So......... having just purchased a very well cared for and meticulously maintained '88 XJS (5spd conversion) I find the throwout bearing is occasionally whining and a new clutch is imminent.
Let the $$ bleed commence!!
Some background - the conversion was done in 2015 at 129k km using an as-is (not rebuilt) Borg-Warner T5 World Class from a 1985 Mustang by a local shop. There were teething issues with the conversion and in June, 2019 at 140k km the gearbox was rebuilt with new clutch by Halton Transmission (reputable local company) who did not do the original conversion. The previous owners notes indicate that the throwout bearing was then replaced 3 months later in September? very odd - need to confirm that this did in fact occur.
Now at 150k km it needs a new throwout bearing (and clutch).
Before I enquire with Halton Tranmission to try and get their insight as to why the premature failure, I thought I would ask the same question to the forum to draw on its broad collective experience of vehicle transmissions beyond XJS OEM varieties.
Ultimate concern is that there is some systemic issue with the conversion that means a new clutch will be required every couple of years

FYI - going forward, I will be getting the clutch replaced by my old Jag mechanic, who seems very competent.

Thanks in advance!

 

What bell housing was used? Was it indexed properly? What's the symption? Just noise if so when? What is the size of the MC bore and what is the size of the Slave cyl bore? The most common problem on these home brew conversions is a misalignment in the bellhousing which rips up the TOB and transmission input shaft bearing. Both sound similar
,

 

Thanks for your prompt response.
I have no idea what bell housing was used, nor whether indexing was done properly.
My jag mechanic diagnosed it is the throwout bearing. I drove it 20km yesterday in start-stop traffic and there is an intermittant whine when depressing the clutch. Occurred several times. If it whines and I keep clutch down and shift it into neutral the whine stops, which I understand indicates TOB? Gear change okay, although I noticed shifting into reverse there is an occasional gear-crunch. TOB related?

No idea re. MC bore and slave cyl bore. MIsalignment of what in the bell housing? I did read that a misaligned clutch plate can cause premature TOB failure. Based on your experinece, do you think this is just shoddy installation, or something more fundamental?

 

You'll need to check the bell alignment and input shaft bearing. When the clutch is in and the trans is in neutral is exactly the condition where the in the input shaft stops and there for also the noise.

If you want it right, the whole sha'bang has to come apart and be checked. The T5 bell literally takes 5 min with a dial gauge to check. It's one of the easiest to check. Tolerance is 5 thou. Nothing leaves my workshop with more than 3. It' really not difficult to do it right.

Bad TOB most often will whine all the time when the clutch is in. Intermittent is almost always a misalignment issue since no clutch is perfectly balanced it can make a harmonic noise with a warn out input shaft bearing at different intervals.

 

Okay - so it looks like Halton Transmission just did crappy work.
I will discuss with my mechanic. I agree - do not want to be replacing the clutch every two years, so taking everything out and checking makes sense.
Any other advice / words of wisdom I shoould relay to my mechanic or Halton Transmission (if I do discuss it with them)?

THANK YOU!!!!!

 

Just watched a couple of you tube videos on bell housing alignment...........you are correct, it looks pretty simple, yet it seems Halton Transmission still managed to screw it up (t.b.c.).

 

Sounds like the throw out bearing is in contact with the pressure plate at all times when running. This might be the reason it continually fails.
I have a kit for my xjs with the supra box and I have not installed it due to the fit up of the thrust bearing being in contact all the time. I need to do some mods on the pivot point angles.

 

Since the hydraulic clutch throw out bearing is adjusted before the transmission is installed and once installed can not be adjusted further extremely careful measurement is called for.
Set the throw out bearing .020 from engagement. Premature clutch wear is an indication of improper. Setting of the throw out bearing. The throw out bearing should not remain in contact with the pressure plate except when shifting.
I’ve got bad news for you. You will need to check the engines throw out bearing. Yes engine back out.remove the engine and drop the oil pan.
Failure to do so means the engine will be destroyed. I’m sorry. Many engines have been destroyed this way.

 

Well who knows. The input shaft could have been worn out before it was installed as the donor car could have had a billion miles. Might be pilot bushing too which can also get torn up from misalignment. If you're have a re-occurring problem then It all just needs to come apart and get checked by someone who cares and understands.

Before I started using new transmissions I was sourcing used units. The two that I purchased both had problems, one T56 had a noisy input shaft bearing and the other T56 had a finicky reverse engagement. Sellers often wanted 1500 to 2500$ for these used transmissions that needed repairs, so I switched to new T56 which cost about 3800 with a bell and a warranty. The one with the reverse problem really hurt becasue I wasn't able to notice the problem until the unit was already in the car.

 

Errrr.......... remove the engine? Engine throwout bearing??? Not exactly sure what you are saying there. It's clutch / transmission related, not engine related per se.

