point can end up high, near the top of the pedal stroke, even when everything is properly set up. They sell an in-line height adjuster to rectify this. We had no such problem, release point is about 1/3-1/4 of the way up from the floor, feels just right.

Been in the car 10 years, driven pretty much every week, zero issues. I plan to use same setup in my XJS once the zombie apocalypse abates and I am more comfortable with my bank account.

Feel free to PM me if you want to chat live.

1 Like

I have one of these on my 5 speed Tremec TKO conversion.
I was wondering about bleeding it so I tested it before I bolted the whole thing in position.
It worked without bleeding.
Two theories.
One. I have never “bled” and hydraulic system I have designed. Just operate the directional control valves and the cylinders slowly operate and expel the air. Recently did this on 6” cylinders which were empty on assembly. Several movements to full stroke both directions and they lock solid mid position. I suspect the air can escape past the sealing systems but the fluid can’t. These systems run at 200 bar so possibly the high pressure is a factor.
Two. The line down to the clutch allows the air to make its way up to the master cylinder where it works its way out of the system…somehow. Didn’t pull the master cylinder to bits but it has the reservoir on top so maybe the continual shuffling of the air with the operation of the clutch allows the air to migrate to the top of the fluid…??

Going back to the original post, as you sure that a S1 XJ6 MOD gearbox is robust enough for a V12 E? I suspect there is something like a 100hp difference.

Hi - Thanks everyone for the helpful info.

Yes - Kirby that’s the style of throwout bearing I was talking about.

As you say Ray - not super complicated to fabricate a mounting system for the OEM style clutch slave. It’s done pretty routinely to these early XJ6 boxes, but if you mount it to the gearbox case it has to be drilled all the way through so I’d have to strip the box which was what I was trying to avoid… But it seems that still may be the best solution.

Bob, the Jag trans/bell combination is different than a T5 installation cause there isn’t a tubular nose that the original throwout rides on (unless it’s one of the ones that uses the original style slave). For the Jag trans the throwout would have to screw to the back of the bell.

@600 The transmissions are the same from what I understand, part numbers for the internal gears and shafts are interchangeable. The trouble can come from the O/D not being up to the task though but there are up-rated internals for that.

Anyway, thanks again guys. I think I’m gonna just strip the case, drill it, install the studs and bosses and go with the OEM style clutch slave.



If it’s from a 4.2L the gearbox is essentially the same as a V12 E-type manual box would be. The O/D might need a rebuild to higher torque spec, but as long as you don’t over stress it by engaging it without the clutch with WOT, it should be fine.

If it’s from a 2.8L the gearing may be a bit strange for a V12, especially the short 1st gear, but still a lot more fun than the BW auto box. :slight_smile:

Hello Mike,
I have carried out the modification to accept the mounting of the Clutch Slave Cylinder à la S3 E Type many times and you should spot face the location area for the studs. Spacers of the appropriate thickness are then used used in lieu of the bosses.



1 Like

Thanks Bill - that’s exactly what I meant. A question as far as placement: I don’t have a box with the bosses to measure so do you know what the distance from the front of the gearbox to the stud center should be by any chance?

Yup Pekka, gonna upgrade the O/D when I rebuild it. Gotta rebuild anyway cause I always seem to find the sliding members stuck hard to the annulus from disuse. BTW surprisingly the 2.8 and 4.2 boxes have the same gearing. Very different final drive ratios however.


How about posting some photos of this process?

Hello Mike,
I’ll look this up for you when I go to work today.

Hello Kirbert,
I don’t have pictures and won’t have pictures of the process until I carry it out again. However, the process is carried out using a CNC machining Centre and is as follows. A similar process can be used with a Manual Milling Machine, but without the automation.

  1. The fixture is basically a purpose built Angle Plate to which the Gearbox Housing is bolted via the Top Cover surface of the Gearbox, using the Threaded Holes for the Top Cover to secure it to the fixture. This sets the Top Cover surface square with the Machining Centre table.

  2. The end surface of the Gearbox (either the front, or rear; either will do) is clocked to be vertical (square with the table). Its a low volume job, so having to clock the end true is not an issue, versus creating an alignment feature as part of the fixture.

  3. The CNC program incorporates four tools:

a. Spot drill to provide a start for the Thread Minor Diameter drill. The spot drill is run deep enough to provide a chamfer of the Threaded hole.

b. Thread Minor Diameter Drill

c. 12.0 Diameter End Mill used in Circular Interpolating a true, flat surface (Spot Face) to seat the Spacers.

d. A Thread Milling Cutter. This is used to Helical Interpolate the Thread, starting at the bottom of the hole, winding out. I Thread Mill the Thread rather than tap the hole, as I don’t drill through into the inside of the Gearbox Housing and results in a Full Thread Form right to the bottom of the hole. I start at the bottom of the hole and Helical Interpolate out to avoid the swarf interferring with the Thread Mill at the bottom of the hole and to take advantage of Climb Milling.