Explain This Clutch/Transaxle Behavior

Silver66fb

Tim Terry

Supporter
Gents,
I have an SPF40 Mark II, with Roush 427SR, Quaife transaxle. I'm using the Quartermaster release bearing (721100 model), from Olthoff.

When I really get on the accelerator and while the rpms are relatively high, I have trouble getting the car out of gear with the clutch pedal all the way to the stop.

Is this a case where I don't have quite enough travel on the release bearing? The car shifts very smoothly at lower rpms.

Thanks for any insight.

Tim
 
IanAnderson

Ian Anderson

Lifetime Supporter
Supporter
Input shaft binding in end of crankshaft.
Either not drilled deep enough or bearing not correct oillite bush not being Oillite or bell housing not being correctly aligned so shaft slightly off centre

Ian
 
I

Ron R.

I think Ian may be on to something. I would also make sure the bolts between the trans/bellhousing/engine are tight.
 
J

Jac Mac

Don't think its the shaft contacting crank issue in this case- high RPM, is the clutch cover diaphragm the type with fingers that form a 'cone' toward release bearing, @ high RPM the centrifugal force can make the 'cone' move toward the throw out bearing effectively increasing the distance & force required to release.
You had throw out bearing issues before when it over extended due to lack of clutch stop, you may need to re-visit that, maybe change type/brand.

Another possible but unlikely problem is the centrifugal forces acting on the synchro hub slider dogs of the gear in use at the time.
 
R

Rod Brace

Also have you checked to make sure that your input shaft is infact centered in the crank the make offset dowels than can correct this but it needs to be checked with a dial indicator so trans are more fussy than others I'm guessing a transaxel would be one of those. Drag racing I have had diaphragm style pressure plates when speed shifting has the clutch stick to the floor till I let off and rpm's came down then clutch pops up. Rod
 
Silver66fb

Tim Terry

Supporter
I'm embarrassed to admit I didn't follow up on this. It is not resolved, but will dig into it this winter. I have the McLeod diaphragm style pressure plate, as supplied by Olthoff. I believe @JacMac might be on to something, but input shaft alignment isn't out of the question. As long as I'm going in there, I might as well go with the slave cylinder and fork setup, which I prefer anyway.
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flatchat

flatchat(Chris)

Supporter
If I may suggest .....
the bottom ( or lower half ) of the bell housing needs to be supported
as the torque from the gearbox is trying to lift the engine thus "bending" the bell because there is nothing below the centre line on these engines and you'll need engine mounts that wont tear apart as well
 

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Silver66fb

Tim Terry

Supporter
Hi, Chris. Did you fabricate that support yourself? What's on the other side of the block plate right there, left side of pic?
 
S

Tom

Anybody have an opinion on the necessity of using similar stays on a block with deep skirts - like an LS motor?
 
C

Ian Clark

Supporter
Hi Tim,

Most likely misalignment between the crank and input shaft of the transaxle. Corrected by offset dowels as mentioned above.

The internal throw out bearing will give you no problems if properly set up. An external slave cylinder and fork is no less fussy to set up but does look more authentic with the correct clutch fork arm, cylinder and return spring.

Since you have the car apart it might be a good time to source an original type bell housing with the lower mounting provisions (Safir Spares). This means the engine/transaxle assembly is supported in six rather than four locations.

It would require some fabrication work to incorporate the new lower mounts into the SPF chassis but would be nice upgrade to your car.

Cheers
Ian
 
J

Jac Mac

spud said:
Anybody have an opinion on the necessity of using similar stays on a block with deep skirts - like an LS motor?
Click to expand...
Ford did it right with the FE engine & dedicated dry sump oil pan that had the lower lugs already cast into the pan along with all the mount points in the T44 housings, not surprising that the LS could be considered a deep skirt alloy copy of the Ford Small blocks.
 

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flatchat

flatchat(Chris)

Supporter
The old small block Ford and Chevy have this prob The SLCs adapter plate is mounted to the chassis as well which helps
The LS and F mod motors have support at the sump level - so no real issue
The early blocks are only supported above the crank centre line - so at full noise with the trans trying to lift the engine ( the adapter plate being Al and 1/2” thick) shifting gears will be cumbersome as the spigot on the input shaft binds in pilot bearing under engine drive load - or “ bounce” and shudder maybe the sensation
Hard to explain but from my experiences
 
manta22

Neil

Supporter
I supported my drive train at three points, the usual engine mounts, at the tail of the Porsche G50 transaxle, and at the adapter plate. The transaxle mount uses an original Porsche transverse mount with rubber bushing inserts, the other mounting points are solid.

To mount the adapter plate I used two of the top adapter mounting bolts that pass through "ears" welded to the bottom of a chassis cross tube. That tube is removable to allow the engine and transaxle to be lifted out as one assembly.

NB: this is a "Chevrolet" (Donovan aluminum block) and not a GT40 or SL-C chassis.
 

Attachments

J

Jac Mac

manta22 said:
I supported my drive train at three points, the usual engine mounts, at the tail of the Porsche G50 transaxle, and at the adapter plate. The transaxle mount uses an original transverse mount with rubber bushing inserts, the other mounting points are solid.

To mount the adapter plate I used two of the top adapter mounting bolts that pass through "ears" welded to the bottom of a chassis cross tube. That tube is removable to allow the engine and transaxle to be lifted out as one assembly.

NB: this is a "Chevrolet" (Donovan aluminum block) and not a GT40 or SL-C chassis.
Click to expand...
Wouldnt that be five points total? , 2 OE mounts, 2 @ Adaptor plate and 1 @ tail end of transaxle.
 
manta22

Neil

Supporter
Almost true, I was counting the end, middle and the other end as 3 but there are actually 2 motor mount bolts, two adapter mount bolts and two transaxle mount bolts, so six points technically.
 
flatchat

flatchat(Chris)

Supporter
Silver66fb said:
Gents,
I have an SPF40 Mark II, with Roush 427SR, Quaife transaxle. I'm using the Quartermaster release bearing (721100 model), from Olthoff.

When I really get on the accelerator and while the rpms are relatively high, I have trouble getting the car out of gear with the clutch pedal all the way to the stop.

Is this a case where I don't have quite enough travel on the release bearing? The car shifts very smoothly at lower rpms.

Thanks for any insight.

Tim
Click to expand...
In this case it maybe that the synchros are not designed for high rev shifting or a case of wrong oil
Eg:- the new tremec TKX uses a full synthetic oil and is advertised for quick shifts up to 7000rpm
 
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