I had a 351 built for my 55 sunliner and its always slid into third gear (C-4) at light throttle and had to rev the motor up to make the va***n wipers work and a slightly rough idle,it will go into 3rd nice and firm if I am on the gas and had been thinking it was a trans issue but at idle revving the motor up to make the va***n wipers work makes me think its a va***n issue. When I had the motor built I wanted a rv cam since it was going to have tall gears and alot of highway drives,since I am going to drive it to Daytona next month I was wanting to see if there was anything I can do to fix the problem so I got the va***n gauge out and did some checking. Va***n was 17 at the trans and carb at idle but when I sped the motor up some the va***n went up to 24 before falling when as went farther up. Instead of a rv grind I think the builder put in a radical 302 cam (302 firing order) so I found a va***n can and installed it and will deal with the motor when I get back,I can get the motor to idle smooth but I really have to advance the timing and then it pings badly and very hard to start so I am thinking it has to be the cam or the ***** retarded the cam during installation.
An RV cam should only be a little bit better sounding @ idle vs the OEM cam. Sounds like the wrong cam. But, have you check for vacuum leaks, old rubber plugs, lines, vac advance diaphram, many places can leak, includining intake gaskets. If is the cam Rhodes Lifters would help.
Over the years I've cured rough idle, flat spot off idle, poor shifts, and nasty plugs all with just tightening the intake manifolds. In the worst of cases I've had to replace the gaskets. Aluminum manifolds need attention more often and Felpro gaskets are the worst, they seem to become an Oil wick. The Wizzard
Its got a mid 80s factory truck 4 bbl cast iron intake and I have been all over it trying to find va***n leaks but found nothing so far,I was wondering if it could have a bad intake but its been aluminum intakes I had problems with. Last night I installed the va***n can and another set of valve covers so the PCV would fit tighter and it seemed to help some,I had 289 valve covers on it and I had to pinch the baffles some to clear the later wider rocker arms so the PCV would not fit all the way in. Advancing the timing too much to make it smooth out gets me thinking its the cam or the installation thats the issue and will most likely have to remove the cam to find out what it is. This motor was built by the guy in Indianapolis that others had issues with on here so who knows what I got.
I put a aluminum intake on a very low mile 302 that never used a drop of oil but it does now,the motor has to come apart to repair a valve guide so its going to get a factory cast iron intake when it goes back togather.
If by sliding you mean slipping that's not vacuum. The vacuum is only going to change the shift point by throttle/modulator pressure. Slipping is line pressure or loss of it from a leak (seals/rings) or mechanical wear.
get you a vacuum reservoir from a later vehicle to help with the vacuum wipers and a vacuum guage to check your system out.
My 351 W has a .540 .544 profile on the cam, I have only a vacuum of 11 at 1000 rpm, I have a c6, shoulda woulda coulda put a manual, but no put a c6, hated shifting. I put in a reservoir can with a storage check valve, hooked up the kick down linkage, shh lokar, and use an adjustable modulator on the trans. It's better now.
I really cant say its actually sliding but shifts funny into third at light throttle,I have to be on the gas for it to shift right but the motor is not really spinning any faster. It could be mechanical issues with the trans but there seems to be some va***n issue with the motor at idle speeds too so there is where I am going to start.
The Jalopy Journal
