Throttle Cable

Yuji

Lifetime Supporter
Re-post

Hi, I read the thread regarding stiff throttle recently and my GTD is also pretty stiff throttle which is somehow OK for track days as only on/off but not comfortable for street. Extremely stiff at the beginning to open the throttle, so not really smooth.
Although I'be changed the std. GTD pedals to Tilton box as attached, but no improvement so far. Now I need to look into the replacement of the throttle cable.
As I'll be in US early March, I'd like to place an order to Summit beforehand so that I could pick it up for hand carry back to Tokyo.

Any recommendation for the cable, either stainless braided housing or polyethylene? What would be the suitable length for GTD?

Thanks in advance for the advice!
 

Attachments

Ron McCall

Supporter
Measure the cable and order a custom cable from Pegasus Racing. They usually ship the same day or the next day at the latest.
 
Yuji, I would check the return springs on the throttle. If they are too stiff, then the pedal will be hard to push. The problem would not be fixed with another cable. This is the problem I have with my Borla 8 stack fuel injection.

The second issue that I would check is the motion or lever ratios. You want to have the pedal have a full motion to get the throttles wide open. If the pedal only moves a small amount to get full throttle then the pedal will feel stiff.

Another consideration is the bend radius of the cable in different locations. A tight bend radius will cause increased friction and make the pedal seem hard. Be sure to get Teflon lined cables.

Simply replacing the cable with a new one with the same throttle springs, motion ratios, and bend radii won't solve your problem if the above are not correct.

Bob Woods
Tornado GT40 in Texas
 
I agree with Bob ,springs can be to heavy because the TB are not as good as they should be to come home on their own.

Change the bellcrank that the cable is attached to.
Longer arm rolling on the back of the pedal and short arm attached to the cable.

It will increase your throw which makes it easier to drive in lower gears.
But you will have to work out the bell crank, place to start is how much cable travel from closed to full throttle, this is how far the short lever on the bellcrank has to travel then work back.

My bellcrank is maybe 2:1. it made a difference.

you will need to remake cable bracket if you change the bellcrank.

Model it with cardboard and pins if you don't have cad.

jim
 

Yuji

Lifetime Supporter
Thank you all for the advice. Will look into what you've suggested besides replacing the cable which has not been changed since built in late '80s.

Regards
 

Yuji

Lifetime Supporter
Ian,

Thank you for the info. for the cable. Looks pretty similar to bike cable, but need to check such a long one in Tokyo. Anyway, good to know the length of the cable.

Regards
 

Ian Anderson

Lifetime Supporter
Hi Yuji

The ones from car builder are long and you can cut them down to length.

For example on the Dax the cable goes directly rearwards from the pedal then down along side the gear change, out into the engine bay then loops around the headers to the throttle pull.

If it was routed forwards then curve through 180 degrees and then down the centre tunnel it would be a different length but again could be cut to length

Ian
 
For what its worth I had a stiff cable issue once after being in heavy traffic and it got seriously hot. It was so extreme I couldn't use the throttle at all and had to drive home on a fast tickover. A change of cable and better heat insulation over exhaust manifold cured it. Probably nothing like your problem but I thought I`d mention it.
 
Yuji,
You can use good quality bicycle brake cable like the ones used in tandem (two seater) race/touring bikes. They come packaged in ~10 foot lengths and are the standard .125" or 3mm diameter. While you're in the states, pick up a can of the pressurized cable lube at your local motorcycle store for periodical maintenance.

Bob, you can remove one of the 3 return springs (opposite bank of your TPS) in your Borla stack to reduce the cable tension, if needed. Besides adjusting your push rods for proper geometry, check that the throttle plates have no binding inside their bore and the flex couplings are not placing an axial load on the throttle plate shafts, then perform your "carb sync" procedure. A little adjustment in these areas will go a long way with any binding issues in that 0-1% TPS position....
 
Tom,

Yes, I have already removed one of the redundant springs. Mine had two springs on the TPS side and three on the non-TPS side. I removed the spring at the end of the non-TPS side. It is still a bit stiff. This would be just fine for track use, but on a long cruise you might get tired of pushing on the throttle.

I really wish Borla would have softer springs wound. Maybe a we could do a group buy if they don't do it. Chime in if you are interested. I have a spring company in town.

Thanks for the other adjustment suggestions.

-Bob
 

Chuck

Supporter
Measure the cable and order a custom cable from Pegasus Racing. They usually ship the same day or the next day at the latest.

If you need to replace the cable, Ron is on point. Pegasus makes a good quality product that proved much better than the Lokar we replaced. Much less resistance and smoother operation. Detailed in a post last December.

Chuck
 

Yuji

Lifetime Supporter
Chuck,

Thanks for the info. of custom cable from Pegasus, which is the one I was looking for with Teflon lined. Will measure the length and place an order.
Since I've not purchased any for a while from Pegasus, I do need to ask their customer service. Usually, I place an order before heading to US to Summit for the delivery to the hotel so that I could pick them up there for hand carry back! I've practiced this way to save shipping charge to Tokyo for years for GTD40 and M3!!

Thanks and Regards
 

Mike Pass

Supporter
Hi Yuji,

One of the things to check is the proximity of the cable at the engine end to the very hot exhaust pipes. I have come across a few instances of the heat melting or partially the plastic inner lining which causes a lot of friction. This is a real problem on most rolling roads which usually only blow a fan at the front of the car so no air flow into the rear clip where it is needed with all those hot pipes cooking away. We had a car where the inner melted on the rolling road and when the cable cooled down it was locked up solid so we had to cut it shorter and bodge it with a piece of spare cable to get it home.
Be very careful how you route the cable in regard to the exhaust pipes and cover this section of the cable with heat resistant reflective covering. I also carry a spare inner cable in my car and a couple of solderless nipples in case the end of the cable comes off. I put two nipples at each end of the cable in case one slips.
I got my cables and spare solderless nipples from Venhill.
Venhill.co.uk Motorcycle Braided Brake Hoses, Lines and Clutch Cables

Still OK after 3 years.

Cheers
Mike
 

Attachments

Ian Anderson

Lifetime Supporter
I had thought about a way to avoid the headers.
If you mount a pair of small rod ends on the firewall immediately index the window.
Through this pass a rod with a crank at each end, one in line with carb pull, orientation to pull forwards up the valley, and the other at the side where the throttle cable from the pedal will attach.

Helps the cable well out the way of the headers

No not done it just haughty about it!

Ian
 

Yuji

Lifetime Supporter
Mike and Ian,

Thanks for additional advice. Yes, the routing of the cable might be an issue as it goes close to the exhaust although having heat shield pipe there. When I'll replace the cable, I'll use heatshield mat, which I bought before. This mat is pretty good, but a bit costly. Gold in color and was told NASA technology. I use this mat for rear body shell to prevent heat from the muffler.

Regards
 

Yuji

Lifetime Supporter
Hi,

Have replaced with the custom made cable from Pegasus and the result is superb! Almost different car and can enjoy even street drive with such a smooth acceleration.

Thank you all for the advice!
Best Regards
 

Dave Bilyk

Dave Bilyk
I replaced my cable with a similar one from Car Builder solutions after the last one was melted on a rolling road. This one has far too much friction, so I've ordered a teflon lined kit from Venhill.
 
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