One of the recuring problems atlast weeks Monterey race was the pump drive cable twisting off. A new one lasted through two races. Following the conventional wisdom on racer FI units I did not use the cable housing. I have a housing with everything removed but the distributor end retainer. I watched the cable as the unit was running and it seemed to wobble, right near where it broke. When I returned home I went back and looked over some of my period Corvette racing photos and the early Z 06 and Grand sports ran FI units with the cable housing. Does anyone know if the housing was used on the LeManns cars in 60? Have any of you had any racing expirience with this problem? The pump does not seem to bind. I am using the cables John D sent me so its not a problem with the cable being wound backward. Any racer ideas as to cause or solutions?
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Re: FI broken pump drive cable
back in the day the gulf cars ran without the outside cover at the SCCA races so IF they did break they could changed out on the race course. my question is could the higher RPM run now raise the pump pressure to where the cable is being overtaxed ??? -
Re: FI broken pump drive cable
Could be. I shifted at around 7000 and if I needed to get by someone the telltale says i went to 7500. But i'm using stamped rockers like they did in the day, I would think they ran around 7000 also. The cable broke under hard aceleration on the main straight.
The wobble in the cable just doesn't look right. i wonder if the angle of the distributor base with the pump is a factor?
were cables made out of a different material or a better process in the day?Comment
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Re: FI broken pump drive cable
Yep, there really is no adjustment od the angle.Comment
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Re: FI broken pump drive cable
I almost forgot..the refractory cement in the head worked. No more hung up #5 exhaust valve!Comment
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Re: FI broken pump drive cable
HI Jerry, I think you answered your own question. When I was a kid working for old Doc Blatchley on the pit crew of the 63 Grady Davis car the FI set up did not have a drive cable housing at the onstart. But the cable kept flying out. One time at the Connesville airport Doc was on turn two and all at once he just coasted off the course. I asked my friend Tim Grabiak (Docs head mechanic) what did he think broke now. Tim said the d drive cable probably fell out. And so it did. So then old JD got a junker housing and cut off the short snubby piece that goes onto the distributor. But guess what happened at high RPM Jerry etal (and others). The cables broke regularly. So one day over a Schimt's beer I said to Timmy don't you think we are messing up by cheating and running just a bare cable floating in the breeze. He said same thing as Clem did. Said it would take too much time to change the cable as the housings is a bear to change (and so they are). So I said to him lets experiment and do one race with a housing and see if the cables break. Tim said Doc might not take to kindly to us experimenting. But old JD being very young and not caring as only got paid with hot dogs and cheep beer said so what.
So next race we (I) put the drive cable housing on and greased the cable up real good and guess what gang. Never broke a cable after that.
Jerry I don't think those cables will stand up that well to 7500 RPM with no housing. Too much whipping around at such high RPM. Others may disagree.
Cheater that may work and make it easy for you Jerry. Instead of using a 65 drive cable housing try using the shorter housing from say a 57. But use the long cable? Why? Because the housing is much easier to swap out. I remember when I was installing the housing in my 63 show car and thought to myself that the thing is just a tad too long and is prone to kink. John
P.S. The last drive cable GM sold over the counter was very stiff and broke quite easily.
Recap: 7500 plus RPM is too much for a drive cable with no housing. We never turned those kind of RPM in the old days. Try the housing and see what happens.Comment
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Re: FI broken pump drive cable
Isn't it amazing how we vintage racers have to relearn the lessons of the past.
John , you are a wealth of experience. Thank you so much for passing on your knowledge and your help.
Now it looks like I'm in the market for an old shorter housing. Anybody have one? JerryComment
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Re: FI broken pump drive cable
Jerry,
Much of the problem with the cable isn't just high RPM. It's the quick increase in RPM during downshifts.
If you "blip" the throttle while downshifting to match engine RPM to drive shaft speed, that additional stress damages or breaks the cable.
These cables survive without issue at constant high RPM but the quick change while shifting adds additional load.
I always used the cable without the housing, as described by JD.Comment
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