Improved clutch on a 948?

[Sarastro]

A couple years ago (but only a couple thousand miles), I had a problem in which some of the nuts in my clutch pressure plate, which affect the height of the release levers, came loose. (This is a Bugeye with a standard 948 engine and clutch, but a ribcase transmission.) Seems like its happening again, so I have to pull the engine and fix the clutch again as soon as I get some time.

So the question: is there any way to put an improved clutch into a 948?

Can a 1275 clutch be used? I've never heard of this being done. I imagine that, if it were possible, that would be a common modification. Presumably, you'd have to use a 1275 flywheel, but maybe that wouldn't fit the crank flange? But could the 948 flywheel be drilled for the 1275 pressure plate?

Or, is there some other option?

Thanks for any illumination.

 

[2091351]

Racing units used a nine (9) spring clutch versus a six (6) spring unit from the factory.

Steve

 

[TexasSprite]

My 59BE was prepped for racing, so I was not surprised when I found a 9 spring clutch and a lightened flywheel as I was refurbishing the drive train. They were in pretty good shape, so I just left them in place. The car came with a smoothcase gearbox which was trashed. I ended up getting a refurbished ribcase gearbox from the late Eric Jones to replace the smoothcase. At the time, I read all sorts of opinions on whether or the combination would work or not. Some insisted that you had to have a backing plate off of a 1275 for the ribcase to work, others said it just bolted on. I was not looking forward to having to pull the engine multiple times to get this figured out. It was clear to me that the geometry of the pivot point for the clutch release lever was different between the smoothcase and the ribcase. so I was concerned about having enough extension in the cluch hydraulics to fully disengage the clutch. Eric's trick was to adapt the front cover of the smoothcase to fit the ribcase. That way, you had the same geometry as the original smoothcase. I think all he had to do was to drill two new holes in the smoothcase cover. Anyway, it all fit together perfectly. I even had to shorten the slave push rod a bit to get the feel of the clutch to be perfect.

 

[Hap Waldrop]

You can redrill a 948 flywheel to use a 1275 clutch, old racer's trick, now most racers use the Tilton race clutch and pressure plate, however you cannot put a 1275 flywheel on a 948 or 1098.

 

[Spridget64SC]

Agree. The 948 flywheel can be machined to accept a 1275 style pressure plate and the 1275 clutch disk. This entails the 3 location pins and the 6 pressure plate mounting bolts. When the factory supported racing modifications for the BL A-Series cars, there were actually heavy duty pressure plates and clutch discs with uprated capacity. The heavy duty pressure plates were dropped, but the uprated clutch disks were assimilated into normal production. These are the ones with all four center springs of thicker wire diameter.

There are sometimes interferences between the 1275 pressure plates and the inside of the smooth case bell housing due to the diameter and height differences of the 1275 pressure plate. These can be addressed by grinding and clearancing. Sometimes a hole is actually created in the bell housing.

With respect to the hydraulics and location of the release arm pivot, between the various release arms, release bearings, pushrods and slave cylinders, the proper actuation of the clutch can be assured. Make sure all pivot pins, bolts and bushings are in good condition and not excessively worn. This may entail more than one engine fit-up. However, if one uses just a few bolts to join the engine with the transmission, proper operation can be confirmed quickly.

The 1275 engine uses a different flywheel mounting strategy (Tapered interference fit) to the crank and 6 bolts. It won't fit a 948. However, a small main journal 1098 flywheel will fit a 948. This can be redrilled for the 948 4 bolt pattern. One of my old race buddies had a lightened one of these flywheels he had redrilled (he was a machinist) for the 1275 assembly. He could attach this flywheel to 948's or small journal 1098's depending upon the class he was racing in.

Yes, the difference between the smoothcase and ribcase front covers is the location of 2 mounting holes. As long as there are bosses on the front cover for the studs to pass through, they can be drilled and the covers used on either transmission. The pivot points are different because the slave cylinders, release arms and release bearings are different between the 948 and the 1275.

Hope all this helps, but again, between all the normal production parts, a 1275 pressure plate can be used with the 948 and either a smooth or ribcase transmission.

Mike Miller

 

[bob67bgt]

I may have a extra 948 flywheel that has been modified to accept a later clutch. I will check later tonight. Bob

 

[bob67bgt]

Well it looks like the flywheel I have is a 1275 redrilled to go on a 948. Pic attached. If I should put it in the scrap metal pile just let me know. It was on a 948 but I do not know how or if it actually worked ok. $10 plus shipping and you can have it. Bob

 

[Sarastro]

Thanks for the offer, but I think I'll hold off until I decide what to do.

Thanks all for the info. There is a shop that specializes in A-series engines not far from here, and does all kinds of machine work, so getting the 948 flywheel redrilled is probably not difficult. Might lighten it a bit at the same time. I suspect that this might be a viable way to go.

There's another variable here: I'm considering selling the Bugeye. There just aren't many places in the LA area to drive it, since I'm not comfortable with it on the freeways. I'd like to get something larger and with more performance, like an MGA or TR4. At one point I thought about putting a 1275 into it, but instead I'd prefer to put the money into a different car. So, if I do decide to sell it, I'll probably just put a standard 948 clutch into it. If I keep it, I might do the 1275.