Transaxle and Clutch drama RF84 Van Diemen

[skarillo]

Fairly new FF owner looking for armchair advice from you experts out there. Acquired a RF84 Van Diemen to be used in SCCA Autocross. Notes from the prior owner say that engine and clutch only have about 1 season worth of run time since their last refresh. I did not disassemble and inspect so can not say what their conditions looked like before I started to use the vehicle. For the first ~50 or so runs car felt great!

In my 5th event on the car the differential blew up first run of the day mid course mid corner. Transmission fluid was always checked morning of each event. Car is using a Hewland MK9

My precious wallet continues to empty the more I have dug into the broken bits. Looking for any advice as to help prevent future catastrophic demise of expensive metal bits.

To start diff blew up. I think the case survived, small chip noticeable on the inside but doesn't look like it should impact anything.




Input shaft shows excessive wear on the splines.




The splines of the clutch are extremely worn down and rounded out.



Cracks all over the clutch disc - if the diff didn't bite the dust fairly certain the clutch disc would have exploded next.



The last odd thing was the uneven wear on the clutch disc itself that touches the flywheel. There is not enough friction surface contact area on the flywheel so its only using about 3/4 of the clutch disc material. You can see the groove it wore in the previous picture.



On the topic of clutches, during the rebuild I plan to change away from this 5 inch and back to a 7. Is there a well known go to option for pressure plate spring pressure? Any advice, tips, tricks, or condolences are welcome.

Thanks
-R

[tlracer]

My initial thoughts on this:

- The whole clutch setup is not standard RF84. Back then it would have had a standard-type clutch & release mechanism with an external slave
- Clutch and flywheel are mismatched as the whole width of the friction material should contact the flywheel face
- Excessive wear on fingers & splines suggests either (a) the clutch release hasn't been set up properly so it was dragging constantly, or (b) continued pressure on the clutch pedal by someone
- The cracks in the clutch disk itself are likely to have been caused by the above
- Has the disc been fitted the wrong way around, ie. back to front?
- It's difficult to tell after the event, but there appear to be some very polished-looking surfaces where the diff case has failed, suggesting it's been cracked and rubbing for some time?
- The minimal visible damage to the crown wheel & pinion, compared to the diff itself, would make me think the failure has been internal, rather than due to an outside cause

I'm not an expert on diffs, I admit, so I'll leave that to someone else!

Going forward, I would have thought maybe returning to a standard 'road car' type clutch would be more forgiving, since race clutches tend to be designed more as an 'on-off' switch. What does anyone else think?

[bassracer]

I would agree to consider taking the time to return things to as original as possible. For a few reasons:

-its not very clear that existing setup and components were well matched and working together well.
-When you change back to 7.25" clutch it's very likely you'll change the clutch disk setup height which must be managed through the type of throwout bearing / spacer that must be adjusted to accommodate these differences.
-Returning to original will minimize the custom work.
-When I had a ford in my 85 for autox I used a tilton 7" clutch with the "buff" -spec pressure plate spring. https://www.pegasusautoracing.com/pr...asp?RecID=4948
-Also, every metallic 7.25" tilton style disk I've had would develop hairline cracks at those radii and were never a problem. I think Taylor told me its very common and not catastrophic (your pictures are WAY worse on that 5"...).
Edit: See factual evidence below from DaveW.
-I blew a diff spider gear on an autox launch once, so these things can happen once parts are tired.

I'm really sorry you're having this amount of repair with a new-to-you car. I hope you are able to find a way to work through it - once it is right again you should have minimal drama going forward with just autox. The key point is making it right.

[DaveW]

Usually, these disk cracks are not catastrophic, but...

With my 2018 WG accident, COVID, and hip operations I didn't inspect my 7.25" clutch (F2000 Zetec engine) for 4 seasons since I hadn't done very many races. My 7.25" disks always had some cracks that made me replace them. I ran 5.5" disks for years with the Pinto setup, and they NEVER cracked.