 

Good points.
Well, I would definitly place my jag mechanic in the 'competant and caring' category, so I have some faith that he will do it properly.
The original used transmission was subsequently rebuilt after being installed the first time, so I would hope any knackered components would have been replaced then.

Apparently a new T5 WC runs around $US 1,800 so not exorbitant

 

or just shim the transmission back enough to clear. The shim doesn’t need to be complex just drill the holes bigger. The transmission alignment isn’t done by the bolts. Rather the two alignment pins. ( which happen to be in the same place as a Chevy relative to the crankshaft.

 

Wow! I’m so sorry to give you really bad news.
When the throw out bearing is pressing against the clutch. It puts pressure on the crankshaft thrust bearing. ( hip bone connect to the thigh bone sorta deal) it’s why the throw out bearing fails quickly. It wasn’t designed to spin along with the engine only come in contact when the clutch is depressed.
The Crankshaft thrust bearing is the same way. Only for the few moments the clutch is pressed on to shift gears.
If you just replace the throw out bearing it will fail again unless it is adjusted to clear.
I have sold several used engines to replace those that aren’t set up right. Because once the crankshaft throw out bearing fails. The block starts to wear and that’s not replaceable. Without spend a whole lot of money.

 

Hey, thanks for clarifying.
I spoke to Halton Transmisison and they reckon it could be the pilot bushing. Apparently no off the shelf bushing / bearing was available, so a machine shop made one out of bronze.
Spoke to my mechanic and he will be taking it in in a few weeks time to investigate. If pilot bushing related, then one potential option is to get the flywheel machined to accept an off the shelf bearing.

 

Highly unlikely.first of all you don’t change the flywheel to use a different pilot shaft bearing. the pilot shaft bearing is in the end of the crankshaft. You’d have to remove the crankshaft from the engine and then on a really big vertical mill bore the hole larger. ( it’s never done that way).
Pilot shaft bearings wear normally. So a degree of slop is normal. Anyway that won’t wear out a throw out bearing. What will wear it out is the bearing race in contact with the clutch.

I’ve always bought a new one and bore it out to the pilot shaft size. It’s what you do when you adapt a different transmission.
I can understand you looking for cheaper and easier. I always do. But to place a correct value on an approach you need to understand how things work, not listen to someone who has failed to do the job correctly.
However it’s your car. Please feel free to do whatever you’d like.
You can maybe skip the crankshaft thrust bearings. If you pull the oil filter, cut it open ( not with a saw it will deposit metal shavings in the filter, they make oil filter cutters for that. A crude way would be to cut open a hole with a sharpened chisel and then use a pair of tin snips to open it up the rest of the way) Then examine the filter for trace metal. ( that’ll be the thrust bearing).
When you drain the oil let it settle for many hours before you gently pour it off. if you see metal at the bottom of the catch can. That’s bad. If not you lucked out. Look at it like a miner panning for gold except if you see those sparkles you don’t get to celebrate.

 

Okay........ the pilot shaft bearing is located at the centre of the flywheel is it not? Hence, machining out the bearing recess in the flywheel to accommodate a larger dia. off-the-shelf bearing might be one potential option.

 

You are pointing to the center of the crankshaft. Yes that’s the pilot shaft. . The flywheel is held onto the crankshaft by those bolts and comes off separately.
The dark circle is the crankshaft and it goes behind the bright flywheel.

so all machining the flywheel will do is make the flywheel not fit. The pilot shaft bearing is stuck in the end of the crankshaft and it’s a brass bushing. The hole in the center of that brass bushing is what needs to fit the pilot shaft on the transmission. The hole will need a little clearance. ( off the top of my head about .005. ) I suspect the bushing is fine. The problem isn’t with the bushing, it’s with the throw out bearing in contact with pressure plate instead of being clear by about .020. Most hydraulic throw out bearings can be rotated in or out to provide sufficient clearance. It’s rare but some might need a shim between the engine block and the bell housing.

 

Thanks for clarifying; appreciated.
two other symptoms- occasional crunch into reverse and it popped out of 2nd gear one time. Both symptoms of pilot bushing issues?
should know more soon!

 

Reverse gear has no syncro’s so it will not shift into reverse if moving without crunching. It’s also possible to shift too fast into reverse and as a result crunch.
Popping out of gear likely is failure to put it fully into gear. It could also be the result of a bent shift fork

 

Clarification: The input shaft can be stabilized one of two ways:

1) A bronze *bushing* that is a solid piece, press-fit into the center of the crankshaft, that has a few thousandths clearance to the tip of the transmission input shaft.

2) A roller *bearing* that supports the input shaft tip. That presses into a machined shoulder in the face of the crankshaft boss that the flywheel mounts to (as depicted in the picture above)