At the last race of the 2022 season, one of the 6 disk segments broke completely free due to cracking similar to that mentioned in a previous post and penetrated through the bottom of the bellhousing and undertray. Luckily it went out the bottom and didn't destroy anything else. Photos below.

[DaveW]

...Going forward, I would have thought maybe returning to a standard 'road car' type clutch would be more forgiving, since race clutches tend to be designed more as an 'on-off' switch. What does anyone else think?

Back in my early FF days, "road-car-type" clutch failures were VERY common. IIRC, the most common failure mode was some of the friction material coming loose and unbalancing the ass'y along with sometimes stacking up on an adjoining segment, preventing clutch disengagement.

They were easy to use, but not very reliable. They didn't like high RPM's.

[Hawke]

In this part of the world, we have to use the standard clutch, and we have standing starts. In the last 20 years I’ve had one plate failure, and the current Greddy plate has been in for at least the last 7 or 8 seasons. Many of us use the Greddy plates, and I can’t recall anyone having to change a plate at the track.

[DaveW]

In this part of the world, we have to use the standard clutch, and we have standing starts. In the last 20 years I’ve had one plate failure, and the current Greddy plate has been in for at least the last 7 or 8 seasons. Many of us use the Greddy plates, and I can’t recall anyone having to change a plate at the track.

That's obviously a much better clutch for racing applications than what was available here in the '70's. I can remember at least a couple of failures like what I described above.

[skarillo]

-When I had a ford in my 85 for autox I used a tilton 7" clutch with the "buff" -spec pressure plate spring. https://www.pegasusautoracing.com/pr...asp?RecID=4948

I'm really sorry you're having this amount of repair with a new-to-you car. I hope you are able to find a way to work through it - once it is right again you should have minimal drama going forward with just autox. The key point is making it right.

This is life with old racing parts of unknown history. I want to put some new stuff where possible in to replace the bad.

Is the "buff" spring pressure the commonly accepted good answer for autox? The other option I see is "white" which offers same torque capacity (not that we make near 200) but a lighter clutch pedal actuation force.

Also my other question is putting this all back together and ensuring everything is aligned happily. Is there a go to order of operation when reinstalling the transmission that helps me know if things are happy? The sheer plate has those dowels from the engine that help position the engine relative to the upper big chassy bolts but with those bolts in place there still exists flex in the chassy without the bell housing adapter ring in place holding it up from the bottom chassy bolts.

I guess in summary - how do you support the rear of the engine off the bottom of the frame / floor pan when wanting everything to line up happily?

[tlracer]

It's a while since I've been up close and personal with an RF84 but, from memory, bolting the whole back end together, then sliding that into the chassis was the way to do it. Like that, nothing's only part supported as the engine & gearbox are already bolted together.

Same process works on most cars where the engine is mounted front and rear, so not at the sides.

[tlracer]

Back in my early FF days, "road-car-type" clutch failures were VERY common. IIRC, the most common failure mode was some of the friction material coming loose and unbalancing the ass'y along with sometimes stacking up on an adjoining segment, preventing clutch disengagement.

They were easy to use, but not very reliable. They didn't like high RPM's.

This side of the pond we're stuck with standard-type clutch and flywheel, same as Hawke described. Avoiding cheap copies and refurbs helps to avoid the worst issues.

[Bobsy SR 6]

In my mind the spline wear shows that these parts have been in service for a while. When splines get pointed at the top, their useful life is over. Usually splines wear from a sliding action but it this case I believe the on/off throttle application has caused the wear. As you can see in the first few pics of the input shaft, the unused areas of the input shaft the spline tops are flat. Once the flat area is worn to a point the part(s) need to be replaced.
The pic of the diff carrier show that the housing sheared at the plane of the ring gear mounting flange. Again I wonder if the constant on/off throttle application has had a part in this failure. I would contact Scott Young at sy-gearboxs.com Scotty is the best and extremely knowledgeable.
It looks like you slave is an annular type due to the 2 braided hoses coming out of the pivot shaft bore. If you change to a single plate style clutch you will have to machine a new height spacer for the slave.
Yes racing is expensive and used race cars are always sold as being “ready to race”.

Good luck and happy racing
Tom

[bassracer]

Is the "buff" spring pressure the commonly accepted good answer for autox? The other option I see is "white" which offers same torque capacity (not that we make near 200) but a lighter clutch pedal actuation force.

I have no experience with the white. I found the buff spring very manageable and wouldn't be re-thinking it if I had to buy one again. I preferred it to the Honda stock PP.

[bob darcey]

Ditto on the "buff" spring. I raced for about five years with an orange spring before switching to buff and believe that was contributory to my first hip replacement.

[Phil Creighton]

As an aside it was pretty normal for the 5.5 inch clutch to underhang the flywheel recess on a FF engine. Since the flywheel was rules controlled it was always a compromise to get the lightest clutch possible. This was high maintenance option that I wouldnt use on an autocross car.
Wouldnt be surpised if the blowup was caused by one of the spider gears breaking and locking it all up.
Phil

[skarillo]

I would contact Scott Young at sy-gearboxs.com Scotty is the best and extremely knowledgeable.
It looks like you slave is an annular type due to the 2 braided hoses coming out of the pivot shaft bore. If you change to a single plate style clutch you will have to machine a new height spacer for the slave.

I have already been in contact with Scott as he helped me source all the replacement diff parts I would need. Those diffs are not that easy to source in the US so don't want another incident. Ultimately I likely will end up sending this whole transmission back to him for inspection and rebuild.

Scott also recommended the Tilton OT-2 Rally clutch with the buff spring. I do plan to swap it away from the hydraulic release bearing.

The failure was quite undramatic. No lock up of the tires ever and car coasted just fine both in and out of gear.

[Fred Michael]

Just my opinion but I would NEVER go back from the hydraulic release bearing. Far simpler than the monkey motion setup. Yes it takes a different bearing when going from 5.5 to 7.25 but that's easy

[Hawke]

Just a question for my American friends. Other than the lower inertial mass of smaller clutches, what difference do plates make, considering that you never use the clutch when racing?

[tlracer]

Just a question for my American friends. Other than the lower inertial mass of smaller clutches, what difference do plates make, considering that you never use the clutch when racing?

They're designed for a specific and different set of demands - rigidity, strength, instantaneous load - rather than mass-production, low-cost and usually lesser extremes of a road clutch, so tend to be more like a mechanical on/off switch.

As an aside, possibly the worst car I ever drove had a race clutch but a synchro gearbox, which meant the two were constantly fighting each other - clutch in...wait for synchro...clutch out - and with a big V8, the resulting driveline shunt was horrible.

[Phil Creighton]

As one who was around FF in the 70's the stock street clutch couldnt stand the bigger grip of the USA slick tires. The straps inside the cover would break frequently so competitors petitioned for race clutches - after all its for reliability not performance! Once the stock clutch was allowed to be replaced the cat was out of the bag. Rules creep.
83 Runoffs we actually had a competitor that ran no clutch - direct drive. False grid at Road Atlanta was downhill. Started up, rolled a few yards and stuffed it in gear.
Phil

[Garey Guzman]

As one who was around FF in the 70's the stock street clutch couldnt stand the bigger grip of the USA slick tires. ..83 Runoffs we actually had a competitor that ran no clutch - direct drive. False grid at Road Atlanta was downhill. Started up, rolled a few yards and stuffed it in gear.
Phil

How'd that guy qualify and finish??

[Phil Creighton]

Dont remember where he finished but was towards the front - the late Kim Campbell in a Van Diemen 82 or 83. I am pretty sure it was the same in qualifying - just rolled down the false grid and stuffed it in gear. He came from go karts so the direct drive wasnt an issue.
Didnt say you had to run a clutch and the only weight was the flywheel inc dowells - theres a whole different clutch story at another Runoffs in S2.
Phil